Logging

Weaver provides structured logging through the Go standard library log/slog, with rotating log files via lumberjack.

Using Logs in Components

Every component embedding weaver.Implements[T] can obtain a logger via Logger(ctx):

func (a *app) DoSomething(ctx context.Context) {
    logger := a.Logger(ctx)

    logger.Info("Processing request", "requestID", "12345")
    logger.Warn("Resource running low", "resource", "memory", "available", "10%")
    logger.Error("Operation failed", "error", errors.New("connection timeout"))
}

Automatic Trace Correlation

Logger(ctx) inspects the OpenTelemetry span in the context:

• When the context carries a valid TraceID, logs automatically include a trace_id field
• When the context carries a valid SpanID, logs automatically include a span_id field

Every business log line can thus be tied to its distributed trace. See OpenTelemetry Integration.

Log Configuration

weaver:
  logger:
    level: info       # level: debug, info, warn, error
    type: json        # format: json or text (console)
    addsource: true   # include source code location
    file:
      filename: "./logs/app.log"  # log file path
      maxsize: 100               # max size of a single file (MB)
      maxage: 7                  # days to retain old logs
      maxbackups: 10             # number of old files to keep
      compress: true             # gzip rotated files
      localtime: true            # use local time

Options Reference

Option	Default	Description
level	info	Log level; invalid values fall back to info
type	console	Output format: json / text / console
addsource	false	Attach source location to log entries
file.filename	empty	When empty, logs go to stdout only
file.maxsize	100	Max size of a single file (MB) before rotation
file.maxage	7	Days to retain rotated files
file.maxbackups	3	Number of rotated files to keep
file.compress	true	Gzip-compress rotated files
file.localtime	true	Use local time for timestamps

Logs are written to stdout and the configured file simultaneously (MultiWriter).