Unfortunate handling of query validation in subscriptions in sangria.

[ValdemarGr]

Some query errors are only thrown on execution or preparation in sangria which causes the following code to fail in F instead of in Either[Throwable, Json] even though the error is in fact a graphql error.

lucuma-graphql-routes/modules/sangria/src/main/scala/lucuma/graphql/routes/SangriaGraphQLService.scala

Lines 63 to 83 in 2051089

	fs2.Stream.eval {
	Dispatcher[F].use { implicit d =>
	Async[F].fromFuture {
	Async[F].delay {
	Executor.prepare(
	schema = schema,
	queryAst = request.query,
	userContext = userData,
	operationName = request.op,
	variables = request.vars.getOrElse(Json.fromJsonObject(JsonObject())),
	exceptionHandler = exceptionHandler
	).map { preparedQuery =>
	preparedQuery
	.execute()
	.map(_.asRight[Throwable])
	.recover { case NonFatal(error) => error.asLeft[Json] }
	}
	}
	}
	}
	} .flatten

An example of this is the following error:

Field 'field' conflict because they return conflicting types 'A!' and 'A'. Use different aliases on the fields to fetch both if this was intentional. (line n, column k):
    field
(line x, column y):
    field

When this occurs the subscription "hangs", no error or anything, which seems to be because a fiber is started but does not interact with the subscription in case of any error outcomes.

lucuma-graphql-routes/modules/core/src/main/scala/lucuma/graphql/routes/Subscriptions.scala

Line 93 in 2051089

f <- es.compile.drain.start

We have deployed the following fix:

    fs2.Stream.eval {
      Dispatcher[F].use { implicit d =>
        Async[F].fromFuture {
          Async[F].delay {
            Executor.prepare(
              schema           = schema,
              queryAst         = request.query,
              userContext      = userData,
              operationName    = request.op,
              variables        = request.vars.getOrElse(Json.fromJsonObject(JsonObject())),
              exceptionHandler = exceptionHandler
            ).map { preparedQuery =>
              preparedQuery
                .execute()
                .map(_.asRight[Throwable])
                .recover { case NonFatal(error) => error.asLeft[Json] }
            }
          }
        }
      }
    } .flatten
+ .attempt
+ .map(_.flatten)

[tpolecat]

👍 Thanks for the report!