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"""WebSocket extension for Apache HTTP Server.

mod_pywebsocket is a WebSocket extension for Apache HTTP Server
intended for testing or experimental purposes. mod_python is required.


Installation:

0. Prepare an Apache HTTP Server for which mod_python is enabled.

1. Specify the following Apache HTTP Server directives to suit your
   configuration.

   If mod_pywebsocket is not in the Python path, specify the following.
   <websock_lib> is the directory where mod_pywebsocket is installed.

       PythonPath "sys.path+['<websock_lib>']"

   Always specify the following. <websock_handlers> is the directory where
   user-written WebSocket handlers are placed.

       PythonOption mod_pywebsocket.handler_root <websock_handlers>
       PythonHeaderParserHandler mod_pywebsocket.headerparserhandler

   To limit the search for WebSocket handlers to a directory <scan_dir>
   under <websock_handlers>, configure as follows:

       PythonOption mod_pywebsocket.handler_scan <scan_dir>

   <scan_dir> is useful in saving scan time when <websock_handlers>
   contains many non-WebSocket handler files.

   If you want to support old handshake based on
   draft-hixie-thewebsocketprotocol-75:

       PythonOption mod_pywebsocket.allow_draft75 On

   Example snippet of httpd.conf:
   (mod_pywebsocket is in /websock_lib, WebSocket handlers are in
   /websock_handlers, port is 80 for ws, 443 for wss.)

       <IfModule python_module>
         PythonPath "sys.path+['/websock_lib']"
         PythonOption mod_pywebsocket.handler_root /websock_handlers
         PythonHeaderParserHandler mod_pywebsocket.headerparserhandler
       </IfModule>

2. Tune Apache parameters for serving WebSocket. We'd like to note that at
   least TimeOut directive from core features and RequestReadTimeout directive
   from mod_reqtimeout should be modified not to kill connections in only a few
   seconds of idle time.

3. Verify installation. You can use example/console.html to poke the server.


Writing WebSocket handlers:

When a WebSocket request comes in, the resource name
specified in the handshake is considered as if it is a file path under
<websock_handlers> and the handler defined in
<websock_handlers>/<resource_name>_wsh.py is invoked.

For example, if the resource name is /example/chat, the handler defined in
<websock_handlers>/example/chat_wsh.py is invoked.

A WebSocket handler is composed of the following two functions:

    web_socket_do_extra_handshake(request)
    web_socket_transfer_data(request)

where:
    request: mod_python request.

web_socket_do_extra_handshake is called during the handshake after the
headers are successfully parsed and WebSocket properties (ws_location,
ws_origin, and ws_resource) are added to request. A handler
can reject the request by raising an exception.

A request object has the following properties that you can use during the extra
handshake (web_socket_do_extra_handshake):
- ws_resource
- ws_origin
- ws_version
- ws_location (Hixie 75 and HyBi 00 only)
- ws_extensions (Hybi 06 and later)
- ws_deflate (HyBi 06 and later)
- ws_protocol
- ws_requested_protocols (HyBi 06 and later)

The last two are a bit tricky.

For HyBi 06 and later, ws_protocol is always set to None when
web_socket_do_extra_handshake is called. If ws_requested_protocols is not
None, you must choose one subprotocol from this list and set it to ws_protocol.

For Hixie 75 and HyBi 00, when web_socket_do_extra_handshake is called,
ws_protocol is set to the value given by the client in Sec-WebSocket-Protocol
(WebSocket-Protocol for Hixie 75) header or None if such header was not found
in the opening handshake request. Finish extra handshake with ws_protocol
untouched to accept the request subprotocol. Then, Sec-WebSocket-Protocol
(or WebSocket-Protocol) header will be sent to the client in response with the
same value as requested. Raise an exception in web_socket_do_extra_handshake to
reject the requested subprotocol.

web_socket_transfer_data is called after the handshake completed
successfully. A handler can receive/send messages from/to the client
using request. mod_pywebsocket.msgutil module provides utilities
for data transfer.

You can receive a message by the following statement.

    message = request.ws_stream.receive_message()

This call blocks until any complete text frame arrives, and the payload data of
the incoming frame will be stored into message. When you're using IETF HyBi 00
or later protocol, receive_message() will return None on receiving
client-initiated closing handshake. When any error occurs, receive_message()
will raise some exception.

You can send a message by the following statement.

    request.ws_stream.send_message(message)

Executing the following statement or just return-ing from
web_socket_transfer_data cause connection close.

    request.ws_stream.close_connection()

When you're using IETF HyBi 00 or later protocol, close_connection will wait
for closing handshake acknowledgement coming from the client. When it couldn't
receive a valid acknowledgement, raises an exception.

A WebSocket handler must be thread-safe if the server (Apache or
standalone.py) is configured to use threads.
"""


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