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<p class=title>Description of the <code>getdns</code> API</p>
<p class=title2>Originally edited by Paul Hoffman</p>
<p class=title2>Currently maintained by the <a
href="mailto:team@getdnsapi.net">getdns team</a></p>
<p class=title2>Document version: "getdns December 2015"</p>

<p>This document describes a modern asynchronous DNS API. This new API is intended to be useful to
application developers and operating system distributors as a way of making
all types of DNS information easily available in many types of programs. The major features
of this new API are:</p>

<ul>
<li>Full support for event-driven programming</li>
<li>Supports DNSSEC in multiple ways</li>
<li>Mirroring of the resolution in <code>getaddrinfo()</code></li>
<li>Easily supports all RRtypes, even those yet to be defined</li>
</ul>

<p>There is more background into the design and future goals of this API
<a href="#Commentary">later in this document</a>.</p>

<p>This document was discussed on the <a href="http://www.vpnc.org/mailman/listinfo/getdns-api">
getdns-api mailing list</a>; future versions of the API might be discussed there as well.
(If you
want to contact the editors off-list, please send mail to <a
href="mailto:team@getdnsapi.net">team@getdnsapi.net</a>.)</p>

<h1>1. The <code>getdns</code> Async Functions</h1>

<p>The API has four async functions:</p>

<ul>

<li><code>getdns_address</code> for doing <code>getaddrinfo()</code>-like address lookups</li>

<li><code>getdns_hostname</code> for doing <code>getnameinfo()</code>-like name lookups</li>

<li><code>getdns_service</code> for getting results from SRV lookups</li>

<li><code>getdns_general</code> for looking up any type of DNS record</li>

</ul>

<h2>1.1 <code>getdns_general()</code></h2>

<div class=forh id="getdnsfuncgeneral">getdns_return_t
getdns_general(
  getdns_context        *context,
  const char            *name,
  uint16_t              request_type,
  getdns_dict           *extensions,
  void                  *userarg,
  getdns_transaction_t  *transaction_id,
  getdns_callback_t     callbackfn
);
</div>

<p class=define><code><b>context</b></code></p>
<p class=descrip>A pointer to the DNS context that is to be used with this call. DNS contexts are
described <a href="#Contexts">later in this document</a>. Note that a context <i>must</i> be created
before calling the function.</p>

<p class=define><code><b>*name</b></code></p>
<p class=descrip>This is a null-terminted string consisting of an
ASCII-based domain name to be looked up.
The values here follow the rules in section 2.1 of RFC 4343
to allow non-ASCII octets and special characters in labels.</p>

<p class=define><code><b>request_type</b></code></p>
<p class=descrip>Specifies the RRtype for the query; the RRtype numbers are listed in the IANA
registry. For example, to get the NS records, <code>request_type</code> would be 2. The API also has
defined macros for most of the RRtypes by name; the definition names all start with
"<code>GETDNS_RRTYPE_</code>". For example, to get the NS records, you can also set the
<code>request_type</code> to <code>GETDNS_RRTYPE_NS</code>.
(The full list of request types is always
<a href="https://www.iana.org/assignments/dns-parameters/dns-parameters.xml">here</a>.)</p>

<p class=define><code><b>*extensions</b></code></p>
<p class=descrip>Specifies the extensions for this request; the value may be NULL if there are no
extensions. See <a href="#Extensions">the section below</a> for information on how to specify
the extensions used for a request.</p>

<p class=define><code><b>*userarg</b></code></p>
<p class=descrip>A void* that is passed to the function, which the function
returns to the callback function untouched. <code>userarg</code> can be used by the callback
function for any user-specific data needed. This can be NULL.</p>

<p class=define><code><b>*transaction_id</b></code></p>
<p class=descrip>A pointer to a value that is filled in by the
function to identify the callback being made.
This pointer can be NULL, in which case it is ignored and no value is assigned.
The <code>getdns_cancel_callback()</code> function uses the
<code>transaction_id</code> to determine which callback is to be cancelled.
If the function fails,
<code>transaction_id</code> is set to 0.</p>

<p class=define><code><b>*callbackfn</b></code></p>
<p class=descrip>A pointer to a callback function that is defined by the application.
Typically, the callback function will do all the processing on the results from
the API. The parameters of the callback are defined below. This really needs
to be a pointer to a function (and not something like NULL); otherwise, the
results are unpredictable.</p>

<p>The async <code>getdns</code> functions return <code>GETDNS_RETURN_GOOD</code> if the call was properly formatted.
It returns <code>GETDNS_RETURN_BAD_DOMAIN_NAME</code> if the API determines that the name passed to
the function was bad, <code>GETDNS_RETURN_BAD_CONTEXT</code> if the context has internal deficiencies,
<code>GETDNS_RETURN_NO_SUCH_EXTENSION</code> if one or more extensions do not exist, or
<code>GETDNS_RETURN_EXTENSION_MISFORMAT</code> if the contents of one or more of the
extensions is incorrect. All of the return values are given <a
href="#ReturnCodes">later in this document</a>.</p>

<h2>1.2 <code>getdns_address()</code></h2>

<div class=forh id="getdnsfuncaddress">getdns_return_t
getdns_address(
  getdns_context        *context,
  const char            *name,
  getdns_dict           *extensions,
  void                  *userarg,
  getdns_transaction_t  *transaction_id,
  getdns_callback_t     callbackfn
);
</div>

<p>There are three critical differences between <code>getdns_address()</code> and
<code>getdns_general()</code> beyond the missing <code>request_type</code> argument:</p>

<ul>

<li>In <code>getdns_address()</code>, the <code>name</code> argument can only take a host name.</li>

<li>You do not need to include a <code>return_both_v4_and_v6</code> extension with the call in
<code>getdns_address()</code>: it will always return both IPv4 and IPv6 addresses.</li>

<li><code>getdns_address()</code> always uses all of namespaces from the context (to better emulate
<code>getaddrinfo()</code>), while <code>getdns_general()</code> only uses the DNS namespace.</li>

</ul>

<h2>1.3 <code>getdns_hostname()</code></h2>

<div class=forh id="getdnsfunchostname">getdns_return_t
getdns_hostname(
  getdns_context        *context,
  getdns_dict           *address,
  getdns_dict           *extensions,
  void                  *userarg,
  getdns_transaction_t  *transaction_id,
  getdns_callback_t     callbackfn
);
</div>

<p>The address is given as a <code>getdns_dict</code> data structure (defined below). The list must
have two names: <code>address_type</code> (whose value is a bindata; it is currently either "IPv4"
or "IPv6" (which are case-sensitive)) and <code>address_data</code> (whose value is a bindata).</p>

<h2>1.4 <code>getdns_service()</code></h2>

<div class=forh id="getdnsfuncservice">getdns_return_t
getdns_service(
  getdns_context        *context,
  const char            *name,
  getdns_dict           *extensions,
  void                  *userarg,
  getdns_transaction_t  *transaction_id,
  getdns_callback_t     callbackfn
);
</div>

<p><code>name</code> must be a domain name for an SRV lookup; the call returns the
relevant SRV information for the name.</p>

<h2>1.5 Callback Functions for <code>getdns</code></h2>

<p>A call to the async <code>getdns</code> functions typically returns before any network or file I/O occurs. After
the API marshalls all the needed information, it calls the callback function that was passed by the
application. The callback function might be called at any time, even before the calling function
has returned. The API guarantees that the callback will be called exactly once unless the calling function
returned an error, in which case the callback function is never called.<p>

<p>The <code>getdns</code> calling function calls the callback with the parameters defined
as follows:</p>
<div class=forh id="getdns_callback_t">
typedef void (*getdns_callback_t)(
                                  getdns_context         *context,
                                  getdns_callback_type_t callback_type,
                                  getdns_dict            *response,
                                  void                   *userarg,
                                  getdns_transaction_t   transaction_id);
</div>

<p class=define><code><b>context</b></code></p>
<p class=descrip>The DNS context that was used in the calling function. See <a
href="#ContextInitial">below</a> for a description of the basic use of contexts, and <a
href="#Contexts">later</a> for more advanced use.</p>

<p class=define><code><b>callback_type</b></code></p>
<p class=descrip>Supplies the reason for the callback. See below for the codes and reasons.</p>

<p class=define><code><b>*response</b></code></p>
<p class=descrip>A response object with the response data.
This is described below.
The application is responsible for cleaning up the response object with getdns_dict_destroy.</p>

<p class=define><code><b>*userarg</b></code></p>
<p class=descrip>Identical to the <code>*userarg</code> passed to the calling function.</p>

<p class=define><code><b>transaction_id</b></code></p>
<p class=descrip>The transaction identifier that was assigned by the calling function.</p>

<p>The following are the values for callback_type.</p>

<p class=define>GETDNS_CALLBACK_COMPLETE</p>
<p class=descrip>The response has the requested data in it</p>
<p class=define>GETDNS_CALLBACK_CANCEL</p>
<p class=descrip>The calling program cancelled the callback; response is NULL</p>
<p class=define>GETDNS_CALLBACK_TIMEOUT</p>
<p class=descrip>The requested action timed out; response is filled in with empty structures</p>
<p class=define>GETDNS_CALLBACK_ERROR</p>
<p class=descrip>The requested action had an error; response is NULL</p>


<h2>1.6 <a id="ContextInitial">Setting Up The DNS Context</a></h2>

<p>Calls to <code>getdns</code> functions require a DNS context, which is a group of API settings
that affect how DNS calls are made. For most applications, a default context is sufficient.</p>

<p>To create a new DNS context, use the function:</p>

<div class=forh>getdns_return_t
getdns_context_create(
  getdns_context  **context,
  int             set_from_os
);
</div>

<p class=cont>The call to <code>getdns_context_create</code> immediately returns a context that can
be used with other API calls; that context contains the API's default values. Most applications will
want <code>set_from_os</code> set to <code>1</code>.</p>

<div class=forh>getdns_return_t
getdns_context_create_with_memory_functions(
  getdns_context  **context,
  int             set_from_os,
  void            *(*malloc)(size_t),
  void            *(*realloc)(void *, size_t),
  void            (*free)(void *)
);
getdns_return_t
getdns_context_create_with_extended_memory_functions(
  getdns_context  **context,
  int             set_from_os,
  void            *userarg,
  void            *(*malloc)(void *userarg, size_t),
  void            *(*realloc)(void *userarg, void *, size_t),
  void            (*free)(void *userarg, void *)
);
</div>

<p>To clean up the context, including cleaning up all outstanding transactions that were called
using this context, use the function:</p>

<div class=forh>void
getdns_context_destroy(
  getdns_context   *context
);
</div>

<p class=cont>When <code>getdns_context_destroy()</code> returns, the
application knows that all outstanding transactions associated with this
context will have been called; callbacks that had not been called before
<code>getdns_context_destroy()</code> was called will be called with a callback_type of
<code>GETDNS_CALLBACK_CANCEL</code>. <code>getdns_context_destroy()</code> returns after
all of the needed cleanup is done and callbacks are made.</p>

<h2>1.7 Canceling a Callback</h2>

<p>To cancel an outstanding callback, use the following function.</p>

<div class=forh>getdns_return_t
getdns_cancel_callback(
  getdns_context        *context,
  getdns_transaction_t  transaction_id
);
</div>

<p class=cont>This causes the API to call the callback with a <code>callback_type</code> of
<code>GETDNS_CALLBACK_CANCEL</code> if the callback for this <code>transaction_id</code> has not
already been called. This will cancel the callback regardless of what the original call was
doing (such as in the middle of a DNS request, while DNSSEC validation is happening, and so on).
The callback code for cancellation should clean up any memory related to the
identified call, such as to deallocate the memory for the userarg.
<code>getdns_cancel_callback()</code> may return immediately, even before the callback finishes its
work and returns. Calling <code>getdns_cancel_callback()</code> with a <code>transaction_id</code>
of a callback that has already been called or an unknown <code>transaction_id</code> returns
<code>GETDNS_RETURN_UNKNOWN_TRANSACTION</code>; otherwise, <code>getdns_cancel_callback()</code>
returns <code>GETDNS_RETURN_GOOD</code>.</p>

<h2>1.8 Event-driven Programs</h2>

<p>Event-driven programs (sometimes called "async programs") require an event
base and event loop (among other things). Different event libraries have
different structures or the event base. Because of this, there is no standard
method to set the event base in the DNS API: those are all added as
extensions. The API is distributed as a core package and one or more sets of
extensions to align with event libraries. It is mandatory to use one of the extension
functions to set the event base in the DNS context; this is required before
calling any event-driven calls like the <code>getdns</code> functions.</p>

<p>Each implementation of the DNS API will specify an extension function that
tells the DNS context which event base is being used. For example, one
implementation of this API that uses the libevent event library might name
this function "<code>getdns_extension_set_libevent_base()</code>" while
another might name it
"<code>getdns_extension_set_eventbase_for_libevent()</code>"; the two
extension functions could have very different calling patterns and return
values. Thus, the application developer <i>must</i> read the API documentation
(not just this design document) in order to determine what extension function
to use to tell the API the event base to use.</p>

<p>The structure of a typical event-driven application might look like the following pseudocode.
The code in italics is specific to the event mechanism.</p>

<pre>
Includes for one or more regular C libraries
<i>An include for the getdns library specific to the event library you use</i>
Definition of your callback function
    Get the DNS data from the allocated pointer
    Process that data
    Check for errors
Definition of main()
    Create context
    <i>Set up your event base</i>
    <i>Point the context to your event base</i>
    Set up the getdns call arguments
    Make the getdns call
    Check if the getdns return is good
    Destroy the context
    Exit
</pre>

<p>The API does not have direct support for a polling interface. Instead, the callback interface is
specifically designed to allow an application that wants to process results in polling instead of in
callbacks to be able to create its own polling interface fairly trivially. Such a program would
create a data structure for the calls, including their <code>transaction_id</code> and
<code>userarg</code>. The <code>userarg</code> could be the polling data structure or have a pointer to it.
The application would have just
one callback function for all requests, and that function would copy the <code>response</code> into
application memory, update the data structure based on the <code>transaction_id</code> index,
and return from the callback. The polling code could then check the data structure for any updates
at its leisure.</p>

<h2>1.9 Calling the API Synchronously (Without Events)</h2>

<p>There are functions parallel to the four <code>getdns</code> async functions,
except that there is no callback. That is, when an application calls one of these
synchronous functions, the
API gathers all the required information and then returns the result. The value returned is exactly the
same as the response returned in the callback if you had used the async version of the function.</p>

