Print to Log using Go Language Simple HTTP Server - go

Question

I am trying to log the IP address of the requestor, what METHOD they are using and what file they are requesting. But for some reason it only outputs on the terminal and doesn't save it to logfile.txt...
package main
import (
"fmt"
"net/http"
"log"
"encoding/json"
"io/ioutil"
)
type Options struct {
Path string
Port string
}
func Log(handler http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Printf("%s %s %s\n", r.RemoteAddr, r.Method, r.URL)
handler.ServeHTTP(w, r)
})
}
func main() {
op := &Options{Path: "./", Port: "8001"}
data, _ := ioutil.ReadFile("./config.json")
json.Unmarshal(data, op)
http.Handle("/", http.FileServer(http.Dir(op.Path)))
err := http.ListenAndServe(":" + op.Port, Log(http.DefaultServeMux))
if err != nil {
log.Fatal("ListenAndServe: ", err)
}
}

Answer 1

In your Log function, you are using fmt.Printf not fmt.Fprintf.
For example,
package main
import (
"fmt"
"log"
"net/http"
"os"
)
var logFile *os.File
func Log(handler http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(logFile, "%s %s %s\n", r.RemoteAddr, r.Method, r.URL)
handler.ServeHTTP(w, r)
})
}
func main() {
var err error
logFile, err = os.Create("logfile.txt")
if err != nil {
log.Fatal("Log file create:", err)
return
}
defer logFile.Close()
}