"Promise already completed" exception with GridFS

[Szabo Akos]

Hi!

I've the following problem: when I upgrade my application from ReactiveMongo 0.12.0 to 0.12.1 or 0.12.2 I get the following exception when serving files from GridFS:

java.lang.IllegalStateException: Promise already completed.

at scala.concurrent.Promise$class.complete(Promise.scala:55)

at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:157)

I read the files this way:

  def find(fileId: UUID): Future[Option[FileData]] = {

    gridFS.find[JsObject, JSONReadFile](Json.obj("_id" -> fileId))

      .headOption.map(_.map(r => FileData(FileMetadata(r.id.as[UUID], r.filename.get, r.contentType, r.uploadDate.map(new DateTime(_))), gridFS.enumerate(r))))

  }

And I convert the Enumerator to Stream in order to stream it to the client in HTTP response:

val fileData = Source.fromPublisher(Streams.enumeratorToPublisher(f.content)).map(ByteString(_))

And this conversion leads to the problem. If I replace this conversion to the following, then the problem does not occur:

val content = f.content.run(Iteratee.consume[Array[Byte]]())

val fileData = Source.fromFuture(content).map(ByteString(_))

I guess this is a kind of hack, so it would be fine to solve it with standard streaming. Or am I doing something wrong?

Thanks,

Akos

[Cédric Chantepie]

Please paste the complete stack trace.

[Cédric Chantepie]

Also, the code from the provided MongoController doesn't raise such issue (see demo app).

[Szabó Ákos]

Hi!

The complete stack trace is the following:
[error] 2017-05-02 08:40:07,499 a.d.Dispatcher - Promise already completed.

java.lang.IllegalStateException: Promise already completed.
    at scala.concurrent.Promise$class.complete(Promise.scala:55)
    at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:157)

    at scala.concurrent.Promise$class.failure(Promise.scala:104)
    at scala.concurrent.impl.Promise$DefaultPromise.failure(Promise.scala:157)
    at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:257)
    at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:251)
    at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:36)
    at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)
    at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply$mcV$sp(BatchingExecutor.scala:91)
    at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply(BatchingExecutor.scala:91)

The MongoController based solution may be working (although I'm doing very similar things in my code), but I need to handle the "NotModified" HTTP response for the sake of efficiency.

Thanks,
Akos

2017. 04. 30. 13:51 keltezéssel, Cédric Chantepie írta:

[Cédric Chantepie]

I don't see reason not to used the MongoController, or at least to have a look at its code which seems ok for me.