<?xml version="1.0"?> <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd"> <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?> <modulesynopsis> <name>mod_isapi</name> <description>ISAPI Extensions within Apache for Windows</description> <status>Base</status> <sourcefile>mod_isapi.c</sourcefile> <identifier>isapi_module</identifier> <compatibility>Win32 only</compatibility> <summary> <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 extension. <strong>Please <em>do not</em> post such problems to Apache's lists or bug reporting pages.</strong></p> </summary> <section id="usage"><title>Usage</title> <p>In the server configuration file, use the <directive module="mod_mime">AddHandler</directive> directive to associate ISAPI files with the <code>isapi-isa</code> handler, and map it to them with their file extensions. To enable any .dll file to be processed as an ISAPI extension, edit the httpd.conf file and add the following line:</p> <example> AddHandler isapi-isa .dll </example> <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> <example> ISAPICacheFile c:/WebWork/Scripts/ISAPI/mytest.dll </example> <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, <directive module="core" >Options</directive> <code>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 <module>mod_isapi</module>.</p> </section> <section id="notes"><title>Additional Notes</title> <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 <directive module="mod_isapi" >ISAPICacheFile</directive> 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> </section> <section id="journal"><title>Programmer's Journal</title> <p>If you are programming Apache 2.0 <module>mod_isapi</module> modules, you must limit your calls to <code>ServerSupportFunction</code> to the following directives:</p> <dl> <dt><code>HSE_REQ_SEND_URL_REDIRECT_RESP</code></dt> <dd>Redirect the user to another location.<br /> This must be a fully qualified URL (<em>e.g.</em> <code>http://server/location</code>).</dd> <dt><code>HSE_REQ_SEND_URL</code></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 (<em>e.g.</em> simply <code>/location</code>).<br /> This redirection is handled by the server, not the browser.<br /> <note type="warning"><title>Warning</title> <p>In their recent documentation, Microsoft appears to have abandoned the distinction between the two <code>HSE_REQ_SEND_URL</code> functions. Apache continues to treat them as two distinct functions with different requirements and behaviors.</p> </note></dd> <dt><code>HSE_REQ_SEND_RESPONSE_HEADER</code></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><code>HSE_REQ_DONE_WITH_SESSION</code></dt> <dd>Apache considers this a no-op, since the session will be finished when the ISAPI returns from processing.</dd> <dt><code>HSE_REQ_MAP_URL_TO_PATH</code></dt> <dd>Apache will translate a virtual name to a physical name.</dd> <dt><code>HSE_APPEND_LOG_PARAMETER</code></dt> <dd> This logged message may be captured in any of the following logs: <ul> <li>in the <code>\"%{isapi-parameter}n\"</code> component in a <directive module="mod_log_config">CustomLog</directive> directive</li> <li>in the <code>%q</code> log component with the <directive module="mod_isapi">ISAPIAppendLogToQuery</directive> <code>On</code> directive</li> <li>in the error log with the <directive module="mod_isapi" >ISAPIAppendLogToErrors</directive> <code>On</code> directive</li> </ul> <p>The first option, the <code>%{isapi-parameter}n</code> component, is always available and preferred.</p> </dd> <dt><code>HSE_REQ_IS_KEEP_CONN</code></dt> <dd>Will return the negotiated Keep-Alive status.</dd> <dt><code>HSE_REQ_SEND_RESPONSE_HEADER_EX</code></dt> <dd>Will behave as documented, although the <code>fKeepConn</code> flag is ignored.</dd> <dt><code>HSE_REQ_IS_CONNECTED</code></dt> <dd>Will report false if the request has been aborted.</dd> </dl> <p>Apache returns <code>FALSE</code> to any unsupported call to <code>ServerSupportFunction</code>, and sets the <code>GetLastError</code> value to <code>ERROR_INVALID_PARAMETER</code>.</p> <p><code>ReadClient</code> retrieves the request body exceeding the initial buffer (defined by <directive module="mod_isapi" >ISAPIReadAheadBuffer</directive>). Based on the <directive>ISAPIReadAheadBuffer</directive> 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 <code>ReadClient</code> to retrieve the remaining request body.