RUBY-3025 Fix cursor batchSize if limit is zero (mongodb#2566)

Author: comandeo-mongo

lib/mongo/cursor.rb

@@ -253,7 +253,12 @@ def try_next
     #
     # @since 2.2.0
     def batch_size
-      @view.batch_size && @view.batch_size > 0 ? @view.batch_size : limit
+      value = @view.batch_size && @view.batch_size > 0 ? @view.batch_size : limit
+      if value == 0
+        nil
+      else
+        value
+      end
     end
 
     # Is the cursor closed?

spec/mongo/cursor_spec.rb

@@ -698,4 +698,54 @@
       end
     end
   end
+
+  describe '#batch_size' do
+    let(:subscriber) { Mrss::EventSubscriber.new }
+
+    let(:subscribed_client) do
+      authorized_client.tap do |client|
+        client.subscribe(Mongo::Monitoring::COMMAND, subscriber)
+      end
+    end
+
+    let(:collection) do
+      subscribed_client[TEST_COLL]
+    end
+
+    let(:view) do
+      collection.find({}, limit: limit)
+    end
+
+    before do
+      collection.drop
+      collection.insert_many([].fill({ "bar": "baz" }, 0, 102))
+    end
+
+    context 'when limit is 0 and batch_size is not set' do
+      let(:limit) do
+        0
+      end
+
+      it 'does not set batch_size' do
+        view.to_a
+        get_more_commands = subscriber.started_events.select { |e| e.command_name == 'getMore' }
+        expect(get_more_commands.length).to eq(1)
+        expect(get_more_commands.first.command.keys).not_to include('batchSize')
+      end
+    end
+
+    context 'when limit is not zero and batch_size is not set' do
+      let(:limit) do
+        1000
+      end
+
+      it 'sets batch_size' do
+        view.to_a
+        get_more_commands = subscriber.started_events.select { |e| e.command_name == 'getMore' }
+
+        expect(get_more_commands.length).to eq(1)
+        expect(get_more_commands.first.command.keys).to include('batchSize')
+      end
+    end
+  end
 end