Fix preserving messages for stateful reconnect with backplane

[BrennanConroy]

Fixes #55575

Changed MessageBuffer.WriteAsync methods to use the hub message type since that's the only information we're using in the method. And updated the SerializedHubMessage usage to assume we're sending a HubInvocationMessage since that's the only message type we currently use with SerializedHubMessage.

Updated tests:

• src/SignalR/server/SignalR/test/Microsoft.AspNetCore.SignalR.Tests/Internal/MessageBufferTests.cs: Added a regression test to ensure unacknowledged serialized messages are resent on reconnect.

• src/SignalR/server/StackExchangeRedis/test/RedisEndToEnd.cs: Added a new E2E stateful reconnect test to verify that messages are preserved during reconnects and introduced a WebSocketWrapper class to simulate ungraceful closures. [1] [2] [3]

[Copilot]

Pull Request Overview

This PR fixes issues with preserving messages during a stateful reconnect in a backplane scenario by updating the MessageBuffer write logic and adding comprehensive tests.

• Updated MessageBuffer.WriteAsync methods to default to HubInvocationMessage for SerializedHubMessage.
• Added a new E2E test to simulate ungraceful WebSocket closure and verify stateful reconnect.
• Introduced a StatefulHub and integrated it into the test startup configuration.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/SignalR/server/StackExchangeRedis/test/RedisEndToEnd.cs	Added a new E2E test for stateful reconnect with a custom WebSocketWrapper.
src/SignalR/server/SignalR/test/Microsoft.AspNetCore.SignalR.Tests/Internal/MessageBufferTests.cs	Added a regression test to validate that unacknowledged serialized messages are resent on reconnect.
src/SignalR/server/StackExchangeRedis/test/StatefulHub.cs	New hub implementation to support stateful reconnect testing.
src/SignalR/server/StackExchangeRedis/test/Startup.cs	Updated endpoints mapping to support the new StatefulHub with stateful reconnect enabled.
src/SignalR/server/Core/src/SerializedHubMessage.cs	Added a Debug.Assert to ensure the message type is compatible with HubInvocationMessage.
src/SignalR/common/Shared/MessageBuffer.cs	Modified WriteAsync methods to use the message type instead of the message instance for better type clarity.

Comments suppressed due to low confidence (1)

src/SignalR/server/SignalR/test/Microsoft.AspNetCore.SignalR.Tests/Internal/MessageBufferTests.cs:183

• The use of square brackets for the InvocationMessage arguments appears to be a syntax error. Consider replacing [1] with a proper array initializer (e.g. new object[] { 1 }).

var invocationMessage = new SerializedHubMessage([new SerializedMessage(protocol.Name, protocol.GetMessageBytes(new InvocationMessage("method1", [1])))]);

[halter73]

Do we want to backport this?

[BrennanConroy]

Yeah, looks like a decent number of people have hit this.

[BrennanConroy]

/backport to release/9.0

[BrennanConroy]

/backport to release/8.0

[github-actions]

Started backporting to release/9.0: https://github.com/dotnet/aspnetcore/actions/runs/14319862207

[github-actions]

Started backporting to release/8.0: https://github.com/dotnet/aspnetcore/actions/runs/14319863946

[github-actions]

@BrennanConroy backporting to "release/8.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Fix preserving messages for stateful reconnect with backplane
Using index info to reconstruct a base tree...
A	src/SignalR/server/SignalR/test/Microsoft.AspNetCore.SignalR.Tests/Internal/MessageBufferTests.cs
M	src/SignalR/server/StackExchangeRedis/test/RedisEndToEnd.cs
Falling back to patching base and 3-way merge...
Auto-merging src/SignalR/server/StackExchangeRedis/test/RedisEndToEnd.cs
CONFLICT (content): Merge conflict in src/SignalR/server/StackExchangeRedis/test/RedisEndToEnd.cs
Auto-merging src/SignalR/server/SignalR/test/Internal/MessageBufferTests.cs
CONFLICT (content): Merge conflict in src/SignalR/server/SignalR/test/Internal/MessageBufferTests.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 Fix preserving messages for stateful reconnect with backplane
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!