|
Apache HTTP Server Version 1.3
Module mod_isapi
This module supports ISAPI Extensions within Apache for Windows.
Status:
Base
Source
File: mod_isapi.c
Module
Identifier: isapi_module
Compatibility:
WIN32 only
Summary
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 extention. Please do
not post such problems to Apache's lists or bug reporting pages.
Directives
Usage
In the server configuration file, use the AddHandler directive to associate ISAPI files
with the isapi-isa 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:
AddHandler isapi-isa .dll
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
the "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, a new
directive; ISAPILogNotSupported Off, is introduced in Apache 1.3.13.
Some servers, like Microsoft IIS, load the ISA into the server, and keep it loaded until
memory usage is too high, or specific configuration options are used. Apache currently loads
and unloads the ISA for each request. This is inefficient, but Apache's request model makes
this method the only method that currently works. Apache 2.0 is expected to support more
effective loading and caching methods, with more precise control over individual ISAPI modules
and directories.
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 1.3 mod_isapi modules, you must limit your calls to
ServerSupportFunction to the following directives:
- HSE_REQ_SEND_URL_REDIRECT_RESP
- Redirect the user to another location.
This must be a fully qualified URL (e.g. http://server/location).
- HSE_REQ_SEND_URL
- Redirect the user to another location.
This cannot be a fully qualified URL, you are not allowed to pass the protocol or a server
name (e.g. simply /location).
This redirection is handled by the server, not the browser.
Warning: 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
- 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.
- HSE_REQ_DONE_WITH_SESSION
- Apache considers this a no-op, since the session will be finished when the ISAPI returns
from processing.
- HSE_REQ_MAP_URL_TO_PATH
- Apache will translate a virtual name to a physical name.
- HSE_APPEND_LOG_PARAMETER Apache 1.3.13 and later
- This logged message may be captured in any of the following logs:
- in the \"%{isapi-parameter}n\" component in a CustomLog directive
- in the %q log component with the ISAPIAppendLogToQuery On directive
- in the error log with the ISAPIAppendLogToErrors On directive
The first option, the %{isapi-parameter}n component, is always available and prefered.
- HSE_REQ_IS_KEEP_CONN Apache 1.3.13 and later
- Will return the negotiated Keep-Alive status.
- HSE_REQ_SEND_RESPONSE_HEADER_EX Apache 1.3.13 and later
- Will behave as documented, although the fKeepConn flag is ignored.
- HSE_REQ_IS_CONNECTED Apache 1.3.13 and later
- Will report false if the request has been aborted.
Apache returns FALSE to any unsupported call to ServerSupportFunction, and sets the
GetLastError value to ERROR_INVALID_PARAMETER.
Prior to Apache 1.3.13, ReadClient was a noop, and any request with a request body greater
than 48kb was rejected by mod_isapi. As of Apache 1.3.13, ReadClient now 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 of Apache 1.3.13, the ALL_HTTP and ALL_RAW and variables are now
available.
Apache 2.0 mod_isapi may support additional features introduced in later versions of the
ISAPI specification, as well as limited emulation of async I/O and the TransmitFile semantics.
Apache 2.0 may also support caching of ISAPI .dlls for performance. No further enhancements to
the Apache 1.3 mod_isapi features are anticipated.
Syntax:
ISAPIReadAheadBuffer size
Default:
49152
Context:
server config
Override:
None
Status:
Base
Module:
mod_isapi
Compatibility:
Apache 1.3.13 and later, Win32 only
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.
Syntax:
ISAPILogNotSupported on|off
Default:
on
Context:
server config
Override:
None
Status:
Base
Module:
mod_isapi
Compatibility:
Apache 1.3.13 and later, Win32 only
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.
Syntax:
ISAPIAppendLogToErrors on|off
Default:
off
Context:
server config
Override:
None
Status:
Base
Module:
mod_isapi
Compatibility:
Apache 1.3.13 and later, Win32 only
Record HSE_APPEND_LOG_PARAMETER requests from ISAPI extentions to the server error log.
Syntax:
ISAPIAppendLogToQuery on|off
Default:
off
Context:
server config
Override:
None
Status:
Base
Module:
mod_isapi
Compatibility:
Apache 1.3.13 and later, Win32 only
Record HSE_APPEND_LOG_PARAMETER requests from ISAPI extentions to the query field (appended
to the CustomLog %q component).
|
