add StringWriter interface to ResponseWriter

[romainmenke]

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This change adds the io.StringWriter interface to the http.ResponseWriter implementation in interceptor.go.

This is a fairly small addition because string values can be trivially converted to bytes.
It does not rely on the underlying http.ResponseWriter to also be a io.StringWriter.

Implementing WriteString is fairly common for http response writers.

[codecov]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (48cf923) 81.81% compared to head (3ef48cb) 81.82%.

❗ Current head 3ef48cb differs from pull request most recent head 74ca0a5. Consider uploading reports for the commit 74ca0a5 to get more accurate results

Files	Patch %	Lines
http/interceptor.go	26.31%	14 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #921   +/-   ##
=======================================
  Coverage   81.81%   81.82%           
=======================================
  Files         160      160           
  Lines        9064     9066    +2     
=======================================
+ Hits         7416     7418    +2     
  Misses       1399     1399           
  Partials      249      249           

Flag	Coverage Δ
default	76.92% <26.31%> (+<0.01%)	⬆️
examples	26.36% <5.26%> (-0.01%)	⬇️
ftw	46.63% <5.26%> (-0.02%)	⬇️
ftw-multiphase	48.81% <5.26%> (-0.02%)	⬇️
tinygo	75.14% <ø> (ø)

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[anuraaga]

Do you mind pointing at an example of another similar code that implements io.StringWriter? This doesn't seem so bad, but I'm wondering when a caller wouldn't just call Write([]byte(s)) themselves without inspecting the interfaces.

[romainmenke]

This used to a thing but now I only find old references.
Like these :

• https://go.googlesource.com/benchmarks/+/master/garbage/nethttp.go#1690
• proposal: net/http: add ResponseWriterAs function golang/go#39558 (comment)

I suspect that WriteString on ResponseWriter is no longer common and that Write([]bytes(s)) is the idiomatic way.

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We still have a bunch of tests to make sure that all middleware we add implements the needed interfaces. But it has been a while (±6 years) since I revisited those tests.

e.g. CloseNotifier is also unimplemented here but that is documented as deprecated in http.

So, yeah, this is ok to close for me :)
It can always be revisited if there is an actual need for this and not because of some legacy requirement.

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Thank you for the super speedy review 🙇

[anuraaga]

Thanks a lot for the investigation @romainmenke! Yeah let's go ahead and close for now then, if we find a strong use case for it we can reintroduce it.