server-fixed.go

package main

import "net/http"
import "fmt"
import "log"
import "io/ioutil"
import "strconv"
import "sync"

const VISITS_COUNTER_FILE = "/tmp/visits-counter"
var mutex = sync.Mutex{}

func updateVisitsCounter () uint64 {
    mutex.Lock()
    defer mutex.Unlock()

    curCounter, err := ioutil.ReadFile(VISITS_COUNTER_FILE)

    if err != nil {
        // @todo error handling
    }

    // convert current value to uint64
    updatedCounter, err := strconv.ParseUint(string(curCounter), 10, 64)

    if err != nil {
        // @todo error handling
    }

    updatedCounter = updatedCounter + 1;

    // write updatedCounter to file
    err = ioutil.WriteFile(VISITS_COUNTER_FILE, []byte(strconv.FormatUint(updatedCounter, 10)), 0640)

    if err != nil {
        // @todo error handling
    }

    return updatedCounter
}

func main () {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        var counter uint64 = updateVisitsCounter()

        fmt.Fprintf(w, "Hello, you're visitor #%d", counter)
    })

    log.Fatal(http.ListenAndServe(":8080", nil))
}