<div class=forh>getdns_return_t
getdns_general_sync(
  getdns_context  *context,
  const char      *name,
  uint16_t        request_type,
  getdns_dict     *extensions,
  getdns_dict     **response
);
</div>

<div class=forh>getdns_return_t
getdns_address_sync(
  getdns_context  *context,
  const char      *name,
  getdns_dict     *extensions,
  getdns_dict     **response
);
</div>

<div class=forh>getdns_return_t
getdns_hostname_sync(
  getdns_context  *context,
  getdns_dict     *address,
  getdns_dict     *extensions,
  getdns_dict     **response
);
</div>

<div class=forh>getdns_return_t
getdns_service_sync(
  getdns_context  *context,
  const char      *name,
  getdns_dict     *extensions,
  getdns_dict     **response
);
</div>

<p>When you are done with the data in the response, use the following function so that the API can
free the memory from its internal pool.</p>

<div class=forh>void
getdns_dict_destroy(
  getdns_dict  *response
);
</div>

<h1>2. Data structures in the API</h1>

<p>The API returns data structures. The data structure is not a representational language like JSON:
it is really just a data structure. Data structures can have four types of members:</p>

<ul>

<li><span class=default>list</span> is an ordered list, like JSON and Python lists.
The members of the list can be any of the four data types.</li>

<li><span class=default>dict</span> is a name-value pair, like a JSON object or Python dict. The
name is a string literal, and the value can be any of the four data types. The order of the
name-value pairs in a dict is not important.</li>

<li><span class=default>int</span> is an integer compatible with uint32_t.</li>

<li><span class=default>bindata</span> is a struct to hold binary data. It is defined as
<code>{ size_t size; uint8_t *binary_stuff; }</code>.</li>

</ul>

<p>The API comes with helper functions to get data from the list and dict data types:</p>

<div class=forh id="datagetters">
/* Lists: get the length, get the data_type of the value at a given
   position, and get the data at a given position */
getdns_return_t getdns_list_get_length(const getdns_list *list, size_t *answer);
getdns_return_t getdns_list_get_data_type(const getdns_list *list, size_t index, getdns_data_type *answer);
getdns_return_t getdns_list_get_dict(const getdns_list *list, size_t index, getdns_dict **answer);
getdns_return_t getdns_list_get_list(const getdns_list *list, size_t index, getdns_list **answer);
getdns_return_t getdns_list_get_bindata(const getdns_list *list, size_t index, getdns_bindata **answer);
getdns_return_t getdns_list_get_int(const getdns_list *list, size_t index, uint32_t *answer);

/* Dicts: get the list of names, get the data_type of the
   value at a given name, and get the data at a given name */
getdns_return_t getdns_dict_get_names(const getdns_dict *dict, getdns_list **answer);
getdns_return_t getdns_dict_get_data_type(const getdns_dict *dict, const char *name, getdns_data_type *answer);
getdns_return_t getdns_dict_get_dict(const getdns_dict *dict, const char *name, getdns_dict **answer);
getdns_return_t getdns_dict_get_list(const getdns_dict *dict, const char *name, getdns_list **answer);
getdns_return_t getdns_dict_get_bindata(const getdns_dict *dict, const char *name, getdns_bindata **answer);
getdns_return_t getdns_dict_get_int(const getdns_dict *dict, const char *name, uint32_t *answer);
</div>

<p>All of these helper getter functions return <code>GETDNS_RETURN_GOOD</code> if the call is successful.
The list functions will return <code>GETDNS_RETURN_NO_SUCH_LIST_ITEM</code> if the index argument is
out of range; the dict functions will return <code>GETDNS_RETURN_NO_SUCH_DICT_NAME</code> if the name
argument doesn't exist in the dict. The functions also return <code>GETDNS_RETURN_WRONG_TYPE_REQUESTED</code>
if the requested data type doesn't match the contents of the indexed argument or name.</p>

<p>This document uses graphical representations of data structures. It is important to note that
this is only a graphical representation; the brackets, commas, quotation marks, comments, and so on
are not part of the data. Also, this document uses macro names instead of some of the int
arguments; of course, the data structures have the actual int in them.</p>

<p>The <code>getdns_dict_get_names</code> helper function creates a newly created list
containing the names in a dict.  The caller is responsible for disposing this list.</p>

<p>The helper getter functions return references to <code>getdns_dict</code>, <code>getdns_list</code> and <code>getdns_bindata</code> data structures.
The user must not directly destroy these retrieved "child" data structures; instead, 
they will automatically be destroyed when the containing "parent" data structure is destroyed.
Because of this, retrieved "child" data structures cannot be used any more after the containing "parent" data structure has been destroyed.</p>

<p>When the name parameter to the <code>getdns_dict_get_</code> functions, starts with a '<code>/</code>' (<code>%x2F</code>) character, it is interpreted as a JSON Pointer as described in RFC 6901, and will then be used to dereference the nested data structures to get to the requested data type.</p>

<h2>2.1 Creating Data Structures</h2>

<p>Some of the features of the API require that you create your own data structures to be used in
arguments passed to the API. For example, if you want to use any extensions for the calling functions,
you need to create a dict. The requisite functions are:</p>

<div class=forh id="datasetters">
/* Lists: create, destroy, and set the data at a given position */
getdns_list * getdns_list_create();
getdns_list * getdns_list_create_with_context(
  getdns_context *context
);
getdns_list * getdns_list_create_with_memory_functions(
  void *(*malloc)(size_t),
  void *(*realloc)(void *, size_t),
  void (*free)(void *)
);
getdns_list * getdns_list_create_with_extended_memory_functions(
  void *userarg,
  void *(*malloc)(void *userarg, size_t),
  void *(*realloc)(void *userarg, void *, size_t),
  void (*free)(void *userarg, void *)
);
void getdns_list_destroy(getdns_list *list);
getdns_return_t getdns_list_set_dict(getdns_list *list, size_t index, const getdns_dict *child_dict);
getdns_return_t getdns_list_set_list(getdns_list *list, size_t index, const getdns_list *child_list);
getdns_return_t getdns_list_set_bindata(getdns_list *list, size_t index, const getdns_bindata *child_bindata);
getdns_return_t getdns_list_set_int(getdns_list *list, size_t index, uint32_t child_uint32);

/* Dicts: create, destroy, and set the data at a given name */
getdns_dict * getdns_dict_create();
getdns_dict * getdns_dict_create_with_context(
  getdns_context *context
);
getdns_dict * getdns_dict_create_with_memory_functions(
  void *(*malloc)(size_t),
  void *(*realloc)(void *, size_t),
  void (*free)(void *)
);
getdns_dict * getdns_dict_create_with_extended_memory_functions(
  void *userarg,
  void *(*malloc)(void *userarg, size_t),
  void *(*realloc)(void *userarg, void *, size_t),
  void (*free)(void *userarg, void *)
);
void getdns_dict_destroy(getdns_dict *dict);
getdns_return_t getdns_dict_set_dict(getdns_dict *dict, const char *name, const getdns_dict *child_dict);
getdns_return_t getdns_dict_set_list(getdns_dict *dict, const char *name, const getdns_list *child_list);
getdns_return_t getdns_dict_set_bindata(getdns_dict *dict, const char *name, const getdns_bindata *child_bindata);
getdns_return_t getdns_dict_set_int(getdns_dict *dict, const char *name, uint32_t child_uint32);
getdns_return_t getdns_dict_remove_name(getdns_dict *dict, const char *name);
</div>

<p>Lists are extended with the <code>getdns_list_set_</code> calls with the <code>index</code> set to the
size of the list (such as 0 for an empty list). Dicts are extended with the <code>getdns_dict_set_</code> calls
with the <code>name</code> set to a name that does not yet exist. Name-value pairs are removed with
<code>getdns_dict_remove_name()</code>.</p>

<p>These helper setter functions return <code>GETDNS_RETURN_GOOD</code> if the call is successful.
The functions return <code>GETDNS_RETURN_WRONG_TYPE_REQUESTED</code> if the requested data type
doesn't match the contents of the indexed argument or name. The list functions will return
<code>GETDNS_RETURN_NO_SUCH_LIST_ITEM</code> if the index argument is higher than the length of the
list. <code>getdns_dict_remove_name()</code> will return
<code>GETDNS_RETURN_NO_SUCH_DICT_NAME</code> if the name argument doesn't exist in the dict. </p>

<p>The helper setter functions store copies of the given "child" values.
It is the responsibility of the caller to dispose of the original values.</p>

<p>When the name parameter to the <code>getdns_dict_set_</code> functions, starts with a '<code>/</code>' (<code>%x2F</code>) character, it is interpreted as a JSON Pointer as described in RFC 6901, and will then be used to dereference the nested data structures to set the given value at the specified name or list index.</p>

<h1>3. <a id="Extensions">Extensions</a></h1>

<p>Extensions are dict data structures. The names in the dict are the names of the extensions.
The definition of each extension describes the value associated with the name. For most extensions,
it is an on-off boolean, and the value is <code>GETDNS_EXTENSION_TRUE</code>. (There is
not currently a good reason to specify an extension name and give it a value of <code>GETDNS_EXTENSION_FALSE</code>,
but that is allowed by the API.)</p>

<p>For example, to create a dict for extensions and specify the extension to only return
results that have been validated with DNSSEC, you might use:</p>

<pre>
/* . . . */
getdns_dict * extensions = getdns_dict_create();
ret = getdns_dict_set_int(extensions, "dnssec_return_only_secure", GETDNS_EXTENSION_TRUE);
/* . . . Do some processing with the extensions and results . . . */
/* Remember to clean up memory*/
getdns_dict_destroy(extensions);
</pre>

<p>The extensions described in this section are are:

<ul>

<li><code>dnssec_return_status</code></li>

<li><code>dnssec_return_only_secure</code></li>

<li><code>dnssec_return_validation_chain</code></li>

<li><code>return_both_v4_and_v6</code></li>

<li><code>add_opt_parameters</code></li>

<li><code>add_warning_for_bad_dns</code></li>

<li><code>specify_class</code></li>

<li><code>return_call_reporting</code></li>

</ul>

<h2>3.1 Extensions for DNSSEC</h2>

<p>If an application wants the API to do DNSSEC validation for a request, it must set one or more DNSSEC-related extensions.
Note that the default is for none of these extensions to be set and the API will not perform DNSSEC.
Note that getting DNSSEC results can take longer in a few circumstances.</p>

<p>To return the DNSSEC status for each DNS record in the <code>replies_tree</code> list, use the
<code>dnssec_return_status</code> extension. The extension's value (an int) is set to
<code>GETDNS_EXTENSION_TRUE</code> to cause the returned status to have the name
<code>dnssec_status</code> (an int) added to the other names in the record's dict ("header",
"question", and so on). The values for that name are <code>GETDNS_DNSSEC_SECURE</code>,
<code>GETDNS_DNSSEC_BOGUS</code>, <code>GETDNS_DNSSEC_INDETERMINATE</code>, and
<code>GETDNS_DNSSEC_INSECURE</code>. Thus, a reply might look like:</p>

<pre>
    {     # This is the first reply
      "dnssec_status": GETDNS_DNSSEC_INDETERMINATE,
      "header": { "id": 23456, "qr": 1, "opcode": 0, ... },
      . . .
</pre>

<p>If instead of returning the status, you want to only see secure results, use the
<code>dnssec_return_only_secure</code> extension. The extension's value (an int) is set to
<code>GETDNS_EXTENSION_TRUE</code> to cause only records that the API can validate as secure with
DNSSEC to be returned in the <code>replies_tree</code> and <code>replies_full</code> lists. No
additional names are added to the dict of the record; the change is that some records might not
appear in the results. When this context option is set, if the API receives DNS replies but none
are determined to be secure, the error code at the top level of the response object is
<code>GETDNS_RESPSTATUS_NO_SECURE_ANSWERS</code>.</p>

<p>Applications that want to do their own validation will want to have the DNSSEC-related records
for a particular response. Use the <code>dnssec_return_validation_chain</code> extension. The
extension's value (an int) is set to <code>GETDNS_EXTENSION_TRUE</code> to cause a set
of additional DNSSEC-related records needed for validation to be returned in the response object.
This set comes as <code>validation_chain</code> (a list) at the top level of the response object.
This list includes all resource record dicts for all the resource records (DS, DNSKEY and their RRSIGs) that are needed to perform the validation from the root up. Thus, a reply might look like:</p>

<pre>
{     # This is the response object
  "validation_chain":
  [ { "name": &lt;bindata for .&gt;,
      "type": GETDNS_RRTYPE_DNSKEY,
      "rdata": { "flags": 256, . . . },
      . . . 
    },
    { "name": &lt;bindata for .&gt;,
      "type": GETDNS_RRTYPE_DNSKEY,
      "rdata": { "flags": 257, . . . },
      . . .
    },
    { "name": &lt;bindata for .&gt;,
      "type": GETDNS_RRTYPE_RRSIG,
      "rdata": { "signers_name": &lt;bindata for .&gt;,
                 "type_covered": GETDNS_RRTYPE_DNSKEY,
                 . . .
               },
    },
    { "name": &lt;bindata for com.&gt;,
      "type": GETDNS_RRTYPE_DS,
      . . .
    },
    { "name": &lt;bindata for com.&gt;,
      "type": GETDNS_RRTYPE_RRSIG
      "rdata": { "signers_name": &lt;bindata for .&gt;,
                 "type_covered": GETDNS_RRTYPE_DS,
                 . . .
               },
      . . .
    },
    { "name": &lt;bindata for com.&gt;,
      "type": GETDNS_RRTYPE_DNSKEY
      "rdata": { "flags": 256, . . . },
      . . .
    },
    { "name": &lt;bindata for com.&gt;,
      "type": GETDNS_RRTYPE_DNSKEY
      "rdata": { "flags": 257, . . . },
      . . .
    },
    { "name": &lt;bindata for com.&gt;,
      "type": GETDNS_RRTYPE_RRSIG
      "rdata": { "signers_name": &lt;bindata for com.&gt;,
                 "type_covered": GETDNS_RRTYPE_DNSKEY,
                 . . .
               },
      . . .
    },
    { "name": &lt;bindata for example.com.&gt;,
      "type": GETDNS_RRTYPE_DS,
      . . .
    },
    { "name": &lt;bindata for example.com.&gt;,
      "type": GETDNS_RRTYPE_RRSIG
      "rdata": { "signers_name": &lt;bindata for com.&gt;,
                 "type_covered": GETDNS_RRTYPE_DS,
                 . . .
               },
      . . .
    },
    { "name": &lt;bindata for example.com.&gt;,
      "type": GETDNS_RRTYPE_DNSKEY
      "rdata": { "flags": 257, ... },
      . . .
    },
    . . .
  ]
  "replies_tree":
  [
  . . .
</pre>

