Trim some HttpHeader parsing logic on browser-wasm

[eerhardt]

Introduce a new feature switch: System.Net.Http.MinimalHeaderValidation. When set to true, this switch will allow for trimming header parsing logic that may not be needed in the app.

Contributes to #44534

Before: 2,644,974 bytes
After: 2,640,488 bytes (with new feature switch set)

So roughly 4.5KB .br compressed savings in a Blazor WASM app. Opening this PR as "draft" to get feedback on the approach. I'm not convinced this savings is worth the tradeoff. Can anyone think of more header parsers that could be removed with the proposed feature switch?

cc @CoffeeFlux @marek-safar

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Issue Details

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Introduce a new feature switch: System.Net.Http.MinimalHeaderValidation. When set to true, this switch will allow for trimming header parsing logic that may not be needed in the app.

Contributes to #44534

Before: 2,644,974 bytes
After: 2,640,488 bytes (with new feature switch set)

So roughly 4.5KB .br compressed savings in a Blazor WASM app. Opening this PR as "draft" to get feedback on the approach. I'm not convinced this savings is worth the tradeoff. Can anyone think of more header parsers that could be removed with the proposed feature switch?

cc @CoffeeFlux @marek-safar

Author:	eerhardt
Assignees:	-
Labels:	area-System.Net.Http
Milestone:	-

[marek-safar]

Are parsers like DateHeaderParser excluded already?

[eerhardt]

Are parsers like DateHeaderParser excluded already?

No. From what I can tell from the code, we won't be able to exclude parsers like that without a re-design of how the KnownHeaders work. The reason being that there is public API that rely on the parsers being there, and exceptions occur if they aren't.

For example, take the Date header:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/Headers/KnownHeaders.cs

Line 45 in 7dc986e

public static readonly KnownHeader Date = new KnownHeader("Date", HttpHeaderType.General | HttpHeaderType.NonTrailing, DateHeaderParser.Parser, null, H2StaticTable.Date, H3StaticTable.Date);

There is a public HttpResponseMessage.Headers.Date property, which relies on the KnownHeaders.Date.Descriptor.Parser:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpGeneralHeaders.cs

Lines 83 to 87 in 7dc986e

	public DateTimeOffset? Date
	{
	get { return HeaderUtilities.GetDateTimeOffsetValue(KnownHeaders.Date.Descriptor, _parent); }
	set { _parent.SetOrRemoveParsedValue(KnownHeaders.Date.Descriptor, value); }
	}

If I try to exclude the DateHeaderParser from the KnownHeaders.Date entry, I get the following exception when using the Headers.Date public property:

Unhandled exception. System.InvalidCastException: Unable to cast object of type 'System.String' to type 'System.DateTimeOffset'.
   at System.Net.Http.Headers.HeaderUtilities.GetDateTimeOffsetValue(HeaderDescriptor descriptor, HttpHeaders store, Nullable`1 defaultValue) in C:\git\runtime\src\libraries\System.Net.Http\src\System\Net\Http\Headers\HeaderUtilities.cs:line 298
   at System.Net.Http.Headers.HttpGeneralHeaders.get_Date() in C:\git\runtime\src\libraries\System.Net.Http\src\System\Net\Http\Headers\HttpGeneralHeaders.cs:line 85
   at System.Net.Http.Headers.HttpResponseHeaders.get_Date() in C:\git\runtime\src\libraries\System.Net.Http\src\System\Net\Http\Headers\HttpResponseHeaders.cs:line 99

[geoffkizer]

How much of the win here is MailAddressParser vs AltSvcHeaderParser?

The AltSvcHeaderParser is strictly internal, so there's no issue really with just disabling it for Blazor. @scalablecory any concerns here?

As I mentioned in the linked issue, we should strongly consider just removing MailAddressParser entirely.

[scalablecory]

Agree AltSvc is only for SocketsHttpHandler and can be removed from browser build.

[geoffkizer]

#52664

[geoffkizer]

Agree AltSvc is only for SocketsHttpHandler and can be removed from browser build.

And to be clear, we don't need to introduce a feature switch to do this.

[eerhardt]

How much of the win here is MailAddressParser vs AltSvcHeaderParser?

It's pretty much 50/50 from my measurements. MailAddressParser ~2KB compressed. AltSvcHeaderParser ~2KB compressed.

[eerhardt]

Closing in favor of #52681 and #52794.