[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       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |   Reviewer:
      Sponsor:               |
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 It would be great if onionoo would be able to support push updates using
 webhooks, something similar to pubsubhubbub
 (https://pubsubhubbub.appspot.com/) which supports push updates for
 RSS/Atom feeds.

 Having push support would make systems like a new Tor Weather much more
 efficient.

 For example, instead of polling onionoo to see if certain nodes are down,
 it would get a push notification whenever a node's status changes.

 It can register for specific nodes or have various other filtering
 conditions, but that can be discussed later.

 Pubsubhubbub supports 2 types of pings (when it has something to notify
 webhooks that were registered):

 1) Thin - where it only says data was changed but doesn't send the actual
 data. The receiving party needs pull the relevant data.

 2) Fat - where it sends the actual data that was changed or is relevant
 for the ping.

 This can be implemented as a single system that polls onionoo or as part
 of onionoo as it knows exactly when certain data changes.

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