<p>Implementations not capable of performing DNSSEC in stub resolution mode may
indicate this by not performing a request and instead return an error of 
<code>GETDNS_RETURN_DNSSEC_WITH_STUB_DISALLOWED</code> when using a context
in which stub resolution is set, and having any of the
<code>dnssec_return_status</code>, <code>dnssec_return_only_secure</code>, or
<code>dnssec_return_validation_chain</code> extensions specified.</p>

<h2>3.2 Returning Both IPv4 and IPv6 Responses</h2>

<p>Many applications want to get both IPv4 and IPv6 addresses in a single call so that the results
can be processed together. The <code>getdns_address</code> and <code>getdns_address_sync</code>
functions are able to do this automatically. If you are using the <code>getdns_general</code> or
<code>getdns_general_sync</code> function, you can enable this with the
<code>return_both_v4_and_v6</code> extension. The extension's value (an int) is set to
<code>GETDNS_EXTENSION_TRUE</code> to cause the results to be the lookup of either A or AAAA records
to include any A and AAAA records for the queried name (otherwise, the extension does nothing).
These results are expected to be used with Happy Eyeballs systems that will find the best socket for
an application.</p>

<h2>3.3 Setting Up OPT Resource Records</h2>

<p>For lookups that need an OPT resource record in the Additional Data section, use the
<code>add_opt_parameters</code> extension. The extension's value (a dict) contains the
parameters; these are described in more detail in RFC 6891. They are:</p>

<ul>

<li><code>maximum_udp_payload_size</code> (an int), a value between 512 and 65535; if not specified,
this defaults to those from the DNS context</li>

<li><code>extended_rcode</code> (an int), a value between 0 and 255; if not specified,
this defaults to those from the DNS context</li>

<li><code>version</code> (an int), a value between 0 and 255; if not specified, this
defaults to 0</li>

<li><code>do_bit</code> (an int), a value between 0 and 1; if not specified, this defaults
to those from the DNS context</li>

<li><code>options</code> (a list) contains dicts for each option to be specified.
Each list time contains two names: <code>option_code</code> (an int) and <code>option_data</code>
(a bindata). The API marshalls the entire set of options into a properly-formatted RDATA
for the resource record.</li>

</ul>

<p>It is very important to note that the OPT resource record specified in the
<code>add_opt_parameters</code> extension might not be the same the one that the API sends in the
query. For example, if the application also includes any of the DNSSEC extensions, the API will make
sure that the OPT resource record sets the resource record appropriately, making the needed changes
to the settings from the <code>add_opt_parameters</code> extension.</p>

<p>The use of this extension can conflict with the values in the DNS context. For example,
the default for an OS might be a maximum payload size of 65535, but the extension might specify
1550. In such a case, the API will honor the values stated in the extension, but will honor the
values from the DNS context if values are not given in the extension.</p>

<h2>3.4 Getting Warnings for Responses that Violate the DNS Standard</h2>

<p>To receive a warning if a particular response violates some parts of the DNS standard, use
the <code>add_warning_for_bad_dns</code> extension. The extension's value (an int) is set to
<code>GETDNS_EXTENSION_TRUE</code> to cause each reply in the <code>replies_tree</code>
to contain an additional name, <code>bad_dns</code> (a list). The list is zero or more
ints that indicate types of bad DNS found in that reply. The list of values is:

<p class=define>GETDNS_BAD_DNS_CNAME_IN_TARGET</p>
<p class=descrip>A DNS query type that does not allow a target to be a CNAME pointed to a CNAME</p>
<p class=define>GETDNS_BAD_DNS_ALL_NUMERIC_LABEL</p>
<p class=descrip>One or more labels in a returned domain name is all-numeric; this is not legal for a hostname</p>
<p class=define>GETDNS_BAD_DNS_CNAME_RETURNED_FOR_OTHER_TYPE</p>
<p class=descrip>A DNS query for a type other than CNAME returned a CNAME response</p>


<h2>3.5 Using Other Class Types</h2>

<p>The vast majority of DNS requests are made with the Internet (IN) class. To make a request in a
different DNS class, use, the <code>specify_class</code> extension. The extension's value (an int)
contains the class number. Few applications will ever use this extension.</p>

<h2>3.6 Extensions Relating to the API</h2>

<p>An application might want to see debugging information for queries such as the length of time it
takes for each query to return to the API. Use the <code>return_call_reporting</code> extension. The
extension's value (an int) is set to <code>GETDNS_EXTENSION_TRUE</code> to add the name
<code>call_reporting</code> (a list) to the top level of the response object. Each member of the
list is a dict that represents one call made for the call to the API. Each member has the following
names:</p>

<ul>
<li><code>query_name</code> (a bindata) is the name that was sent</li>
<li><code>query_type</code> (an int) is the type that was queried for</li>
<li><code>query_to</code> (a bindata) is the address to which the query was sent</li>
<li><code>run_time/ms</code> (a bindata) is the difference between the time the successful
query started and ended in milliseconds, represented
as a uint32_t (this does not include time taken for connection set up
or transport fallback)</li>
<li><code>entire_reply</code> (a bindata) is the entire response received</li>
<li><code>dnssec_result</code> (an int) is the DNSSEC status, or <code>GETDNS_DNSSEC_NOT_PERFORMED</code>
if DNSSEC validation was not performed</li>
</ul>

<h1>4. Response Data from Queries</h1>

<p>The callback function contains a pointer to a response object.
A response object is always a dict. The response
object always contains at least three names: <code>replies_full</code> (a list) and
<code>replies_tree</code> (a list), and <code>status</code> (an int).
<code>replies_full</code> is a list of DNS replies (each is bindata) as they appear on the wire.
<code>replies_tree</code> is a list of DNS replies (each is a dict) with the various part of the
reply parsed out. <code>status</code> is a status code for the query.</p>

<p>Because the API might be extended in the future, a response object might also contain names other
than <code>replies_full</code>, <code>replies_tree</code>, and <code>status</code>. Similarly, any
of the dicts described here might be extended in later versions of the API. Thus, an application
using the API must not assume that it knows all possible names in a dict.</p>

<p>The following lists the status codes for response objects. Note that, if the status is that there
are no responses for the query, the lists in <code>replies_full</code> and <code>replies_tree</code>
will have zero length.</p>

<p class=define>GETDNS_RESPSTATUS_GOOD</p>
<p class=descrip>At least one response was returned</p>
<p class=define>GETDNS_RESPSTATUS_NO_NAME</p>
<p class=descrip>Queries for the name yielded all negative responses</p>
<p class=define>GETDNS_RESPSTATUS_ALL_TIMEOUT</p>
<p class=descrip>All queries for the name timed out</p>
<p class=define>GETDNS_RESPSTATUS_NO_SECURE_ANSWERS</p>
<p class=descrip>The context setting for getting only secure responses was specified, and at least one DNS response was received, but no DNS response was determined to be secure through DNSSEC.</p>
<p class=define>GETDNS_RESPSTATUS_ALL_BOGUS_ANSWERS</p>
<p class=descrip>The context setting for getting only secure responses was specified, and at least one DNS response was received, but all received responses for the requested name were bogus.</p>


<p>The top level of <code>replies_tree</code> can optionally have the following names: <code>canonical_name</code> (a
bindata), <code>intermediate_aliases</code> (a list), <code>answer_ipv4_address</code> (a bindata),
<code>answer_ipv6_address</code> (a bindata),  and <code>answer_type</code> (an int).</p>

<ul>

<li>The value of <code>canonical_name</code> is the name that the API used for its lookup. It is in
FQDN presentation format.</li>

<li>The values in the <code>intermediate_aliases</code> list are domain names from any CNAME or
unsynthesized DNAME found when resolving the original query. The list might have zero entries
if there were no CNAMEs in the path. These may be useful, for example, for name comparisons
when following the rules in RFC 6125.</li>

<li>The value of <code>answer_ipv4_address</code> and <code>answer_ipv6_address</code> are
the addresses of the server from which the answer was received.</li>

<li>The value of <code>answer_type</code> is the type of name service that generated the response.
The values are:</li>

</ul>

<p class=define>GETDNS_NAMETYPE_DNS</p>
<p class=descrip>Normal DNS (RFC 1035)</p>
<p class=define>GETDNS_NAMETYPE_WINS</p>
<p class=descrip>The WINS name service (some reference needed)</p>


<p>If the call was <code>getdns_address</code> or <code>getdns_address_sync</code>, the top level
of <code>replies_tree</code> has an additional name, <code>just_address_answers</code> (a list).
The value of <code>just_address_answers</code> is a list that contains all of the A and AAAA
records from the answer sections of any of the replies, in the order they appear in the replies.
Each item in the list is a dict with at least two names: <code>address_type</code> (whose value is
a bindata; it is currently either "IPv4" or "IPv6") and <code>address_data</code> (whose value is a bindata).
Note that the <code>dnssec_return_only_secure</code> extension affects
what will appear in the <code>just_address_answers</code> list. Also note if later versions of the
DNS return other address types, those types will appear in this list as well.</p>

<p>The API can make service discovery through SRV records easier. If 
the call was <code>getdns_service</code> or <code>getdns_service_sync</code>,
the top level of <code>replies_tree</code> has an additional name,
<code>srv_addresses</code> (a list).
The list is ordered by priority and weight based on the weighting
algorithm in RFC 2782, lowest priority value first. Each element
of the list is dict has at least two names: <code>port</code> and <code>domain_name</code>. If the
API was able to determine the address of the target domain name (such as from its cache or from the
Additional section of responses), the dict for an element will also contain
<code>address_type</code> (whose value is a bindata; it is currently either "IPv4" or "IPv6") and
<code>address_data</code> (whose value is a bindata). Note that the
<code>dnssec_return_only_secure</code> extension affects what will appear in the
<code>srv_addresses</code> list.</p>

<h2>4.1 Structure of DNS <code>replies_tree</code></h2>

<p>The names in each entry in the the <code>replies_tree</code> list for DNS responses include
<code>header</code> (a dict), <code>question</code> (a dict), <code>answer</code> (a list),
<code>authority</code> (a list), and <code>additional</code> (a list), corresponding to the sections
in the DNS message format. The answer, authority, and additional lists each contain zero or more
dicts, with each dict in each list representing a resource record.</p>

<p>The names in the <code>header</code> dict are all the fields from Section 4.1.1. of RFC 1035.
They are: <code>id</code>, <code>qr</code>, <code>opcode</code>, <code>aa</code>, <code>tc</code>,
<code>rd</code>, <code>ra</code>, <code>z</code>, <code>rcode</code>, <code>qdcount</code>,
<code>ancount</code>, <code>nscount</code>, and <code>arcount</code>. All are ints.</p>

<p>The names in the <code>question</code> dict are the three fields from Section 4.1.2. of RFC 1035:
<code>qname</code> (a bindata), <code>qtype</code> (an int), and <code>qclass</code> (an int).</p>

<p>Resource records are a bit different than headers and question sections in that the RDATA portion
often has its own structure. The other names in the resource record dicts are <code>name</code> (a
bindata), <code>type</code> (an int), <code>class</code> (an int), <code>ttl</code> (an int) and
<code>rdata</code> (a dict); there is no name equivalent to the RDLENGTH field.
The <code>OPT</code> resource record does not have the <code>class</code> and the <code>ttl</code> name, but in stead provides <code>udp_payload_size</code> (an int), <code>extended_rcode</code> (an int), <code>version</code> (an int), <code>do</code> (an int), and <code>z</code> (an int).</p>

<p>The <code>rdata</code> dict has different names for each response type. There is a <a
href="#TypeList">complete list of the types defined</a> in the API. For names that end in
"-obsolete" or "-unknown", the bindata is the entire RDATA field. For example, the
<code>rdata</code> for an A record has a name <code>ipv4_address</code> (a bindata); the
<code>rdata</code> for an SRV record has the names <code>priority</code> (an int),
<code>weight</code> (an int), <code>port</code> (an int), and <code>target</code> (a bindata).</p>

<p>Each <code>rdata</code> dict also has a <code>rdata_raw</code> field (a bindata). This is useful
for types not defined in this version of the API. It also might be of value if a later version of
the API allows for additional parsers. Thus, doing a query for types not known by the API still will
return a result: an <code>rdata</code> with just a <code>rdata_raw</code>.</p>

<p>It is expected that later extensions to the API will give some DNS types different names. It is
also possible that later extensions will change the names for some of the DNS types listed above.</p>

<p>For example, a response to a <code>getdns_address()</code> call for www.example.com would
look something like this:</p>

<pre>
{     # This is the response object
  "replies_full": [ &lt;bindata of the first response&gt;, &lt;bindata of the second response&gt; ],
  "just_address_answers":
  [
    {
      "address_type": &lt;bindata of "IPv4"&gt;,
      "address_data": &lt;bindata of 0x0a0b0c01&gt;,
    },
    {
      "address_type": &lt;bindata of "IPv6"&gt;,
      "address_data": &lt;bindata of 0x33445566334455663344556633445566&gt;
    }
  ],
  "canonical_name": &lt;bindata of "www.example.com"&gt;,
  "answer_type": GETDNS_NAMETYPE_DNS,
  "intermediate_aliases": [],
  "replies_tree":
  [
    {     # This is the first reply
      "header": { "id": 23456, "qr": 1, "opcode": 0, ... },
      "question": { "qname": &lt;bindata of "www.example.com"&gt;, "qtype": 1, "qclass": 1 },
      "answer":
      [
        {
          "name": &lt;bindata of "www.example.com"&gt;,
          "type": 1,
          "class": 1,
          "ttl": 33000,
          "rdata":
          {
            "ipv4_address": &lt;bindata of 0x0a0b0c01&gt;
            "rdata_raw": &lt;bindata of 0x0a0b0c01&gt;
          }
        }
      ],
      "authority":
      [
        {
          "name": &lt;bindata of "ns1.example.com"&gt;,
          "type": 1,
          "class": 1,
          "ttl": 600,
          "rdata":
          {
            "ipv4_address": &lt;bindata of 0x65439876&gt;
            "rdata_raw": &lt;bindata of 0x65439876&gt;
          }
        }
      ]
      "additional": [],
      "canonical_name": &lt;bindata of "www.example.com"&gt;,
      "answer_type": GETDNS_NAMETYPE_DNS
    },
    {     # This is the second reply
      "header": { "id": 47809, "qr": 1, "opcode": 0, ... },
      "question": { "qname": &lt;bindata of "www.example.com"&gt;, "qtype": 28, "qclass": 1 },
      "answer":
      [
        {
          "name": &lt;bindata of "www.example.com"&gt;,
          "type": 28,
          "class": 1,
          "ttl": 1000,
          "rdata":
          {
            "ipv6_address": &lt;bindata of 0x33445566334455663344556633445566&gt;
            "rdata_raw": &lt;bindata of 0x33445566334455663344556633445566&gt;
          }
       }
      ],
      "authority": [  # Same as for other record... ]
      "additional": [],
    },
  ]
}
</pre>

