JAX-RS method returns StreamingOutput fails with "Access to ivy environment outside a process request thread is not possible"

Question

Hi Ivy team

I want to build a JAX-RS API returning response in a streaming manner (chunked transfer encoding). The code looks like below:

@Path("{applicationName}/streams")
public class StreamingResponseRestSResource {

    @GET
    public Response getStreamingResponse() {

        // This works by keeping a reference then pass it to the anonymous class.
        // It may NOT work in all situations.
        final Logger logger = Ivy.log();


        StreamingOutput streamingOutput = new StreamingOutput() {

            @Override
            public void write(OutputStream output) throws IOException,
                    WebApplicationException {

                PrintWriter out = new PrintWriter(new BufferedWriter(
                        new OutputStreamWriter(output)), true);

                Ivy.log().error("HHH - BREAK HERE");

                logger.error("HHH - It works with passed reference of Logger");

                IntStream.range(0, 100_000)
                    .forEach(c -> out.println("HHH - Count up to " + c));

            }
        };

        return Response.ok(streamingOutput).build();
    }
}

Full code here: http://pastebin.com/tEAMGFB3

If I do

curl -i -u Developer:Developer http://localhost:8081/ivy/api/designer/streams

the response would be:

{ "errorId": "1578A42A15718503", "errorMessage": "Access to ivy environment outside a process request thread is not possible.\nCurrent thread: Thread[http-nio-8081-exec-14,5,main]", "statusCode": 500 }

If I comment out the line ...

Ivy.log().error("HHH - BREAK HERE");

...the error disappears.

Is there anyway to fix the access to Ivy with StreamingOutput implementation?

Accepted Answer

You can achieve it by using internal API that can change in future versions without any comment.

Use a custom StreamingOutput class which does the ivy context setup:

public abstract class IvyStreamingOutput implements StreamingOutput {

    private final IProcessModelVersion pmv;
    private final ISession session;

    public IvyStreamingOutput()
    {
        this(MetaData.getProcessModelVersion(), MetaData.getSession());
    }

    public IvyStreamingOutput(IProcessModelVersion pmv, ISession session) 
    {
        this.pmv = pmv;
        this.session = session;
    }

    @Override
    public final void write(OutputStream stream) 
            throws IOException, WebApplicationException 
    {
        IProcessModelVersionRequest streamRequest = RequestFactory.createRestRequest(pmv, session);
        MetaData.pushRequest(streamRequest);
        try
        {
          writeInIvyContext(stream);
        }
        finally
        {
          MetaData.popRequest();
        }
    }

    public abstract void writeInIvyContext(OutputStream stream)
            throws IOException, WebApplicationException ;

}

Then you can implement any logic that requires the Ivy.XYZ() methods within the writeInIvyContext(OutputStream stream) method.

JAX-RS method returns StreamingOutput fails with "Access to ivy environment outside a process request thread is not possible"

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