Laszlo

Hello, I am Laszlo

.NET developer

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Kestrel HTTP/2 Internals

01/05/2025

In the previous post I explored some of the inner workings of Kestrel. Kestrel is one of the servers built into ASP.NET Core.

First, I investigated how HTTP socket connections are dispatched to a request processor, such as the Http2Connection.

In a different post I looked into how HEADER frames work with HTTP/2 responses, and what are the main building blocks of writing headers to the response stream in Kestrel.

Lastly, I explored how HEADER and CONTINUATION frames are used in ASP.NET Core to serve response headers larger to the frame size.

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Switch Expression or Visitor pattern

12/07/2024

A few months ago I looked into optimizing dictionary lookups using switch expressions.

In this post I investigate a seemingly similar problem, but with vastly different constraints, that eventually demand a vastly different solution.

Problem Definition

Given a set of polymorphic objects and a DTO. A method needs to iterate all the polymorphic objects and evaluate them against the DTO. Each polymorphic object evaluates a different (C#) property of the DTO. While there are a few designs to achieve this, in this case I seek for a design that does not introduce a coupling between the polymorphic objects and the DTO. I compare two possible solutions in this post.

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Range Indexer

11/20/2024

With C# 12's collection expression feature, the range indexers has become also more powerful.

These two constructs along with the C#'s spreads feature allow to easily create new collections by slicing and concatenating existing ones. For example, given the following snippet:

int[] a = [1, 2];
int[] b = [3, 4, 5];
int[] c = [..a, ..b[..1]];

When executing the snippet, variable c will reference an integer array containing 1 2 and 3 values. While these operations are universal in many languages for a longer time, they are only introduced as new in C# 12.

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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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