<p>In DNS responses, domain names are treated special. RFC 1035 describes a form of name compression
that requires that the entire record be available for analysis. The API deals with this by
converting compressed names into full names when returning names in the <code>replies_tree</code>.
This conversion happens for <code>qname</code> in <code>question</code>; <code>name</code> in the
<code>answer</code>, <code>authority</code>, and <code>additional</code>; and in domain names in the
data in names under <code>rdata</code> where the response type is AFSDB, CNAME, MX, NS, PTR, RP, RT, and SOA.</p>

<h2>4.2 Converting Domain Names</h2>

<p>Names in DNS fields are stored in a fashion very different from the normal presentation format
normally used in applications. The DNS format is described in the first paragraph in Section 3.1 of
RFC 1035; the presentation format here is a null-terminated string with interior dots. These helper
functions only work with names in the DNS format that are not compressed. They are useful for
converting domain names in the <code>replies_tree</code> to and from the FQDN presentation
format.</p>

<p><code>getdns_convert_dns_name_to_fqdn()</code> converts a domain name in DNS format to the
presentation format. For example, the hex sequence <code>03 77 77 77 07 65 78 61 6d 70 6c 65 03 63
6f 6d 00</code> would be converted to "www.example.com".
<code>getdns_convert_fqdn_to_dns_name()</code> does the reverse: it converts a null-terminated
string in FQDN format to bytes in DNS format.</p>

<div class=forh>
getdns_return_t
getdns_convert_dns_name_to_fqdn(
  const getdns_bindata *dns_name_wire_fmt,
  char **fqdn_as_string
);

getdns_return_t
getdns_convert_fqdn_to_dns_name(
  const char *fqdn_as_string,
  getdns_bindata **dns_name_wire_fmt
);
</div>

<p>The returned values are allocated with the default system allocator, namely <code>malloc</code>.
The caller is responsible of disposing these allocations with <code>free</code>. </p>

<h1>5. Additional Definitions and Descriptions</h1>

<h2>5.1 A Few Needed Definitions</h2>

<div class=forh id="Various">typedef struct getdns_context getdns_context;
typedef uint64_t   getdns_transaction_t;
typedef enum getdns_data_type {
    t_dict, t_list, t_int, t_bindata
} getdns_data_type;
typedef struct getdns_bindata {
    size_t size;
    uint8_t *data;
} getdns_bindata;
typedef struct getdns_dict getdns_dict;
typedef struct getdns_list getdns_list;
</div>

<h2>5.2 <a id="ReturnCodes">Return Codes</a></h2>

<p>The return codes for all the functions are:</p>

<p class=define>GETDNS_RETURN_GOOD</p>
<p class=descrip>Good</p>
<p class=define>GETDNS_RETURN_GENERIC_ERROR</p>
<p class=descrip>Generic error</p>
<p class=define>GETDNS_RETURN_BAD_DOMAIN_NAME</p>
<p class=descrip>Badly-formed domain name in first argument</p>
<p class=define>GETDNS_RETURN_BAD_CONTEXT</p>
<p class=descrip>The context has internal deficiencies</p>
<p class=define>GETDNS_RETURN_CONTEXT_UPDATE_FAIL</p>
<p class=descrip>Did not update the context</p>
<p class=define>GETDNS_RETURN_UNKNOWN_TRANSACTION</p>
<p class=descrip>An attempt was made to cancel a callback with a transaction_id that is not recognized</p>
<p class=define>GETDNS_RETURN_NO_SUCH_LIST_ITEM</p>
<p class=descrip>A helper function for lists had an index argument that was too high.</p>
<p class=define>GETDNS_RETURN_NO_SUCH_DICT_NAME</p>
<p class=descrip>A helper function for dicts had a name argument that for a name that is not in the dict.</p>
<p class=define>GETDNS_RETURN_WRONG_TYPE_REQUESTED</p>
<p class=descrip>A helper function was supposed to return a certain type for an item, but the wrong type was given.</p>
<p class=define>GETDNS_RETURN_NO_SUCH_EXTENSION</p>
<p class=descrip>A name in the extensions dict is not a valid extension.</p>
<p class=define>GETDNS_RETURN_EXTENSION_MISFORMAT</p>
<p class=descrip>One or more of the extensions have a bad format.</p>
<p class=define>GETDNS_RETURN_DNSSEC_WITH_STUB_DISALLOWED</p>
<p class=descrip>A query was made with a context that is using stub resolution and a DNSSEC extension specified.</p>
<p class=define>GETDNS_RETURN_MEMORY_ERROR</p>
<p class=descrip>Unable to allocate the memory required.</p>
<p class=define>GETDNS_RETURN_INVALID_PARAMETER</p>
<p class=descrip>A required parameter had an invalid value.</p>
<p class=define>GETDNS_RETURN_NOT_IMPLEMENTED</p>
<p class=descrip>The library did not have the requested API feature implemented.</p>


<h2>5.3 <a id="TypeList">Types of RDATA Returned in the API</a></h2>

<p>The names in the <code>rdata</code> dicts in replies are:</p>


<p class=define>A (1)</p>
<p class=descrip><code>ipv4_address</code> (a bindata)</p>

<p class=define>NS (2)</p>
<p class=descrip><code>nsdname</code> (a bindata)</p>

<p class=define>MD (3)</p>
<p class=descrip><code>madname</code> (a bindata)</p>

<p class=define>MF (4)</p>
<p class=descrip><code>madname</code> (a bindata)</p>

<p class=define>CNAME (5)</p>
<p class=descrip><code>cname</code> (a bindata)</p>

<p class=define>SOA (6)</p>
<p class=descrip><code>mname</code> (a bindata), <code>rname</code>  (a bindata),
<code>serial</code> (an int), <code>refresh</code> (an int), <code>refresh</code> (an int),
<code>retry</code> (an int), and <code>expire</code> (an int)</p>

<p class=define>MB (7)</p>
<p class=descrip><code>madname</code> (a bindata)</p>

<p class=define>MG (8)</p>
<p class=descrip><code>mgmname</code> (a bindata)</p>

<p class=define>MR (9)</p>
<p class=descrip><code>newname</code> (a bindata)</p>

<p class=define>NULL (10)</p>
<p class=descrip><code>anything</code> (a bindata)</p>

<p class=define>WKS (11)</p>
<p class=descrip><code>address</code> (a bindata), <code>protocol</code> (an int),
and <code>bitmap</code> (a bindata)</p>

<p class=define>PTR (12)</p>
<p class=descrip><code>ptrdname</code> (a bindata)</p>

<p class=define>HINFO (13)</p>
<p class=descrip><code>cpu</code> (a bindata) and <code>os</code> (a bindata)</p>

<p class=define>MINFO (14)</p>
<p class=descrip><code>rmailbx</code> (a bindata) and <code>emailbx</code> (a bindata)</p>

<p class=define>MX (15)</p>
<p class=descrip><code>preference</code> (an int) and <code>exchange</code> (a bindata)</p>

<p class=define>TXT (16)</p>
<p class=descrip><code>txt_strings</code> (a list) which contains zero or more bindata elements
that are text strings</p>

<p class=define>RP (17)</p>
<p class=descrip><code>mbox_dname</code> (a bindata) and <code>txt_dname</code> (a bindata)</p>

<p class=define>AFSDB (18)</p>
<p class=descrip><code>subtype</code> (an int) and <code>hostname</code> (a bindata)</p>

<p class=define>X25 (19)</p>
<p class=descrip><code>psdn_address</code> (a bindata)</p>

<p class=define>ISDN (20)</p>
<p class=descrip><code>isdn_address</code> (a bindata) and <code>sa</code> (a bindata)</p>

<p class=define>RT (21)</p>
<p class=descrip><code>preference</code> (an int) and <code>intermediate_host</code> (a bindata)</p>

<p class=define>NSAP (22)</p>
<p class=descrip><code>nsap</code> (a bindata)</p>

<p class=define>SIG (24)</p>
<p class=descrip><code>sig_obsolete</code> (a bindata)</p>

<p class=define>KEY (25)</p>
<p class=descrip><code>key_obsolete</code> (a bindata)</p>

<p class=define>PX (26)</p>
<p class=descrip><code>preference</code> (an int), <code>map822</code> (a bindata), and <code>mapx400</code> (a bindata)</p>

<p class=define>GPOS (27)</p>
<p class=descrip><code>longitude</code> (a bindata), <code>latitude</code> (a bindata), and <code>altitude</code> (a bindata)</p>

<p class=define>AAAA (28)</p>
<p class=descrip><code>ipv6_address</code> (a bindata)</p>

<p class=define>LOC (29)</p>
<p class=descrip><code>loc_obsolete</code> (a bindata)</p>

<p class=define>NXT (30)</p>
<p class=descrip><code>nxt_obsolete</code> (a bindata)</p>

<p class=define>EID (31)</p>
<p class=descrip><code>eid_unknown</code> (a bindata)</p>

<p class=define>NIMLOC (32)</p>
<p class=descrip><code>nimloc_unknown</code> (a bindata)</p>

<p class=define>SRV (33)</p>
<p class=descrip><code>priority</code> (an int), <code>weight</code> (an int),
<code>port</code> (an int), and <code>target</code> (a bindata)</p>

<p class=define>ATMA (34)</p>
<p class=descrip><code>format</code> (an int) and <code>address</code> (a bindata)</p>

<p class=define>NAPTR (35)</p>
<p class=descrip><code>order</code> (an int), <code>preference</code> (an int), <code>flags</code>
(a bindata), <code>service</code> (a bindata), <code>regexp</code> (a bindata), and
<code>replacement</code> (a bindata).</p>

<p class=define>KX (36)</p>
<p class=descrip><code>preference</code> (an int) and <code>exchanger</code> (a bindata)</p>

<p class=define>CERT (37)</p>
<p class=descrip><code>type</code> (an int), <code>key_tag</code> (an int), <code>algorithm</code> (an int),
and <code>certificate_or_crl</code> (a bindata)</p>

<p class=define>A6 (38)</p>
<p class=descrip><code>a6_obsolete</code> (a bindata)</p>

<p class=define>DNAME (39)</p>
<p class=descrip><code>target</code> (a bindata)</p>

<p class=define>SINK (40)</p>
<p class=descrip><code>sink_unknown</code> (a bindata)</p>

<p class=define>OPT (41)</p>
<p class=descrip><code>options</code> (a list). Each element of the <code>options</code> list is a
dict with two names: <code>option_code</code> (an int) and <code>option_data</code> (a bindata).</p>

<p class=define>APL (42)</p>
<p class=descrip><code>apitems</code> (a list).
Each element of the <code>apitems</code> list is a dict with four names:
<code>address_family</code> (an int), <code>prefix</code> (an int),
<code>n</code> (an int), and <code>afdpart</code> (a bindata)</p>

<p class=define>DS (43)</p>
<p class=descrip><code>key_tag</code> (an int), <code>algorithm</code> (an int), <code>digest_type</code> (an int), 
and <code>digest</code> (a bindata)</p>

<p class=define>SSHFP (44)</p>
<p class=descrip><code>algorithm</code> (an int), <code>fp_type</code> (an int),
and <code>fingerprint</code> (a bindata)</p>

<p class=define>IPSECKEY (45)</p>
<p class=descrip><code>algorithm</code> (an int), <code>gateway_type</code> (an int), <code>precedence</code> (an int),
<code>gateway</code>, and <code>public_key</code> (a bindata)</p>

<p class=define>RRSIG (46)</p>
<p class=descrip> <code>type_covered</code> (an int), <code>algorithm</code> (an int),
<code>labels</code> (an int), <code>original_ttl</code> (an int), <code>signature_expiration</code>
(an int), <code>signature_inception</code> (an int), <code>key_tag</code> (an int),
<code>signers_name</code> (a bindata), and <code>signature</code> (a bindata)</p>

<p class=define>NSEC (47)</p>
<p class=descrip><code>next_domain_name</code> (a bindata) and <code>type_bit_maps</code> (a bindata)</p>

<p class=define>DNSKEY (48)</p>
<p class=descrip><code>flags</code> (an int), <code>protocol</code> (an int), <code>algorithm</code> (an int), 
and <code>public_key</code> (a bindata)</p>

<p class=define>DHCID (49)</p>
<p class=descrip><code>dhcid_opaque</code> (a bindata)</p>

<p class=define>NSEC3 (50)</p>
<p class=descrip><code>hash_algorithm</code> (an int), <code>flags</code> (an int),
<code>iterations</code> (an int), <code>salt</code> (a bindata),
<code>next_hashed_owner_name</code> (a bindata), and
<code>type_bit_maps</code> (a bindata)</p>

<p class=define>NSEC3PARAM (51)</p>
<p class=descrip><code>hash_algorithm</code> (an int), <code>flags</code> (an int),
<code>iterations</code> (an int), and
<code>salt</code> (a bindata)</p>

<p class=define>TLSA (52)</p>
<p class=descrip><code>certificate_usage</code> (an int), <code>selector</code> (an int),
<code>matching_type</code> (an int), and <code>certificate_association_data</code> (a
bindata).</p>

<p class=define>HIP (55)</p>
<p class=descrip><code>pk_algorithm</code> (an int),
<code>hit</code> (a bindata), <code>public_key</code>
(a bindata), and <code>rendezvous_servers</code> (a list) with each element a bindata with the dname of the rendezvous_server.</p>

<p class=define>NINFO (56)</p>
<p class=descrip><code>ninfo_unknown</code> (a bindata)</p>

