Phase 4: Persistent Connections (Keep-Alive)

[mgrossmann]

Implement HTTP/1.1 persistent connections. Biggest performance win — reduces TCP handshakes for multi-resource page loads by 80%+.

Description

REQUEST_VERSION evaluation, idle timeout, request counter, worker pool exhaustion mitigation.

Files to edit

• src/httprese.c — Evaluate REQUEST_VERSION: HTTP/1.1 + no Connection: close → keepalive=1; HTTP/1.0 + Connection: keep-alive → keepalive=1; else → keepalive=0. If keepalive: transition to CSTATE_IN instead of CSTATE_CLOSE. Increment request_count, close if >= keepalive_max. Reset per-request state but keep socket open.
• src/httpin.c — Add idle timeout between requests using selectex() with configurable timeout. No data within keepalive_timeout → CSTATE_CLOSE.
• src/httpresp.c — Send Connection: keep-alive or Connection: close header based on keepalive state.
• include/httpd.h — Add keepalive (UCHAR), request_count (USHRT) to HTTPC (existing unused bytes). Add cfg_keepalive_timeout, cfg_keepalive_max to HTTPD.

Worker pool exhaustion mitigation

• Short idle timeout (5s default)
• keepalive_max limit (100 requests)
• Worker pool auto-scales (mintask → maxtask)

Acceptance criteria

• Browser DevTools show connection reuse (single TCP for HTML+CSS+JS+images)
• Connection closes after keepalive_timeout idle
• Connection closes after keepalive_max requests
• HTTP/1.0 clients get Connection: close
• Worker pool does not deadlock under 9+ concurrent connections
• mvsMF works identically (no changes needed)

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Notion task: TSK-8