feat: avoid rewrapping response writer when capturing metrics #22
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This is a first attempt at addressing #19.
First we refactor the common code for
rw
from being generated to sitting in its own file.Then we add an indirection to
Wrap
, so that it becomes possible to associate the metrics with the returnedhttp.ResponseWriter
.Then we add an interface to recover the
Metrics
from a wrappedResponseWriter
. If we can do that, then we directly call the wrapped function and return the existingMetrics
.This unfortunately introduces an asymmetry: consumers of the library that use
Wrap()
directly will not be able to useMetrics()
. That kinda makes sense:Wrap()
is not necessary used for metrics. We could move the metrics init toWrap()
and always track them, but that would probably be an unexpected semantic change (with probable performance impact of its own). So I opted against it.WDYT? Does the general direction make sense?
Closes #19