Add complete handler in startGraphQLSubscription

CHANGELOG.md

@@ -11,6 +11,10 @@
   [@joe-re](https://github.com/joe-re) in [#4082](https://github.com/apollographql/apollo-client/pull/4082)
 - Make `isApolloError` available for external use.  <br/>
   [@FredyC](https://github.com/FredyC) in [#4223](https://github.com/apollographql/apollo-client/pull/4223)
+- The `QueryManager` now calls `complete` on the observables used by
+  Apollo Client's Subscription handling. This gives finite subscriptions a
+  chance to handle cleanup.  <br/>
+  [@sujeetsr](https://github.com/sujeetsr) in [#4290](https://github.com/apollographql/apollo-client/pull/4290)
 - Documentation updates.  <br/>
   [@lifedup](https://github.com/lifedup) in [#3931](https://github.com/apollographql/apollo-client/pull/3931)  <br />
   [@Dem0n3D](https://github.com/Dem0n3D) in [#4008](https://github.com/apollographql/apollo-client/pull/4008)  <br />

packages/apollo-client/src/__mocks__/mockLinks.ts

@@ -130,6 +130,12 @@ export class MockSubscriptionLink extends ApolloLink {
     }, result.delay || 0);
   }
 
+  public simulateComplete() {
+    const { observer } = this;
+    if (!observer) throw new Error('subscription torn down');
+    if (observer.complete) observer.complete();
+  }
+
   public onSetup(listener: any): void {
     this.setups = this.setups.concat([listener]);
   }

packages/apollo-client/src/__tests__/graphqlSubscriptions.ts

@@ -258,4 +258,24 @@ describe('GraphQL Subscriptions', () => {
     link.simulateResult(errorResult);
     return Promise.all(promises);
   });
+
+  it('should call complete handler when the subscription completes', done => {
+    const link = mockObservableLink();
+    const client = new ApolloClient({
+      link,
+      cache: new InMemoryCache({ addTypename: false }),
+    });
+    const completeFn = jest.fn();
+
+    let count = 0;
+    const sub = client.subscribe(defaultOptions).subscribe({
+      complete() {
+        completeFn();
+      }
+    });
+
+    link.simulateComplete();
+    expect(completeFn).toHaveBeenCalled();
+    done();
+  });
 });

packages/apollo-client/src/core/QueryManager.ts

@@ -943,6 +943,13 @@ export class QueryManager<TStore> {
               }
             });
           },
+          complete: () => {
+            observers.forEach(obs => {
+              if (obs.complete) {
+                obs.complete();
+              }
+            });
+          }
         };
 
         // TODO: Should subscriptions also accept a `context` option to pass