WebSockets over HTTP/2

Directory.Build.props

@@ -6,7 +6,7 @@
     <Copyright>© Microsoft Corporation. All rights reserved.</Copyright>
     <PackageIcon></PackageIcon>
     <PackageIconFullPath></PackageIconFullPath>
-    <LangVersion>10.0</LangVersion>
+    <LangVersion>11.0</LangVersion>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <StrongNameKeyId>Microsoft</StrongNameKeyId>
     <EmbedUntrackedSources>true</EmbedUntrackedSources>

docs/docfx/articles/websockets.md

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 YARP enables proxying WebSocket and SPDY connections by default. This support works with both the [direct forwarding](direct-forwarding.md) and [full pipeline](getting-started.md) approaches.
 
-[WebSockets](https://www.rfc-editor.org/rfc/rfc6455.html) is a bidirectional streaming protocol built on HTTP/1.1.
+[WebSockets](https://www.rfc-editor.org/rfc/rfc6455.html) is a bidirectional streaming protocol built on HTTP/1.1 and later adapted to [HTTP/2](https://datatracker.ietf.org/doc/html/rfc8441).
 
 [SPDY](https://www.chromium.org/spdy/spdy-protocol/) is the precursor to HTTP/2 and is commonly used in Kubernetes environments.
 
-## Upgrades
+## HTTP/1.1 Upgrades
 
-WebSockets and SPDY are built on top of HTTP/1.1 using a feature called [connection upgrades](https://datatracker.ietf.org/doc/html/rfc7230#section-6.7). YARP proxies the initial request, and if the destination server responds with `101 Switching Protocols`, upgrades the connection to an opaque, bidirectional stream using the new protocol. YARP does not allow upgrading to other protocols like HTTP/2 this way.
+WebSockets and SPDY are built on top of HTTP/1.1 using a feature called [connection upgrades](https://datatracker.ietf.org/doc/html/rfc7230#section-6.7). YARP proxies the initial request, and if the destination server responds with `101 Switching Protocols`, upgrades the connection to an opaque, bidirectional stream using the new protocol. YARP does not support upgrading to other protocols like HTTP/2 this way.
 
 ## HTTP/2
 
-YARP and its underlying components (ASP.NET Core and HttpClient) do not support [WebSockets over HTTP/2](https://datatracker.ietf.org/doc/html/rfc8441). Even if YARP is configured to proxy requests to the destination using HTTP/2, it will detect WebSocket and SPDY requests and use HTTP/1.1 to proxy them.
+YARP supports [WebSockets over HTTP/2](https://datatracker.ietf.org/doc/html/rfc8441) starting in .NET 7 and YARP 2.0. Kestrel is the only available AspNetCore server that will accept incoming HTTP/2 WebSocket requests and that support is automatically enabled. Browsers can detect this support advertised by the server and automatically switch to HTTP/2.
 
-See https://github.com/microsoft/reverse-proxy/issues/1375 for future work here.
+The incoming and outgoing protocol versions do not need to match. The incoming WebSocket request can be HTTP/1.1 or 2. There is no configuration specific to WebSockets for outgoing requests, YARP will use the [ForwarderRequestConfig](xref:Yarp.ReverseProxy.Forwarder.ForwarderRequestConfig)'s Version and VersionPolicy to determine the outbound version to use. These default to HTTP/2 and RequestVersionOrLower.
+
+WebSockets require different HTTP headers for HTTP/2 so YARP will add and remove these headers as needed when adapting between the different versions.
+
+After the initial handshake WebSockets function the same way over both HTTP versions.