RFR [11] 8197564: HTTP Client implementation - JEP 321

[Chris Hegarty]

Hi Sebastien,

> On 5 Apr 2018, at 11:07, Sebastien Deleuze <sdeleuze at pivotal.io> wrote:
> 
> Hi,
> 
> I am currently implementing a draft support for JDK new HTTP client in Spring Framework 5 [1] (using JDK 10 for now) in order to be able to leverage it as a WebClient [2] engine.

Great that you are trying this out.

> Our integration tests all pass with regular HTTP/1.1 web services

Good to hear this.

> (we have not tested the HTTP/2 support yet), but not with streaming APIs.

Reactive streams APIs consist of both Publishers and Subscribers, but
in your specific case you appear to most interested in Publishers. I'll
assume "streaming APIs” here means "RS Publishers", since the HTTP
Client quite obvious interoperates with Subscribers.

> Based on my current understanding, it seems the CompletableFuture<HttpResponse> returned by HttpClient#sendAsync completes only when all the data of the response body is available, not asap the status code + headers are available like with Jetty or Reactor Netty clients (which prevents to consume infinite streams via Reactive Streams API).

As Michael has already said, it can operate either way depending on the
actual higher-level Java type that the body is being converted to. In
fact, you can even write your own BodyHandler that returns a Subscriber
with an already complete body CF. So there is no issue working with
infinite streams via RS, if that is what you want.

I believe what you are actually seeking is a
`BodyHandler<Publisher<List<ByteBuffer>>>`, that makes its HttpResponse
available once the headers have been received. This has come up just
recently, in this email thread [1]. A JIRA issue has been filed to track
the addition of such a BodyHandler [2].

In the interim, until the new handler can been added, it should be
possible to either write your own ( Daniel has similar,
`static class PublishingBodySubscriber implements
    BodySubscriber<Publisher<List<ByteBuffer>>>`, in a test [3] ). Or
if your library, or reactor, provides functionality similar to
`io.reactivex.processors.PublishProcessor`, then you can use it as the
BodyHandler type and write a delegating BodySubscriber that
completes its body CF immediately with an instance of that processor.

> Is consuming streaming HTTP/1.1 endpoints (like JSON streaming or SSE) supported by current implementation?


Yes, but of course not out of the box, you need to hook up to a JSON
Subscriber, etc.

-Chris.

[1] http://mail.openjdk.java.net/pipermail/net-dev/2018-April/011314.html
[2] https://bugs.openjdk.java.net/browse/JDK-8201186
[3] http://hg.openjdk.java.net/jdk/sandbox/file/c59f684f1eda/test/jdk/java/net/httpclient/ResponsePublisher.java