Python端口转发/复用服务器

Question

我想搭建一个服务器，让它监听UDP的162端口（这是SNMP陷阱的端口），然后把收到的数据转发给多个客户端。还有一个很重要的点是，源端口和地址要保持不变（也就是地址伪装）。

我觉得最合适的工具可能是Twisted或者Scapy，或者也可以用普通的套接字（sockets），但我在Twisted的文档里找不到关于源地址伪装的相关内容。

有没有什么解决方案呢？

补充：我加了悬赏，可能用iptables也能解决这个问题？

Answer 1

我试了大家推荐的答案，但没用。最后我用上了这个用Python写的简单TCP重定向工具：

#!/usr/bin/env python

import socket
import threading
import select
import sys

terminateAll = False

class ClientThread(threading.Thread):
    def __init__(self, clientSocket, targetHost, targetPort):
        threading.Thread.__init__(self)
        self.__clientSocket = clientSocket
        self.__targetHost = targetHost
        self.__targetPort = targetPort

    def run(self):
        print "Client Thread started"

        self.__clientSocket.setblocking(0)

        targetHostSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        targetHostSocket.connect((self.__targetHost, self.__targetPort))
        targetHostSocket.setblocking(0)

        clientData = ""
        targetHostData = ""
        terminate = False
        while not terminate and not terminateAll:
            inputs = [self.__clientSocket, targetHostSocket]
            outputs = []

            if len(clientData) > 0:
                outputs.append(self.__clientSocket)

            if len(targetHostData) > 0:
                outputs.append(targetHostSocket)

            try:
                inputsReady, outputsReady, errorsReady = select.select(inputs, outputs, [], 1.0)
            except Exception, e:
                print e
                break

            for inp in inputsReady:
                if inp == self.__clientSocket:
                    try:
                        data = self.__clientSocket.recv(4096)
                    except Exception, e:
                        print e

                    if data != None:
                        if len(data) > 0:
                            targetHostData += data
                        else:
                            terminate = True
                elif inp == targetHostSocket:
                    try:
                        data = targetHostSocket.recv(4096)
                    except Exception, e:
                        print e

                    if data != None:
                        if len(data) > 0:
                            clientData += data
                        else:
                            terminate = True

            for out in outputsReady:
                if out == self.__clientSocket and len(clientData) > 0:
                    bytesWritten = self.__clientSocket.send(clientData)
                    if bytesWritten > 0:
                        clientData = clientData[bytesWritten:]
                elif out == targetHostSocket and len(targetHostData) > 0:
                    bytesWritten = targetHostSocket.send(targetHostData)
                    if bytesWritten > 0:
                        targetHostData = targetHostData[bytesWritten:]

        self.__clientSocket.close()
        targetHostSocket.close()
        print "ClienThread terminating"

if __name__ == '__main__':
    if len(sys.argv) != 5:
        print 'Usage:\n\tpython SimpleTCPRedirector <host> <port> <remote host> <remote port>'
        print 'Example:\n\tpython SimpleTCPRedirector localhost 8080 www.google.com 80'
        sys.exit(0)     

    localHost = sys.argv[1]
    localPort = int(sys.argv[2])
    targetHost = sys.argv[3]
    targetPort = int(sys.argv[4])

    serverSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    serverSocket.bind((localHost, localPort))
    serverSocket.listen(5)
    print "Waiting for client..."
    while True:
        try:
            clientSocket, address = serverSocket.accept()
        except KeyboardInterrupt:
            print "\nTerminating..."
            terminateAll = True
            break
        ClientThread(clientSocket, targetHost, targetPort).start()

    serverSocket.close()

Answer 2

我对 twisted 或 scapy 这些库不太熟悉，但用普通的 Python 套接字来做这件事其实很简单。这样做还有一个额外的好处，就是代码会更容易在不同的环境中运行。以下是我在有限测试中发现可以正常工作的代码：

#!/usr/bin/python
from socket import *
bufsize = 1024 # Modify to suit your needs
targetHost = "somehost.yourdomain.com"
listenPort = 1123

def forward(data, port):
    print "Forwarding: '%s' from port %s" % (data, port)
    sock = socket(AF_INET, SOCK_DGRAM)
    sock.bind(("localhost", port)) # Bind to the port data came in on
    sock.sendto(data, (targetHost, listenPort))

def listen(host, port):
    listenSocket = socket(AF_INET, SOCK_DGRAM)
    listenSocket.bind((host, port))
    while True:
        data, addr = listenSocket.recvfrom(bufsize)
        forward(data, addr[1]) # data and port

listen("localhost", listenPort)