Play currently supports WebSockets through the existing HTTP/1.1 upgrade path. Even when HTTP/2 is enabled for a server backend, WebSocket handling still depends on backend support for bootstrapping WebSockets over HTTP/2.

RFC 8441 defines this mechanism using HTTP/2 Extended CONNECT:

https://www.rfc-editor.org/rfc/rfc8441.html

Upstream Tracking

Pekko HTTP:

• Support WebSockets over HTTP/2 via RFC 8441 Extended CONNECT apache/pekko-http#1112

Netty:

• Websocket over HTTP2 netty/netty#8011
• [Feature] WebSocket over HTTP/2 (h2+h2c) netty/netty#12352

Current State

Pekko HTTP backend

Play’s Pekko HTTP backend can enable HTTP/2, but Pekko HTTP does not currently expose WebSockets over HTTP/2 via RFC 8441.

Until Pekko HTTP supports RFC 8441, Play cannot support WebSockets over HTTP/2 on this backend without implementing or bypassing Pekko HTTP internals.

Netty backend

Netty has some low-level RFC 8441 / Extended CONNECT building blocks, but high-level WebSocket-over-HTTP/2 support is still tracked upstream.

Expected Outcome

Once backend support exists, Play should investigate exposing WebSockets over HTTP/2 without requiring application code changes where possible.

Likely work items:

• verify RFC 8441 support in the backend
• add integration tests for WebSockets over HTTP/2
• document backend-specific support and limitations
• ensure abnormal stream termination maps cleanly to Play’s WebSocket close behavior
• check compatibility with existing raw and typed WebSocket APIs

Notes

This is currently a tracking issue. There is no immediate Play-side implementation path until the relevant backend support exists.