Question

For each of below python socket functions, describe network traffic (resulting TCP packets) that is generated at the TCP level. Note: s represents an open socket.

Python network APIs Resulting TCP packets

s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)

s.connect(('127.0.0.1', 8080))

s.send('ABC'.encode('utf-8'))

data = s.recv(2000)

s.shutdown(socket.SHUT_WR)

Answer 1

import socket # Create a TCP/IP socket sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # Bind the socket to the port server_address = ('localhost', 10000) print('Starting up on {} port {}'.format(*server_address)) sock.bind(server_address) # Listen for incoming connections sock.listen(1) while True: # Wait for a connection print('waiting for a connection') connection, client_address = sock.accept() try: print('connection from', client_address) # Receive the data in small chunks and retransmit it while True: data = connection.recv(16) print('received {!r}'.format(data)) if data: print('sending data back to the client') connection.sendall(data) else: print('no data from', client_address) break finally: # Clean up the connection print("Closing current connection") connection.close() # create an INET, STREAMing socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # now connect to the web server on port 80 - the normal http port s.connect(("www.python.org", 80)) # create an INET, STREAMing socket serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # bind the socket to a public host, and a well-known port serversocket.bind((socket.gethostname(), 80)) # become a server socket serversocket.listen(5) import socket import time s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind(('', 8088)) s.listen(10) while 1: c, addr = s.accept() print c, addr c.send('hello') c.close() s.shutdown() and import socket s = socket.socket() s.connect(('127.0.0.1', 8080)) while 1: print s.recv(2048) # Set up the variables we'll use >>> uni_greeting = u'Hi, my name is %s.' >>> utf8_greeting = uni_greeting.encode('utf-8') >>> uni_name = u'José' # Note the accented e. >>> utf8_name = uni_name.encode('utf-8') # Plugging a Unicode into another Unicode works fine >>> uni_greeting % uni_name u'Hi, my name is Josxe9.' # Plugging UTF-8 into another UTF-8 string works too >>> utf8_greeting % utf8_name 'Hi, my name is Josxc3xa9.' # You can plug Unicode into a UTF-8 byte sequence... >>> utf8_greeting % uni_name # UTF-8 invisibly decoded into Unicode; note the return type u'Hi, my name is Josxe9.' # But plugging a UTF-8 string into a Unicode doesn't work so well... >>> uni_greeting % utf8_name # Invisible decoding doesn't work in this direction. Traceback (most recent call last): File "<stdin>", line 1, in <module> UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 3: ordinal not in range(128) # Unless you plug in ASCII-compatible data, that is. >>> uni_greeting % u'Bob'.encode('utf-8') u'Hi, my name is Bob.' # And you can forget about string interpolation completely if you're using UTF-16. >>> uni_greeting.encode('utf-16') % uni_name Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: unsupported format character '' (0x0) at index 33 import socket, sys s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) HOST = '127.0.0.1' PORT = 1060 if sys.argv[1:] == ['server']: s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) s.bind((HOST, PORT)) s.listen(1) while True: print 'Listening at', s.getsockname() sc, sockname = s.accept() print 'Processing up to 1024 bytes at a time from', sockname n = 0 while True: message = sc.recv(1024) if not message: break sc.sendall(message.upper()) # send it back uppercase n += len(message) print '\r%d bytes processed so far' % (n,), sys.stdout.flush() print sc.close() print 'Completed processing' elif len(sys.argv) == 3 and sys.argv[1] == 'client' and sys.argv[2].isdigit(): bytes = (int(sys.argv[2]) + 15) // 16 * 16 # round up to // 16 message = 'capitalize this!' # 16-byte message to repeat over and over print 'Sending', bytes, 'bytes of data, in chunks of 16 bytes' s.connect((HOST, PORT)) sent = 0 while sent < bytes: s.sendall(message) sent += len(message) print '\r%d bytes sent' % (sent,), sys.stdout.flush() print s.shutdown(socket.SHUT_WR) print 'Receiving all the data the server sends back' received = 0 while True: data = s.recv(42) if not received: print 'The first data received says', repr(data) received += len(data) if not data: break print '\r%d bytes received' % (received,), s.close() else: print >>sys.stderr, 'usage: tcp_deadlock.py server | client <bytes>'