<p class=define>RKEY (57)</p>
<p class=descrip><code>rkey_unknown</code> (a bindata)</p>

<p class=define>TALINK (58)</p>
<p class=descrip><code>talink_unknown</code> (a bindata)</p>

<p class=define>CDS (59)</p>
<p class=descrip><code>key_tag</code> (an int), <code>algorithm</code> (an int), <code>digest_type</code> (an int), 
and <code>digest</code> (a bindata)</p>

<p class=define>CDNSKEY (60)</p>
<p class=descrip><code>flags</code> (an int), <code>protocol</code> (an int), <code>algorithm</code> (an int), 
and <code>public_key</code> (a bindata)</p>

<p class=define>OPENPGPKEY (61)</p>
<p class=descrip><code>openpgpkey_unknown</code> (a bindata)</p>

<p class=define>CSYNC (62)</p>
<p class=descrip><code>serial</code> (an int), <code>flags</code> (an int), and <code>type_bit_maps</code> (a bindata)</p>

<p class=define>SPF (99)</p>
<p class=descrip><code>text</code> (a bindata)</p>

<p class=define>UINFO (100)</p>
<p class=descrip><code>uinfo_unknown</code> (a bindata)</p>

<p class=define>UID (101)</p>
<p class=descrip><code>uid_unknown</code> (a bindata)</p>

<p class=define>GID (102)</p>
<p class=descrip><code>gid_unknown</code> (a bindata)</p>

<p class=define>UNSPEC (103)</p>
<p class=descrip><code>unspec_unknown</code> (a bindata)</p>

<p class=define>NID (104)</p>
<p class=descrip><code>preference</code> (an int) and
<code>node_id</code> (a bindata)</p>

<p class=define>L32 (105)</p>
<p class=descrip><code>preference</code> (an int) and <code>locator32</code> (a bindata)</p>

<p class=define>L64 (106)</p>
<p class=descrip><code>preference</code> (an int) and <code>locator64</code> (a bindata)</p>

<p class=define>LP (107)</p>
<p class=descrip><code>preference</code> (an int) and <code>fqdn</code> (a bindata)</p>

<p class=define>EUI48 (108)</p>
<p class=descrip><code>eui48_address</code> (a bindata)</p>

<p class=define>EUI64 (109)</p>
<p class=descrip><code>eui64_address</code> (a bindata)</p>

<p class=define>TKEY (249)</p>
<p class=descrip><code>algorithm</code> (a bindata), <code>inception</code> (an int),
<code>expiration</code> (an int), <code>mode</code> (an int), <code>error</code> (an int),
<code>key_data</code> (a bindata), and <code>other_data</code> (a bindata)</p>

<p class=define>TSIG (250)</p>
<p class=descrip><code>algorithm</code> (a bindata), <code>time_signed</code> (a bindata),
<code>fudge</code> (an int), <code>mac</code> (a bindata), <code>original_id</code> (an int),
<code>error</code> (an int), and <code>other_data</code> (a bindata)</p>

<p class=define>MAILB (253)</p>
<p class=descrip><code>mailb-unknown</code> (a bindata)</p>

<p class=define>MAILA (254)</p>
<p class=descrip><code>maila-unknown</code> (a bindata)</p>

<p class=define>URI (256)</p>
<p class=descrip><code>priority</code> (an int), <code>weight</code> (an int),
and <code>target</code> (a bindata)</p>

<p class=define>CAA (257)</p>
<p class=descrip><code>flags</code> (an int), <code>tag</code> (a bindata), and <code>value</code> (a bindata)</p>

<p class=define>TA (32768)</p>
<p class=descrip><code>ta_unknown</code> (a bindata)</p>

<p class=define>DLV (32769)</p>
<p class=descrip>Identical to DS (43)</p>


<h1>6. Examples</h1>

<p>This section gives examples of code that calls the API to do many common tasks.
The purpose of the code here is to give application developers a quick hands-on
demo of using the API.</p>

<p>Note that the examples here all use getdns_libevent.h as the include that will call in the API
code as well as calling in libevent as the event library. They also use
<code>getdns_context_set_libevent_base()</code> as the name of the function to set the event base in
the DNS context. If you are using a different event library, you will of course use a different
<code>#include</code> at the beginning of your code, and a different name for the event base
function.</p>

<h2>6.1 Get Both IPv4 and IPv6 Addresses for a Domain Name Using Quick Results</h2>

<p>This is an example of a common call to <code>getdns_address()</code>.</p>

<br><div class="highlight"><pre><span class="cp">#include &lt;assert.h&gt;</span>
<span class="cp">#include &lt;inttypes.h&gt;</span>
<span class="cp">#include &lt;stdio.h&gt;</span>
<span class="cp">#include &lt;getdns_libevent.h&gt;</span>

<span class="cm">/* Set up the callback function, which will also do the processing of the results */</span>
<span class="kt">void</span> <span class="nf">callback</span><span class="p">(</span><span class="n">getdns_context</span>        <span class="o">*</span><span class="n">context</span><span class="p">,</span>
              <span class="kt">getdns_callback_type_t</span> <span class="n">callback_type</span><span class="p">,</span>
              <span class="n">getdns_dict</span>           <span class="o">*</span><span class="n">response</span><span class="p">,</span> 
              <span class="kt">void</span>                  <span class="o">*</span><span class="n">userarg</span><span class="p">,</span>
              <span class="kt">getdns_transaction_t</span>   <span class="n">transaction_id</span><span class="p">)</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span> <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="kt">uint32_t</span>        <span class="n">status</span><span class="p">;</span>
    <span class="n">getdns_bindata</span>  <span class="o">*</span><span class="n">address_data</span><span class="p">;</span>
    <span class="kt">char</span>            <span class="o">*</span><span class="n">first</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">,</span> <span class="o">*</span><span class="n">second</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>

    <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">context</span><span class="p">;</span> <span class="cm">/* unused parameter */</span>

    <span class="n">printf</span><span class="p">(</span> <span class="s">&quot;Callback for query </span><span class="se">\&quot;</span><span class="s">%s</span><span class="se">\&quot;</span><span class="s"> with request ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot;.</span><span class="se">\n</span><span class="s">&quot;</span>
          <span class="p">,</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span><span class="n">userarg</span><span class="p">,</span> <span class="n">transaction_id</span> <span class="p">);</span>

    <span class="k">switch</span><span class="p">(</span><span class="n">callback_type</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_CANCEL</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; was cancelled.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_TIMEOUT</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; timed out.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_ERROR</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;An error occurred for transaction ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot;.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">default</span><span class="o">:</span> <span class="k">break</span><span class="p">;</span>
    <span class="p">}</span>
    <span class="n">assert</span><span class="p">(</span> <span class="n">callback_type</span> <span class="o">==</span> <span class="n">GETDNS_CALLBACK_COMPLETE</span> <span class="p">);</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_int</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;status&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">status</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get </span><span class="se">\&quot;</span><span class="s">status</span><span class="se">\&quot;</span><span class="s"> from response&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">status</span> <span class="o">!=</span> <span class="n">GETDNS_RESPSTATUS_GOOD</span><span class="p">)</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;The search had no results, and a return value of %&quot;</span><span class="n">PRIu32</span><span class="s">&quot;.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">status</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;/just_address_answers/0/address_data&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get first address&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">first</span> <span class="o">=</span> <span class="n">getdns_display_ip_address</span><span class="p">(</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert first address to string</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;/just_address_answers/1/address_data&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get second address&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">second</span> <span class="o">=</span> <span class="n">getdns_display_ip_address</span><span class="p">(</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert second address to string</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">first</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The address is %s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">first</span><span class="p">);</span>
        <span class="n">free</span><span class="p">(</span><span class="n">first</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">second</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The address is %s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">second</span><span class="p">);</span>
        <span class="n">free</span><span class="p">(</span><span class="n">second</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">r</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">assert</span><span class="p">(</span> <span class="n">r</span> <span class="o">!=</span> <span class="n">GETDNS_RETURN_GOOD</span> <span class="p">);</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;: %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">r</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="n">getdns_dict_destroy</span><span class="p">(</span><span class="n">response</span><span class="p">);</span> 
<span class="p">}</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span>      <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_context</span>      <span class="o">*</span><span class="n">context</span>    <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="k">struct</span> <span class="n">event_base</span>   <span class="o">*</span><span class="n">event_base</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_dict</span>         <span class="o">*</span><span class="n">extensions</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="kt">char</span>                <span class="o">*</span><span class="n">query_name</span> <span class="o">=</span> <span class="s">&quot;www.example.com&quot;</span><span class="p">;</span>
    <span class="cm">/* Could add things here to help identify this call */</span>
    <span class="kt">char</span>                <span class="o">*</span><span class="n">userarg</span>    <span class="o">=</span> <span class="n">query_name</span><span class="p">;</span>
    <span class="kt">getdns_transaction_t</span> <span class="n">transaction_id</span><span class="p">;</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_context_create</span><span class="p">(</span><span class="o">&amp;</span><span class="n">context</span><span class="p">,</span> <span class="mi">1</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the context failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">event_base</span> <span class="o">=</span> <span class="n">event_base_new</span><span class="p">()))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the event base failed.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_extension_set_libevent_base</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">event_base</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Setting the event base failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_address</span><span class="p">(</span> <span class="n">context</span><span class="p">,</span> <span class="n">query_name</span><span class="p">,</span> <span class="n">extensions</span>
                                <span class="p">,</span> <span class="n">userarg</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">transaction_id</span><span class="p">,</span> <span class="n">callback</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error scheduling asynchronous request&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="p">{</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Request with transaction ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; scheduled.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">if</span> <span class="p">(</span><span class="n">event_base_dispatch</span><span class="p">(</span><span class="n">event_base</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">)</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error dispatching events</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>
    <span class="p">}</span>

    <span class="cm">/* Clean up */</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">event_base</span><span class="p">)</span>
        <span class="n">event_base_free</span><span class="p">(</span><span class="n">event_base</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">context</span><span class="p">)</span>
        <span class="n">getdns_context_destroy</span><span class="p">(</span><span class="n">context</span><span class="p">);</span>

    <span class="cm">/* Assuming we get here, leave gracefully */</span>
    <span class="n">exit</span><span class="p">(</span><span class="n">EXIT_SUCCESS</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>



<h2>6.2 Get IPv4 and IPv6 Addresses for a Domain Name</h2>

<p>This example is similar to the previous one, except that it retrieves more information than just
the addresses, so it traverses the replies_tree. In this case, it gets both the addresses and
their TTLs.</p>

<br><div class="highlight"><pre><span class="cp">#include &lt;assert.h&gt;</span>
<span class="cp">#include &lt;inttypes.h&gt;</span>
<span class="cp">#include &lt;stdio.h&gt;</span>
<span class="cp">#include &lt;getdns_libevent.h&gt;</span>

<span class="cm">/* Set up the callback function, which will also do the processing of the results */</span>
<span class="kt">void</span> <span class="nf">callback</span><span class="p">(</span><span class="n">getdns_context</span>        <span class="o">*</span><span class="n">context</span><span class="p">,</span>
              <span class="kt">getdns_callback_type_t</span> <span class="n">callback_type</span><span class="p">,</span>
              <span class="n">getdns_dict</span>           <span class="o">*</span><span class="n">response</span><span class="p">,</span> 
              <span class="kt">void</span>                  <span class="o">*</span><span class="n">userarg</span><span class="p">,</span>
              <span class="kt">getdns_transaction_t</span>   <span class="n">transaction_id</span><span class="p">)</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span> <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_list</span>    <span class="o">*</span><span class="n">replies_tree</span><span class="p">;</span>
    <span class="kt">size_t</span>          <span class="n">n_replies</span><span class="p">,</span> <span class="n">i</span><span class="p">;</span>

    <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">context</span><span class="p">;</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">userarg</span><span class="p">;</span> <span class="cm">/* unused parameters */</span>

    <span class="k">switch</span><span class="p">(</span><span class="n">callback_type</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_CANCEL</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; was cancelled.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_TIMEOUT</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; timed out.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_ERROR</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;An error occurred for transaction ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot;.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">default</span><span class="o">:</span> <span class="k">break</span><span class="p">;</span>
    <span class="p">}</span>
    <span class="n">assert</span><span class="p">(</span> <span class="n">callback_type</span> <span class="o">==</span> <span class="n">GETDNS_CALLBACK_COMPLETE</span> <span class="p">);</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_list</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;replies_tree&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">replies_tree</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get </span><span class="se">\&quot;</span><span class="s">replies_tree</span><span class="se">\&quot;</span><span class="s"> from response&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_length</span><span class="p">(</span><span class="n">replies_tree</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">n_replies</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get replies_tree</span><span class="se">\&#39;</span><span class="s">s length&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">for</span> <span class="p">(</span><span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o">&lt;</span> <span class="n">n_replies</span> <span class="o">&amp;&amp;</span> <span class="n">r</span> <span class="o">==</span> <span class="n">GETDNS_RETURN_GOOD</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">getdns_dict</span> <span class="o">*</span><span class="n">reply</span><span class="p">;</span>
        <span class="n">getdns_list</span> <span class="o">*</span><span class="n">answer</span><span class="p">;</span>
        <span class="kt">size_t</span>       <span class="n">n_answers</span><span class="p">,</span> <span class="n">j</span><span class="p">;</span>

        <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_dict</span><span class="p">(</span><span class="n">replies_tree</span><span class="p">,</span> <span class="n">i</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">reply</span><span class="p">)))</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get address %zu from just_address_answers&quot;</span><span class="p">,</span> <span class="n">i</span><span class="p">);</span>

        <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_list</span><span class="p">(</span><span class="n">reply</span><span class="p">,</span> <span class="s">&quot;answer&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">answer</span><span class="p">)))</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get </span><span class="se">\&quot;</span><span class="s">address_data</span><span class="se">\&quot;</span><span class="s"> from address&quot;</span><span class="p">);</span>

        <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_length</span><span class="p">(</span><span class="n">answer</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">n_answers</span><span class="p">)))</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get answer section</span><span class="se">\&#39;</span><span class="s">s length&quot;</span><span class="p">);</span>

