[tor-bugs] #33897 [Circumvention/Snowflake]: Remove buffering from WebRTCPeer

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#33897: Remove buffering from WebRTCPeer
-------------------------------------+--------------------------
 Reporter:  dcf                      |          Owner:  dcf
     Type:  enhancement              |         Status:  assigned
 Priority:  Medium                   |      Milestone:
Component:  Circumvention/Snowflake  |        Version:
 Severity:  Normal                   |     Resolution:
 Keywords:  turbotunnel              |  Actual Points:
Parent ID:                           |         Points:
 Reviewer:                           |        Sponsor:
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Comment (by dcf):

 It's not enough to simply remove the buffer and drop `Write`s that occur
 before the data channel is established. That's because not every `Write`
 represents a turbotunnel packet that will be retransmitted if
 lost—specifically the [https://gitweb.torproject.org/pluggable-
 transports/snowflake.git/tree/client/lib/snowflake.go?id=6c2e3adc41c2c6d1ed794adac019a5a6eb069536#n46
 magic token and ClientID] are transmitted first, notionally outside the
 turbotunnel layer, and can't be dropped.

 My plan for this ticket is to refactor `WebRTCPeer` so that
 `NewWebRTCPeer` never returns a partially connected object—it always gives
 you back something with a connected data channel that is ready to directly
 translate `c.Write` into `c.transport.Send`. How it works now is you get
 an object whose internal `transport` field (representing the data channel)
 is initially `nil`, and only becomes non-`nil` asynchronously some time
 later, while you're using it.

 I think this design will allow for the removal of some locks and other
 internal state, for overall simpler code. But it's going to take a little
 hack-and-slash refactoring. I've already filed #33982 and #33984 for some
 changes that suggested themselves while I was rewriting things.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33897#comment:1>
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