Add Brotli compression provider

[khellang]

Probably needs a few more tests, like for ordering. Should the Brotli provider be added by default?

Closes https://github.com/aspnet/BasicMiddleware/issues/217

[khellang]

Any pointers on tests you'd like to see?

[Tratcher]

Can you recycle some of the existing Flush tests? And at least one that shows what happens when the accept-encoding header includes gzip and br.

[khellang]

And at least one that shows what happens when the accept-encoding header includes gzip and br.

Is the intention that gzip will be preferred over Brotli and that you have to explicitly configure it if you want it the other way around?

[Tratcher]

Right

[khellang]

I guess this will also fix https://github.com/aspnet/BasicMiddleware/issues/216, as I had to take the "registration" order into account when selecting a compression provider when you have multiple matching providers with the same (or missing) quality value.

[khellang]

@Tratcher I added some benchmarks and ran them on the dev branch (before) and this branch (after) and they look pretty similar:

Before

BenchmarkDotNet=v0.10.14, OS=macOS High Sierra 10.13.4 (17E202) [Darwin 17.5.0]
Intel Core i7-4870HQ CPU 2.50GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.300
  [Host]     : .NET Core 2.1.1 (CoreCLR 4.6.26606.02, CoreFX 4.6.26606.05), 64bit RyuJIT
  Job-BPKSVL : .NET Core 2.1.1 (CoreCLR 4.6.26606.02, CoreFX 4.6.26606.05), 64bit RyuJIT

Runtime=Core  Server=True  Toolchain=.NET Core 2.1  
RunStrategy=Throughput  

Method	AcceptEncoding	Mean	Error	StdDev	Op/s	Gen 0	Allocated
GetCompressionProvider	*	1.660 us	0.0092 us	0.0086 us	602,399.9	0.0076	1.52 KB
GetCompressionProvider	br, compress, gzip	2.145 us	0.0149 us	0.0139 us	466,270.2	0.0076	1.71 KB
GetCompressionProvider	gzip, compress	1.862 us	0.0089 us	0.0079 us	537,140.7	0.0095	1.64 KB
GetCompressionProvider	gzip, compress, br	2.085 us	0.0197 us	0.0184 us	479,597.7	0.0076	1.71 KB
GetCompressionProvider	gzip;q=0.8, compress;q=0.6, br;q=0.4	2.193 us	0.0171 us	0.0152 us	456,060.6	0.0076	1.71 KB
GetCompressionProvider	identity	1.499 us	0.0093 us	0.0082 us	667,231.6	0.0076	1.52 KB

After

BenchmarkDotNet=v0.10.14, OS=macOS High Sierra 10.13.4 (17E202) [Darwin 17.5.0]
Intel Core i7-4870HQ CPU 2.50GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.300
  [Host]     : .NET Core 2.1.1 (CoreCLR 4.6.26606.02, CoreFX 4.6.26606.05), 64bit RyuJIT
  Job-YFUDVB : .NET Core 2.1.1 (CoreCLR 4.6.26606.02, CoreFX 4.6.26606.05), 64bit RyuJIT

Runtime=Core  Server=True  Toolchain=.NET Core 2.1  
RunStrategy=Throughput  

Method	AcceptEncoding	Mean	Error	StdDev	Op/s	Gen 0	Allocated
GetCompressionProvider	*	1.582 us	0.0092 us	0.0081 us	632,169.5	0.0095	1.64 KB
GetCompressionProvider	br, compress, gzip	2.052 us	0.0124 us	0.0116 us	487,361.5	0.0114	1.73 KB
GetCompressionProvider	gzip, compress	1.569 us	0.0092 us	0.0082 us	637,229.3	0.0076	1.48 KB
GetCompressionProvider	gzip, compress, br	2.066 us	0.0173 us	0.0153 us	484,111.3	0.0076	1.73 KB
GetCompressionProvider	gzip;q=0.8, compress;q=0.6, br;q=0.4	2.193 us	0.0159 us	0.0133 us	456,019.0	0.0076	1.73 KB
GetCompressionProvider	identity	1.304 us	0.0087 us	0.0081 us	766,637.0	0.0076	1.44 KB

[khellang]

Anything more I can do to get this over the finish line 🏁? 👼

[Tratcher]

Just waiting on a feature sign-off from @shirhatti. He'll be back Monday.

[khellang]

Rebased and swapped defaults 👌🏻

[Tratcher]

Sorry, I just realized we'd swapped the branches under you and this was targeting 3.0 (master). I changed the base branch back to 2.2 since we want this sooner than later 😁, but unfortunately that requires one more rebase. I can get to it later today if you don't.

[khellang]

Rebased. Hopfully it went OK 🙏

[Tratcher]

Great, thanks.

[khellang]

Wee! Thank you 😄

[shirhatti]

By adding brotli as the default we might have broken anyone running on full Fx. Whoops

[Tratcher]

We do not add brotli on net461.