Pickle EOFError: Ran out of input when recv from a socket

Question

I am running a very simple python (3.x) client-server program (both locally on my PC) for a school project (not intended for the real world) which just sends messages back-a

Answer 1

The problem with your code is that recv(4096), when used on a TCP socket, might return different amount of data from what you might have expected, as they are sliced at packet boundaries.

The easy solution is to prefix each message with length; for sending like

import struct
packet = pickle.dumps(foo)
length = struct.pack('!I', len(packet)
packet = length + packet

then for receiving

import struct

buf = b''
while len(buf) < 4:
    buf += socket.recv(4 - len(buf))

length = struct.unpack('!I', buf)[0]
# now recv until at least length bytes are received,
# then slice length first bytes and decode.

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However, Python standard library already has a support for message oriented pickling socket, namely multiprocessing.Connection, that supports sending and receiving pickles with ease using the Connection.send and Connection.recv respectively.

Thus you can code your server as

from multiprocessing.connection import Listener

PORT = 1234
server_sock = Listener(('localhost', PORT))
conn = server_sock.accept()

unpickled_data = conn.recv()

and client as

from multiprocessing.connection import Client

client = Client(('localhost', 1234))
client.send(['hello', 'world'])