fix(microservices): cleanup upstream subscription in client-side gRPC stream calls

packages/microservices/client/client-grpc.ts

@@ -232,11 +232,17 @@ export class ClientGrpcProxy extends ClientProxy implements ClientGrpc {
             callArgs.unshift(maybeMetadata);
           }
           const call = client[methodName](...callArgs);
-          upstreamSubjectOrData.subscribe(
-            (val: unknown) => call.write(val),
-            (err: unknown) => call.emit('error', err),
-            () => call.end(),
-          );
+
+          const upstreamSubscription: Subscription =
+            upstreamSubjectOrData.subscribe(
+              (val: unknown) => call.write(val),
+              (err: unknown) => call.emit('error', err),
+              () => call.end(),
+            );
+
+          return () => {
+            upstreamSubscription.unsubscribe();
+          };
         });
       }
       return new Observable(observer => {

packages/microservices/test/client/client-grpc.spec.ts

@@ -267,11 +267,12 @@ describe('ClientGrpcProxy', () => {
       });
     });
     describe('when stream request', () => {
+      let clientCallback: (err: Error | null | undefined, response: any) => void;
       const writeSpy = sinon.spy();
       const methodName = 'm';
       const obj = {
         [methodName]: callback => {
-          callback(null, {});
+          clientCallback = callback;
           return {
             write: writeSpy,
           };
@@ -287,6 +288,11 @@ describe('ClientGrpcProxy', () => {
         stream$ = client.createUnaryServiceMethod(obj, methodName)(upstream);
       });
 
+      afterEach(() => {
+        // invoke client callback to allow resources to be cleaned up
+        clientCallback(null, {});
+      })
+
       it('should subscribe to request upstream', () => {
         const upstreamSubscribe = sinon.spy(upstream, 'subscribe');
         stream$.subscribe(