UDP代理實現

Question

我正在嘗試構建一個簡單的TCP和UDP代理。 TCP代理沒問題，但是UDP處理起來有點復雜。 經典的代理方案就是這樣。

1. 偵聽來自客戶端的傳入數據包
2. 收到數據包后，將其發送到目的地（服務器）
3. 偵聽來自服務器的可能的響應數據包
4. 將響應數據包發送回客戶端

好的，這應該很簡單。 但是，當嘗試使用Synapse或Indy實現此功能時，我遇到了問題。 當我從客戶端收到數據包時，我將創建一個內部UDP客戶端，以將數據包轉發到目標。 然后，我必須聽聽目的地的可能回應。 現在的問題是什么是最佳的實現方案？ 沒有像TCP這樣的單個請求/響應。 隨着時間的推移，目標可以響應多個答案，或者根本不響應。 如果我繼續偵聽一個客戶端數據包的響應，那么將來我將錯過來自此客戶端或其他客戶端的其他數據包。

我正在為這個問題尋找一個好的設計。 這是示例通信，以供參考。 請注意來自目的地的多個響應

- 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

編輯：

作為記錄。 UDP代理可能只是雜亂地實現，以使其無法使用。 這是一個很大的可能性，但是從理論上講它確實是可行的。 但我會盡力而為。 如果我能找到穩定的工作解決方案，那就更好了。 否則，我會學到新的東西並承認失敗。

我決不會固執，不願將頭穿過牆壁。 我仍然希望有人有一個好主意:)

Answer 1

UDP出現問題的不僅是代理服務器-狀態防火牆和NAT設備之類的網絡設備也會運行到UDP。

處理它的典型方法是超時。 一旦在超時時間內未觀察到代理客戶端與服務器之間的UDP通信，“連接”將被斷開。 看到流量時，將重置超時。

同樣，擁有一個當前的代理連接也不應阻止同時打開另一個-您的代理應該能夠處理該連接。

Answer 2

典型的UDP客戶端-服務器通信可能如下所示：

• 客戶端將UDP數據包發送到端口1000
• 服務器接收數據包並將響應發送回端口1001（或端口1000！）。

您的代理應該只偵聽端口1000和1001上的數據包。當數據包進入端口1000時，將其發送到服務器上的端口1000。 當數據包到達端口1001時，它來自服務器，需要通過端口1001發送到適當的客戶端。 這幾乎就是樂趣結束的地方。 UDP在會話或連接管理方面一無所獲：這完全取決於您要代理的特定UDP協議。 如果您從2個不同的客戶端接收到UDP數據包，並且從服務器收到了“響應”數據包，則UDP本身沒有任何內容可告訴您將數據包轉發到何處。 建立在UDP之上的協議可能有某種保持狀態的方法，也可能沒有。

通用的解決方案是不可能的，您需要閱讀RFC，並為要支持的每個UDP協議實現特定的幫助程序。