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Apache WebSocket module
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examples
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LICENSE
README.md
SConstruct
mod_websocket.c
websocket_plugin.h

README.md

apache-websocket

The apache-websocket module is an Apache 2.x module that may be used to process requests using the WebSocket protocol. The module consists of a plugin architecture for handling WebSocket messaging. Doing so does not require any knowledge of internal Apache structures.

This implementation supports both draft-75 and draft-76 of the WebSocket protocol. Support for draft-75 is disabled by default, but it may be enabled through the configuration.

This implementation also includes support for handling subprotocols.

Download

$ git clone git://github.com/disconnect/apache-websocket.git

Building and Installation

SCons may be used to build the module. However, it is currently only configured to build under Mac OS X and Windows.

$ scons
$ sudo scons install

For Windows, do not include the word sudo when installing the module. Also, the SConstruct file is hard-coded to look for the Apache headers and libraries in C:\Program Files\Apache Software Foundation\Apache2.2. You will need to install the headers and libraries when installing Apache. The Build Headers and Libraries option is disabled by default, so you will have to perform a Custom installation of Apache. Refer to the Apache document entitled Using Apache HTTP Server on Microsoft Windows for more information.

Alternatively, you may use apxs to build and install the module. Under Linux (at least under Ubuntu 10.04 LTS), use:

$ sudo apxs2 -i -a -c mod_websocket.c

You probably only want to use the -a option the first time you issue the command, as it may overwrite your configuration each time you execute it (see below).

You may use apxs under Mac OS X if you do not want to use SCons. In that case, use:

$ sudo apxs -i -a -c mod_websocket.c

Plugins

While the module is used to handle the WebSocket protocol, plugins are used to implement the application-specific handling of WebSocket messages.

A plugin need only have one function exported that returns a pointer to an initialized WebSocketPlugin structure. The WebSocketPlugin structure consists of the structure size, structure version, and several function pointers. The size should be set to the sizeof the WebSocketPlugin structure, the version should be set to 0, and the function pointers should be set to point to the various functions that will service the requests. The only required function is the on_message function for handling incoming messages.

See examples/mod_websocket_echo.c for a simple example implementation of an "echo" plugin. A sample client.html is included as well. If you try it and you get a message that says Connection Closed, you are most likely using a client that only supports draft-75 of the protocol, but you have not enabled support for it.

If you provide an on_connect function, return a non-null value to accept the connection, and null if you wish to decline the connection. The return value will be passed to your other methods for that connection. During your on_connect function, you may access the Apache request_rec structure if you wish. You will have to include the appropriate Apache include files. If you do not wish to do that, you may also access the headers (both input and output) using the provided functions. There are also protocol-specific handling functions for selecting the desired protocol for the WebSocket session. You may not access the send or close functions while connecting, as the connection will not be completed until you return from the function.

If your plugin does not depend on Apache, you do not need to use apxs to build them. Also, it does not need to be placed in the same directory as the WebSocket module. You may use SCons (or some other build system) to be build and install the plugins.

Configuration

The http.conf file is used to configure WebSocket plugins to handle requests for particular locations. Inside each Location block, set the handler, using the SetHandler keyword, to websocket-handler. Next, add a WebSocketHandler entry that contains two parameters. The first is the name of the dynamic plugin library that will service the requests for the specified location, and the second is the name of the function in the dynamic library that will initialize the plugin. You may optionally include a flag for supporting the draft-75 version of the WebSocket protocol (it will default to "off" if you do not include it). It is enabled using the SupportDraft75 keyword, along with a value of On.

Here is an example of the configuration changes to http.conf that are used to handle the WebSocket plugin requests directed at /echo. The server will initialize the module by calling the echo_init function in mod_websocket_echo.so:

LoadModule websocket_module   libexec/apache2/mod_websocket.so

<IfModule mod_websocket.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler libexec/apache2/mod_websocket_echo.so echo_init
    SupportDraft75 On
  </Location>
</IfModule>

Under Linux, the module-specific configuration may be contained in a single file called /etc/apache2/mods-available/websocket.load (your version of Linux may vary). Since the directory containing the module is different from Mac OS X, it may look more like this:

LoadModule websocket_module   /usr/lib/apache2/modules/mod_websocket.so

<IfModule mod_websocket.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler /usr/lib/apache2/modules/mod_websocket_echo.so echo_init
    SupportDraft75 On
  </Location>
</IfModule>

This is the configuration that may be overwritten when the -a option is included using axps2, so be careful.

Under Windows, the initialization function is of the form _echo_init@0, as it is using the __stdcall calling convention:

LoadModule websocket_module modules/mod_websocket.so

<IfModule mod_websocket.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler modules/mod_websocket_echo.so _echo_init@0
    SupportDraft75 On
  </Location>
</IfModule>

Authors

  • The original code was written by self.disconnect.

License

Please see the file called LICENSE.

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