        <span class="k">else</span> <span class="k">for</span> <span class="p">(</span><span class="n">j</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">j</span> <span class="o">&lt;</span> <span class="n">n_answers</span> <span class="o">&amp;&amp;</span> <span class="n">r</span> <span class="o">==</span> <span class="n">GETDNS_RETURN_GOOD</span><span class="p">;</span> <span class="n">j</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
            <span class="n">getdns_dict</span>    <span class="o">*</span><span class="n">rr</span><span class="p">;</span>
            <span class="n">getdns_bindata</span> <span class="o">*</span><span class="n">address</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>

            <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_dict</span><span class="p">(</span><span class="n">answer</span><span class="p">,</span> <span class="n">j</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">rr</span><span class="p">)))</span>
                <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could net get rr %zu from answer section&quot;</span><span class="p">,</span> <span class="n">j</span><span class="p">);</span>

            <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">rr</span><span class="p">,</span> <span class="s">&quot;/rdata/ipv4_address&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address</span><span class="p">)</span> <span class="o">==</span> <span class="n">GETDNS_RETURN_GOOD</span><span class="p">)</span>
                <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The IPv4 address is &quot;</span><span class="p">);</span>

            <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">rr</span><span class="p">,</span> <span class="s">&quot;/rdata/ipv6_address&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address</span><span class="p">)</span> <span class="o">==</span> <span class="n">GETDNS_RETURN_GOOD</span><span class="p">)</span>
                <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The IPv6 address is &quot;</span><span class="p">);</span>

            <span class="k">if</span> <span class="p">(</span><span class="n">address</span><span class="p">)</span> <span class="p">{</span>
                <span class="kt">char</span> <span class="o">*</span><span class="n">address_str</span><span class="p">;</span>
                <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">address_str</span> <span class="o">=</span> <span class="n">getdns_display_ip_address</span><span class="p">(</span><span class="n">address</span><span class="p">)))</span> <span class="p">{</span>
                    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert second address to string&quot;</span><span class="p">);</span>
                    <span class="n">r</span> <span class="o">=</span> <span class="n">GETDNS_RETURN_MEMORY_ERROR</span><span class="p">;</span>
                    <span class="k">break</span><span class="p">;</span>
                <span class="p">}</span>
                <span class="n">printf</span><span class="p">(</span><span class="s">&quot;%s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">address_str</span><span class="p">);</span>
                <span class="n">free</span><span class="p">(</span><span class="n">address_str</span><span class="p">);</span>
            <span class="p">}</span>
        <span class="p">}</span>
    <span class="p">}</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">r</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">assert</span><span class="p">(</span> <span class="n">r</span> <span class="o">!=</span> <span class="n">GETDNS_RETURN_GOOD</span> <span class="p">);</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;: %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">r</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="n">getdns_dict_destroy</span><span class="p">(</span><span class="n">response</span><span class="p">);</span> 
<span class="p">}</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span>      <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_context</span>      <span class="o">*</span><span class="n">context</span>    <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="k">struct</span> <span class="n">event_base</span>   <span class="o">*</span><span class="n">event_base</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_dict</span>         <span class="o">*</span><span class="n">extensions</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="kt">char</span>                <span class="o">*</span><span class="n">query_name</span> <span class="o">=</span> <span class="s">&quot;www.example.com&quot;</span><span class="p">;</span>
    <span class="cm">/* Could add things here to help identify this call */</span>
    <span class="kt">char</span>                <span class="o">*</span><span class="n">userarg</span>    <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="kt">getdns_transaction_t</span> <span class="n">transaction_id</span><span class="p">;</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_context_create</span><span class="p">(</span><span class="o">&amp;</span><span class="n">context</span><span class="p">,</span> <span class="mi">1</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the context failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">event_base</span> <span class="o">=</span> <span class="n">event_base_new</span><span class="p">()))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the event base failed.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_extension_set_libevent_base</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">event_base</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Setting the event base failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_address</span><span class="p">(</span> <span class="n">context</span><span class="p">,</span> <span class="n">query_name</span><span class="p">,</span> <span class="n">extensions</span>
                                <span class="p">,</span> <span class="n">userarg</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">transaction_id</span><span class="p">,</span> <span class="n">callback</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error scheduling asynchronous request&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">event_base_dispatch</span><span class="p">(</span><span class="n">event_base</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">)</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error dispatching events</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="cm">/* Clean up */</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">event_base</span><span class="p">)</span>
        <span class="n">event_base_free</span><span class="p">(</span><span class="n">event_base</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">context</span><span class="p">)</span>
        <span class="n">getdns_context_destroy</span><span class="p">(</span><span class="n">context</span><span class="p">);</span>

    <span class="cm">/* Assuming we get here, leave gracefully */</span>
    <span class="n">exit</span><span class="p">(</span><span class="n">EXIT_SUCCESS</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>



<h2>6.3 Get Addresses for a Domain Name And Their Associated DNSSEC Validation Status</h2>

<p>This example shows how to check for secure DNSSEC results using the
<code>dnssec_return_status</code> extension. In the innermost loop of the
callback function, add a check for the DNSSEC status. It shows how to add two
extensions to the <code>extensions</code> argument of the call.</p>

<pre>
getdns_dict *extensions = getdns_dict_create();
r = getdns_dict_set_int(extensions, "return_both_v4_and_v6", GETDNS_EXTENSION_TRUE);
r = getdns_dict_set_int(extensions, "dnssec_return_status", GETDNS_EXTENSION_TRUE);
. . .
if (rr_type == GETDNS_RRTYPE_A) {
    uint32_t dnssec_status;
    r = getdns_dict_get_int(answer, "dnssec_status", &amp;dnssec_status);
    if (dnssec_status != GETDNS_DNSSEC_SECURE) {
        // Log the DNSSEC status somewhere

    } else {
        // Deal with the record however you were going to
    }
}
. . .
</pre>

<p>You can put the DNSSEC status check outside the check for the particular type of record you care about, but
you will then get log messages for bad status on records you might not care about as well.</p>

<h2>6.4 Using the API Synchronously with <code>getdns_general_sync()</code></h2>

<p>This example is the same as the earlier examples, but uses <code>getdns_general_sync()</code>
and thus does not use the async code. Note that the processing of the answers is essentially the same
as it is for the synchronous example, it is just done in <code>main()</code>.</p>

<br><div class="highlight"><pre><span class="cp">#include &lt;stdio.h&gt;</span>
<span class="cp">#include &lt;assert.h&gt;</span>
<span class="cp">#include &lt;getdns_core_only.h&gt;</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span>  <span class="n">r</span><span class="p">;</span> <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_context</span>  <span class="o">*</span><span class="n">context</span>    <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_dict</span>     <span class="o">*</span><span class="n">response</span>   <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_dict</span>     <span class="o">*</span><span class="n">extensions</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_bindata</span>  <span class="o">*</span><span class="n">address_data</span><span class="p">;</span>
    <span class="kt">char</span>            <span class="o">*</span><span class="n">first</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">,</span> <span class="o">*</span><span class="n">second</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>

    <span class="cm">/* Create the DNS context for this call */</span>
    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_context_create</span><span class="p">(</span><span class="o">&amp;</span><span class="n">context</span><span class="p">,</span> <span class="mi">1</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the context failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">extensions</span> <span class="o">=</span> <span class="n">getdns_dict_create</span><span class="p">()))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not create extensions dict.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_set_int</span><span class="p">(</span><span class="n">extensions</span><span class="p">,</span> <span class="s">&quot;return_both_v4_and_v6&quot;</span><span class="p">,</span> <span class="n">GETDNS_EXTENSION_TRUE</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to set an extension do both IPv4 and IPv6 failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_general_sync</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="s">&quot;example.com&quot;</span><span class="p">,</span> <span class="n">GETDNS_RRTYPE_A</span><span class="p">,</span> <span class="n">extensions</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">response</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error scheduling synchronous request&quot;</span><span class="p">);</span>
    
    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;/just_address_answers/0/address_data&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get first address&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">first</span> <span class="o">=</span> <span class="n">getdns_display_ip_address</span><span class="p">(</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert first address to string</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;/just_address_answers/1/address_data&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get second address&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">second</span> <span class="o">=</span> <span class="n">getdns_display_ip_address</span><span class="p">(</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert second address to string</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">first</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The address is %s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">first</span><span class="p">);</span>
        <span class="n">free</span><span class="p">(</span><span class="n">first</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">second</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The address is %s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">second</span><span class="p">);</span>
        <span class="n">free</span><span class="p">(</span><span class="n">second</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="cm">/* Clean up */</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">response</span><span class="p">)</span>
        <span class="n">getdns_dict_destroy</span><span class="p">(</span><span class="n">response</span><span class="p">);</span> 

    <span class="k">if</span> <span class="p">(</span><span class="n">extensions</span><span class="p">)</span>
        <span class="n">getdns_dict_destroy</span><span class="p">(</span><span class="n">extensions</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">context</span><span class="p">)</span>
        <span class="n">getdns_context_destroy</span><span class="p">(</span><span class="n">context</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">r</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">assert</span><span class="p">(</span> <span class="n">r</span> <span class="o">!=</span> <span class="n">GETDNS_RETURN_GOOD</span> <span class="p">);</span>

        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;: %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">r</span><span class="p">);</span>
        <span class="n">exit</span><span class="p">(</span><span class="n">EXIT_FAILURE</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="cm">/* Assuming we get here, leave gracefully */</span>
    <span class="n">exit</span><span class="p">(</span><span class="n">EXIT_SUCCESS</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>



<h2>6.5 Getting Names from the Reverse Tree with <code>getdns_hostname()</code></h2>

<p>This example shows how to use <code>getdns_hostname()</code> to get names from the DNS reverse tree.</p>

<br><div class="highlight"><pre><span class="cp">#include &lt;assert.h&gt;</span>
<span class="cp">#include &lt;inttypes.h&gt;</span>
<span class="cp">#include &lt;stdio.h&gt;</span>
<span class="cp">#include &lt;getdns_libevent.h&gt;</span>

<span class="cm">/* Set up the callback function, which will also do the processing of the results */</span>
<span class="kt">void</span> <span class="nf">callback</span><span class="p">(</span><span class="n">getdns_context</span>        <span class="o">*</span><span class="n">context</span><span class="p">,</span>
              <span class="kt">getdns_callback_type_t</span> <span class="n">callback_type</span><span class="p">,</span>
              <span class="n">getdns_dict</span>           <span class="o">*</span><span class="n">response</span><span class="p">,</span> 
              <span class="kt">void</span>                  <span class="o">*</span><span class="n">userarg</span><span class="p">,</span>
              <span class="kt">getdns_transaction_t</span>   <span class="n">transaction_id</span><span class="p">)</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span> <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_list</span>    <span class="o">*</span><span class="n">answer</span><span class="p">;</span>
    <span class="kt">size_t</span>          <span class="n">n_answers</span><span class="p">,</span> <span class="n">i</span><span class="p">;</span>

    <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">context</span><span class="p">;</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">userarg</span><span class="p">;</span> <span class="cm">/* unused parameters */</span>

    <span class="k">switch</span><span class="p">(</span><span class="n">callback_type</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_CANCEL</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; was cancelled.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_TIMEOUT</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;Transaction with ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot; timed out.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">case</span> <span class="nl">GETDNS_CALLBACK_ERROR</span><span class="p">:</span>
        <span class="n">printf</span><span class="p">(</span><span class="s">&quot;An error occurred for transaction ID %&quot;</span><span class="n">PRIu64</span><span class="s">&quot;.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">transaction_id</span><span class="p">);</span>
        <span class="k">return</span><span class="p">;</span>
    <span class="k">default</span><span class="o">:</span> <span class="k">break</span><span class="p">;</span>
    <span class="p">}</span>
    <span class="n">assert</span><span class="p">(</span> <span class="n">callback_type</span> <span class="o">==</span> <span class="n">GETDNS_CALLBACK_COMPLETE</span> <span class="p">);</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_get_list</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="s">&quot;/replies_tree/0/answer&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">answer</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get </span><span class="se">\&quot;</span><span class="s">answer</span><span class="se">\&quot;</span><span class="s"> section from first reply in the response&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_length</span><span class="p">(</span><span class="n">answer</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">n_answers</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get replies_tree</span><span class="se">\&#39;</span><span class="s">s length&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">for</span> <span class="p">(</span><span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o">&lt;</span> <span class="n">n_answers</span> <span class="o">&amp;&amp;</span> <span class="n">r</span> <span class="o">==</span> <span class="n">GETDNS_RETURN_GOOD</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">getdns_dict</span>    <span class="o">*</span><span class="n">rr</span><span class="p">;</span>
        <span class="n">getdns_bindata</span> <span class="o">*</span><span class="n">dname</span><span class="p">;</span>
        <span class="kt">char</span>           <span class="o">*</span><span class="n">dname_str</span><span class="p">;</span>

        <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_list_get_dict</span><span class="p">(</span><span class="n">answer</span><span class="p">,</span> <span class="n">i</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">rr</span><span class="p">)))</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not get rr %zu from answer section&quot;</span><span class="p">,</span> <span class="n">i</span><span class="p">);</span>

        <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">getdns_dict_get_bindata</span><span class="p">(</span><span class="n">rr</span><span class="p">,</span> <span class="s">&quot;/rdata/ptrdname&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">dname</span><span class="p">))</span>
            <span class="k">continue</span><span class="p">;</span> <span class="cm">/* Not a PTR */</span>

        <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_convert_dns_name_to_fqdn</span><span class="p">(</span><span class="n">dname</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">dname_str</span><span class="p">)))</span>
            <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not convert PTR dname to string&quot;</span><span class="p">);</span>

        <span class="k">else</span> <span class="p">{</span>
            <span class="n">printf</span><span class="p">(</span><span class="s">&quot;The dname is %s</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">dname_str</span><span class="p">);</span>
            <span class="n">free</span><span class="p">(</span><span class="n">dname_str</span><span class="p">);</span>
        <span class="p">}</span>
    <span class="p">}</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">r</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">assert</span><span class="p">(</span> <span class="n">r</span> <span class="o">!=</span> <span class="n">GETDNS_RETURN_GOOD</span> <span class="p">);</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;: %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span> <span class="n">r</span><span class="p">);</span>
    <span class="p">}</span>
    <span class="n">getdns_dict_destroy</span><span class="p">(</span><span class="n">response</span><span class="p">);</span> 
<span class="p">}</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
    <span class="kt">getdns_return_t</span>      <span class="n">r</span><span class="p">;</span>  <span class="cm">/* Holder for all function returns */</span>
    <span class="n">getdns_context</span>      <span class="o">*</span><span class="n">context</span>      <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="k">struct</span> <span class="n">event_base</span>   <span class="o">*</span><span class="n">event_base</span>   <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_bindata</span>       <span class="n">address_type</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">4</span><span class="p">,</span> <span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="p">)</span><span class="s">&quot;IPv4&quot;</span> <span class="p">};</span>
    <span class="n">getdns_bindata</span>       <span class="n">address_data</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">4</span><span class="p">,</span> <span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="p">)</span><span class="s">&quot;</span><span class="se">\x08\x08\x08\x08</span><span class="s">&quot;</span> <span class="p">};</span>
    <span class="n">getdns_dict</span>         <span class="o">*</span><span class="n">address</span>      <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="n">getdns_dict</span>         <span class="o">*</span><span class="n">extensions</span>   <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="cm">/* Could add things here to help identify this call */</span>
    <span class="kt">char</span>                <span class="o">*</span><span class="n">userarg</span>      <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
    <span class="kt">getdns_transaction_t</span> <span class="n">transaction_id</span><span class="p">;</span>

