SignalR MessagePackHubProtocol should handle the EXTENSION value type.

[Cousnouf]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I am using the signal R client to get data from a signal R server. Unfortunately, the MessagePackHubProtocol doesn't handle the EXTENSION value type.
It's commented out and it would be really useful uncommented.

Describe the solution you'd like

Uncomment the code, and break to get out of the switch. Of course remove the RuntimeException throwing.
Adapt the relevant unit test MessagePackHubProtocolTest.

Additional context

No response

[github-actions]

Triage Summary

Area: area-signalr — The issue is specifically about MessagePackHubProtocol in SignalR, which lives under src/SignalR/.
Type: Feature — The request asks to enable support for the MessagePack EXTENSION value type, which is currently commented out/unimplemented in the hub protocol.

Potential Duplicates

• None found — Searches for "SignalR MessagePackHubProtocol EXTENSION type" and "MessagePack extension type SignalR hub protocol" did not surface any matching open issues.

Notes

• The reporter suggests the fix involves uncommenting existing (disabled) code in MessagePackHubProtocol and removing the associated RuntimeException throw, plus updating MessagePackHubProtocolTest. This implies the skeleton may already exist in the codebase.
• The issue was filed using the Feature request template, which aligns with the content.

Generated by Issue Triage Agent for dotnet/aspnetcore for issue #66895 · sonnet46 683.9K · ◷

[BrennanConroy]

What is the EXTENSION value type? And what code do we have commented out?

[Cousnouf]

Hello, It's the code commented here: https://github.com/dotnet/aspnetcore/blob/2c960bf4b248197a5e1ffe63bdbfc845a8338129/src/SignalR/clients/java/signalr/messagepack/src/main/java/com/microsoft/signalr/messagepack/MessagePackHubProtocol.java#L626 It would be really more useful uncommented. Regards, Marc Le jeu. 28 mai 2026 à 18:15, Brennan ***@***.***> a écrit :

…

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[Surya-5555]

@BrennanConroy I noticed this issue doesn't have the help-wanted label yet — could you confirm if community contributions are welcome here before I proceed with the PR? Happy to wait for the go-ahead!

[Surya-5555]

@BrennanConroy here's a high-level implementation plan — happy to hear if this looks right before I proceed:

Root Cause
The EXTENSION value type case in readValue() inside MessagePackHubProtocol.java has working code commented out and replaced with a RuntimeException, meaning any MessagePack payload containing an EXTENSION type value causes the client to crash instead of handling it gracefully.

Proposed Changes

1. MessagePackHubProtocol.java (line 626)

   • Uncomment the existing EXTENSION handling code
   • Remove the throw new RuntimeException("Extension types are not supported")
   • Add a break to properly exit the switch case
   • Result: EXTENSION type values will be read and returned as byte[]

2. MessagePackHubProtocolTest.java

   • Add a test case that sends a MessagePack message containing an EXTENSION type value
   • Verify it deserializes correctly as byte[] without throwing

Scope
Change is isolated to the Java SignalR client only — no impact on other clients or server-side code.

Risk
Low — the implementation skeleton already exists, just commented out. No new logic is being introduced.

Happy to wait for your confirmation before proceeding!

[Cousnouf]

@Surya-5555 the comment:
//Convert this to an object?
Could also be removed

[Surya-5555]

Thanks @Cousnouf — noted, I'll remove that comment as well. As per the contributing guidelines of this repo, waiting for maintainer confirmation before proceeding with the PR!