[SOLVED] Write a minimal thread pool using go routines and channels

main.go

package main

import (
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"sync"
	"time"
)

const (
	workers = 3
	jobs = 5
)

func main() {
	jsonPath := os.Args[1]

	ext := filepath.Ext(jsonPath)
	if ext != ".json" {
		log.Fatalf("file '%s' is not a json file", jsonPath)
	}

	if _, err := os.Stat("./data"); os.IsNotExist(err) {
		if err := os.Mkdir("./data", 0755); err != nil {
			log.Fatalf("something went wrong: %s", err.Error())
		}
	}

	jsonFile, err := os.Open(jsonPath)
	if err != nil {
		log.Fatalf("can't open '%s'", jsonPath)
	}

	defer jsonFile.Close()

	b, err := ioutil.ReadAll(jsonFile)
	if err != nil {
		log.Fatalf("can't open '%s'", jsonPath)
	}

	var urls []string

	if err := json.Unmarshal(b, &urls); err != nil {
		log.Fatalf("can't unmarshal '%s'", jsonPath)
	}

	httpClient := &http.Client{Timeout: 30 * time.Second}

	jobsChan := make(chan string, jobs)

	var wg sync.WaitGroup

	for w := 1; w <= workers; w++ {
		go worker(w, &wg, httpClient, jobsChan)
	}

	for _, url := range urls {
		jobsChan <- url

		wg.Add(1)
	}

	wg.Wait()
}

func worker(workerID int, wg *sync.WaitGroup, httpClient *http.Client, jobs <-chan string) {
	for job := range jobs {
		log.Printf("#%d - Downloading %s", workerID, job)

		downloadImage(job, httpClient)

		wg.Done()

		log.Printf("#%d - Completed %s", workerID, job)
	}
}

func downloadImage(url string, httpClient *http.Client) {
	resp, err := httpClient.Get(url)
	if err != nil {
		log.Fatal(err)
	}

	defer resp.Body.Close()

	imagePath := fmt.Sprintf("./data/%s", filepath.Base(url))

	f, err := os.Create(imagePath)
	if err != nil {
		log.Fatal(err)
	}

	defer f.Close()

	if _, err := io.Copy(f, resp.Body); err != nil {
		log.Fatal(err)
	}
}