Index

1. Python Socket Programming

• sockets are often used to establish a connection between machines
  • Python has a socket module for this purpose
• the Python socket module maps onto the standard C socket library
• sockets provide a ISO OSI-7 transport level layer interface
  • either UDP or TCP transports can be used
  • both use the Port level of addressing within UDP or TCP

2. Simple server

• #!/usr/bin/python
  
  from socket import *
  myHost = ’’
  myPort = 2000
  
  s = socket(AF_INET, SOCK_STREAM)    # create a TCP socket
  s.bind((myHost, myPort))            # bind it to the server port
  s.listen(5)                         # allow 5 simultaneous
                                      # pending connections
  
  
  while 1:
      # wait for next client to connect
      connection, address = s.accept() # connection is a new socket
      while 1:
          data = connection.recv(1024) # receive up to 1K bytes
          if data:
              connection.send(’echo -> ’ + data)
          else:
              break
      connection.close()              # close socket

3. Simple client

• #!/usr/bin/python
  
  import sys
  from socket import *
  serverHost = ’localhost’            # servername is localhost
  serverPort = 2000                   # use arbitrary port > 1024
  
  s = socket(AF_INET, SOCK_STREAM)    # create a TCP socket
  
  
  s.connect((serverHost, serverPort)) # connect to server on the port
  s.send(’Hello world’)               # send the data
  data = s.recv(1024)                 # receive up to 1K bytes
  print data

4. Streaming an MP3 file though stdout and stdin

• stdin is the default input file descriptor
• stdout is the default output file descriptor
• try this:

• cat 01.mp3 | madplay -

• cat is a program which reads a file and writes it to stdout
• the | symbol is the pipe which connects the stdout of the left program to the stdin of the right program
• madplay is a mp3 player which has been told to read its file from -
  • where - means stdin
• you should aim to replace the program cat with your own Python client which streams the mp3 file from your Python server
• the client only needs to write the mp3 file to stdout
  • where madplay will read it and play it!
    

5. SSH component of your Python client

• #!/usr/bin/python
  
  #
  #  secure shell pipe module
  #
  
  import os
  import sys
  from socket import *
  
  
  localPortNo=8000
  maxTries=10
  blockSize=65536*16

• def createTCPSocketSSH (remoteHostname, remotePort=22, localPort=-1):
      global localPortNo
      if localPort == -1:
          localPort = localPortNo
          localPortNo = localPortNo+1
      tryNo = 1
      while 1:
          command = "ssh -f -g -A -X -N -T -L%d:localhost:%d %s\n" \
                    % (localPort, remotePort, remoteHostname)
          result = os.system(command)
          if result == 0:
              break
          localPort = localPort+1
          tryNo = tryNo + 1
          if tryNo == maxTries:
              os.exit(1)
  
  
      # create a TCP socket which connects to our ssh pipe
      s = socket(AF_INET, SOCK_STREAM)
      s.connect(("localhost", localPort))
      return s

Index

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