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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<TITLE>Apache module mod_isapi</TITLE>
</HEAD>
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<!--#include virtual="header.html" -->
<H1 ALIGN="CENTER">Module mod_isapi</H1>
<P>This module supports ISAPI Extensions within Apache for Windows.</P>
<P><A
HREF="module-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base
<BR>
<A
HREF="module-dict.html#SourceFile"
REL="Help"
><STRONG>Source File:</STRONG></A> mod_isapi.c
<BR>
<A
HREF="module-dict.html#ModuleIdentifier"
REL="Help"
><STRONG>Module Identifier:</STRONG></A> isapi_module
<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> WIN32 only
</P>
<H2>Summary</H2>
<P>This module implements the Internet Server extension API. It allows
Internet Server extensions (<EM>e.g.</EM> ISAPI .dll modules) to be
served by Apache for Windows, subject to the noted restrictions.</P>
<P>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 extention. <STRONG>Please <EM>do not</EM>
post such problems to Apache's lists or bug reporting pages.</STRONG></P>
<H2>Directives</H2>
<UL>
<LI><A HREF="#isapifilecache">ISAPIFileCache</A>
<LI><A HREF="#isapireadaheadbuffer">ISAPIReadAheadBuffer</A>
<LI><A HREF="#isapilognotsupported">ISAPILogNotSupported</A>
<LI><A HREF="#isapiappendlogtoerrors">ISAPIAppendLogToErrors</A>
<LI><A HREF="#isapiappendlogtoquery">ISAPIAppendLogToQuery</A>
</UL>
<H2>Usage</H2>
<P>In the server configuration file, use the AddHandler directive to
associate ISAPI files with the <CODE>isapi-isa</CODE> handler, and map
it to the with their file extensions. To enable any .dll file to be
processed as an ISAPI extention, edit the httpd.conf file and add the
following line:</P>
<PRE>
AddHandler isapi-isa .dll
</PRE>
<P>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 httpd.conf:
<PRE>
ISAPICacheFile c:/WebWork/Scripts/ISAPI/mytest.dll
</PRE>
<P>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, <CODE>Options ExecCGI</CODE> must be set for
the directory that contains the ISAPI .dll file.</P>
<P>Review the <A HREF="#notes">Additional Notes</A> and the
<A HREF="#journal">Programmer's Journal</A> for additional details and
clarification of the specific ISAPI support offered by mod_isapi.</P>
<H2><A NAME="notes">Additional Notes</A></H2>
<P>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 <CODE>ISAPILogNotSupported Off</CODE>
exists to quiet this noise.</P>
<P>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 ISAPICacheFile 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.</P>
<P>Also, remember that while Apache supports ISAPI Extensions, it
<STRONG>does not support ISAPI Filters.</STRONG> Support for filters may
be added at a later date, but no support is planned at this time.</P>
<H2><A NAME="journal">Programmer's Journal</A></H2>
<P>If you are programming Apache 2.0 mod_isapi modules, you must limit your
calls to ServerSupportFunction to the following directives:</P>
<DL>
<DT>HSE_REQ_SEND_URL_REDIRECT_RESP
<DD>Redirect the user to another location.<BR>
This must be a fully qualified URL (e.g. http://server/location).
<DT>HSE_REQ_SEND_URL
<DD>Redirect the user to another location.<BR>
This cannot be a fully qualified URL, you are not allowed
to pass the protocol or a server name (e.g. simply /location).<BR>
This redirection is handled by the server, not the browser.<BR>
<STRONG>Warning:</STRONG> in their recent documentation, Microsoft
appears to have abandoned the distinction between the two
HSE_REQ_SEND_URL functions. Apache continues to treat them as two
distinct functions with different requirements and behaviors.
<DT>HSE_REQ_SEND_RESPONSE_HEADER
<DD>Apache accepts a response body following the header if it follows
the blank line (two consecutive newlines) in the headers string
argument. This body cannot contain NULLs, since the headers
argument is NULL terminated.
<DT>HSE_REQ_DONE_WITH_SESSION
<DD>Apache considers this a no-op, since the session will be finished
when the ISAPI returns from processing.
<DT>HSE_REQ_MAP_URL_TO_PATH
<DD>Apache will translate a virtual name to a physical name.
