[tor-bugs] #28732 [Obfuscation/Snowflake]: Standardize on ArrayBuffer as the type of WebRTC messages

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#28732: Standardize on ArrayBuffer as the type of WebRTC messages
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     Reporter:  dcf                    |      Owner:  (none)
         Type:  defect                 |     Status:  new
     Priority:  Medium                 |  Milestone:
    Component:  Obfuscation/Snowflake  |    Version:
     Severity:  Normal                 |   Keywords:
Actual Points:                         |  Parent ID:
       Points:                         |   Reviewer:
      Sponsor:                         |
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 Two problems:
  1. The proxy receives binary messages over an
 [https://developer.mozilla.org/en-US/docs/Web/API/RTCDataChannel
 RTCDataChannel] without specifying what the type of those messages should
 be. Some debugging code is written to handle the type
 [https://developer.mozilla.org/en-US/docs/Web/API/ArrayBuffer
 ArrayBuffer], but when I tried it the type was actually
 [https://developer.mozilla.org/en-US/docs/Web/API/Blob Blob], which
 crashed the debug code.
  1. Snowflake uses exclusively binary WebRTC data, but the test code uses
 strings as message contents rather than one of the binary data types.

 This wasn't a huge problem, because strings `ArrayBuffer`s and `Blob`s are
 all valid to pass to `WebSocket.send`. The only other thing we do other
 than `send` them is take their length for the purpose of rate limiting,
 and that ''is'' broken.

 https://gitweb.torproject.org/user/dcf/snowflake.git/log/?h=arraybuffer&id=73f328fef8a9351afc47bb65a68b549fbab90cad
 https://gitweb.torproject.org/user/dcf/snowflake.git/diff/?h=arraybuffer&id=73f328fef8a9351afc47bb65a68b549fbab90cad&id2=5817c257c1568c403a41e108d195b209e4e5f589

 This branch sets [https://developer.mozilla.org/en-
 US/docs/Web/API/RTCDataChannel/binaryType binaryType = "arraybuffer"] so
 that we don't get unexpected `Blob` objects. It then makes changes to the
 test and rate-limiting code to standardize on the ArrayBuffer interface
 everywhere.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28732>
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