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<H1><A NAME="SECTION006200000000000000000"> </A>
<BR>
4.2 Overview of a Handler
</H1>
<P>
A <i class="dfn">handler</i> is a function that processes a particular phase of a
request. Apache processes requests in phases - read the request,
process headers, provide content, etc. For every phase, it will call
handlers, provided by either the Apache core or one of its modules,
such as mod_python, which passes control to functions provided b the
user and written in Python. A handler written in Python is not any
different than a handler written in C, and follows these rules:
<P>
<a name='l2h-15'> </a>A handler function will always be passed a reference to a
<tt class="class">Request</tt> object. (Throughout this manual, the <tt class="class">Request</tt>
object is often referred to by the <code>req</code> variable.)
<P>
Every handler can return:
<P>
<UL>
<LI><tt class="constant">apache.OK</tt>, meaning this phase of the request was handled by this
handler and no errors occurred.
<P>
</LI>
<LI><tt class="constant">apache.DECLINED</tt>, meaning this handler refused to handle this phase of
the requestand Apache needs to look for another handler.
<P>
</LI>
<LI><tt class="constant">apache.<i>HTTP_ERROR</i></tt>, meaning an HTTP error occurred.
<var>HTTP_ERROR</var> can be:
<P>
<dl><dd><pre class="verbatim">
HTTP_CONTINUE = 100
HTTP_SWITCHING_PROTOCOLS = 101
HTTP_PROCESSING = 102
HTTP_OK = 200
HTTP_CREATED = 201
HTTP_ACCEPTED = 202
HTTP_NON_AUTHORITATIVE = 203
HTTP_NO_CONTENT = 204
HTTP_RESET_CONTENT = 205
HTTP_PARTIAL_CONTENT = 206
HTTP_MULTI_STATUS = 207
HTTP_MULTIPLE_CHOICES = 300
HTTP_MOVED_PERMANENTLY = 301
HTTP_MOVED_TEMPORARILY = 302
HTTP_SEE_OTHER = 303
HTTP_NOT_MODIFIED = 304
HTTP_USE_PROXY = 305
HTTP_TEMPORARY_REDIRECT = 307
HTTP_BAD_REQUEST = 400
HTTP_UNAUTHORIZED = 401
HTTP_PAYMENT_REQUIRED = 402
HTTP_FORBIDDEN = 403
HTTP_NOT_FOUND = 404
HTTP_METHOD_NOT_ALLOWED = 405
HTTP_NOT_ACCEPTABLE = 406
HTTP_PROXY_AUTHENTICATION_REQUIRED= 407
HTTP_REQUEST_TIME_OUT = 408
HTTP_CONFLICT = 409
HTTP_GONE = 410
HTTP_LENGTH_REQUIRED = 411
HTTP_PRECONDITION_FAILED = 412
HTTP_REQUEST_ENTITY_TOO_LARGE = 413
HTTP_REQUEST_URI_TOO_LARGE = 414
HTTP_UNSUPPORTED_MEDIA_TYPE = 415
HTTP_RANGE_NOT_SATISFIABLE = 416
HTTP_EXPECTATION_FAILED = 417
HTTP_UNPROCESSABLE_ENTITY = 422
HTTP_LOCKED = 423
HTTP_FAILED_DEPENDENCY = 424
HTTP_INTERNAL_SERVER_ERROR = 500
HTTP_NOT_IMPLEMENTED = 501
HTTP_BAD_GATEWAY = 502
HTTP_SERVICE_UNAVAILABLE = 503
HTTP_GATEWAY_TIME_OUT = 504
HTTP_VERSION_NOT_SUPPORTED = 505
HTTP_VARIANT_ALSO_VARIES = 506
HTTP_INSUFFICIENT_STORAGE = 507
HTTP_NOT_EXTENDED = 510
</pre></dl>
<P>
</LI>
</UL>
<P>
As an alternative to <i>returning</i> an HTTP error code, handlers can
signal an error by <i>raising</i> the <tt class="constant">apache.SERVER_RETURN</tt>
exception, and providing an HTTP error code as the exception value,
e.g.
<P>
<dl><dd><pre class="verbatim">
raise apache.SERVER_RETURN, apache.HTTP_FORBIDDEN
</pre></dl>
<P>
Handlers can send content to the client using the <tt class="method">Request.write()</tt>
method. Before sending the body of the response, headers must be
sent using the <tt class="method">Request.send_http_header()</tt> method.
<P>
Client data, such as POST requests, can be read by using the
<tt class="method">Request.read()</tt> function.
<P>
<b>NOTE:</b> The directory of the Apache <code>Python*Handler</code>
directive in effect is prepended to the <code>sys.path</code>. If the
directive was specified in a server config file outside any
<code><Directory></code>, then the directory is unknown and not prepended.
<P>
An example of a minimalistic handler might be:
<P>
<dl><dd><pre class="verbatim">
from mod_python import apache
def requesthandler(req):
req.content_type = "text/plain"
req.send_http_header()
req.write("Hello World!")
return apache.OK
</pre></dl>
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<span class="release-info">Release 2.7.8, documentation updated on April 19, 2002.</span>
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