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<h1 align="CENTER">Module mod_isapi</h1>
<p>This module supports ISAPI Extensions within Apache for
Windows.</p>
rel="Help"><strong>Status:</strong></a> Base<br />
<a href="module-dict.html#SourceFile"
<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
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>
<li><a
href="#isapireadaheadbuffer">ISAPIReadAheadBuffer</a></li>
<li><a
href="#isapilognotsupported">ISAPILogNotSupported</a></li>
<li><a
href="#isapiappendlogtoerrors">ISAPIAppendLogToErrors</a></li>
<li><a
href="#isapiappendlogtoquery">ISAPIAppendLogToQuery</a></li>
</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:</p>
<pre>
</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 id="notes" 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 id="journal" 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</dt>
<dd>Redirect the user to another location.<br />
This must be a fully qualified URL (e.g.
http://server/location).</dd>
<dt>HSE_REQ_SEND_URL</dt>
<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.</dd>
<dt>HSE_REQ_SEND_RESPONSE_HEADER</dt>
<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.</dd>
<dt>HSE_REQ_DONE_WITH_SESSION</dt>
<dd>Apache considers this a no-op, since the session will be
finished when the ISAPI returns from processing.</dd>
<dt>HSE_REQ_MAP_URL_TO_PATH</dt>
<dd>Apache will translate a virtual name to a physical
name.</dd>
<dt>HSE_APPEND_LOG_PARAMETER</dt>
<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>
<li>in the %q log component with the
ISAPIAppendLogToQuery On directive</li>
<li>in the error log with the ISAPIAppendLogToErrors On
directive</li>
</ul>
The first option, the %{isapi-parameter}n component, is
always available and prefered.
</dd>
<dt>HSE_REQ_IS_KEEP_CONN</dt>
<dd>Will return the negotiated Keep-Alive status.</dd>
<dt>HSE_REQ_SEND_RESPONSE_HEADER_EX</dt>
<dd>Will behave as documented, although the fKeepConn flag is
ignored.</dd>
<dt>HSE_REQ_IS_CONNECTED</dt>
<dd>Will report false if the request has been aborted.</dd>
</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 id="isapifilecache" 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</em> [<em>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 id="isapireadaheadbuffer"
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 extensions when they are initially 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 extension's author.</p>
<hr />
<h2><a id="isapilognotsupported"
name="isapilognotsupported">ISAPILogNotSupported
directive</a></h2>
<!--%plaintext <?INDEX {\tt ISAPILogNotSupported} directive> -->
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> ISAPILogNotSupported
on|off<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
extensions 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 id="isapiappendlogtoerrors"
name="isapiappendlogtoerrors">ISAPIAppendLogToErrors
directive</a></h2>
<!--%plaintext <?INDEX {\tt ISAPIAppendLogToErrors} directive> -->
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> ISAPIAppendLogToErrors
on|off<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
extensions to the server error log.</p>
<hr />
<h2><a id="isapiappendlogtoquery"
name="isapiappendlogtoquery">ISAPIAppendLogToQuery
directive</a></h2>
<!--%plaintext <?INDEX {\tt ISAPIAppendLogToQuery} directive> -->
<a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> ISAPIAppendLogToQuery
on|off<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
extensions to the query field (appended to the CustomLog %q
component).</p>
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