<DT>HSE_APPEND_LOG_PARAMETER
<DD>This logged message may be captured in any of the following logs:
<UL>
<LI>in the \"%{isapi-parameter}n\" component in a CustomLog directive
<LI>in the %q log component with the ISAPIAppendLogToQuery On directive
<LI>in the error log with the ISAPIAppendLogToErrors On directive
</UL>
The first option, the %{isapi-parameter}n component, is always available
and prefered.
<DT>HSE_REQ_IS_KEEP_CONN
<DD>Will return the negotiated Keep-Alive status.
<DT>HSE_REQ_SEND_RESPONSE_HEADER_EX
<DD>Will behave as documented, although the fKeepConn flag is ignored.
<DT>HSE_REQ_IS_CONNECTED
<DD>Will report false if the request has been aborted.
</DL>
<P>Apache returns FALSE to any unsupported call to ServerSupportFunction, and
sets the GetLastError value to ERROR_INVALID_PARAMETER.</P>
<P>ReadClient retrieves the request body exceeding the initial buffer
(defined by ISAPIReadAheadBuffer). Based on the ISAPIReadAheadBuffer
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 to
retrieve the remaining request body.</P>
<P>WriteClient is supported, but only with the HSE_IO_SYNC flag or
no option flag (value of 0). Any other WriteClient request will
be rejected with a return value of FALSE, and a GetLastError
value of ERROR_INVALID_PARAMETER.</P>
<P>GetServerVariable 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
and ALL_RAW values.</P>
<P>Apache 2.0 mod_isapi supports additional features introduced in later
versions of the ISAPI specification, as well as limited emulation of
async I/O and the TransmitFile semantics. Apache also supports preloading
ISAPI .dlls for performance, neither of which were not available under
Apache 1.3 mod_isapi.</P>
<HR>
<H2><A NAME="isapifilecache">ISAPIFileCache directive</A></H2>
<!--%plaintext <?INDEX {\tt ISAPIFileCache} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> ISAPIFileCache <EM>file [file...]</EM><BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> None<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_isapi<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 2.0 and later, Win32 only<P>
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.
<P>
<HR>
<H2><A NAME="isapireadaheadbuffer">ISAPIReadAheadBuffer directive</A></H2>
<!--%plaintext <?INDEX {\tt ISAPIReadAheadBuffer} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> ISAPIReadAheadBuffer <EM>size</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> 49152<BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> None<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_isapi<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.3.13 and later, Win32 only<P>
Defines the maximum size of the Read Ahead Buffer sent to
ISAPI extentions when they are initally invoked. All
remaining data must be retrieved using the ReadClient
callback; some ISAPI extensions may not support the
ReadClient function. Refer questions to the ISAPI extention's
author.
<P>
<HR>
<H2><A NAME="isapilognotsupported">ISAPILogNotSupported directive</A></H2>
<!--%plaintext <?INDEX {\tt ISAPILogNotSupported} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> ISAPILogNotSupported <EM>on|off</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> on<BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> None<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_isapi<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.3.13 and later, Win32 only<P>
Logs all requests for unsupported features from ISAPI extentions
in the server error log. While this should be turned off once
all desired ISAPI modules are functioning, it defaults to on
to help administrators track down problems.
<P>
<HR>
<H2><A NAME="isapiappendlogtoerrors">ISAPIAppendLogToErrors directive</A></H2>
<!--%plaintext <?INDEX {\tt ISAPIAppendLogToErrors} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> ISAPIAppendLogToErrors <EM>on|off</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> off<BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> None<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_isapi<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.3.13 and later, Win32 only<P>
Record HSE_APPEND_LOG_PARAMETER requests from ISAPI extentions
to the server error log.
<P>
<HR>
<H2><A NAME="isapiappendlogtoquery">ISAPIAppendLogToQuery directive</A></H2>
<!--%plaintext <?INDEX {\tt ISAPIAppendLogToQuery} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> ISAPIAppendLogToQuery <EM>on|off</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> off<BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Override"
REL="Help"
><STRONG>Override:</STRONG></A> None<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Base<BR>
<A
HREF="directive-dict.html#Module"
REL="Help"
><STRONG>Module:</STRONG></A> mod_isapi<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.3.13 and later, Win32 only<P>
Record HSE_APPEND_LOG_PARAMETER requests from ISAPI extentions
to the query field (appended to the CustomLog %q component).
<P>
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