Function assertEventStream

packages/executor/src/execution/execute.ts:1851–1883

(
  result: unknown,
  signal?: AbortSignal,
  onSignalAbort?: (handler: () => void) => void,
)

}

function assertEventStream(
  result: unknown,
  signal?: AbortSignal,
  onSignalAbort?: (handler: () => void) => void,
): AsyncIterable<unknown> {
  signal?.throwIfAborted();
  if (result instanceof Error) {
    throw result;
  }

  // Assert field returned an event stream, otherwise yield an error.
  if (!isAsyncIterable(result)) {
    throw createGraphQLError(
      'Subscription field must return Async Iterable. ' + `Received: ${inspect(result)}.`,
    );
  }
  if (onSignalAbort) {
    return {
      [Symbol.asyncIterator]() {
        const asyncIterator = result[Symbol.asyncIterator]();

        if (asyncIterator.return) {
          onSignalAbort?.(() => {
            asyncIterator.return?.();
          });
        }

        return asyncIterator;
      },
    };
  }
  return result;
}

function executeDeferredFragment(
  exeContext: ExecutionContext,