Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 5 ■ NETWORK DATA AND NETWORK ERRORS
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
HOST = sys.argv.pop() if len(sys.argv) == 3 else '127.0.0.1'
PORT = 1060
format = struct.Struct('!I') # for messages up to 2**32 - 1 in length
def recvall(sock, length):
» data = ''
» while len(data) < length:
» » more = sock.recv(length - len(data))
» » if not more:
» » » raise EOFError('socket closed %d bytes into a %d-byte message'
» » » » » » % (len(data), length))
» » data += more
» return data
def get(sock):
» lendata = recvall(sock, format.size)
» (length,) = format.unpack(lendata)
» return recvall(sock, length)
def put(sock, message):
» sock.send(format.pack(len(message)) + message)
if sys.argv[1:] == ['server']:
» s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
» s.bind((HOST, PORT))
» s.listen(1)
» print 'Listening at', s.getsockname()
» sc, sockname = s.accept()
» print 'Accepted connection from', sockname
» sc.shutdown(socket.SHUT_WR)
» while True:
» » message = get(sc)
» » if not message:
» » » break
» » print 'Message says:', repr(message)
» sc.close()
» s.close()
elif sys.argv[1:] == ['client']:
» s.connect((HOST, PORT))
» s.shutdown(socket.SHUT_RD)
» put(s, 'Beautiful is better than ugly.')
» put(s, 'Explicit is better than implicit.')
» put(s, 'Simple is better than complex.')
» put(s, '')
» s.close()
else:
» print >>sys.stderr, 'usage: streamer.py server|client [host]'
Note how careful we have to be! Even though four bytes of length is such a tiny amount of data that
we cannot imagine recv() not returning it all at once, our code is still correct only if we carefully wrap
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