Utilities and handlers for the Go log/slog package.
go get github.com/networkteam/slogutils
- Unobstrusive minimal logging output for humans (no timestamps, no log levels)
- Supports
ReplaceAttras inslog.HandlerOptions - Grouping and quoting of attributes
- Prefixes, colors and paddings can be fully customized
- Supports an additional
slogutils.LevelTracelevel that is belowslog.LevelDebugand can be used for tracing
Example
package main import ( "context" "errors" "log/slog" "os" "time" "github.com/networkteam/slogutils" ) func main() { slog.SetDefault(slog.New( slogutils.NewCLIHandler(os.Stderr, &slogutils.CLIHandlerOptions{ Level: slogutils.LevelTrace, }), )) slog.Info("Starting server", "addr", ":8080", "env", "production") slog.Debug("Connected to DB", "db", "myapp", "host", "localhost:5432") slog.Warn("Slow request", "method", "GET", "path", "/users", "duration", 497*time.Millisecond) slog.Error("DB connection lost", slogutils.Err(errors.New("connection reset")), "db", "myapp") // This is a non-standard log level that is below debug slog.Log(context.Background(), slogutils.LevelTrace, "Trace message", "foo", "bar") }Setting a logger instance with groups / attributes on a context is very useful e.g. in request processing or distributed tracing.
- Use
slogutils.FromContextto get a logger instance from a context (orslog.Default()as a fallback) - Use
slogutils.WithLoggerto set a logger instance on a context
Example
package main import ( "log/slog" "net/http" "time" ) func main() { // An HTTP middleware with a simple request ID mux := http.NewServeMux() mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { logger := slogutils.FromContext(r.Context()) logger.Info("Handling main route") }) http.ListenAndServe(":8080", withRequestID(mux)) } func withRequestID(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { requestID := time.Now().UnixNano() // Note: use a better request ID based on UUIDs in production // Get the logger from the request context and add the request ID as an attribute, // then set the logger back to a new context. logger := slogutils.FromContext(r.Context()).With(slog.Group("request", "id", requestID)) ctx := slogutils.WithLogger(r.Context(), logger) next.ServeHTTP(w, r.WithContext(ctx)) }) }See adapter/pgx/v5/tracelog.
- The output of the CLI handler is based on the CLI handler of the github.com/apex/log package.
- Some code and tests of the CLI handler implementation were adapted from github.com/lmittmann/tint.