Set Content-Length header in server responses

[hlbarber]

Motivation and Context

• https://httpwg.org/specs/rfc7230.html#header.content-length
• Closes Set Content-Length where appropiate in server responses #1146

Description

• Add Content-Length header to non-streaming server responses
• Add a Content-Length checks to the existing httpResponseTests

[hlbarber]

Some ambiguity exists on whether this should be left to hyper (which will perform it) or whether we should eagerly add the Content-Length headers at this level.

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• AWS SDK (ignoring whitespace)
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)

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Rust Wrk benchmark report:

Duration: 90 sec, Connections: 32, Threads: 2

Measurement	Deviation	Current	Old
Requests/sec	4.09%	50176.2	48205.28
Total requests	4.13%	4520878	4341481
Total errors	NaN%	0	0
Total successes	4.13%	4520878	4341481
Average latency ms	-7.14%	0.65	0.7
Minimum latency ms	0.00%	0.02	0.02
Maximum latency ms	2.29%	16.94	16.56
Stdev latency ms	-30.91%	0.38	0.55
Transfer Mb	4.13%	469.95	451.3
Connect errors	NaN%	0	0
Read errors	NaN%	0	0
Write errors	NaN%	0	0
Status errors (not 2xx/3xx)	NaN%	0	0
Timeout errors	NaN%	0	0

[david-perez]

Looks good!

Linking your findings here for posterity: smithy-lang/smithy#1244.

It'd be nice if we documented somewhere, perhaps in serverRenderContentLengthHeader, all the research you did regarding when Hyper adds/removes Content-Length in HTTP1/HTTP2.

We should contribute a PR to awslabs/smithy adding an @httpResponseTests asserting Content-Length header has the expected value (despite it being a SHOULD in the HTTP RFC, which you can bring up in the PR, because they are already asserting it in @httpRequestTests for clients).

[hlbarber]

@david-perez

We should contribute a PR to awslabs/smithy adding an @httpResponseTests asserting Content-Length header has the expected value

Posted an issue inquiring about this, will follow with a PR shortly after if needed

smithy-lang/smithy#1255

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• AWS SDK (ignoring whitespace)
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• Server Test Python (ignoring whitespace)

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Rust Wrk benchmark report:

Duration: 90 sec, Connections: 32, Threads: 2

Measurement	Deviation	Current	Old
Requests/sec	-3.93%	87562.02	91140.42
Total requests	-3.90%	7887516	8207639
Total errors	NaN%	0	0
Total successes	-3.90%	7887516	8207639
Average latency ms	-9.52%	1.14	1.26
Minimum latency ms	0.00%	0.02	0.02
Maximum latency ms	0.42%	24.01	23.91
Stdev latency ms	-6.70%	2.09	2.24
Transfer Mb	-3.90%	819.91	853.19
Connect errors	NaN%	0	0
Read errors	NaN%	0	0
Write errors	NaN%	0	0
Status errors (not 2xx/3xx)	NaN%	0	0
Timeout errors	NaN%	0	0

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• AWS SDK (ignoring whitespace)
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