FormData and marshalling, easier/possible to use

[ktoso]

Let's say I'm in Java and want to test a route which deals with FormData (I actually really do 😉), I'd want to say:

    final HttpRequest request =
      HttpRequest
        .POST("/") // the below method does not exist (FormData also does not exist in javadsl)
        .withFormData(FormData.create(Pair.create("name", "Kapi"), Pair.create("age", "42")));

but can't since HttpRequest (or even HttpMessage) is not aware of FormData (i.e. the method withFormData does not exist). We also can't provide it on the type since it's in akka-http-core and we'd need marshallers, which are in akka-http (PredefinedToEntityMarshallers).

I don't have a good idea how to solve this simply...? One would have to manually call marshalling and use withEntity I guess now...? Open to other ideas (are we need a full DSL for request building for java?)

[ktoso]

// cc @rkuhn @sirthias @jrudolph

[ktoso]

Maybe providing a Marshaller of FormData => Entity would be enough, in javadsl Marshallers?

[jrudolph]

In any case, withFormData isn't enough to specify the request because it could either be url encoded or multipart formdata.

[jrudolph]

On the other hand, there's also still #15674 which is somewhat of a pain to port because of all the complexity that's inside, so having a simple solution that works for forms with textual data would really be nice.

[ktoso]

Right, that's true as well.
So what do you propose for now for Java users - should marshalling infra be called explicitly?
Then we must provide the ToEntityMarshaller for FormData in an accessible way for Java anyway.
Or am I missing some way of doing this already?

[ktoso]

Ah right, yeah it definitely links to #15674 in some ways.

[jrudolph]

At some point I added Multipart.FormData.toEntity already, so that's already usable from Scala without needing any marshallers. I think we should also add a model.FormData.toEntity, to simplify this as well.

Having done that, it would be easy to add the helper methods to the Java side HttpMessage even if the model itself is still missing on the Java side.

[jrudolph]

It's only a little bit of code that move have to move to FormData: https://github.com/akka/akka/blob/release-2.3-dev/akka-http/src/main/scala/akka/http/scaladsl/marshalling/PredefinedToEntityMarshallers.scala#L56

[ktoso]

Ok, so we don't feel it's against the purity of the core or sth like that ;-)
I'll give the move a shot then

Again, huge thanks for all the hints @jrudolph - it's really invaluable.

[ktoso]

Managed to solve it by reusing the hinted at code :)