Structured logging in Go

log/slog writes key-value pairs, at a level, in text or JSON.

func logging() string {
    var out strings.Builder
    logger := slog.New(slog.NewJSONHandler(&out, &slog.HandlerOptions{
        Level: slog.LevelInfo,
    }))

    logger.Info("loaded content", "steps", 1015, "langs", 10)
    logger.Debug("not shown at info level")

    request := logger.With("request_id", "abc123")
    request.Warn("slow response", slog.Duration("took", 250*time.Millisecond))

    return fmt.Sprintf("%d log lines",
        len(strings.Split(strings.TrimSpace(out.String()), "\n")))
}

How it works

1. Attributes are pairs after the message.
2. With returns a logger that carries fields for you.
3. A JSON handler is what a log pipeline wants.

Keywords and builtins used here

• func
• len
• return
• string
• var

The run, in numbers

Lines

15

Characters to type

460

Tokens

116

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 66 seconds.

Type this snippet

Step 2 of 2 in Programs & logging, step 15 of 26 in Standard library & project layout.

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