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I am trying to build a simple TCP and UDP proxies. No problem with the TCP proxy, however the UDP is a little more complex to handle. The classic proxy scenario would be like this.

  1. Listen for incoming packets from clients
  2. When packet is received send it to destination (server)
  3. Listen for possible response packets from server
  4. Send response packets back to the clients

Ok this should be simple. But when trying to implement this using Synapse or Indy I have a problem. when I receive a packet from a client, I make an internal UDP client, to forward the packet to the destination. Then I have to listen to the possible responses from the destination. Now the question is what is the best implementation for this? There is no single request / response like in TCP. Destination can response with multiple answers over time, or does not respond at all. If I continue to listen for response over one client packet, then I will miss other future packets from this or other clients.

I am looking for a good design to this problem. Here is a sample communication for the reference. Note the multiple responses from the destination at one point

- bind UDP port 40222 on interface 0.0.0.0
- ready
- add 127.0.0.1:4569

127.0.0.1:4569 -> 192.168.90.10:4569
c3 ef 00 00 00 00 00 03 00 00 06 01 0b 02 00 02   ................
02 0a 37 30 30 35 35 35 31 32 31 32 04 0d 4e 6f   ..7005551212..No
74 20 41 76 61 69 6c 61 62 6c 65 09 04 00 00 00   t Available.....
08 08 04 00 00 00 08 06 06 31 36 31 34 30 31 01   .........161401.
08 34 31 33 31 33 39 34 37 0d 08 34 31 33 31 33   .41313947..41313
39 34 37                                          947

192.168.90.10:4569 -> 127.0.0.1:4569
a9 e7 43 ef 00 00 00 09 00 01 06 08 0e 02 00 03   ..C.............
0f 09 34 31 38 32 32 31 37 38 33 06 06 31 36 31   ..418221783..161
34 30 31                                          401

127.0.0.1:4569 -> 192.168.90.10:4569
c3 ef 29 e7 00 00 00 4f 01 01 06 09 10 20 39 36   ..)....O..... 96
64 66 37 31 32 38 61 62 35 39 39 37 65 36 37 36   df7128ab5997e676
65 62 38 63 61 30 33 39 38 66 33 34 30 65         eb8ca0398f340e

192.168.90.10:4569 -> 127.0.0.1:4569
a9 e7 43 ef 00 00 00 56 01 02 06 07 09 04 00 00   ..C....V........
00 08                                             ..

127.0.0.1:4569 -> 192.168.90.10:4569
c3 ef 29 e7 00 00 00 56 02 02 06 04               ..)....V....

192.168.90.10:4569 -> 127.0.0.1:4569
a9 e7 43 ef 00 00 02 85 02 02 04 0e               ..C.........

192.168.90.10:4569 -> 127.0.0.1:4569
a9 e7 43 ef 00 00 02 96 03 02 02 08 54 54 54 54   ..C.........TTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54               TTTTTTTTTTTT

127.0.0.1:4569 -> 192.168.90.10:4569
c3 ef 29 e7 00 00 02 96 02 04 06 04               ..).........

192.168.90.10:4569 -> 127.0.0.1:4569
29 e7 02 aa 54 54 54 54 54 54 54 54 54 54 54 54   )...TTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54                                       TTTT

192.168.90.10:4569 -> 127.0.0.1:4569
29 e7 02 be 54 54 54 54 54 54 54 54 54 54 54 54   )...TTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54                                       TTTT

192.168.90.10:4569 -> 127.0.0.1:4569
29 e7 02 d2 54 54 54 54 54 54 54 54 54 54 54 54   )...TTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54                                       TTTT

192.168.90.10:4569 -> 127.0.0.1:4569
29 e7 02 e6 54 54 54 54 54 54 54 54 54 54 54 54   )...TTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54                                       TTTT

192.168.90.10:4569 -> 127.0.0.1:4569
29 e7 02 fa 54 54 54 54 54 54 54 54 54 54 54 54   )...TTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54 54 54 54 54 54 54 54 54 54 54 54 54   TTTTTTTTTTTTTTTT
54 54 54 54                                       TTTT

EDIT:

For the record. Maybe the UDP proxy is just to messy to implement, for it to be usable. This is a strong probability, while theoretically it is certainly doable. But I will try just for the fun of it. If I get a stable working solution, then even better. Otherwise I will learn something new and admit defeat.

In no way I am trying to be stubborn and going with my head through the wall. I am still hoping somebody has a good idea :)

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2 回答 2

1

不只是代理会遇到 UDP 的问题——状态防火墙和 NAT 设备等网络设备也会遇到这种问题。

处理它的典型方法是超时。一旦在超时时间内没有观察到代理客户端和服务器之间的 UDP 流量，“连接”就会被断开。当看到流量时，超时被重置。

此外，拥有一个当前代理连接不应阻止另一个同时打开 - 您的代理应该能够处理。

于 2011-03-23T10:56:50.230 回答
0

典型的 UDP 客户端-服务器通信可能如下所示：

  • 客户端向 1000 端口发送 UDP 数据包
  • 服务器接收数据包并将响应发送回端口 1001（或端口 1000！）

您的代理应该只监听端口 1000 和 1001 上的数据包。当数据包进入端口 1000 时，将其发送到服务器上的端口 1000。当数据包到达端口 1001 时，它来自服务器，需要在端口 1001 上发送到相应的客户端。这几乎是乐趣结束的地方。UDP 在会话或连接管理方面没有提供任何功能：这完全取决于您尝试代理的特定 UDP 协议。如果您收到来自 2 个不同客户端的 UDP 数据包，并且您收到来自服务器的“响应”数据包，则 UDP 本身没有任何内容可以告诉您将该数据包转发到哪里。建立在 UDP 之上的协议可能有也可能没有某种维护状态的方式。

通用解决方案是不可能的，您可以阅读 RFC，并为您想要支持的每个 UDP 协议实现特定的帮助程序。

于 2011-03-23T10:12:10.503 回答