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Apache HTTP Server Version 2.2
Description: | ISAPI Extensions within Apache for Windows |
---|---|
Status: | Base |
Module Identifier: | isapi_module |
Source File: | mod_isapi.c |
Compatibility: | Win32 only |
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.
In the server configuration file, use
the AddHandler
directive to
associate ISAPI files with the isapi-handler
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:
AddHandler isapi-handler .dll
isapi-isa
was the proper handler name, rather than
isapi-handler
. For compatibility, configurations may
continue using isapi-isa
through all versions of Apache
prior to 2.3.0.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:
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, Options
ExecCGI
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
mod_isapi
.
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 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.
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.
If you are programming Apache 2.0 mod_isapi
modules, you must limit your calls to ServerSupportFunction
to the following directives:
HSE_REQ_SEND_URL_REDIRECT_RESP
http://server/location
).HSE_REQ_SEND_URL
/location
).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.
HSE_REQ_SEND_RESPONSE_HEADER
HSE_REQ_DONE_WITH_SESSION
HSE_REQ_MAP_URL_TO_PATH
HSE_APPEND_LOG_PARAMETER
\"%{isapi-parameter}n\"
component in a
CustomLog
directive%q
log component with the
ISAPIAppendLogToQuery
On
directiveISAPIAppendLogToErrors
On
directiveThe first option, the %{isapi-parameter}n
component,
is always available and preferred.
HSE_REQ_IS_KEEP_CONN
HSE_REQ_SEND_RESPONSE_HEADER_EX
fKeepConn
flag is ignored.HSE_REQ_IS_CONNECTED
Apache returns FALSE
to any unsupported call to
ServerSupportFunction
, and sets the
GetLastError
value to
ERROR_INVALID_PARAMETER
.
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.
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
.
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.
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
.
Description: | Record HSE_APPEND_LOG_PARAMETER requests from
ISAPI extensions to the error log |
---|---|
Syntax: | ISAPIAppendLogToErrors on|off |
Default: | ISAPIAppendLogToErrors off |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_isapi |
Record HSE_APPEND_LOG_PARAMETER
requests from ISAPI
extensions to the server error log.
Description: | Record HSE_APPEND_LOG_PARAMETER requests from
ISAPI extensions to the query field |
---|---|
Syntax: | ISAPIAppendLogToQuery on|off |
Default: | ISAPIAppendLogToQuery on |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_isapi |
Record HSE_APPEND_LOG_PARAMETER
requests from ISAPI
extensions to the query field (appended to the CustomLog
%q
component).
Description: | ISAPI .dll files to be loaded at startup |
---|---|
Syntax: | ISAPICacheFile file-path [file-path]
... |
Context: | server config, virtual host |
Status: | Base |
Module: | mod_isapi |
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 ServerRoot
.
Description: | Fake asynchronous support for ISAPI callbacks |
---|---|
Syntax: | ISAPIFakeAsync on|off |
Default: | ISAPIFakeAsync off |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_isapi |
While set to on, asynchronous support for ISAPI callbacks is simulated.
Description: | Log unsupported feature requests from ISAPI extensions |
---|---|
Syntax: | ISAPILogNotSupported on|off |
Default: | ISAPILogNotSupported off |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_isapi |
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.
Description: | Size of the Read Ahead Buffer sent to ISAPI extensions |
---|---|
Syntax: | ISAPIReadAheadBuffer size |
Default: | ISAPIReadAheadBuffer 49152 |
Context: | server config, virtual host, directory, .htaccess |
Override: | FileInfo |
Status: | Base |
Module: | mod_isapi |
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.