Event Logging using qlog

quic-go logs HTTP/3 events defined in draft-ietf-quic-qlog-h3-events, providing detailed insights into HTTP/3 frame processing and datagram handling. This complements the QUIC-layer events to give a complete picture of HTTP/3 connections.

Enabling qlog for HTTP/3

HTTP/3 qlogging is enabled by setting the Tracer callback on the quic.Config, just like for QUIC connections. However, to log HTTP/3 events in addition to QUIC events, the tracer needs to support the HTTP/3 event schema.

The http3/qlog package provides DefaultConnectionTracer, which automatically includes both QUIC and HTTP/3 event schemas:

import (
	"github.com/quic-go/quic-go"
	h3qlog "github.com/quic-go/quic-go/http3/qlog"
)

quic.Config{
  Tracer: h3qlog.DefaultConnectionTracer,
}

This tracer writes qlog files to a directory specified by the QLOGDIR environment variable, if set. Each connection will produce a separate qlog file containing both QUIC and HTTP/3 events.

As described in the qlog documentation, applications can implement the quic.Config.Tracer callback to add custom logic to the qlog tracing.

Redacting Field Values

By default, qlog logs HTTP/3 HEADERS frames, including all header and trailer field values. Applications can redact sensitive values by wrapping a connection tracer with h3qlog.RedactHeaders:

tracer := h3qlog.RedactHeaders(
  h3qlog.DefaultConnectionTracer,
  func(name, value string) string {
    switch name {
    case "Authorization", "Cookie", "Set-Cookie":
      return "***"
    default:
      return value
    }
  },
)

The callback receives canonical field names (e.g. Authorization) for sent and received header and trailer fields. Pseudo-header fields are excluded.