[tor-bugs] #31385 [Circumvention/Snowflake]: Snowflake client fails after bootstrap

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#31385: Snowflake client fails after bootstrap
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 Reporter:  cypherpunks              |          Owner:  cohosh
     Type:  defect                   |         Status:  assigned
 Priority:  Medium                   |      Milestone:
Component:  Circumvention/Snowflake  |        Version:
 Severity:  Normal                   |     Resolution:
 Keywords:                           |  Actual Points:
Parent ID:                           |         Points:
 Reviewer:                           |        Sponsor:
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Comment (by cohosh):

 After more tests, it looks like the client version has nothing to do with
 it.

 Most of my connections (including ones through webextension snowflakes)
 seem to be doing fine. A few are failing in one of two ways:
 1. the proxy fails to answer in time
 2. the proxy answers and the datachannel is opened but the client never
 gets downstream bytes

 Unfortunately for case 2, if the client has already sent its upstream
 bytes, those bytes are lost forever and so all subsequent snowflakes will
 look like they are failing even if their connection to the bridge is fine.
 This is what the sequencing layer in #29206 is for. #29206 will also help
 alleviate some these symptoms by allowing the 30s timeout window to be
 lessened so that snowflakes can be gathered more quickly (#25429).

 I'm currently running the snowflake reachability tests from #30368 to try
 to get a sense of how many snowflakes are unreliable and I'll post back
 here with more info.

 I'll also try to have a look at what's going on with case 1 and how often
 that's happening.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31385#comment:12>
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