Adds v2 Call interface based on okhttp and retrofit

[codefromthecrypt]

In Zipkin v1, we had a pair of SPI interfaces: SpanConsumer
and AsyncSpanConsumer.

For example, this would define the same thing twice:

void SpanConsumer.accept(List<Span> spans);

// and

void AsyncSpanConsumer.accept(List<Span> spans, Callback<Void> spans);

in v2, it looks like this (inspired by Retrofit and OkHttp's call):

Call<Void> accept(List<Span> spans);

// then make a call like this..
call = spanConsumer.accept(spans);

// to do a blocking call..
call.execute();

// to do an async call..
call.enqueue(callback);

// to cancel
call.cancel();

The important part of this design is that it reduces the redundant
interfaces. We end up making less work for users and implementors
at the cost of an intermediary type: Call.

This design is near identical to Retrofit's Call, which is itself similar to
OkHttp's call. The mild difference here is that the underlying remote
work may not always be http even if the first impl (elasticsearch)
happens to be.

Many thanks to @JakeWharton and @swankjesse for the prior art.

[codefromthecrypt]

This change still needs polish but raising for early feedback cc @anuraaga @shakuzen @llinder

[codefromthecrypt]

Did significant polishing on flight, but needs unit tests

[swankjesse]

Neat.

[anuraaga]

Since you're using assertj, just wondering any reason not to use

assertThatThrownBy(() -> call.enqueue(callback)).isInstanceOf(IllegalStateException.class);

[codefromthecrypt]

Will play with that in next change to the file. Thx for the tip!

…

On 27 Aug 2017 2:15 pm, "Anuraag Agrawal" ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In zipkin/src/test/java/zipkin/internal/v2/CallTest.java <#1705 (comment)>: > + + try { + call.enqueue(callback); + failBecauseExceptionWasNotThrown(IllegalStateException.class); + } catch (IllegalStateException e) { + + } + } + + @test public void enqueuesOnce() throws Exception { + Call<Void> call = Call.create(null); + call.enqueue(callback); + + try { + call.enqueue(callback); + failBecauseExceptionWasNotThrown(IllegalStateException.class); Since you're using assertj, just wondering any reason not to use assertThatThrownBy? — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#1705 (review)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAD613YFk-rY-ILSdphtxFkM7Vw1omEUks5scQmYgaJpZM4PBfRH> .

[codefromthecrypt]

here's follow-ups needed to compete the read side of elasticsearch storage #1708