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<title>Misc.Magic_number</title>
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<h1>Module <a href="type_Misc.Magic_number.html">Misc.Magic_number</a></h1>
<pre><span id="MODULEMagic_number"><span class="keyword">module</span> Magic_number</span>: <code class="code"><span class="keyword">sig</span></code> <a href="Misc.Magic_number.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><hr width="100%">
<p>a typical magic number is "Caml1999I011"; it is formed of an
alphanumeric prefix, here Caml1990I, followed by a version,
here 011. The prefix identifies the kind of the versioned data:
here the I indicates that it is the magic number for .cmi files.</p>
<p>All magic numbers have the same byte length, <code class="code">magic_length</code>, and
this is important for users as it gives them the number of bytes
to read to obtain the byte sequence that should be a magic
number. Typical user code will look like:</p>
<pre class="codepre"><code class="code"> <span class="keyword">let</span> ic = open_in_bin path <span class="keyword">in</span>
<span class="keyword">let</span> magic =
<span class="keyword">try</span> really_input_string ic <span class="constructor">Magic_number</span>.magic_length
<span class="keyword">with</span> <span class="constructor">End_of_file</span> <span class="keywordsign">-></span> ... <span class="keyword">in</span>
<span class="keyword">match</span> <span class="constructor">Magic_number</span>.parse magic <span class="keyword">with</span>
<span class="keywordsign">|</span> <span class="constructor">Error</span> parse_error <span class="keywordsign">-></span> ...
<span class="keywordsign">|</span> <span class="constructor">Ok</span> info <span class="keywordsign">-></span> ...
</code></pre>
<p>A given compiler version expects one specific version for each
kind of object file, and will fail if given an unsupported
version. Because versions grow monotonically, you can compare
the parsed version with the expected "current version" for
a kind, to tell whether the wrong-magic object file comes from
the past or from the future.</p>
<p>An example of code block that expects the "currently supported version"
of a given kind of magic numbers, here <code class="code"><span class="constructor">Cmxa</span></code>, is as follows:</p>
<pre class="codepre"><code class="code"> <span class="keyword">let</span> ic = open_in_bin path <span class="keyword">in</span>
<span class="keyword">begin</span>
<span class="keyword">try</span> <span class="constructor">Magic_number</span>.(expect_current <span class="constructor">Cmxa</span> (get_info ic)) <span class="keyword">with</span>
<span class="keywordsign">|</span> <span class="constructor">Parse_error</span> error <span class="keywordsign">-></span> ...
<span class="keywordsign">|</span> <span class="constructor">Unexpected</span> error <span class="keywordsign">-></span> ...
<span class="keyword">end</span>;
...
</code></pre>
<p>Parse errors distinguish inputs that are <code class="code"><span class="constructor">Not_a_magic_number</span> str</code>,
which are likely to come from the file being completely
different, and <code class="code"><span class="constructor">Truncated</span> str</code>, raised by headers that are the
(possibly empty) prefix of a valid magic number.</p>
<p>Unexpected errors correspond to valid magic numbers that are not
the one expected, either because it corresponds to a different
kind, or to a newer or older version.</p>
<p>The helper functions <code class="code">explain_parse_error</code> and <code class="code">explain_unexpected_error</code>
will generate a textual explanation of each error,
for use in error messages.</p>
<pre><code><span id="TYPEnative_obj_config"><span class="keyword">type</span> <code class="type"></code>native_obj_config</span> = {</code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTnative_obj_config.flambda">flambda</span> : <code class="type">bool</code>;</code></td>
</tr></table>
<code>}</code>
<div class="info ">
<div class="info-desc">
<p>native object files have a format and magic number that depend
on certain native-compiler configuration parameters. This
configuration space is expressed by the <code class="code">native_obj_config</code>
type.</p>
</div>
</div>
<pre><span id="VALnative_obj_config"><span class="keyword">val</span> native_obj_config</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEnative_obj_config">native_obj_config</a></code></pre><div class="info ">
<div class="info-desc">
<p>the native object file configuration of the active/configured compiler.</p>
</div>
</div>
<pre><span id="TYPEversion"><span class="keyword">type</span> <code class="type"></code>version</span> = <code class="type">int</code> </pre>
<pre><code><span id="TYPEkind"><span class="keyword">type</span> <code class="type"></code>kind</span> = </code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Exec"><span class="constructor">Exec</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmi"><span class="constructor">Cmi</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmo"><span class="constructor">Cmo</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cma"><span class="constructor">Cma</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmx"><span class="constructor">Cmx</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEnative_obj_config">native_obj_config</a></code></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmxa"><span class="constructor">Cmxa</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEnative_obj_config">native_obj_config</a></code></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmxs"><span class="constructor">Cmxs</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Cmt"><span class="constructor">Cmt</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Ast_impl"><span class="constructor">Ast_impl</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTkind.Ast_intf"><span class="constructor">Ast_intf</span></span></code></td>
