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Large HTTP/2 Header Frames

10/19/2024

In a previous post I explored how HTTP2 handles header frames in .NET 8. In this post I explore how it is planned to handle larger HTTP2 response header values.

Recap

• RFC7540 describes the HTTP/2 protocol's related details.

• In HTTP/2 a request-response pair is serialized in a stream.

• A stream consists of message frames.

• Frames have a type, frame header, a given size and corresponding data. Frames are associated with a given stream with the stream ID.

• HTTP/2 requests start with HEADER frame. A header frame may be followed by CONTINUATION frames containing further headers.

• The HTTP/2 request headers HPack encoded and split into HEADER and CONTINUATION frames.

• In ASP.NET Core's Kestrel HPackHeaderWriter static class writes the headers.

  • HPackHeaderWriter iterates over the headers/trailers (except for the response status header which is written separately) using the Http2FrameWriter types.

• Http2FrameWriter creates the buffer which it passes as a Span<byte> to the header writer. The default size of the buffer is 16K, but it can be updated via Kestrel's option by setting the Http2Limits's MaxFrameSize property. Clients can also influence the frame size by sending a value in the SETTING frame.

Planned changes

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HTTP/2 Header Frames

10/05/2024

I have recently come across a GitHub issue 'Allow the encoder to split headers across frames' in the dotnet/aspnetcore repository, that made me look into and understand some of the details how HTTP/2 encodes headers.

In this post I will summarize my key findings on how ASP.NET Core writes these headers today. In this post I use version ASP.NET Core 8 with .NET 8. My findings are based on the current state of the source code and the corresponding RFC7540.

HTTP/2

Here are my key learnings:

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Collection Expressions

09/15/2024

C# 12 introduced a new language feature: collection expressions or collection literal. It provides a neat way to initialize collections: enumerables, lists, spans, etc.

An example of using the collection expressions:

int[] a = [6, 7];

In this case the compiler generates code for variable a referencing an array with two elements: 6 and 7.

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Preview .NET with BenchmarkDotnet

09/08/2024

In a previous post I explored how someone can setup a custom .NET SDK and Runtime for development. It consists of a script downloads the .NET runtime to a custom folder, another script that sets up environment variables to use the given .NET version with Visual Studio and a global.json / nuget.config for build time dependencies with Visual Studio and the .NET CLI.

In this post I evolve the previous setup:

• Install and use an alpha release of .NET 10 Runtime with .NET 9 SDK.

• Setup BenchmarkDotNet performance measurements to use .NET 10

Update the runtime to .NET 10

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Setup Local Preview .NET

09/01/2024

In this blog post I will detail how to setup early preview versions of .NET for development. My findings apply for .NET 9, but the methods should be applicable in general to most versions of .NET (considering version specific details).

While a preview version of .NET can be downloaded at any time from the dotnet website, installing the forthcoming preview version requires somewhat more investment.

The findings of this post are based on ASP.NET Core, which uses a similar, but more complex approach in its restore.cmd command. This blog post will focus on the key components to have the latest SDK or a custom runtime available.

The preview versions of .NET can heavily change. Features may get added, removed, changed, or their performance might significantly improve. It is always suggested to choose and use an LTS or STS release for production applications. However, in certain cases a developer might want to test the latest preview features, in which case the methods described in this blog post will help.

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