WebSocket server + HTTP upgrade handoff

[resetius]

WebSocket server + HTTP upgrade handoff (lib split, no std::function)

Goal

Add server-side WebSocket support and integrate it with THttpServer via a clean connection takeover mechanism, while keeping ws optional and avoiding std::function (single virtual dispatch only).

High-level design

• Keep ws as a standalone library (users of core/http must not link it).
• http must be able to hand off an upgraded TCP connection (socket + prefetched bytes) to an external handler without knowing anything about WebSocket.
• HTTP → WS integration is done via a small bridge library.
• Use virtual interfaces (one dispatch point), no type-erasure callbacks.

Library split

• coroio_core
• coroio_http (generic upgrade/takeover hook, no WS dependency)
• coroio_ws (WebSocket protocol + server session)
• coroio_http_ws (HTTP<->WS bridge)

Checklist

WebSocket server (ws)

• Add server-side WebSocket session support
• Support accepting an already-upgraded connection (socket + prefetch)
• Provide minimal public API for running a WS session loop

HTTP upgrade / takeover (http)

• Introduce a generic connection takeover mechanism
• Allow router to stop HTTP processing and transfer socket ownership
• Do not introduce std::function in hot paths

HTTP<->WS bridge (http_ws)

• Implement WebSocket upgrade handler using virtual interface
• Perform handshake and start WS session
• Allow routing upgrade requests by path

Testing / validation

• Standalone WebSocket server example (no HTTP)
• Integration test: HTTP upgrade → WebSocket session

Non-goals

• Forcing ws dependency on core/http users
• Adding multiple layers of dynamic dispatch