[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:  new
 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 serna):

 I can do this.
 \\

 > The broker could instead tell each proxy how long to wait before polling
 again. The broker could even dynamically adjust the rate based on an
 estimate of supply and demand.
 \\
 What information would you use to determine the time dynamically? I was
 thinking in using {{{clientDeniedCount}}} and {{{proxyIdleCount}}} from
 the metrics but it resets every 24 hours which can be a bit misleading.
 \\

 > One way to do this would be a custom header in responses to /proxy
 requests:
 > {{{
 > Snowflake-Next-Poll: Thu, 22 Mar 2018 18:05:47 GMT
 > }}}
 > Or using a relative time offset:
 > {{{
 > Snowflake-Next-Poll: 600
 > }}}
 \\
 The second one seems like the best option. A timestamp can be confusing to
 read and would depend on the operating system clock which can be offset.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25598#comment:3>
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