[tor-bugs] #25598 [Circumvention/Snowflake]: Let the broker inform proxies how often to poll

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#25598: Let the broker inform proxies how often to poll
-------------------------------------+--------------------------------
 Reporter:  dcf                      |          Owner:  (none)
     Type:  enhancement              |         Status:  needs_revision
 Priority:  Medium                   |      Milestone:
Component:  Circumvention/Snowflake  |        Version:
 Severity:  Normal                   |     Resolution:
 Keywords:  starter                  |  Actual Points:
Parent ID:                           |         Points:
 Reviewer:                           |        Sponsor:
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Comment (by cohosh):

 Replying to [comment:5 serna]:


 > Here's how it would work with a hardcoded 20sec poll rate:
 https://github.com/BubuAnabelas/snowflake/pull/1
 >
 > The broker sends the ` Snowflake-Next-Poll ` header and the proxy reads
 it set it as it's next poll interval.

 Thank you serna for looking at this!

 This ticket is related to how proxies and the broker interact (you've
 already commented on #29207) and also #30704 which discusses how to make
 changes between the broker and the proxy backwards compatible. The changes
 proposed here don't have any backwards compatibility issues so will work
 fine as proposed, but as mentioned in #30704, we might eventually want to
 bundle everything into the body in case the mechanism for signaling
 changes from HTTP to something else. This is more likely for the client
 interactions with the broker than the proxy, but who knows :)

 We can always move this header to the body later with the other changes in
 #29207, but i'd suggest for now to make sure that the proxy behaves
 properly if the header is missing. It looks like dcf already mentioned a
 change to handle this, the call to [https://developer.mozilla.org/en-
 US/docs/Web/API/XMLHttpRequest/getResponseHeader getResponseHeader]
 returns `null` if the header doesn't exist and so this check should be
 separated from the calculation and if the header doesn't exist the proxy
 should behave normally with the default poll period.

 Thanks again for the great work \o/

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25598#comment:9>
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