Feature Request: Full HTTP/2 support (RFC 8441) for WebSocket connections via reverse proxy

Summary

When Collabora Online (built-in CODE server via Nextcloud's richdocumentscode app) is deployed behind a reverse proxy (HAProxy) with HTTP/2 enabled end-to-end, document loading fails due to WebSocket tunneling incompatibilities. HTTP/2 support for WebSocket connections (RFC 8441) would resolve this.

Environment

• Collabora Online: built-in CODE server (richdocumentscode Nextcloud app)
• Nextcloud version: latest (as of April 2026)
• Reverse proxy: HAProxy 3.2.14 (OPNsense)
• Web server: Apache + php-fpm
• Internal Collabora port: 9983 (HTTP, no TLS)
• OS: RHEL-based Linux

Current Behavior

When HAProxy has HTTP/2 enabled on the backend connection (HAProxy → Apache/Nextcloud), the WebSocket tunnel through Nextcloud's proxy.php fails with:

net::ERR_HTTP2_PROTOCOL_ERROR
net::ERR_CONTENT_LENGTH_MISMATCH
Document loading failed due to timeout: Please check for failing network requests

The coolwsd process runs correctly on port 9983 and responds to direct HTTP requests:

curl http://localhost:9983/
OK

The issue is not with coolwsd itself, but with the WebSocket tunneling layer when HTTP/2 is involved in the proxy chain.

Workaround

Force HTTP/1.1 on the HAProxy backend connection. This works but prevents end-to-end HTTP/2 optimization:

• Disable HTTP/2 on HAProxy backend pool
• Keep only HTTP/1.1 in ALPN for backend
• Add timeout tunnel 3600s to backend options

Expected Behavior

Collabora Online should work correctly in HTTP/2 reverse proxy environments. WebSocket over HTTP/2 has been standardized since RFC 8441 (September 2018) — nearly 8 years ago.

Feature Request

1. Ensure coolwsd fully supports RFC 8441 (WebSocket over HTTP/2)
2. Ensure the WebSocket handshake and tunneling work correctly when the proxy chain uses HTTP/2 (either end-to-end or partially)
3. Document the recommended HAProxy/nginx configuration for HTTP/2 deployments in the official docs

Why This Matters

HTTP/2 is now the standard for modern web deployments and brings significant performance improvements (multiplexing, header compression, reduced latency). Requiring a downgrade to HTTP/1.1 on the backend is a workaround that should not be necessary in 2026.

References

• RFC 8441: https://www.rfc-editor.org/rfc/rfc8441
• Related Nextcloud richdocuments issue: https://github.com/nextcloud/richdocuments/issues
• HAProxy WebSocket documentation: https://www.haproxy.com/blog/websockets-load-balancing-with-haproxy

Start by tracing the WebSocket tunnel through Nextcloud's proxy.php to the built-in CODE server on port 9983, and review the RFC 8441 requirements for the HTTP/2 proxy chain. Compare behavior with HAProxy's HTTP/1.1 workaround. Done means HTTP/2 WebSocket connections work without that downgrade and the recommended HAProxy/nginx configuration is documented.