RUBY-2317 Consider CursorNotFound to be a resumable change stream error

lib/mongo/error/operation_failure.rb

@@ -166,6 +166,12 @@ def write_retryable_code?
       # @since 2.6.0
       def change_stream_resumable?
         if @result && @result.is_a?(Mongo::Operation::GetMore::Result)
+          # CursorNotFound exceptions are always resumable because the server
+          # is not aware of the cursor id, and thus cannot determine if
+          # the cursor is a change stream and cannot add the
+          # ResumableChangeStreamError label.
+          return true if code == 43
+
           # Connection description is not populated for unacknowledged writes.
           if connection_description.max_wire_version >= 9
             label?('ResumableChangeStreamError')

spec/mongo/collection/view/change_stream_resume_spec.rb

@@ -196,17 +196,17 @@
         change_stream.to_enum
       end
 
-      it 'propagates cursor not found error' do
+      it 'resumes on a cursor not found error' do
         original_cursor_id = cursor.id
 
         client.use(:admin).command({
           killCursors: collection.name,
           cursors: [cursor.id]
         })
 
-        lambda do
+        expect do
           enum.next
-        end.should raise_error(Mongo::Error::OperationFailure, /cursor.*not found/)
+        end.not_to raise_error
       end
     end
 
@@ -218,17 +218,17 @@
         collection.insert_one(a:2)
       end
 
-      it 'propagates cursor not found error' do
+      it 'resumes on a cursor not found error' do
         original_cursor_id = cursor.id
 
         client.use(:admin).command({
           killCursors: collection.name,
           cursors: [cursor.id]
         })
 
-        lambda do
+        expect do
           change_stream.try_next
-        end.should raise_error(Mongo::Error::OperationFailure, /cursor.*not found/)
+        end.not_to raise_error
       end
     end
   end

spec/mongo/error/operation_failure_spec.rb

@@ -227,6 +227,46 @@
         end
       end
 
+      context 'when the error code is 43 (CursorNotFound)' do
+        let(:error) { Mongo::Error::OperationFailure.new(nil, result, code: 43, code_name: 'CursorNotFound') }
+        let(:result) do
+          Mongo::Operation::GetMore::Result.new(
+            Mongo::Protocol::Message.new, description)
+        end
+
+        context 'wire protocol < 9' do
+          let(:description) do
+            Mongo::Server::Description.new('',
+              'minWireVersion' => 0,
+              'maxWireVersion' => 8,
+            )
+          end
+
+          it 'returns true' do
+            # CursorNotFound exceptions are resumable even if they don't have
+            # a ResumableChangeStreamError label because the server is not aware
+            # of the cursor id, and thus cannot determine if it is a change stream.
+            expect(error.change_stream_resumable?).to be true
+          end
+        end
+
+        context 'wire protocol >= 9' do
+          let(:description) do
+            Mongo::Server::Description.new('',
+              'minWireVersion' => 0,
+              'maxWireVersion' => 9,
+            )
+          end
+
+          it 'returns true' do
+            # CursorNotFound exceptions are resumable even if they don't have
+            # a ResumableChangeStreamError label because the server is not aware
+            # of the cursor id, and thus cannot determine if it is a change stream.
+            expect(error.change_stream_resumable?).to be true
+          end
+        end
+      end
+
       context 'not a getMore response' do
         let(:result) do
           Mongo::Operation::Result.new(

spec/spec_tests/data/change_streams/change-streams-resume-whitelist.yml

@@ -1105,3 +1105,69 @@ tests:
           fullDocument:
             x:
               $numberInt: "1"
+  -
+    # CursorNotFound is special-cased to be resumable regardless of server versions or error labels, so this test has
+    # no maxWireVersion.
+    description: "change stream resumes after CursorNotFound"
+    minServerVersion: "4.2"
+    failPoint:
+      configureFailPoint: failCommand
+      mode: { times: 1 }
+      data:
+          failCommands: ["getMore"]
+          errorCode: 43
+          closeConnection: false
+    target: collection
+    topology:
+      - replicaset
+      - sharded
+    changeStreamPipeline: []
+    changeStreamOptions: {}
+    operations:
+      -
+        database: *database_name
+        collection: *collection_name
+        name: insertOne
+        arguments:
+          document:
+            x: 1
+    expectations:
+      -
+        command_started_event:
+          command:
+            aggregate: *collection_name
+            cursor: {}
+            pipeline:
+              -
+                $changeStream: {}
+          command_name: aggregate
+          database_name: *database_name
+      -
+        command_started_event:
+          command:
+            getMore: 42
+            collection: *collection_name
+          command_name: getMore
+          database_name: *database_name
+      -
+        command_started_event:
+          command:
+            aggregate: *collection_name
+            cursor: {}
+            pipeline:
+              -
+                $changeStream: {}
+          command_name: aggregate
+          database_name: *database_name
+    result:
+      success:
+        -
+          _id: "42"
+          documentKey: "42"
+          operationType: insert
+          ns:
+            db: *database_name
+            coll: *collection_name
+          fullDocument:
+            x:
+              $numberInt: "1"