Monitor web page changes with Go

main.go

package main

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

const LOOP_EVERY_SECONDS = 5

var client = &http.Client{}

var url string
var cookies string
var lastData string

func checkChanges(newData string) {
    if newData == lastData {
        log.Println("No changes.")
        return
    }

    log.Println("Changes noticed!")
    os.Exit(0)
}

func makeRequest() {
    req, err := http.NewRequest("GET", url, nil)
    if err != nil {
        log.Println(err)
        return
    }

    // Set cookies if they were passed as argument
    if cookies != "" {
        req.Header.Set("Cookie", cookies)
    }

    // Send request
    resp, err := client.Do(req)
    if err != nil {
        log.Println(err)
        return
    }

    // Save response body into data variable
    data, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Println(err)
        return
    }

    // If lastData is equal to "", it means that it is
    // the first request and we set lastData to current
    // response body
    // Otherwise, we compare previous and current HTML
    if lastData == "" {
        lastData = string(data)
    } else {
        checkChanges(string(data))
    }
}

func scheduleRequests() {
    // Infinite loop to run every LOOP_EVERY_SECONDS seconds
    for range time.Tick(time.Second * LOOP_EVERY_SECONDS) {
        makeRequest()
    }
}

func main() {
    // Exit program if URL is missing
    if len(os.Args) < 2 {
        log.Println("Missing URL.")
        os.Exit(0)
    }

    // Set url variable
    url = os.Args[1]

    // Set cookie variable if passed as argument
    if len(os.Args) == 3 {
        cookies = os.Args[2]
    }

    // Make initial request to set first lastData
    makeRequest()

    // Continue with requests, loop every LOOP_EVERY_SECONDS seconds
    scheduleRequests()
}