Initial working proxy.

It listens, and sends.  When the connection is
closed, it closes (both sides now!)

req.txt

@@ -0,0 +1,11 @@
+attrs==19.3.0
+Automat==0.8.0
+constantly==15.1.0
+hyperlink==19.0.0
+idna==2.8
+incremental==17.5.0
+pkg-resources==0.0.0
+PyHamcrest==1.9.0
+six==1.12.0
+Twisted==19.7.0
+zope.interface==4.6.0

tcp-proxy.py

@@ -0,0 +1,92 @@
+#!/usr/bin/env python3
+
+import sys
+
+from twisted.internet import defer
+from twisted.internet import protocol
+from twisted.internet import reactor
+from twisted.python import log
+
+HOST = '127.0.0.1'
+PORT = 2002
+LISTEN_PORT = 9999
+LISTEN_ON = '127.0.0.1'
+
+
+class ProxyClientProtocol(protocol.Protocol):
+    def connectionMade(self):
+        log.msg("Client: connected to peer")
+        self.cli_queue = self.factory.cli_queue
+        self.cli_queue.get().addCallback(self.serverDataReceived)
+
+    def serverDataReceived(self, chunk):
+        if chunk is False:
+            self.cli_queue = None
+            log.msg("Client: disconnecting from peer")
+            self.factory.continueTrying = False
+            self.transport.loseConnection()
+        elif self.cli_queue:
+            log.msg("Client: writing %d bytes to peer" % len(chunk))
+            self.transport.write(chunk)
+            self.cli_queue.get().addCallback(self.serverDataReceived)
+        else:
+            self.factory.cli_queue.put(chunk)
+
+    def dataReceived(self, chunk):
+        log.msg("Client: %d bytes received from peer" % len(chunk))
+        self.factory.svr_queue.put(chunk)
+
+    def connectionLost(self, why):
+        log.msg("connectionLost because: %s" % why)
+        # if self.cli_queue:
+        #     self.cli_queue = None
+        #     log.msg("Client: peer disconnect unexpectedly")
+        self.factory.svr_queue.put(False)
+        self.cli_queue = None
+        self.transport.loseConnection()
+
+# class ProxyClientFactory(protocol.ReconnectingClientFactory):
+class ProxyClientFactory(protocol.ClientFactory):    
+    maxDelay = 10
+    # continueTrying = True
+    # continueTrying = False
+    protocol = ProxyClientProtocol
+
+    def __init__(self, svr_queue, cli_queue):
+        self.svr_queue = svr_queue
+        self.cli_queue = cli_queue
+
+class ProxyServer(protocol.Protocol):
+    def connectionMade(self):
+        self.svr_queue = defer.DeferredQueue()
+        self.cli_queue = defer.DeferredQueue()
+        self.svr_queue.get().addCallback(self.clientDataReceived)
+
+        factory = ProxyClientFactory(self.svr_queue, self.cli_queue)
+        reactor.connectTCP(HOST, PORT, factory)
+
+    def clientDataReceived(self, chunk):
+        if chunk is False:
+            self.transport.loseConnection()
+        else:
+            log.msg("Server: writing %d bytes to original client" % len(chunk))
+            self.transport.write(chunk)
+            self.svr_queue.get().addCallback(self.clientDataReceived)
+
+    def dataReceived(self, chunk):
+        log.msg("Server: %d bytes received" % len(chunk))
+        self.cli_queue.put(chunk)
+
+    def connectionLost(self, why):
+        log.msg("lost connection %s" % why)
+        self.cli_queue.put(False)
+
+
+
+if __name__ == "__main__":
+    log.startLogging(sys.stdout)
+    factory = protocol.Factory()
+    factory.protocol = ProxyServer
+    reactor.listenTCP(LISTEN_PORT, factory, interface=LISTEN_ON)
+    reactor.run()
+