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apache-websocket

The apache-websocket module is an Apache 2.x server module that may be used to process requests using the WebSocket protocol (RFC 6455) by an Apache 2.x server. 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 protocol versions 7, 8, and 13, along with the older draft-76 of the WebSocket protocol. Support for draft-75 is disabled by default, but it may be enabled through the draft-76 module configuration.

Due to the extensive differences between the newer drafts and draft-76 implementations, and because of the Apache module architecture, two separate modules are used to support the different protocols.

Although draft-76 is technically obsolete, it is the protocol version that is currently implemented by most of the web browsers. When all of the browsers finally move to support the latest protocol, simply remove the draft-76 module and configuration to drop support.

Download

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

Building and Installation

SCons may be used to build the module.

$ 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), use:

$ sudo apxs2 -i -a -c mod_websocket.c
$ sudo apxs2 -i -a -c mod_websocket_draft76.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
$ sudo apxs -i -a -c mod_websocket_draft76.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 likely using a client that does not support these versions of the protocol.

A more extensive example may be found in examples/mod_websocket_dumb_increment.c. That plugin implements the dumb-increment-protocol (see libwebsockets by Andy Green for more information on the protocol). There is a test client for testing the module in increment.html. It uses the WebSocket client API which supports passing supported protocols in the WebSocket constructor. If your browser does not support this, either upgrade your browser or modify the plugin so that it doesn't verify the protocol.

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 only safely access the send or close functions in your on_connect function from a separate thread, as the connection will not be completed until you return from the function.

You may use apxs, SCons, or some other build system to be build and install the plugins. Also, it does not need to be placed in the same directory as the WebSocket module.

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. For the draft-76 implementation only, 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 under Mac OS X. 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
LoadModule websocket_draft76_module   libexec/apache2/mod_websocket_draft76.so

<IfModule mod_websocket.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler libexec/apache2/mod_websocket_echo.so echo_init
  </Location>
  <Location /dumb-increment>
    SetHandler websocket-handler
    WebSocketHandler libexec/apache2/mod_websocket_dumb_increment.so dumb_increment_init
  </Location>
</IfModule>

<IfModule mod_websocket_draft76.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler libexec/apache2/mod_websocket_echo.so echo_init
    SupportDraft75 On
  </Location>
  <Location /dumb-increment>
    SetHandler websocket-handler
    WebSocketHandler libexec/apache2/mod_websocket_dumb_increment.so dumb_increment_init
    SupportDraft75 On
  </Location>
</IfModule>

If your settings are the same between the two modules, you may try to remove the <IfModule mod_websocket_draft76.c> section of the configuration (you will still need the LoadModule line if you want to support draft-76).

Since we are dealing with messages, not streams, we need to specify a maximum message size. The default size is 32 megabytes. You may override this value by specifying a MaxMessageSize configuration setting. This option is not available for the draft-76 implementation. Here is an example of how to set the maximum message size is set to 64 megabytes:

<IfModule mod_websocket.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler /usr/lib/apache2/modules/mod_websocket_echo.so echo_init
    MaxMessageSize 67108864
  </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). If you did not use apxs2 with the -a option to initially create the module, you will have to make a link between /etc/apache2/mods-enabled/websocket.load and /etc/apache2/mods-available/websocket.load. Take a look at the already enabled modules to see how it should look. Since the directory containing the module is different from Mac OS X, the configuration will look more like this:

LoadModule websocket_module   /usr/lib/apache2/modules/mod_websocket.so
LoadModule websocket_draft76_module   /usr/lib/apache2/modules/mod_websocket_draft76.so

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

<IfModule mod_websocket_draft76.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
LoadModule websocket_draft76_module   modules/mod_websocket_draft76.so

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

<IfModule mod_websocket_draft76.c>
  <Location /echo>
    SetHandler websocket-handler
    WebSocketHandler modules/mod_websocket_echo.so _echo_init@0
    SupportDraft75 On
  </Location>
</IfModule>

For all architectures, to drop draft-76 support, remove the loading of the draft-76 module along with the module configuration block. Here is how the example configuration could look under Mac OS X after removing the the websocket_draft76_module references:

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
  </Location>
</IfModule>

Authors

The original code was written by self.disconnect.

License

Please see the file called LICENSE.