Chapter 16: Signaling Path — TCP/TLS Corking for HTTP/2

The Problem

With TCP_NODELAY, each SSL_write produces a separate TLS record → separate TCP segment. nghttp2 sends HTTP/2 frames one at a time. A single HTTP/2 response produces 3-5 frames → 3-5 TCP segments.

The Cork Solution

Without cork: nghttp2 frame 1 → SSL_write → TLS record 1 → write() → TCP segment 1 nghttp2 frame 2 → SSL_write → TLS record 2 → write() → TCP segment 2 nghttp2 frame 3 → SSL_write → TLS record 3 → write() → TCP segment 3 = 3 syscalls, 3 TLS records (87 bytes overhead), 3 TCP segments With TLS cork: nghttp2 frame 1 → tls_write → buffered nghttp2 frame 2 → tls_write → buffered nghttp2 frame 3 → tls_write → buffered uncork → SSL_write(all) → 1 TLS record → write() → 1 TCP segment = 1 syscall, 1 TLS record (29 bytes overhead), 1 TCP segment

Implementation Layers

// The cork wraps the write callback at two levels:
tcp_on_write:
  cork_tcp();           // hold kernel writes
  tls_on_write:
    cork_tls();         // buffer plaintext
    http_session_on_write:
      nghttp2_session_send:
        on_send(frame1) → tls_write → buffered
        on_send(frame2) → tls_write → buffered
        on_send(frameN) → tls_write → buffered
    uncork_tls();        // one SSL_write → one TLS record
  uncork_tcp();          // one write() → one TCP segment

Prototype Gerrit Changes

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