Golang : How to log each HTTP request to your web server?

Problem:

You want to log each HTTP request made to your web server complete with duration (start time - end time), requester IP address, URI accessed and you also want to save the log messages into a file for viewing later.

How to do that?

NOTE: Saving HTTP requests log to file can be useful for troubleshooting purpose or assist in identifying attackers on your server. However, do take note that the log's file size will grow and needs to be rolled-over from time to time to keep the filesize from taking up all the disk space.

Solution:

Create a request logger function and wrap it on the HTTP request multiplexer.

Here you go!

 package main

 import (
 "log"
 "net/http"
 "os"
 "time"
 )

 func RequestLogger(targetMux http.Handler) http.Handler {
 return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 start := time.Now()

 targetMux.ServeHTTP(w, r)

 // log request by who(IP address)
 requesterIP := r.RemoteAddr

 log.Printf(
 "%s\t\t%s\t\t%s\t\t%v",
 r.Method,
 r.RequestURI,
 requesterIP,
 time.Since(start),
 )
 })
 }

 func SayGoodByeWorld(w http.ResponseWriter, r *http.Request) {
 html := "Good Bye World"
 w.Write([]byte(html))
 }

 func SayHelloWorld(w http.ResponseWriter, r *http.Request) {
 html := "Hello World"
 w.Write([]byte(html))
 }

 func main() {
 fileName := "webrequests.log"

 // https://www.socketloop.com/tutorials/golang-how-to-save-log-messages-to-file
 logFile, err := os.OpenFile(fileName, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)

 if err != nil {
 panic(err)
 }

 defer logFile.Close()

 // direct all log messages to webrequests.log
 log.SetOutput(logFile)

 mux := http.NewServeMux()
 mux.HandleFunc("/", SayHelloWorld)
 mux.HandleFunc("/bye", SayGoodByeWorld)

 http.ListenAndServe(":8080", RequestLogger(mux))
 }