</tr></table>
<pre><code><span id="TYPEinfo"><span class="keyword">type</span> <code class="type"></code>info</span> = {</code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTinfo.kind">kind</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a></code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTinfo.version">version</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEversion">version</a></code>;</code></td>
<td class="typefieldcomment" align="left" valign="top" ><code>(*</code></td><td class="typefieldcomment" align="left" valign="top" ><div class="info ">
<div class="info-desc">
<p>Note: some versions of the compiler use the same <code class="code">version</code> suffix
for all kinds, but others use different versions counters for different
kinds. We may only assume that versions are growing monotonically
(not necessarily always by one) between compiler versions.</p>
</div>
</div>
</td><td class="typefieldcomment" align="left" valign="bottom" ><code>*)</code></td>
</tr></table>
<code>}</code>
<pre><span id="TYPEraw"><span class="keyword">type</span> <code class="type"></code>raw</span> = <code class="type">string</code> </pre>
<div class="info ">
<div class="info-desc">
<p>the type of raw magic numbers,
such as "Caml1999A027" for the .cma files of OCaml 4.10</p>
</div>
</div>
<h4 id="3_Parsingmagicnumbers">Parsing magic numbers</h4>
<pre><code><span id="TYPEparse_error"><span class="keyword">type</span> <code class="type"></code>parse_error</span> = </code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTparse_error.Truncated"><span class="constructor">Truncated</span></span> <span class="keyword">of</span> <code class="type">string</code></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTparse_error.Not_a_magic_number"><span class="constructor">Not_a_magic_number</span></span> <span class="keyword">of</span> <code class="type">string</code></code></td>
</tr></table>
<pre><span id="VALexplain_parse_error"><span class="keyword">val</span> explain_parse_error</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> option -> <a href="Misc.Magic_number.html#TYPEparse_error">parse_error</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>Produces an explanation for a parse error. If no kind is provided,
we use an unspecific formulation suggesting that any compiler-produced
object file would have been satisfying.</p>
</div>
</div>
<pre><span id="VALparse"><span class="keyword">val</span> parse</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEraw">raw</a> -><br> (<a href="Misc.Magic_number.html#TYPEinfo">info</a>, <a href="Misc.Magic_number.html#TYPEparse_error">parse_error</a>) result</code></pre><div class="info ">
<div class="info-desc">
<p>Parses a raw magic number</p>
</div>
</div>
<pre><span id="VALread_info"><span class="keyword">val</span> read_info</span> : <code class="type">in_channel -><br> (<a href="Misc.Magic_number.html#TYPEinfo">info</a>, <a href="Misc.Magic_number.html#TYPEparse_error">parse_error</a>) result</code></pre><div class="info ">
<div class="info-desc">
<p>Read a raw magic number from an input channel.</p>
<p>If the data read <code class="code">str</code> is not a valid magic number, it can be
recovered from the <code class="code"><span class="constructor">Truncated</span> str <span class="keywordsign">|</span> <span class="constructor">Not_a_magic_number</span> str</code>
payload of the <code class="code"><span class="constructor">Error</span> parse_error</code> case.</p>
<p>If parsing succeeds with an <code class="code"><span class="constructor">Ok</span> info</code> result, we know that
exactly <code class="code">magic_length</code> bytes have been consumed from the
input_channel.</p>
<p>If you also wish to enforce that the magic number
is at the current version, see <a href="Misc.Magic_number.html#VALread_current_info"><code class="code"><span class="constructor">Misc</span>.<span class="constructor">Magic_number</span>.read_current_info</code></a> below.</p>
</div>
</div>
<pre><span id="VALmagic_length"><span class="keyword">val</span> magic_length</span> : <code class="type">int</code></pre><div class="info ">
<div class="info-desc">
<p>all magic numbers take the same number of bytes</p>
</div>
</div>
<h4 id="3_Checkingthatmagicnumbersarecurrent">Checking that magic numbers are current</h4>
<pre><code><span id="TYPEunexpected"><span class="keyword">type</span> <code class="type">'a</code> unexpected</span> = {</code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTunexpected.expected">expected</span> : <code class="type">'a</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTunexpected.actual">actual</span> : <code class="type">'a</code>;</code></td>
</tr></table>
<code>}</code>
<pre><code><span id="TYPEunexpected_error"><span class="keyword">type</span> <code class="type"></code>unexpected_error</span> = </code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTunexpected_error.Kind"><span class="constructor">Kind</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> <a href="Misc.Magic_number.html#TYPEunexpected">unexpected</a></code></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTunexpected_error.Version"><span class="constructor">Version</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a><br> * <a href="Misc.Magic_number.html#TYPEversion">version</a> <a href="Misc.Magic_number.html#TYPEunexpected">unexpected</a></code></code></td>
