After 7 days of repeated delivery failures, give up on inbox (#5131)

- A successful delivery cancels it out
- An incoming delivery from account of the inbox cancels it out

app/controllers/activitypub/inboxes_controller.rb

@@ -32,6 +32,7 @@ class ActivityPub::InboxesController < Api::BaseController
     end
 
     Pubsubhubbub::UnsubscribeWorker.perform_async(signed_request_account.id) if signed_request_account.subscribed?
+    DeliveryFailureTracker.track_inverse_success!(signed_request_account)
   end
 
   def process_payload

app/lib/delivery_failure_tracker.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+class DeliveryFailureTracker
+  FAILURE_DAYS_THRESHOLD = 7
+
+  def initialize(inbox_url)
+    @inbox_url = inbox_url
+  end
+
+  def track_failure!
+    Redis.current.sadd(exhausted_deliveries_key, today)
+    Redis.current.sadd('unavailable_inboxes', @inbox_url) if reached_failure_threshold?
+  end
+
+  def track_success!
+    Redis.current.del(exhausted_deliveries_key)
+    Redis.current.srem('unavailable_inboxes', @inbox_url)
+  end
+
+  def days
+    Redis.current.scard(exhausted_deliveries_key) || 0
+  end
+
+  class << self
+    def filter(arr)
+      arr.reject(&method(:unavailable?))
+    end
+
+    def unavailable?(url)
+      Redis.current.sismember('unavailable_inboxes', url)
+    end
+
+    def available?(url)
+      !unavailable?(url)
+    end
+
+    def track_inverse_success!(from_account)
+      new(from_account.inbox_url).track_success! if from_account.inbox_url.present?
+      new(from_account.shared_inbox_url).track_success! if from_account.shared_inbox_url.present?
+    end
+  end
+
+  private
+
+  def exhausted_deliveries_key
+    "exhausted_deliveries:#{@inbox_url}"
+  end
+
+  def today
+    Time.now.utc.strftime('%Y%m%d')
+  end
+
+  def reached_failure_threshold?
+    days >= FAILURE_DAYS_THRESHOLD
+  end
+end

app/models/account.rb

@@ -190,7 +190,8 @@ class Account < ApplicationRecord
     end
 
     def inboxes
-      reorder(nil).where(protocol: :activitypub).pluck("distinct coalesce(nullif(accounts.shared_inbox_url, ''), accounts.inbox_url)")
+      urls = reorder(nil).where(protocol: :activitypub).pluck("distinct coalesce(nullif(accounts.shared_inbox_url, ''), accounts.inbox_url)")
+      DeliveryFailureTracker.filter(urls)
     end
 
     def triadic_closures(account, limit: 5, offset: 0)

app/workers/activitypub/delivery_worker.rb

@@ -15,7 +15,10 @@ class ActivityPub::DeliveryWorker
     perform_request
 
     raise Mastodon::UnexpectedResponseError, @response unless response_successful?
+
+    failure_tracker.track_success!
   rescue => e
+    failure_tracker.track_failure!
     raise e.class, "Delivery failed for #{inbox_url}: #{e.message}", e.backtrace[0]
   end
 
@@ -34,4 +37,8 @@ class ActivityPub::DeliveryWorker
   def response_successful?
     @response.code > 199 && @response.code < 300
   end
+
+  def failure_tracker
+    @failure_tracker ||= DeliveryFailureTracker.new(@inbox_url)
+  end
 end