Support empty rebalance reason

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 0.8.2 (Unreleased)
 - [Enhancement] Defer scheduler background thread creation until needed allowing for forks.
+- [Fix] Rebalance reason can be empty on a SG when no network.
 
 ## 0.8.1 (2024-02-01)
 - [Enhancement] Introduce "Lags" health view.

lib/karafka/web/tracking/consumers/contracts/subscription_group.rb

@@ -19,7 +19,7 @@ class SubscriptionGroup < Web::Contracts::Base
               required(:stateage) { |val| val.is_a?(Integer) && val >= 0 }
               required(:rebalance_age) { |val| val.is_a?(Integer) && val >= 0 }
               required(:rebalance_cnt) { |val| val.is_a?(Integer) && val >= 0 }
-              required(:rebalance_reason) { |val| val.is_a?(String) && !val.empty? }
+              required(:rebalance_reason) { |val| val.is_a?(String) }
               required(:poll_age) { |val| val.is_a?(Numeric) && val >= 0 }
             end
 

lib/karafka/web/ui/pro/views/consumers/consumer/_subscription_group.erb

@@ -76,7 +76,13 @@
 
   <span class="text-end mt-3">
     <small>
-      Last rebalance reason: <%= subscription_group.rebalance_reason %>
+      Last rebalance reason:
+
+      <% if subscription_group.rebalance_reason.empty? %>
+        Unknown
+      <% else %>
+        <%= subscription_group.rebalance_reason %>
+      <% end %>
     </small>
   </span>
 </div>

spec/lib/karafka/web/tracking/consumers/contracts/subscription_group_spec.rb

@@ -86,10 +86,27 @@
     it { expect(contract.call(subscription_group)).not_to be_success }
   end
 
+  context 'when rebalance_reason in state is missing' do
+    before { subscription_group[:state].delete(:rebalance_reason) }
+
+    it { expect(contract.call(subscription_group)).not_to be_success }
+  end
+
+  context 'when rebalance_reason is not a string' do
+    before { subscription_group[:state][:rebalance_reason] = rand }
+
+    it { expect(contract.call(subscription_group)).not_to be_success }
+  end
+
+  context 'when rebalance_reason is empty' do
+    before { subscription_group[:state][:rebalance_reason] = '' }
+
+    it { expect(contract.call(subscription_group)).to be_success }
+  end
+
   %i[
     state
     join_state
-    rebalance_reason
   ].each do |key|
     context "when #{key} in state is missing" do
       before { subscription_group[:state].delete(key) }

spec/lib/karafka/web/ui/pro/controllers/consumers_spec.rb

@@ -399,6 +399,30 @@
       end
     end
 
+    context 'when subscription has an unknown rebalance reason' do
+      before do
+        topics_config.consumers.reports = reports_topic
+
+        report = Fixtures.consumers_reports_json(symbolize_names: true)
+
+        sg = report[:consumer_groups][:example_app6_app][:subscription_groups][:c4ca4238a0b9_0]
+        sg[:state][:rebalance_reason] = ''
+
+        produce(reports_topic, report.to_json)
+
+        get 'consumers/1/subscriptions'
+      end
+
+      it do
+        expect(response).to be_ok
+        expect(body).to include('Rebalance count:')
+        expect(body).to include('Unknown')
+        expect(body).to include('This process does not consume any')
+        expect(body).not_to include(pagination)
+        expect(body).not_to include(support_message)
+      end
+    end
+
     context 'when subscriptions exist and was reported in a transactional fashion' do
       before do
         topics_config.consumers.states = states_topic