Question

I have a ServerResource which responds to GET requests by sending binary data back. The issue is that the source of the binary data will be downloaded asynchronously via a separate REST call (probably via HttpAsyncClient). Is it possible to create a Representation that I can feed data to as it arrives from the async download? I need to be able to do it without blocking any threads, so some sort of NIO solution is required.

I suspect I can do this with WriteableRepresetation, but I’m not exactly sure how as the documentation says

For this you just need to create a subclass and override the abstract Representation.write(WritableByteChannel) method. This method will later be called back by the connectors when the actual representation’s content is needed.

implying that when the method is called, all of the content must already be available.

I’m using v2.1.

Answer 1

After playing around with it for a bit, it looks like this is possible using a ReadableRepresentation. I dont know if there is a better way to create the ReadableByteChannel than using a Pipe or not, but that’s the only way I saw without having to implement my own Channel.

private static final byte[] HELLO_WORLD = "hello world\n".getBytes(Charsets.UTF_8);

public static class HelloWorldResource extends ServerResource {
    @Get
    public Representation represent() throws Exception {
        final Pipe pipe = Pipe.open();

        // this simulates another process generating the data
        Thread t = new Thread(new Runnable() {
            private final ByteBuffer buf = ByteBuffer.allocate(1);
            private final Pipe.SinkChannel sink = pipe.sink();

            private int offset = 0;

            @Override
            public void run() {
                while (offset < HELLO_WORLD.length) {
                    try {
                        buf.clear();
                        buf.put(HELLO_WORLD[offset++]);
                        buf.flip();

                        while (buf.hasRemaining()) {
                            sink.write(buf);
                        }

                        Thread.sleep(500);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }

                try {
                    sink.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
        t.setDaemon(true);
        t.start();

        return new ReadableRepresentation(pipe.source(), MediaType.TEXT_PLAIN);
    }
}

public static class HelloWorldApplication extends Application {
    @Override
    public synchronized Restlet createInboundRoot() {
        Router router = new Router(getContext());
        router.attach("/hello", HelloWorldResource.class);

        return router;
    }
}

public static void main(String[] args) throws Exception {
    Component component = new Component();
    component.getDefaultHost().attach("", new HelloWorldApplication());

    Server server = component.getServers().add(Protocol.HTTP, 8090);

    component.start();
}