Go is a beautiful language

gistfile1.txt

λ go run cmd/releaser/main.go
API: 2019/08/22 16:27:51 Starting API server on 0.0.0.0:8080
Metrics: 2019/08/22 16:27:51 Starting metrics server on 0.0.0.0:8090
2019/08/22 17:27:53 'GET /' 404 from localhost:8080, User-Agent: curl/7.54.0
2019/08/22 17:27:53 'GET /' 404 from localhost:8080, User-Agent: curl/7.54.0

middleware.go

package api

import (
	"net/http"
)

// loggedResponseWriter is a wrapper around
// http.ResponseWriter that adds some useful logging metrics,
// namely capturing the final status code of the request.
// It itself implements http.ResponseWriter so it can be passed
// straight into, e.g. ServeHTTP() methods.
type loggedResponseWriter struct {
	w          http.ResponseWriter
	statusCode int
}

func (lw *loggedResponseWriter) Header() http.Header {
	return lw.w.Header()
}

func (lw *loggedResponseWriter) Write(body []byte) (int, error) {
	return lw.w.Write(body)
}

func (lw *loggedResponseWriter) WriteHeader(statusCode int) {
	lw.w.WriteHeader(statusCode)
	lw.statusCode = statusCode
}

// LoggerMiddleware creates a wrapper function for adding a logging middleware.
func LoggerMiddleware(server *Server) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			lw := &loggedResponseWriter{w: w}
			next.ServeHTTP(lw, r)
			server.Logger.Printf(
				"'%s %s' %d from %s, User-Agent: %s",
				r.Method,
				r.RequestURI,
				lw.statusCode,
				r.Host,
				r.UserAgent(),
			)
		})
	}
}