fix: do not hang in LRO forever if API returned nothing (#436)

* fix: do not hang in LRO forever if API returned nothing

* add test

src/longrunning.ts

@@ -375,6 +375,16 @@ export class Operation extends EventEmitter {
             setImmediate(emit, 'progress', metadata, rawResponse);
             previousMetadataBytes = rawResponse!.metadata!.value;
           }
+          // special case: some APIs fail to set either result or error
+          // but set done = true (e.g. speech with silent file).
+          // Don't hang forever in this case.
+          if (rawResponse!.done) {
+            const error = new GoogleError(
+                'Long running operation has finished but there was no result');
+            error.code = status.UNKNOWN;
+            setImmediate(emit, 'error', error);
+            return;
+          }
           setTimeout(() => {
             now = new Date();
             delay = Math.min(delay * delayMult, maxDelay);

test/longrunning.ts

@@ -81,6 +81,11 @@ const ERROR_OP = {
   error: ERROR,
   response: null,
 };
+const BAD_OP = {
+  name: OPERATION_NAME,
+  metadata: METADATA,
+  done: true,
+};
 const mockDecoder = val => {
   return val.toString();
 };
@@ -405,6 +410,27 @@ describe('longrunning', () => {
             });
       });
 
+      it('does not hang on invalid API response', done => {
+        const func = (argument, metadata, options, callback) => {
+          callback(null, PENDING_OP);
+        };
+        const client = mockOperationsClient({finalOperation: BAD_OP});
+        const apiCall = createApiCall(func, client);
+        apiCall()
+            .then(responses => {
+              const operation = responses[0];
+              const promise = operation.promise();
+              return promise;
+            })
+            .then(() => {
+              done(new Error('Should not get here.'));
+            })
+            .catch(error => {
+              expect(error).to.be.an('error');
+              done();
+            });
+      });
+
       it('uses provided promise constructor', done => {
         const client = mockOperationsClient();
         const desc = new longrunning.LongrunningDescriptor(