Classes and functions

The module defines the following functions:

Listener(address=None, family=None, backlog=1, authenticate=False, authkey=None)

Returns a wrapper for a bound socket or Windows named pipe which is 'listening' for connections.

Client(address, family=None, authenticate=False, authkey=None)

Attempts to set up a connection to the listener which is using address address, returning a connection object.

The type of the connection is determined by family argument, but this can generally be omitted since it can usually be inferred from the format of address.

If authentication or authkey is a string then digest authentication is used. The key used for authentication will be either authkey or currentProcess.getAuthKey() if authkey is None. If authentication fails then AuthenticationError is raised. See Authentication keys.

The module exports two exception types:

exception AuthenticationError

Exception raised when there is an authentication error.

exception BufferTooShort

Exception raise by the recvBytesInto() method of a connection object when the supplied buffer object is too small for the message read.

If e is an instance of BufferTooShort then e.args[0] will give the message as a byte string.

Listener objects

Instances of Listener have the following methods:

__init__(address=None, family=None, backlog=1, authenticate=False, authkey=None)

address

The address to be used by the bound socket or named pipe of the listener object.

family

The type of the socket (or named pipe) to use.

This can be one of the strings 'AF_INET' (for a TCP socket), 'AF_UNIX' (for a Unix domain socket) or 'AF_PIPE' (for a Windows named pipe). Of these only the first is guaranteed to be available.

If family is None than the family is inferred from the format of address. If address is also None then a default is chosen. This default is the family which is assumed to be the fastest available. See Address formats.

Note that if family is 'AF_UNIX' then the associated file will have only be readable/writable by the user running the current process -- use os.chmod() is you need to let other users access the socket.

backlog

If the listener object uses a socket then backlog is passed to the listen() method of the socket once it has been bound.

authenticate

If authenticate is true or authkey is not None then digest authentication is used.

authkey

If authkey is a string then it will be used as the authentication key; otherwise it must be None.

If authkey is None and authenticate is true then currentProcess.getAuthKey() is used as the authentication key.

If authkey is None and authentication is false then no authentication is done.

If authentication fails then AuthenticationError is raised. See Authentication keys.

accept()

Accept a connection on the bound socket or named pipe of the listener object. If authentication is attempted and fails then AuthenticationError is raised.

Returns a connection object <connection-object.html> object.

close()

Close the bound socket or named pipe of the listener object.

This is called automatically when the listener is garbage collected. However it is advisable to call it explicitly.

Listener objects have the following read-only properties:

address

The address which is being used by the listener object.

last_accepted

The address from which the last accepted connection came.

If this is unavailable then None is returned.

Address formats

• An 'AF_INET' address is a tuple of the form (hostname, port) where hostname is a string and port is an integer

• An 'AF_UNIX' address is a string representing a filename on the filesystem.

• An 'AF_PIPE' address is a string of the form r'\\.\pipe\PipeName'.

  To use Client to connect to a named pipe on a remote computer called ServerName one should use an address of the form r'\\ServerName\pipe\PipeName' instead.

Note that any string beginning with two backslashes is assumed by default to be an 'AF_PIPE' address rather than an 'AF_UNIX' address.

Authentication keys

When one uses the recv() method of a connection object, the data received is automatically unpickled. Unfortunately unpickling data from an untrusted source is a security risk. Therefore Listener and Client use the hmac module to provide digest authentication.

An authentication key is a string which can be thought of as a password: once a connection is established both ends will demand proof that the other knows the authentication key. (Demonstrating that both ends are using the same key does not involve sending the key over the connection.)

If authentication is requested but do authentication key is specified then the return value of currentProcess().getAuthKey() is used (see Process objects). This value will automatically inherited by any Process object that the current process creates. This means that (by default) all processes of a multi-process program will share a single authentication key which can be used when setting up connections between the themselves.

Suitable authentication keys can also be generated by using os.urandom().

Example

The following server code creates a listener which uses 'secret password' as an authentication key. It then waits for a connection and sends some data to the client:

from processing.connection import Listener
from array import array

address = ('localhost', 6000)     # family is deduced to be 'AF_INET'
listener = Listener(address, authkey='secret password')

conn = listener.accept()
print 'connection accepted from', listener.last_accepted

conn.send([2.25, None, 'junk', float])

conn.sendBytes('hello')

conn.sendBytes(array('i', [42, 1729]))

conn.close()
listener.close()

The following code connects to the server and receives some data from the server:

from processing.connection import Client
from array import array

address = ('localhost', 6000)
conn = Client(address, authkey='secret password')

print conn.recv()                 # => [2.25, None, 'junk', float]

print conn.recvBytes()            # => 'hello'

arr = array('i', [0, 0, 0, 0, 0])
print conn.recvBytesInto(arr)    # => 8
print arr                         # => array('i', [42, 1729, 0, 0, 0])

conn.close()