XEP-0065: SOCKS5 Bytestreams

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本文介绍SOCKS5 ByteStreams (S5B) 协议的工作原理，包括直接连接与中介连接两种场景下的协商流程、TCP及SOCKS5连接建立过程、数据交换方式等关键信息。

[b]SOCKS5 Bytestreams ("S5B")
out-of-band bytestream[/b]

[b]Requester[/b]
The entity that starts a bytestream negotiation with a Target. [7]
[b]Target[/b]
The entity with which the Requester is attempting to establish a bytestream.
[b]Proxy[/b]
An entity that is willing to be a middleman for the bytestream between the Requester and the Target.
[b]StreamHost[/b]
The system that the Target connects to and that is "hosting" the bytestream; the Streamhost can be either the Requester or a Proxy.
[b]StreamID[/b]
A relatively unique Stream ID for this connection; this is generated by the Requester for tracking purposes and MUST be less than 128 characters in length.

* "----" ... communications over XMPP
* "____" ... communications over TCP
* "\\\\" and "////" ... communications over SOCKS 5
* "====" ... communications over the bytestream itself

[b]Direct Connections[/b]
In this situation, the StreamHost is the Requester

Requester                           Target
   |                                  |
   | Send S5B initiation request      |
   | -------------------------------> |
   |                                  |
   | Open TCP socket                  |
   | <_______________________________ |
   |                                  |
   | Request SOCKS 5 connection       |
   | <\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ |
   |                                  |
   | Acknowledge SOCKS 5 connection   |
   | ///////////////////////////////> |
   |                                  |
   | Send S5B acceptance              |
   | <------------------------------- |
   |                                  |
   | Exchange data over S5B           |
   | <==============================> |
   |

1. Requester Initiates S5B Negotiation

<iq from='requester@example.com/foo'
    id='hu3vax16'
    to='target@example.org/bar'
    type='set'>
  <query xmlns='http://jabber.org/protocol/bytestreams'
         sid='vxf9n471bn46'>
    <streamhost
        jid='requester@example.com/foo'
        host='192.168.4.1'
        port='5086'/>
  </query>
</iq>

2. the Target attempts to open a standard TCP socket on the network address of the StreamHost/Requester.

3. Target Establishes SOCKS5 Connection with StreamHost

CMD = X'01'
ATYP = X'03'
DST.ADDR = SHA1 Hash of: (SID + Requester JID + Target JID)
DST.PORT = 0

4. StreamHost Acknowledges Connection

STATUS = X'00'

5. Target Notifies Requester of Bytestream

<iq from='target@example.org/bar'
    id='hu3vax16'
    to='requester@example.com/foo'
    type='result'>
  <query xmlns='http://jabber.org/protocol/bytestreams'
         sid='vxf9n471bn46'>
    <streamhost-used jid='requester@example.com/foo'/>
  </query>
</iq>

[b]Mediated Connections[/b]
In this situation, the StreamHost is not the Requester but a Proxy, which means that the Requester needs to discover the network address of the StreamHost before sending the initiation request to the Target, needs to negotiate a connection with the StreamHost in the same way that the Target does, and needs to ask the StreamHost to activate the bytestream before it can be used.

1. Requester Initiates Negotiation

<iq from='requester@example.com/foo'
    id='npq71g53'
    to='target@example.org/bar'
    type='set'>
  <query xmlns='http://jabber.org/protocol/bytestreams'
         sid='vxf9n471bn46'>
    <streamhost
        host='24.24.24.1'
        jid='streamer.example.com'
        port='7625'/>
  </query>
</iq>

2. the Target attempts to open a standard TCP socket on the network address of the Proxy.

3. Target Establishes SOCKS5 Connection with StreamHost

CMD = X'01'
ATYP = X'03'
DST.ADDR = SHA1 Hash of: (SID + Requester JID + Target JID)
DST.PORT = 0

4. StreamHost Acknowledges Connection

STATUS = X'00'

5. Target Acknowledges Bytestream

<iq from='target@example.org/bar'
    id='npq71g53'
    to='requester@example.com/foo'
    type='result'>
  <query xmlns='http://jabber.org/protocol/bytestreams'
         sid='vxf9n471bn46'>
    <streamhost-used jid='streamer.example.com'/>
  </query>
</iq>

6. Requester Establishes SOCKS5 Connection with StreamHost

CMD = X'01'
ATYP = X'03'
DST.ADDR = SHA1 Hash of: (SID + Requester JID + Target JID)
DST.PORT = 0

7. StreamHost Acknowledges Connection to Requester

STATUS = X'00'

8. Requester Requests Activation of Bytestream

<iq from='requester@example.com/foo'
    id='oqx6t1c9'
    to='streamer.example.com'
    type='set'>
  <query xmlns='http://jabber.org/protocol/bytestreams'
         sid='vxf9n471bn46'>
    <activate>target@example.org/bar</activate>
  </query>
</iq>

9. Proxy Informs Requester of Activation

<iq from='streamer.example.com'
    id='oqx6t1c9'
    to='requester@example.com/foo'
    type='result'/>