Asynchronous handlers in Request Pipeline

[AndreyChechel]

Is there any value in supporting asynchronous handlers in Request Pipeline events?

Currently, some handlers are called asynchronously, the others - synchronously, e.g.:

• Async sample:
  

  apollo-server/packages/apollo-server-core/src/requestPipeline.ts

  Lines 224 to 230 in 8b918e5

  	await dispatcher.invokeHookAsync(
  	'didResolveOperation',
  	requestContext as WithRequired<
  	typeof requestContext,
  	'document' | 'operation' | 'operationName'
  	>,
  	);

• Sync sample (don't be confused with await - invokeDidStartHook is synchronous):
  

  apollo-server/packages/apollo-server-core/src/requestPipeline.ts

  Lines 232 to 238 in 8b918e5

  	const executionDidEnd = await dispatcher.invokeDidStartHook(
  	'executionDidStart',
  	requestContext as WithRequired<
  	typeof requestContext,
  	'document' | 'operation' | 'operationName'
  	>,
  	);

The scenario we've faced is, we'd like to use a plugin to start a DB transaction before execute function is called, and commit or rollback the transaction depending on whether the execution was successful or not.

The executionDidStart / executionDidEnd events look as good places where that logic could be implemented. The problem is handlers for the both events are invoked synchronously, thus, making us unable to await transaction actions to complete.

[ruizmarc]

We also have a use case in which we need to check the rate limit asynchronously based on the request of the user before executing the query. And at this moment, we cannot do it with the request pipeline as it is synchronous.

It would be great to have an asynchronous handler in the request pipeline :D

[abernix]

@ruizmarc The request pipeline is not all synchronous; this statement is untrue. Some life-cycle events are synchronous because they absolutely must be. Which request pipeline life-cycle method are you trying to use? I might suggest checking out didResolveOperation:

apollo-server/packages/apollo-server-plugin-base/src/index.ts

Lines 39 to 44 in b3cbb42

	didResolveOperation?(
	requestContext: WithRequired<
	GraphQLRequestContext<TContext>,
	'metrics' | 'source' | 'document' | 'operationName' | 'operation'
	>,
	): ValueOrPromise<void>;

If you were to return a Promise (or identically, implement that handler as an async function) you could prevent execution, if necessary, by throwing.

[ruizmarc]

Oh! didResolveOperation definetly resolves our use case! We were looking at the wrong hook!

Thanks for the info! 🥇

[abernix]

I suspect most of this will be covered by the new request pipeline API, which is mostly async (whenever possible!). Please do take a look at #2008, which starts to document these new life-cycle hooks, and let us know if you don't find a hook that meets your needs. Thanks!