Golang download multiple files in parallel using goroutines
concurrency, go
Solution
That's because your main goroutine is exiting. You need to add a WaitGroup to wait until all the goroutines exit. For example,
var wg sync.WaitGroup
for i, file := range flr.FileList {
wg.Add(1)
go download_file(file, tr, wg)
if i >= 2 {
break
}
}
wg.Wait()
...
func download_file(file File, token TokenResponse, wg sync.WaitGroup) {
...
wg.Done()
}
Problem
Is it possible to download and save files in parallel using goroutines? Below is my code which downloads files from my dropbox: ``` package main import ( "encoding/json" "fmt" "io" "io/ioutil" "net/http" "net/url" "os" "path/filepath" ) const app_key string = "<app_key>" const app_secret string = "<app_secret>" var code string type TokenResponse struct { AccessToken string `json:"access_token"` } type File struct { Path string } type FileListResponse struct { FileList []File `json:"contents"` } func download_file(file File, token TokenResponse) { download_file := fmt.Sprintf("https://api-content.dropbox.com/1/files/dropbox/%s?access_token=%s", file.Path, token.AccessToken) resp, _ := http.Get(download_file) defer resp.Body.Close() filename := filepath.Base(file.Path) out, err := os.Create(filename) if err != nil { panic(err) } defer out.Close() io.Copy(out, resp.Body) } func main() { authorize_url := fmt.Sprintf("https://www.dropbox.com/1/oauth2/authorize?response_type=code&client_id=%s", app_key) // Get code fmt.Printf("1. Go to: %s\n", authorize_url) fmt.Println("2. Click 'Allow' (you might have to log in first)") fmt.Println("3. Copy the authorization code.") fmt.Printf("Enter the authorization code here: ") fmt.Scanf("%s", &code) // End get code // Get access token data := url.Values{} data.Add("code", code) data.Add("grant_type", "authorization_code") data.Add("client_id", app_key) data.Add("client_secret", app_secret) resp, _ := http.PostForm("https://api.dropbox.com/1/oauth2/token", data) defer resp.Body.Close() contents, _ := ioutil.ReadAll(resp.Body) var tr TokenResponse json.Unmarshal(contents, &tr) // End get access token // Get file list file_list_url := fmt.Sprintf("https://api.dropbox.com/1/metadata/dropbox/Camera Uploads?access_token=%s", tr.AccessToken) resp2, _ := http.Get(file_list_url) defer resp2.Body.Close() contents2, _ := ioutil.ReadAll(resp2.Body) var flr FileListResponse json.Unmarshal(contents2, &flr) // End get file list for i, file := range flr.FileList { download_file(file, tr) if i >= 2 { break } } } ``` It doesn't work when I prefix the download_file function with the `go` command. ``` go download_file(file, tr) ```