</tr></table>
<pre><span id="VALcheck_current"><span class="keyword">val</span> check_current</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -><br> <a href="Misc.Magic_number.html#TYPEinfo">info</a> -><br> (unit, <a href="Misc.Magic_number.html#TYPEunexpected_error">unexpected_error</a>) result</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">check_current kind info</code> checks that the provided magic <code class="code">info</code>
is the current version of <code class="code">kind</code>'s magic header.</p>
</div>
</div>
<pre><span id="VALexplain_unexpected_error"><span class="keyword">val</span> explain_unexpected_error</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEunexpected_error">unexpected_error</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>Provides an explanation of the <code class="code">unexpected_error</code>.</p>
</div>
</div>
<pre><code><span id="TYPEerror"><span class="keyword">type</span> <code class="type"></code>error</span> = </code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTerror.Parse_error"><span class="constructor">Parse_error</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEparse_error">parse_error</a></code></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTerror.Unexpected_error"><span class="constructor">Unexpected_error</span></span> <span class="keyword">of</span> <code class="type"><a href="Misc.Magic_number.html#TYPEunexpected_error">unexpected_error</a></code></code></td>
</tr></table>
<pre><span id="VALread_current_info"><span class="keyword">val</span> read_current_info</span> : <code class="type">expected_kind:<a href="Misc.Magic_number.html#TYPEkind">kind</a> option -><br> in_channel -><br> (<a href="Misc.Magic_number.html#TYPEinfo">info</a>, <a href="Misc.Magic_number.html#TYPEerror">error</a>) result</code></pre><div class="info ">
<div class="info-desc">
<p>Read a magic number as <code class="code">read_info</code>,
and check that it is the current version as its kind.
If the <code class="code">expected_kind</code> argument is <code class="code"><span class="constructor">None</span></code>, any kind is accepted.</p>
</div>
</div>
<h4 id="3_Informationonmagicnumbers">Information on magic numbers</h4>
<pre><span id="VALstring_of_kind"><span class="keyword">val</span> string_of_kind</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>a user-printable string for a kind, eg. "exec" or "cmo", to use
in error messages.</p>
</div>
</div>
<pre><span id="VALhuman_name_of_kind"><span class="keyword">val</span> human_name_of_kind</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>a user-meaningful name for a kind, eg. "executable file" or
"bytecode object file", to use in error messages.</p>
</div>
</div>
<pre><span id="VALcurrent_raw"><span class="keyword">val</span> current_raw</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -> <a href="Misc.Magic_number.html#TYPEraw">raw</a></code></pre><div class="info ">
<div class="info-desc">
<p>the current magic number of each kind</p>
</div>
</div>
<pre><span id="VALcurrent_version"><span class="keyword">val</span> current_version</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -> <a href="Misc.Magic_number.html#TYPEversion">version</a></code></pre><div class="info ">
<div class="info-desc">
<p>the current version of each kind</p>
</div>
</div>
<h4 id="3_Rawrepresentations">Raw representations</h4>
<p>Mainly for internal usage and testing.</p>
<pre><span id="TYPEraw_kind"><span class="keyword">type</span> <code class="type"></code>raw_kind</span> = <code class="type">string</code> </pre>
<div class="info ">
<div class="info-desc">
<p>the type of raw magic numbers kinds,
such as "Caml1999A" for .cma files</p>
</div>
</div>
<pre><span id="VALparse_kind"><span class="keyword">val</span> parse_kind</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEraw_kind">raw_kind</a> -> <a href="Misc.Magic_number.html#TYPEkind">kind</a> option</code></pre><div class="info ">
<div class="info-desc">
<p>parse a raw kind into a kind</p>
</div>
</div>
<pre><span id="VALraw_kind"><span class="keyword">val</span> raw_kind</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEkind">kind</a> -> <a href="Misc.Magic_number.html#TYPEraw_kind">raw_kind</a></code></pre><div class="info ">
<div class="info-desc">
<p>the current raw representation of a kind.</p>
<p>In some cases the raw representation of a kind has changed
over compiler versions, so other files of the same kind
may have different raw kinds.
Note that all currently known cases are parsed correctly by <code class="code">parse_kind</code>.</p>
</div>
</div>
<pre><span id="VALraw"><span class="keyword">val</span> raw</span> : <code class="type"><a href="Misc.Magic_number.html#TYPEinfo">info</a> -> <a href="Misc.Magic_number.html#TYPEraw">raw</a></code></pre><div class="info ">
<div class="info-desc">
<p>A valid raw representation of the magic number.</p>
<p>Due to past and future changes in the string representation of
magic numbers, we cannot guarantee that the raw strings returned
for past and future versions actually match the expectations of
those compilers. The representation is accurate for current
versions, and it is correctly parsed back into the desired
version by the parsing functions above.</p>
</div>
</div>
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