Respect SETTINGS_MAX_HEADER_LIST_SIZE on HTTP/2 and HTTP/3

[MihaZupan]

Closes #78193

This PR does approximate header list length calculations for HTTP/2 and HTTP/3 in order to enforce the SETTINGS_MAX_HEADER_LIST_SIZE setting. It is a slight overestimation of the actual size (mainly from counting the overhead of HPACK framing), therefore making the client slightly more strict than the spec describes.
ASP.NET Core on the other hand is slightly less strict than the spec describes dotnet/aspnetcore#44668 (this is good, you don't want the client/server to be the other way around).

Do we care about the calculated length being exactly correct? Given this limit is generally really high and should only be hit in exceptional cases, I don't think we do. Doing precise bookkeeping would mainly represent a maintenance burden for us (and a slight performance overhead). The current approach of taking the encoded length from HPACK works well as long as we don't support the dynamic table/compression for request headers.

cc: @Tratcher

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Issue Details

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Closes #78193

This PR does approximate header list length calculations for HTTP/2 and HTTP/3 in order to enforce the SETTINGS_MAX_HEADER_LIST_SIZE setting. It is a slight overestimation of the actual size (mainly from counting the overhead of HPACK framing), therefore making the client slightly more strict than the spec describes.
ASP.NET Core on the other hand is slightly less strict than the spec describes (dotnet/aspnetcore#44668).

Do we care about the calculated length being exactly correct? Given this limit is generally really high and should only be hit in exceptional cases, I don't think we do. Doing precise bookkeeping would mainly represent a maintenance burden for us (and a slight performance overhead). The current approach of taking the encoded length from HPACK works well as long as we don't support the dynamic table/compression for request headers.

cc: @Tratcher

Author:	MihaZupan
Assignees:	MihaZupan
Labels:	area-System.Net.Http
Milestone:	8.0.0

[CarnaViire]

LGTM

[MihaZupan]

@Tratcher can you please take a look at this one if this reduced change still makes sense to you?

[MihaZupan]

/backport to release/7.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3787989385