Golang apache logging

log.go

package main

import (
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

const (
	ApacheLogFormat         = "%s - - [%s] \"%s\" %d %d %.0f\n"
	ApacheLogCombinedFormat = "%s - - [%s] \"%s\" %d %d %.0f %s \"%s\"\n"
)

type LogRecord struct {
	http.ResponseWriter

	ip                    string
	time                  time.Time
	method, uri, protocol string
	status                int
	responseBytes         int64
	elapsedTime           time.Duration
	referrer              string
	userAgent             string
}

func (r *LogRecord) Log(out io.Writer, format string) {
	timeFormatted := r.time.Format("02/Jan/2006 15:04:05")
	requestLine := fmt.Sprintf("%s %s %s", r.method, r.uri, r.protocol)

	switch format {
	case ApacheLogFormat:
		fmt.Fprintf(out, ApacheLogFormat, r.ip, timeFormatted, requestLine, r.status, r.responseBytes,
			r.elapsedTime.Seconds()*1000)
		break
	case ApacheLogCombinedFormat:
		fmt.Fprintf(out, ApacheLogCombinedFormat, r.ip, timeFormatted, requestLine, r.status, r.responseBytes,
			r.elapsedTime.Seconds()*1000, r.referrer, r.userAgent)
		break
	}
}

func (r *LogRecord) Write(p []byte) (int, error) {
	written, err := r.ResponseWriter.Write(p)
	r.responseBytes += int64(written)
	return written, err
}

func (r *LogRecord) WriteHeader(status int) {
	r.status = status
	r.ResponseWriter.WriteHeader(status)
}

type ApacheLogHandler struct {
	handler http.Handler
	out     io.Writer
}

func NewApacheLoggingHandler(handler http.Handler, out io.Writer) http.Handler {
	return &ApacheLogHandler{
		handler: handler,
		out:     out,
	}
}

func (h *ApacheLogHandler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
	clientIP := r.RemoteAddr

	// Use the real client IP address if beyond a proxy or load balancer
	if len(r.Header["X-Forwarded-For"]) > 0 {
		clientIP = r.Header.Get("X-Forwarded-For")
	}

	if colon := strings.LastIndex(clientIP, ":"); colon != -1 {
		clientIP = clientIP[:colon]
	}

	referrer := "-"
	if r.Header.Get("Referer") != "" {
		referrer = fmt.Sprintf("\"%s\"", r.Header.Get("Referer"))
	}

	record := &LogRecord{
		ResponseWriter: rw,
		ip:             clientIP,
		time:           time.Time{},
		method:         r.Method,
		uri:            r.RequestURI,
		protocol:       r.Proto,
		status:         http.StatusOK,
		elapsedTime:    time.Duration(0),
		referrer:       referrer,
		userAgent:      r.Header.Get("User-Agent"),
	}

	startTime := time.Now()
	h.handler.ServeHTTP(record, r)
	finishTime := time.Now()

	record.time = finishTime.UTC()
	record.elapsedTime = finishTime.Sub(startTime)

	record.Log(h.out, ApacheLogCombinedFormat)
}

main.go

func main() {
	mux := http.DefaultServeMux
	mux.HandleFunc("/", indexHandler)
	loggingHandler := NewApacheLoggingHandler(mux, os.Stderr)
	server := &http.Server{
		Addr:    fmt.Sprintf(":%s", 2345),
		Handler: loggingHandler,
	}
	server.ListenAndServe()
}