</p> <p><code>WriteClient</code> is supported, but only with the <code>HSE_IO_SYNC</code> flag or no option flag (value of <code>0</code>). Any other <code>WriteClient</code> request will be rejected with a return value of <code>FALSE</code>, and a <code>GetLastError</code> value of <code>ERROR_INVALID_PARAMETER</code>.</p> <p><code>GetServerVariable</code> is supported, although extended server variables do not exist (as defined by other servers.) All the usual Apache CGI environment variables are available from <code>GetServerVariable</code>, as well as the <code>ALL_HTTP</code> and <code>ALL_RAW</code> values.</p> <p>Apache 2.0 <module>mod_isapi</module> supports additional features introduced in later versions of the ISAPI specification, as well as limited emulation of async I/O and the <code>TransmitFile</code> semantics. Apache also supports preloading ISAPI .dlls for performance, neither of which were not available under Apache 1.3 <code>mod_isapi</code>.</p> </section> <directivesynopsis> <name>ISAPICacheFile</name> <description>ISAPI .dll files to be loaded at startup</description> <syntax>ISAPICacheFile <var>file-path</var> [<var>file-path</var>] ...</syntax> <contextlist><context>server config</context><context>virtual host</context> </contextlist> <usage> <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. If the path name is not absolute, it will be treated relative to <directive module="core">ServerRoot</directive>.</p> </usage> </directivesynopsis> <directivesynopsis> <name>ISAPIReadAheadBuffer</name> <description>Size of the Read Ahead Buffer sent to ISAPI extensions</description> <syntax>ISAPIReadAheadBuffer <var>size</var></syntax> <default>ISAPIReadAheadBuffer 49152</default> <contextlist><context>server config</context><context>virtual host</context> <context>directory</context><context>.htaccess</context></contextlist> <override>FileInfo</override> <usage> <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 <code>ReadClient</code> callback; some ISAPI extensions may not support the <code>ReadClient</code> function. Refer questions to the ISAPI extension's author.</p> </usage> </directivesynopsis> <directivesynopsis> <name>ISAPILogNotSupported</name> <description>Log unsupported feature requests from ISAPI extensions</description> <syntax>ISAPILogNotSupported on|off</syntax> <default>ISAPILogNotSupported off</default> <contextlist><context>server config</context><context>virtual host</context> <context>directory</context><context>.htaccess</context></contextlist> <override>FileInfo</override> <usage> <p>Logs all requests for unsupported features from ISAPI extensions in the server error log. This may help administrators to track down problems. Once set to on and all desired ISAPI modules are functioning, it should be set back to off.</p> </usage> </directivesynopsis> <directivesynopsis> <name>ISAPIAppendLogToErrors</name> <description>Record <code>HSE_APPEND_LOG_PARAMETER</code> requests from ISAPI extensions to the error log</description> <syntax>ISAPIAppendLogToErrors on|off</syntax> <default>ISAPIAppendLogToErrors off</default> <contextlist><context>server config</context><context>virtual host</context> <context>directory</context><context>.htaccess</context></contextlist> <override>FileInfo</override> <usage> <p>Record <code>HSE_APPEND_LOG_PARAMETER</code> requests from ISAPI extensions to the server error log.</p> </usage> </directivesynopsis> <directivesynopsis> <name>ISAPIAppendLogToQuery</name> <description>Record <code>HSE_APPEND_LOG_PARAMETER</code> requests from ISAPI extensions to the query field</description> <syntax>ISAPIAppendLogToQuery on|off</syntax> <default>ISAPIAppendLogToQuery on</default> <contextlist><context>server config</context><context>virtual host</context> <context>directory</context><context>.htaccess</context></contextlist> <override>FileInfo</override> <usage> <p>Record <code>HSE_APPEND_LOG_PARAMETER</code> requests from ISAPI extensions to the query field (appended to the <directive module="mod_log_config">CustomLog</directive> <code>%q</code> component).</p> </usage> </directivesynopsis> <directivesynopsis> <name>ISAPIFakeAsync</name> <description>Fake asynchronous support for ISAPI callbacks</description> <syntax>ISAPIFakeAsync on|off</syntax> <default>ISAPIFakeAsync off</default> <contextlist><context>server config</context><context>virtual host</context> <context>directory</context><context>.htaccess</context></contextlist> <override>FileInfo</override> <usage> <p>While set to on, asynchronous support for ISAPI callbacks is simulated.</p> </usage> </directivesynopsis> </modulesynopsis>