Refactors tracing handler to use HttpServerParser

[hyleung]

This commit introduces an implementaton of HttpServerParser and
refactors the server tracing handler such that span name customization
is done via the HttpServerParser instead of directly in the tracing
handler.

In order to make this work, needed to add a wrapper around the standard
Ratpack Response so that things like the PathBinding and original
ServerRequest are available to the HttpServerParser.

Closes #51

[codecov]

Codecov Report

Merging #52 into master will decrease coverage by 0.07%.
The diff coverage is 90%.

@@             Coverage Diff              @@
##             master      #52      +/-   ##
============================================
- Coverage      79.9%   79.82%   -0.08%     
- Complexity       33       36       +3     
============================================
  Files             6        7       +1     
  Lines           209      228      +19     
  Branches          7        7              
============================================
+ Hits            167      182      +15     
- Misses           35       37       +2     
- Partials          7        9       +2

Impacted Files	Coverage Δ	Complexity Δ
.../main/java/ratpack/zipkin/ServerTracingModule.java	86.11% <100%> (-0.2%)	6 <0> (-1)
...k/zipkin/internal/DefaultServerTracingHandler.java	96.29% <100%> (+0.84%)	2 <0> (ø)	⬇️
...ava/ratpack/zipkin/internal/ServerHttpAdapter.java	66.66% <100%> (-16.67%)	4 <1> (-1)
...tpack/zipkin/internal/RatpackHttpServerParser.java	80% <80%> (ø)	5 <5> (?)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ecdc3b6...0a79dbb. Read the comment docs.

[codefromthecrypt]

Looks good. FYI I will be raising something soon for "http.template", which is a tag that is uniform across templated requests, though not guaranteed to be a URI template.

[hyleung]

@adriancole thanks for taking a look! I'm wondering if I can get rid of all the explicit Span start/finish stuff that's in DefaultServerTracingHandler. As far as I can tell, that should all be taken care of by the HttpServerHandler.

ratpack-zipkin/src/main/java/ratpack/zipkin/internal/DefaultServerTracingHandler.java

Lines 46 to 55 in ae1a836

	final Span span = handler.handleReceive(extractor, request);
	final Tracer.SpanInScope scope = tracing.tracer().withSpanInScope(span);
	ctx.getResponse().beforeSend(response -> {
	ServerResponse serverResponse = new ServerResponseImpl(response, request, ctx.getPathBinding());
	handler.handleSend(serverResponse, null, span);
	span.finish();
	scope.close();
	});
	span.start();

[hyleung]

I don't actually know whether this is "a thing" - i.e. wanting to be able @Inject a SpanCustomizer into a handler and add tags, etc. I guess it might be useful if it's something that you don't want to implement as a general "policy" using something like a custom HttpServerParser ¯\(ツ)/¯

[codefromthecrypt]

maybe harder hitting comment could be.. "place the scan in scope so that downstream code, such as logging can see the ids"

[codefromthecrypt]

I think you asked.. yes, removing explicit start/finish was a good choice!