Apache Module mod_isapi

This module implements the Internet Server extension API. It allows Internet Server extensions (e.g. ISAPI .dll modules) to be served by Apache for Windows, subject to the noted restrictions.

ISAPI extension modules (.dll files) are written by third parties. The Apache Group does not author these modules, so we provide no support for them. Please contact the ISAPI's author directly if you are experiencing problems running their ISAPI extension. Please do not post such problems to Apache's lists or bug reporting pages.

was the proper handler name, rather than isapi-handler

. As of 2.3 development versions of the Apache server, isapi-isa

is no longer valid. You will need to change your configuration to use isapi-handler

instead.There is no capability within the Apache server to leave a requested module loaded. However, you may preload and keep a specific module loaded by using the following syntax in your apache2.conf:

ISAPICacheFile c:/WebWork/Scripts/ISAPI/mytest.dll

Whether or not you have preloaded an ISAPI extension, all ISAPI extensions are governed by the same permissions and restrictions as CGI scripts. That is, OptionsExecCGI

must be set for the directory that contains the ISAPI .dll file.

Review the Additional Notes and the Programmer's Journal for additional details and clarification of the specific ISAPI support offered by

Apache's ISAPI implementation conforms to all of the ISAPI 2.0 specification, except for some "Microsoft-specific" extensions dealing with asynchronous I/O. Apache's I/O model does not allow asynchronous reading and writing in a manner that the ISAPI could access. If an ISA tries to access unsupported features, including async I/O, a message is placed in the error log to help with debugging. Since these messages can become a flood, the directive ISAPILogNotSupported Off

exists to quiet this noise.

Some servers, like Microsoft IIS, load the ISAPI extension into the server and keep it loaded until memory usage is too high, or unless configuration options are specified. Apache currently loads and unloads the ISAPI extension each time it is requested, unless the

directive is specified. This is inefficient, but Apache's memory model makes this the most effective method. Many ISAPI modules are subtly incompatible with the Apache server, and unloading these modules helps to ensure the stability of the server.ISAPICacheFile

Also, remember that while Apache supports ISAPI Extensions, it does not support ISAPI Filters. Support for filters may be added at a later date, but no support is planned at this time.

).In their recent documentation, Microsoft appears to have abandoned the distinction between the two HSEREQSEND_URL

functions. Apache continues to treat them as two distinct functions with different requirements and behaviors.

directiveThe first option, the %{isapi-parameter}n

component, is always available and preferred.

flag is ignored.HSEREQIS_CONNECTED

, and sets the GetLastError

retrieves the request body exceeding the initial buffer (defined by

). Based on the ISAPIReadAheadBufferISAPIReadAheadBuffer

setting (number of bytes to buffer prior to calling the ISAPI handler) shorter requests are sent complete to the extension when it is invoked. If the request is longer, the ISAPI extension must use ReadClient

is supported, but only with the HSEIOSYNC

request will be rejected with a return value of FALSE

is supported, although extended server variables do not exist (as defined by other servers.) All the usual Apache CGI environment variables are available from GetServerVariable

, as well as the ALL_HTTP

supports additional features introduced in later versions of the ISAPI specification, as well as limited emulation of async I/O and the mod_isapiTransmitFile

semantics. Apache httpd also supports preloading ISAPI .dlls for performance.

Specifies a space-separated list of file names to be loaded when the Apache server is launched, and remain loaded until the server is shut down. This directive may be repeated for every ISAPI .dll file desired. The full path name of each file should be specified. If the path name is not absolute, it will be treated relative to

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Apache HTTP Server Version 2.4