Kestrel: Libuv transport marked as obsolete

Earlier versions of ASP.NET Core used Libuv as an implementation detail of how asynchronous input and output was performed. In ASP.NET Core 2.0, an alternative, xref:System.Net.Sockets.Socket-based transport was developed. In ASP.NET Core 2.1, Kestrel switched to using the Socket-based transport by default. Libuv support was maintained for compatibility reasons.

At this point, use of the Socket-based transport is far more common than the Libuv transport. Consequently, Libuv support is marked as obsolete in .NET 5 and will be removed entirely in .NET 6.0.

As part of this change, Libuv support for new operating system platforms (like Windows Arm64) won't be added in the .NET 5 timeframe.

For discussion on blocking issues that require the use of the Libuv transport, see the GitHub issue at dotnet/aspnetcore#23409.

Version introduced

5.0 Preview 8

Old behavior

The Libuv APIs aren't marked as obsolete.

New behavior

The Libuv APIs are marked as obsolete.

Reason for change

The Socket-based transport is the default. There aren't any compelling reasons to continue using the Libuv transport.

Recommended action

Discontinue use of the Libuv package and extension methods.

Affected APIs

• WebHostBuilderLibuvExtensions
• WebHostBuilderLibuvExtensions.UseLibuv
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.ThreadCount
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.NoDelay
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.MaxWriteBufferSize
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.MaxReadBufferSize
• Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.Backlog

<!-- ### Category ASP.NET Core ### Affected APIs - `T:Microsoft.AspNetCore.Hosting.WebHostBuilderLibuvExtensions` - `Overload:Microsoft.AspNetCore.Hosting.WebHostBuilderLibuvExtensions.UseLibuv` - `T:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions` - `P:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.ThreadCount` - `P:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.NoDelay` - `P:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.MaxWriteBufferSize` - `P:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.MaxReadBufferSize` - `P:Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.LibuvTransportOptions.Backlog` -->