websockify/utils

wsproxy: WebSockets to TCP Proxy

How it works

At the most basic level, wsproxy just translates WebSockets traffic to normal socket traffic. wsproxy accepts the WebSockets handshake, parses it, and then begins forwarding traffic between the client and the target in both directions. WebSockets payload data is UTF-8 encoded so in order to transport binary data it must use an encoding that can be encapsulated within UTF-8. wsproxy uses base64 to encode all traffic to and from the client. Also, WebSockets traffic starts with '\0' (0) and ends with '\xff' (255). Some buffering is done in case the data from the client is not a full WebSockets frame (i.e. does not end in 255).

Additional features

These are not necessary for the basic operation.

• Daemonizing: When the -f option is not specified, wsproxy runs in the background as a daemon process.

• SSL (the wss:// WebSockets URI): This is detected automatically by wsproxy by sniffing the first byte sent from the client and then wrapping the socket if the data starts with '\x16' or '\x80' (indicating SSL).

• Flash security policy: wsproxy detects flash security policy requests (again by sniffing the first packet) and answers with an appropriate flash security policy response (and then closes the port). This means no separate flash security policy server is needed for supporting the flash WebSockets fallback emulator.

• Session recording: This feature that allows recording of the traffic sent and received from the client to a file using the --record option.

Implementations

There are two implementations of wsproxy included: a python implementation and a C implementation.

Here is the feature support matrix for the wsproxy implementations:

Implementation	Basic Proxying	Daemonizing	SSL/wss	Flash Policy Server	Session Recording
python	yes	yes	yes 1	yes	yes
C	yes	yes	yes	yes	no

• Note 1: to use SSL/wss with python 2.5 or older, see the following section on Building the Python ssl module.

Building the Python ssl module (for python 2.5 and older)

• Install the build dependencies. On Ubuntu use this command:

  sudo aptitude install python-dev bluetooth-dev

• Download, build the ssl module and symlink to it:

  cd noVNC/utils

  wget http://pypi.python.org/packages/source/s/ssl/ssl-1.15.tar.gz

  tar xvzf ssl-1.15.tar.gz

  cd ssl-1.15

  make

  cd ../

  ln -sf ssl-1.15/build/lib.linux-*/ssl ssl