    <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_context_create</span><span class="p">(</span><span class="o">&amp;</span><span class="n">context</span><span class="p">,</span> <span class="mi">1</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the context failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">event_base</span> <span class="o">=</span> <span class="n">event_base_new</span><span class="p">()))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Trying to create the event base failed.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_extension_set_libevent_base</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">event_base</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Setting the event base failed&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="p">(</span><span class="n">address</span> <span class="o">=</span> <span class="n">getdns_dict_create</span><span class="p">()))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not create address dict.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_set_bindata</span><span class="p">(</span><span class="n">address</span><span class="p">,</span> <span class="s">&quot;address_type&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_type</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not set address_type in address dict.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_dict_set_bindata</span><span class="p">(</span><span class="n">address</span><span class="p">,</span> <span class="s">&quot;address_data&quot;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">address_data</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Could not set address_data in address dict.</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">r</span> <span class="o">=</span> <span class="n">getdns_hostname</span><span class="p">(</span> <span class="n">context</span><span class="p">,</span> <span class="n">address</span><span class="p">,</span> <span class="n">extensions</span>
                                 <span class="p">,</span> <span class="n">userarg</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">transaction_id</span><span class="p">,</span> <span class="n">callback</span><span class="p">)))</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error scheduling asynchronous request&quot;</span><span class="p">);</span>

    <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">event_base_dispatch</span><span class="p">(</span><span class="n">event_base</span><span class="p">)</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">)</span>
        <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">&quot;Error dispatching events</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">);</span>

    <span class="cm">/* Clean up */</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">event_base</span><span class="p">)</span>
        <span class="n">event_base_free</span><span class="p">(</span><span class="n">event_base</span><span class="p">);</span>

    <span class="k">if</span> <span class="p">(</span><span class="n">context</span><span class="p">)</span>
        <span class="n">getdns_context_destroy</span><span class="p">(</span><span class="n">context</span><span class="p">);</span>

    <span class="cm">/* Assuming we get here, leave gracefully */</span>
    <span class="n">exit</span><span class="p">(</span><span class="n">EXIT_SUCCESS</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>



<h1>7. More Helper Functions</h1>

<p>The following two functions convert individual labels of IDNs between their Unicode
encoding and their ASCII encoding. They follow the rules for IDNA 2008 described in
RFC 5890-5892.</p>
<div class=forh>char *
getdns_convert_ulabel_to_alabel(
  const char  *ulabel
);
</div>
<div class=forh>char *
getdns_convert_alabel_to_ulabel(
  const char  *alabel
);
</div>

<p>If an application wants the API do perform DNSSEC validation without using the extensions, it
can use the <code>getdns_validate_dnssec()</code> helper function.</p>
<div class=forh>getdns_return_t
getdns_validate_dnssec(
  getdns_list     *to_validate,
  getdns_list     *bundle_of_support_records,
  getdns_list     *trust_anchor_records
);
</div>
<p class=cont>
The <code>to_validate</code> is a list of resource records being validated together with the associated signatures.
The API will use the resource records in <code>bundle_of_support_records</code> to construct the validation chain and the DNSKEY or DS records in <code>trust_anchor_records</code> as trust anchors.
The function returns one of <code>GETDNS_DNSSEC_SECURE</code>, <code>GETDNS_DNSSEC_BOGUS</code>, <code>GETDNS_DNSSEC_INDETERMINATE</code>, or <code>GETDNS_DNSSEC_INSECURE</code>.
</p>

<p class=cont>
The default list of trust anchor records that is used by the library to validate DNSSEC can
be retrieved by using the <code>getdns_root_trust_anchor</code> helper function.</p>
<div class=forh>getdns_list *
getdns_root_trust_anchor(
  time_t *utc_date_of_anchor
);
</div>
<p class=cont>
When there are no default trust anchors <code>NULL</code> is returned.
Upon successful return, the variable of type <code>time_t</code>, referenced by
<code>utc_date_of_anchor</code> is set to the number of seconds since epoch
the trust anchors were obtained.
</p>

<p>There are two functions that help process data:</p>

<div class=forh>
char *
getdns_pretty_print_dict(
  const getdns_dict  *some_dict
);
</div>
<p class=cont>This returns a string that is the nicely-formatted version
of the dict and all of the named elements in it.</p>

<div class=forh>
char *
getdns_display_ip_address(
  const getdns_bindata  *bindata_of_ipv4_or_ipv6_address
);
</div>
<p class=cont>This returns a string that is the nicely-formatted version
of the IPv4 or IPv6 address in it. The API determines they type of address
by the length given in the bindata.</p>

<p class=cont>All memory locations returned by these helper functions are allocated by the default system allocator, namely <code>malloc</code>.
The caller is responsible of disposing these allocations with <code>free</code>.</p>

<h1>8. <a id="Contexts">DNS Contexts</a></h1>

<p>Many calls in the DNS API require a DNS context. A DNS
context contains the information that the API needs in order to process DNS calls, such as the
locations of upstream DNS servers, DNSSEC trust anchors, and so on. The internal structure of the
DNS context is opaque, and might be different on each OS. When a context is passed to any function,
it must be an allocated context; the context must not be NULL.</p>

<p>A typical application using this API doesn't need to know anything about contexts. Basically,
the application creates a default context, uses it in the functions that require a context, and
then deallocates it when done. Context manipulation is available for more DNS-aware programs,
but is unlikely to be of interest to applications that just want the results of lookups for
A, AAAA, SRV, and PTR records.</p>

<p>It is expected that contexts in implementations of the API will not necessarily be thread-safe,
but they will not be thread-hostile. A context should not be used by multiple threads: create a new
context for use on a different thread. It is just fine for an application to have many contexts,
and some DNS-heavy applications will certainly want to have many even if the application uses
a single thread.</p>

<p>See <a href="#ContextInitial">above</a> for the method for creating and destroying
contexts. When the context is used in the API for the first time and <code>set_from_os</code> is
<code>1</code>, the API starts replacing some of the values with values from the OS, such as
those that would be found in res_query(3), /etc/resolv.conf, and so on, then proceeds with the new
function. Some advanced users will not want the API to change the values to the OS's defaults; if
<code>set_from_os</code> is <code>0</code>, the API will not do any updates to the initial
values based on changes in the OS. For example, this might be useful if the API is acting
as a stub resolver that is using a specific upstream recursive resolver chosen by the
application, not the one that might come back from DHCP.</p>

<h2>8.1 Updating the Context Automatically</h2>

<p>The context returned by <code>getdns_context_create()</code> is updated by the API by default,
such as when changes are made to /etc/resolv.conf. When there is a change, the callback function
that is set in <code>getdns_context_set_context_update_callback()</code> (described below) is
called.</p>

<p>Many of the defaults for a context come from the operating system under which the API is running.
In specific, it is important that the implementation should try to replicate as best as possible the
logic of a local <code>getaddrinfo()</code> when creating a new context. This includes making
lookups in WINS for NetBIOS, mDNS lookups, nis names, and any other name lookup that
<code>getaddrinfo()</code> normally does automatically. The API should look at nsswitch, the Windows
resolver, and so on.</p>

<p>In the function definitions below, the choice listed <span class=default>in bold</span> is the one used
for the API default context.</p>

<h2>8.2 Updating the Context Manually</h2>

<p>Setting specific values in a context are done with value-specific
functions shown here. The setting functions all return either <code>GETDNS_RETURN_GOOD</code> for
success or <code>GETDNS_RETURN_CONTEXT_UPDATE_FAIL</code> for a failure to update the context.</p>

<p>An application can be notified when the context is changed.</p>

<div class=forh>
getdns_return_t
getdns_context_set_context_update_callback(
  getdns_context  *context,
  void            (*value)(getdns_context *context, getdns_context_code_t changed_item)
);</div>
<p class=cont>The value is a pointer to the callback function that will be
called when any context is changed. Such changes might be from automatic
changes from the API (such as changes to /etc/resolv.conf), or might be from any of the
API functions in this section being called. The second argument to the callback function
specifies which of the context changed; the context codes are listed
<a href="#ContextCodes">later in this document</a>.</p>
<p class=cont>Calling getdns_context_set_context_update_callback with a second argument of NULL prevents updates to the context from causing callbacks.</p>

<h2>8.3 Contexts for Basic Resolution</h2>

<div class=forh>
getdns_return_t
getdns_context_set_resolution_type(
  getdns_context       *context,
  getdns_resolution_t  value
);</div>
<p class=cont>Specifies whether DNS queries are performed with nonrecurive lookups or
as a stub resolver. The value is <span class=default><code>GETDNS_RESOLUTION_RECURSING</code></span> or
<code>GETDNS_RESOLUTION_STUB</code>.</p>

<p>All implementations of this API can act as recursive resolvers, and that must be the
default mode of the default context.
Some implementations of this API are expected to also be able to act as stub resolvers.
If an
implementation of this API is only able to act as a recursive resolver, a call to
<code>getdns_context_set_resolution_type(somecontext, GETDNS_RESOLUTION_STUB)</code> will
return <code>GETDNS_RETURN_CONTEXT_UPDATE_FAIL</code>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_namespaces(
  getdns_context      *context,
  size_t              namespace_count,
  getdns_namespace_t  *namespaces
);</div>
<p class=cont>The <code>namespaces</code> array contains an ordered list
of namespaces that will be queried.
<b>Important:</b> this context setting is ignored for the <code>getdns_general</code> and
<code>getdns_general_sync</code> functions; it is used for the other funtions.
The values
are <code>GETDNS_NAMESPACE_DNS</code>,
<code>GETDNS_NAMESPACE_LOCALNAMES</code>,
<code>GETDNS_NAMESPACE_NETBIOS</code>,
<code>GETDNS_NAMESPACE_MDNS</code>, and
<code>GETDNS_NAMESPACE_NIS</code>. When a normal lookup is done,
the API does the lookups in the order given and stops when it gets the
first result; a different method with the same result would be to run
the queries in parallel and return when it gets the first result.
Because lookups might be done over different mechanisms because of the
different namespaces, there can be information leakage that is similar
to that seen with <code>getaddrinfo()</code>. The
default is <span class=default>determined by the OS</span>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_dns_transport(
  getdns_context      *context,
  getdns_transport_t  value
);</div>
<p class=cont>Specifies what transport is used for DNS lookups.
The value is <span class=default>
<code>GETDNS_TRANSPORT_UDP_FIRST_AND_FALL_BACK_TO_TCP</code></span>,
<code>GETDNS_TRANSPORT_UDP_ONLY</code>,
<code>GETDNS_TRANSPORT_TCP_ONLY</code>, or
<code>GETDNS_TRANSPORT_TCP_ONLY_KEEP_CONNECTIONS_OPEN</code>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_dns_transport_list(
  getdns_context           *context,
  size_t                   transport_count, 
  getdns_transport_list_t  *transports
);</div>
<p class=cont>The <code>transports</code> array contains an ordered list of transports that will be used for DNS lookups.
If only one transport value is specified it will be the only transport used.
Should it not be available basic resolution will fail.
Fallback transport options are specified by including multiple values in the list.
The values are <span class=default>
<code>GETDNS_TRANSPORT_UDP</code></span>,
<code>GETDNS_TRANSPORT_TCP</code>, or
<code>GETDNS_TRANSPORT_TLS</code>.
The default is <span class=default> a list containing <code>GETDNS_TRANSPORT_UDP</code> then <code>GETDNS_TRANSPORT_TCP</code></span>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_idle_timeout(
  getdns_context  *context,
  uint64_t        timeout
);</div>
<p class=cont>Specifies number of milliseconds the API will leave an idle TCP or TLS connection open for (idle means no outstanding responses and no pending queries).
The default is <span class=default>0</span>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_limit_outstanding_queries(
  getdns_context  *context,
  uint16_t        limit
);</div>
<p class=cont>Specifies limit the number of outstanding DNS queries.
The API will block itself from sending more queries if it is about to exceed
this value, and instead keep those queries in an internal queue.
The a value of <span class=default>0</span> indicates that
the number of outstanding DNS queries is unlimited.</p>

<div class=forh>
getdns_return_t
getdns_context_set_timeout(
  getdns_context  *context,
  uint64_t        timeout
);</div>
<p class=cont>Specifies number of milliseconds the API will wait for request to return.
The default is <span class=default>not specified</span>.</p>

<h2>8.4 Context for Recursive Resolvers</h2>

<div class=forh>
getdns_return_t
getdns_context_set_follow_redirects(
  getdns_context      *context,
  getdns_redirects_t  value
);</div>
<p class=cont>Specifies whether or not DNS queries follow redirects.
The value is <span class=default><code>GETDNS_REDIRECTS_FOLLOW</code></span> for normal
following of redirects though CNAME and DNAME; or
<code>GETDNS_REDIRECTS_DO_NOT_FOLLOW</code> to cause any lookups that would have gone
through CNAME and DNAME to return the CNAME or DNAME, not the eventual target.</p>

<div class=forh>
getdns_return_t
getdns_context_set_dns_root_servers(
  getdns_context  *context,
  getdns_list     *addresses
);</div>
<p class=cont>The list contains dicts that are addresses to be used for looking up top-level
domains; the default is the list of <b>"normal" IANA root servers</b>. Each dict in the list
contains at least two names: <code>address_type</code> (whose value is a bindata; it is currently
either "IPv4" or "IPv6") and <code>address_data</code> (whose value is a bindata).</p>

