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    <p>First advice: simplify. Lets first see if we can get this thing working <em>without</em> protocol buffers:</p> <h1>client.py</h1> <pre><code>import socket import sys import struct address = ('localhost', 6005) client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) client_socket.connect(address) messages = ["foobar", "barbaz", "bazquxfad", "Jimmy Carter"] for s in messages: totallen = 4 + len(s) pack1 = struct.pack('&gt;I', totallen) # the first part of the message is length client_socket.sendall(s) </code></pre> <h1>server.py</h1> <pre><code>import socket import sys import struct address = ('localhost', 6005) server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) server_socket.bind(address) while True: print "Listening" # totallen = server_socket.recv(4) # totallenRecv = struct.unpack('&gt;I', totallen)[0] # messagelen = totallenRecv - 4 message = server_socket.recv(1000) print message </code></pre> <p>Now, I'm not an expert on sockets (this might be the first question I've answered about them), but if you run this example, you get the expected output. What that tells me is that each send corresponds to a single <code>.recv</code>. Presumably, the <code>sockets</code> library is handling the details of the <em>length</em>. Of course, on the recieving side, it's quite possible that you <em>want</em> to know the length so that you can pass a proper maxlen. If this is the case, then I think you probably need to send 2 messages. The first message will have length 4 and be the integer length. The second message should have the data. e.g.:</p> <h1>client2.py</h1> <pre><code>import socket import sys import struct address = ('localhost', 6005) client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) client_socket.connect(address) messages = ["foobar", "barbaz", "bazquxfad", "Jimmy Carter"] for s in messages: totallen = len(s) pack1 = struct.pack('&gt;I', totallen) # the first part of the message is length client_socket.sendall(pack1) client_socket.sendall(s) </code></pre> <h1>server2.py</h1> <pre><code>import socket import sys import struct address = ('localhost', 6005) server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) server_socket.bind(address) while True: print "Listening" totallen = server_socket.recv(4) totallenRecv = struct.unpack('&gt;I', totallen)[0] message = server_socket.recv(totallenRecv) print message </code></pre> <p>Now the serialization should be pretty easy. After all, proto buffers serialize to strings just fine.</p>
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    1. POhowto program protocol buffer in python to send messages via socket
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    1. USmgilson
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    1. COThanks so much for your help! your code works fine. However, because I plan to use UDP protocol (SOCK_DGRAM), I wonder whether sending 2 packages is a good way to do it. For example, if pack1 is lost, then totallenRecv may not get the correct length to unpack the 2nd message. Thanks again.
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