log

A super-lightweight wrapper around apex/log to make it context aware. Inspired by juju/zaputil/zapctx.

Usage

All the methods in log.Interface are defined, with a context.Context as the first parameter.

WithFields(ctx context.Context, fields log.Fielder) context.Context
WithField(ctx context.Context, key string, value interface{}) context.Context
WithError(ctx context.Context, err error) context.Context
Entry(ctx context.Context) log.Interface
Debug(ctx context.Context, msg string)
Info(ctx context.Context, msg string)
Warn(ctx context.Context, msg string)
Error(ctx context.Context, msg string)
Fatal(ctx context.Context, msg string)
Debugf(ctx context.Context, msg string, v ...interface{})
Infof(ctx context.Context, msg string, v ...interface{})
Warnf(ctx context.Context, msg string, v ...interface{})
Errorf(ctx context.Context, msg string, v ...interface{})
Fatalf(ctx context.Context, msg string, v ...interface{})
Trace(ctx context.Context, msg string) *log.Entry

A common usecase is adding default fields to HTTP logs:

package main

import (
  "net/http"

  apex "github.com/apex/log"
  "github.com/mhemmings/log"
)

func middleware(next http.HandlerFunc) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    f := apex.Fields{
      "method": r.Method,
      "url":    r.URL.Path,
    }
    ctx := log.WithFields(r.Context(), f)
    next.ServeHTTP(w, r.WithContext(ctx))
  })
}

func handler(w http.ResponseWriter, r *http.Request) {
  log.Info(r.Context(), "handling request") // logs message with fields "method" and "url"
  w.Write([]byte("Hello world"))
}

func main() {
  http.Handle("/", middleware(handler))
  http.ListenAndServe(":8080", nil)
}