framing

Posted 2020-09-25 alben-xue

framing：
如何分割消息，使得接收方能够识别消息的开始，由于传递给sendall()的数据可能在实际网络传输的时候被分割成多个数据包，接收消息的程序可能需要进行多个recv()调用才能读取完整的消息。

关于framing需要考虑这样的问题：
接收方合适最终停止调用recv()才是安全的，整个消息或数据合适才能完整无缺的传达？合适才能将接收到的信息作为一个整体来解析或处理？

模式一，
发送方循环不断的发送数据，知道所有的数据都被传递给sendall()为止，然后使用close()关闭套接字，接收方只需要不断地调用recv()，直到recv()最后返回一个空格字符为止。

#!/usr/bin/env python3
#-*- encoding:utf8 -*-

import socket
from argparse import ArgumentParser

def server(address):
    sock = socket.socket(socket.AF_INET , socket.SOCK_STREAM)
    sock.setsockopt(socket.SOL_SOCKET , socket.SO_REUSEADDR , 1)
    sock.bind(address)
    sock.listen(1)

    print(‘Run this script in another window with "-c" to connect‘)
    print(‘listening at‘ , sock.getsockname())

    sc,sockname = sock.accept()
    print(‘Accepted connection from ‘ , sockname)
    sc.shutdown(socket.SHUT_WR)

    message = b‘‘
    while True:
        more = sc.recv(8192)
        if not more:
            print(‘Receive None!‘)
            break
        print(‘Receive {} Bytes‘.format(len(more)))
        message += more
    print(‘Message:\n‘)
    print(message.decode())
    sc.close()
    sock.close()


def client(address):
    sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
    sock.connect(address)
    sock.shutdown(socket.SHUT_RD)
    sock.sendall(b‘Beautiful is better than ugly.\n‘)
    sock.sendall(b‘Explicit is better than implicit.\n‘)
    sock.sendall(b‘Simple is better than complex.\n‘)
    sock.close()

if __name__ == "__main__":
    parser = ArgumentParser(description=‘Transmit and receive a data stream‘)
    parser.add_argument(‘hostname‘ , nargs=‘?‘ , default=‘127.0.0.1‘,
                        help=‘IP or hostname (default:%(default)s)‘)
    parser.add_argument(‘-c‘ , action=‘store_true‘ , help=‘run as the client‘)
    parser.add_argument(‘-p‘ , type=int , metavar = ‘port‘ , default = 1060 ,
                        help=‘TCP port number (default:%(default)s)‘)
    args = parser.parse_args()
    function = client if args.c else server
    function((args.hostname , args.p))