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

spec/lib/delivery_failure_tracker_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe DeliveryFailureTracker do
+  subject { described_class.new('http://example.com/inbox') }
+
+  describe '#track_success!' do
+    before do
+      subject.track_failure!
+      subject.track_success!
+    end
+
+    it 'marks URL as available again' do
+      expect(described_class.available?('http://example.com/inbox')).to be true
+    end
+
+    it 'resets days to 0' do
+      expect(subject.days).to be_zero
+    end
+  end
+
+  describe '#track_failure!' do
+    it 'marks URL as unavailable after 7 days of being called' do
+      6.times { |i| Redis.current.sadd('exhausted_deliveries:http://example.com/inbox', i) }
+      subject.track_failure!
+
+      expect(subject.days).to eq 7
+      expect(described_class.unavailable?('http://example.com/inbox')).to be true
+    end
+
+    it 'repeated calls on the same day do not count' do
+      subject.track_failure!
+      subject.track_failure!
+
+      expect(subject.days).to eq 1
+    end
+  end
+
+  describe '.filter' do
+    before do
+      Redis.current.sadd('unavailable_inboxes', 'http://example.com/unavailable/inbox')
+    end
+
+    it 'removes URLs that are unavailable' do
+      result = described_class.filter(['http://example.com/good/inbox', 'http://example.com/unavailable/inbox'])
+
+      expect(result).to include('http://example.com/good/inbox')
+      expect(result).to_not include('http://example.com/unavailable/inbox')
+    end
+  end
+
+  describe '.track_inverse_success!' do
+    let(:from_account) { Fabricate(:account, inbox_url: 'http://example.com/inbox', shared_inbox_url: 'http://example.com/shared/inbox') }
+
+    before do
+      Redis.current.sadd('unavailable_inboxes', 'http://example.com/inbox')
+      Redis.current.sadd('unavailable_inboxes', 'http://example.com/shared/inbox')
+
+      described_class.track_inverse_success!(from_account)
+    end
+
+    it 'marks inbox URL as available again' do
+      expect(described_class.available?('http://example.com/inbox')).to be true
+    end
+
+    it 'marks shared inbox URL as available again' do
+      expect(described_class.available?('http://example.com/shared/inbox')).to be true
+    end
+  end
+end