[tor-bugs] #18723 [Onionoo]: Support registering webhooks for push updates

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#18723: Support registering webhooks for push updates
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 Reporter:  erans        |          Owner:
     Type:  enhancement  |         Status:  new
 Priority:  Low          |      Milestone:
Component:  Onionoo      |        Version:
 Severity:  Normal       |     Resolution:
 Keywords:               |  Actual Points:
Parent ID:               |         Points:
 Reviewer:               |        Sponsor:
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Comment (by karsten):

 Thanks for the suggestion!  I agree that this would be great to have.  But
 it's also something that feels non-trivial to do right, and the potential
 gain is quite hard to measure.  So, for now, I suggest to just poll
 Onionoo once every few minutes and not worry too much about efficiency.

 First, here's why I'm not worried about efficiency (which is something
 that I'm quite often worried about!): your application can include an `If-
 Modified-Since` header in its request, and if the underlying has not
 changed, sending a response is done very efficiently.  Your request will
 typically not hit Onionoo's Jetty server, but be answered by Apache.  If
 you're writing a system like Weather with only one or a few instances
 running, then the additional load will be trivial.  Just go for it.

 But let's discuss this possibility anyway.  It would be a nice feature for
 clients to subscribe to a certain query, rather than just getting a
 response once.  I'd just want to avoid writing this functionality
 ourselves and re-use some existing code.  Actually, I wonder if we could
 use Redis pub/sub for this, which would also mean using Redis to answer
 standard (non-subscribe) requests.

 Is this something you'd want to help with, or are you happy using
 potentially less efficient polling if it gets the job done?  I'd
 understand either way.  I just want to be honest that this feature might
 not be available anytime soon if I have to write it.  But I'd be happy
 keeping it in the product backlog.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18723#comment:1>
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