<h2>8.5 Context for Local Naming</h2>

<div class=forh>
getdns_return_t
getdns_context_set_append_name(
  getdns_context        *context,
  getdns_append_name_t  value
);</div>
<p class=cont>Specifies whether to append a suffix to the query string
before the API starts resolving a name.
The value is <span class=default>
<code>GETDNS_APPEND_NAME_ALWAYS</code></span>,
<code>GETDNS_APPEND_NAME_ONLY_TO_SINGLE_LABEL_AFTER_FAILURE</code>,
<code>GETDNS_APPEND_NAME_ONLY_TO_MULTIPLE_LABEL_NAME_AFTER_FAILURE</code>,
or <code>GETDNS_APPEND_NAME_NEVER</code>. This controls
whether or not to append the suffix given by <code>getdns_context_set_suffix</code></p>

<div class=forh>
getdns_return_t
getdns_context_set_suffix(
  getdns_context  *context,
  getdns_list     *value
);</div>
<p class=cont>The value is a list of bindatas that are strings that are
to be appended based on <code>getdns_context_set_append_name</code>; the default is an <span
class=default>empty list</span>. The values here follow the rules in section 2.1 of RFC 4343
to allow non-ASCII octets and special characters in labels.</p>

<h2>8.6 Context for DNSSEC</h2>

<p>These context settings affect queries that have extensions that specify the use of DNSSEC.</p>

<p>Applications that need to specify the DNSSEC trust anchors can use:</p>
<div class=forh>
getdns_return_t
getdns_context_set_dnssec_trust_anchors(
  getdns_context  *context,
  getdns_list     *value
);</div>
<p class=cont>The value is a list of bindatas that are the DNSSEC trust anchors. The default
is the trust anchors from the <span class=default>IANA root</span>. The trust anchors
are expressed as RDATAs from DNSKEY resource records.</p>

<p>In the rare case that an application needs to set the DNSSEC skew, it can:</p>
<div class=forh>
getdns_return_t
getdns_context_set_dnssec_allowed_skew(
  getdns_context  *context,
  uint32_t        value
);</div>
<p class=cont>The value is the number of seconds of skew that is allowed in either direction when
checking an RRSIG's Expiration and Inception fields. The default
is <span class=default>0</span>.</p>

<h2>8.7 Context Specific to Stub Resolvers</h2>

<p>An application can change the quering mechanism of a context to be to act as a stub
resolver. Such an application might first get the default information to make this change
from the operating system, probably through DHCP.</p>

<p>Note that if a context is changed to being a stub resolver, this automatically prevents the application
from using the extenstions for DNSSEC. An application that wants to both do DNSSEC and stub resolution
must do its own DNSSEC processing, possibly with the <code>getdns_validate_dnssec()</code> function.</p>

<div class=forh>
getdns_return_t
getdns_context_set_upstream_recursive_servers(
  getdns_context  *context,
  getdns_list     *upstream_list
);</div>
<p class=cont>The list of dicts define where a stub resolver will send queries. Each dict contains
at least two names: <code>address_type</code> (whose value is a bindata; it is currently either
"IPv4" or "IPv6") and <code>address_data</code> (whose value is a bindata).
For IPv6 link-local addresses, a <code>scope_id</code> name (a bindata) can be provided.  It might also contain
<code>port</code> to specify which port to use to contact these DNS servers; the default is 53. If
the stub and a recursive resolver both support TSIG (RFC 2845), the <code>upstream_list</code> entry
can also contain <code>tsig_algorithm</code> (a bindata) that is the name of the TSIG hash
algorithm, <code>tsig_name</code> (a bindata) that is the name of the TSIG key, and <code>tsig_secret</code> (a bindata) that is the TSIG key.</p>

<h2>8.8 Context for EDNS</h2>

<p>These context settings affect queries that have extensions that specify the use of OPT resource records.
These come from RFC 6891.</p>

<div class=forh>
getdns_return_t
getdns_context_set_edns_maximum_udp_payload_size(
  getdns_context  *context,
  uint16_t        value
);</div>
<p class=cont>The value is between 512 and 65535; when not set, outgoing values will
adhere to the suggestions in RFC 6891 and may follow a scheme that uses multiple values
to maximize receptivity.</p>

<div class=forh>
getdns_return_t
getdns_context_set_edns_extended_rcode(
  getdns_context  *context,
  uint8_t         value
);</div>
<p class=cont>The value is between 0 and 255; the default
is <span class=default>0</span>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_edns_version(
  getdns_context  *context,
  uint8_t         value
);</div>
<p class=cont>The value is between 0 and 255; the default
is <span class=default>0</span>.</p>

<div class=forh>
getdns_return_t
getdns_context_set_edns_do_bit(
  getdns_context  *context,
  uint8_t         value
);</div>
<p class=cont>The value is between 0 and 1; the default
is <span class=default>0</span>.</p>

<h2>8.9 Context Use of Custom Memory Management Functions</h2>

<div class=forh>
getdns_return_t
getdns_context_set_memory_functions(
  getdns_context *context,
  void           *(*malloc) (size_t),
  void           *(*realloc) (void *, size_t),
  void           (*free) (void *)
);</div>
<p class=cont>The given memory management functions will be used for creating the response dicts.
The response dicts inherit the custom memory management functions from the context and will deallocate themselves (and their members) with the custom deallocator.
By default, the system <span class=default>malloc</span>, <span class=default>realloc</span>, and <span>free</span> are used.</p>

<div class=forh>
getdns_return_t
getdns_context_set_extended_memory_functions(
  getdns_context *context,
  void           *userarg,
  void           *(*malloc)(void *userarg, size_t sz),
  void           *(*realloc)(void *userarg, void *ptr, size_t sz),
  void           (*free)(void *userarg, void *ptr)
);</div>
<p class=cont>The given extended memory management functions will be used for creating the response dicts.
The value of <code>userarg</code> argument will be passed to the custom <code>malloc</code>, <code>realloc</code>, and <code>free</code>.
The response dicts inherit the custom memory management functions and the value for <code>userarg</code> from the context and will deallocate themselves (and their members) with the custom deallocator.</p>

<h2>8.10 <a id="ContextCodes">Context Codes</a></h2>

<p>The context codes for <code>getdns_context_set_context_update_callback()</code> are:</p>

<p class=define>GETDNS_CONTEXT_CODE_NAMESPACES</p>
<p class=descrip>Change related to <code>getdns_context_set_namespaces</code></p>
<p class=define>GETDNS_CONTEXT_CODE_RESOLUTION_TYPE</p>
<p class=descrip>Change related to <code>getdns_context_set_resolution_type</code></p>
<p class=define>GETDNS_CONTEXT_CODE_FOLLOW_REDIRECTS</p>
<p class=descrip>Change related to <code>getdns_context_set_follow_redirects</code></p>
<p class=define>GETDNS_CONTEXT_CODE_UPSTREAM_RECURSIVE_SERVERS</p>
<p class=descrip>Change related to <code>getdns_context_set_upstream_recursive_servers</code></p>
<p class=define>GETDNS_CONTEXT_CODE_DNS_ROOT_SERVERS</p>
<p class=descrip>Change related to <code>getdns_context_set_dns_root_servers</code></p>
<p class=define>GETDNS_CONTEXT_CODE_DNS_TRANSPORT</p>
<p class=descrip>Change related to <code>getdns_context_set_dns_transport</code></p>
<p class=define>GETDNS_CONTEXT_CODE_LIMIT_OUTSTANDING_QUERIES</p>
<p class=descrip>Change related to <code>getdns_context_set_limit_outstanding_queries</code></p>
<p class=define>GETDNS_CONTEXT_CODE_APPEND_NAME</p>
<p class=descrip>Change related to <code>getdns_context_set_append_name</code></p>
<p class=define>GETDNS_CONTEXT_CODE_SUFFIX</p>
<p class=descrip>Change related to <code>getdns_context_set_suffix</code></p>
<p class=define>GETDNS_CONTEXT_CODE_DNSSEC_TRUST_ANCHORS</p>
<p class=descrip>Change related to <code>getdns_context_set_dnssec_trust_anchors</code></p>
<p class=define>GETDNS_CONTEXT_CODE_EDNS_MAXIMUM_UDP_PAYLOAD_SIZE</p>
<p class=descrip>Change related to <code>getdns_context_set_edns_maximum_udp_payload_size</code></p>
<p class=define>GETDNS_CONTEXT_CODE_EDNS_EXTENDED_RCODE</p>
<p class=descrip>Change related to <code>getdns_context_set_edns_extended_rcode</code></p>
<p class=define>GETDNS_CONTEXT_CODE_EDNS_VERSION</p>
<p class=descrip>Change related to <code>getdns_context_set_edns_version</code></p>
<p class=define>GETDNS_CONTEXT_CODE_EDNS_DO_BIT</p>
<p class=descrip>Change related to <code>getdns_context_set_edns_do_bit</code></p>
<p class=define>GETDNS_CONTEXT_CODE_DNSSEC_ALLOWED_SKEW</p>
<p class=descrip>Change related to <code>getdns_context_set_dnssec_allowed_skew</code></p>
<p class=define>GETDNS_CONTEXT_CODE_MEMORY_FUNCTIONS</p>
<p class=descrip>Change related to <code>getdns_context_set_memory_functions</code></p>
<p class=define>GETDNS_CONTEXT_CODE_TIMEOUT</p>
<p class=descrip>Change related to <code>getdns_context_set_timeout</code></p>
<p class=define>GETDNS_CONTEXT_CODE_IDLE_TIMEOUT</p>
<p class=descrip>Change related to <code>getdns_context_set_idle_timeout</code></p>


<h2>8.11 Getting API information and current Contexts</h2>
<p>An application might want to see information about the API itself and inspect the current context.
Use the <code>getdns_context_get_api_information</code> function.</p>
<div class=forh>
getdns_dict *
getdns_context_get_api_information(
  getdns_context *context
);
</div>
<p>The returned <code>getdns_dict</code> will contain the following name/value pairs:</p>
<ul>
<li><code>version_string</code> (a bindata) represents the version string for this version of the DNS
API.</li>

<li><code>implementation_string</code> (a bindata) is a string set by the API implementer. It might
be human-readable, and it might have information in it useful to an application developer (but it doesn't
have to).</li>

<li><code>resolution_type</code> (an int) is the type of resolver that the API is acting as in this context:
<code>GETDNS_RESOLUTION_RECURSING</code> or <code>GETDNS_RESOLUTION_STUB</code> (it will be
a recursing resolver unless the application changed this in a context.</li>

<li><code>all_context</code> (a dict) with names for all the types of context. This can be used with
getdns_pretty_print_dict() for debugging.</li>

</ul>

<h1>9. The Generated Files</h1>

<p>There is <a href="getdns-0.901.tgz">a tarball</a> that includes the .h files,
the examples, and so on. The examples all make, even though there is no API implementation, based
on a pseudo-implementation in the tarball; see make-examples-PLATFORM.sh. Note that this currently builds fine
on the Macintosh and Ubuntu; help is definitely appreciated on making the build process
work on more platforms if it fails there.</p>

<h1>10. <a id="Commentary">Commentary</a></h1>

<p>The following description of the API may be of value to those who might implement the design, and
those who are using an implementation of the design.</p>

<h2>10.1 API Design Considerations</h2>

<p>The genesis of this DNS API design was seeing other DNS API designs flounder. There are other
DNS APIs already available (such as draft-hayatnagarkar-dnsext-validator-api, as well
as DNSSEC APIs in BIND and Unbound), but there has been very little uptake of them. In talking to
application developers, there was a consistent story: that they felt that the APIs were developed by and
for DNS people, not applications developers.</p>

<p>This API design comes from talking to a small handful of applications developers about what they
would want to see in a modern DNS API. Now that the API is public, it would be great to hear from many
more application developers about whether it would meet their needs if it was implemented. My goal
is to create a design that is a natural follow-on to <code>getaddrinfo()</code> that has all the
capabilities that most application developers might want now or in the next few years: access to all
types of DNS records (including those which are yet to be defined), full DNSSEC awareness, IDN
handling, and parity for IPv4 and IPv6 addresses.</p>

<p>Note that this is just a design for a new API: there is no implementation of the design yet, but
at least one is being worked on. The process of designing the API without implementing it at the
same time has the huge advantage that major design changes could be made without any worry about
"but we already coded it the other way". In the early revisions of this document, many fundamental
design choices changed over and over, and even bike-shedding-like changes were allowed because they
didn't involve any programming effort.</p>

<p>This work was done independently, not through the IETF because the IETF generally doesn't take on
API work, and has explicitly avoided DNS API work in the past.</p>

<p>This API design has a Creative Commons license so that it can be
used widely by potential API implementers. This also allows other people who want to fork the design
to do so cleanly. Of course, any implementation of this API can choose whatever kind of license the
API implementer wishes, but it would be fabulous if one or more such implementations had Creative
Commons or BSD-ish licenses.</p>

<p>The API relies heavily on C macros and hopefully has no magic numbers.</p>

<h2>10.2 API Implementation Considerations</h2>

<p>All implementations of this API must act as recursive resolvers, and some might choose not to be
able to act as stub resolvers. Note that all implementations of this API must be DNSSEC validators.</p>

<p>Because there are many C event libraries available, and they have different calling routines,
it is the implementation of an API that determines which event library is used. This is certainly
not optimal for C programmers, but they appear to have gotten used to is so far. All implementations
of this API must support synchronous calls with <code>getdns_general_sync()</code>.</p>

<p>Versions are differentiated by version strings instead of version numbers. The version string for
this API is "getdns April 2013". Each implementation is free to set the implementation string as it
feels fit.</p>

<p>The API's .h file contains a macro called <code>GETDNS_COMPILATION_COMMENT</code>. This can be useful
to an application which will use the API because it can check the string without calling any
functions. Each time the API implementation is compiled, this string should be updated with unique
information about the implementation build.</p>

<p>The implementation of both the async and sync <code>getdns</code> functions will
copy all the values of the parameters into local memory, in case the application changes or
deallocates them.</p>

<hr width=90%>

<p><a rel="license" href="https://creativecommons.org/licenses/by/3.0/deed.en_US"><img alt="Creative
Commons License" style="border-width:0" <!-- src="https://i.creativecommons.org/l/by/3.0/80x15.png" -->
/></a><br />This work is licensed under a <a rel="license"
href="https://creativecommons.org/licenses/by/3.0/deed.en_US">Creative Commons Attribution 3.0
Unported License</a>.</p>

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