4.2 Overview of a Request Handler

A handler 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 by the user and written in Python. A handler written in Python is not any different from a handler written in C, and follows these rules:

A handler function will always be passed a reference to a request object. (Throughout this manual, the request object is often referred to by the req variable.)

Every handler can return:

apache.OK, meaning this phase of the request was handled by this handler and no errors occurred.
apache.DECLINED, meaning this handler has not handled this phase of the request to completion and Apache needs to look for another handler in subsequent modules.

apache.HTTP_ERROR, meaning an HTTP error occurred. HTTP_ERROR can be any of the following:

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

As an alternative to returning an HTTP error code, handlers can signal an error by raising the apache.SERVER_RETURN exception, and providing an HTTP error code as the exception value, e.g.

raise apache.SERVER_RETURN, apache.HTTP_FORBIDDEN

Handlers can send content to the client using the req.write() method.

Client data, such as POST requests, can be read by using the req.read() function.

NOTE: The directory of the Apache Python*Handler directive in effect is prepended to the sys.path. If the directive was specified in a server config file outside any <Directory>, then the directory is unknown and not prepended.

An example of a minimalistic handler might be:

from mod_python import apache

def requesthandler(req):
    req.content_type = "text/plain"
    req.write("Hello World!")
    return apache.OK