Merge pull request #5632 from VladRassokhin/do-not-donwload-twice

Do not re-download iso multiple times from different urls

common/step_download.go

@@ -61,10 +61,12 @@ func (s *StepDownload) Run(state multistep.StateBag) multistep.StepAction {
 
 	ui.Say(fmt.Sprintf("Downloading or copying %s", s.Description))
 
-	var finalPath string
+	// First try to use any already downloaded file
-	for _, url := range s.Url {
+	// If it fails, proceed to regualar download logic
-		ui.Message(fmt.Sprintf("Downloading or copying: %s", url))
 
+	var downloadConfigs = make([]*DownloadConfig, len(s.Url))
+	var finalPath string
+	for i, url := range s.Url {
 		targetPath := s.TargetPath
 		if targetPath == "" {
 			// Determine a cache key. This is normally just the URL but
@@ -90,6 +92,20 @@ func (s *StepDownload) Run(state multistep.StateBag) multistep.StepAction {
 			Checksum:   checksum,
 			UserAgent:  "Packer",
 		}
+		downloadConfigs[i] = config
+
+		if match, _ := NewDownloadClient(config).VerifyChecksum(config.TargetPath); match {
+			ui.Message(fmt.Sprintf("Found already downloaded, initial checksum matched, no download needed: %s", url))
+			finalPath = config.TargetPath
+			break
+		}
+	}
+
+	if finalPath == "" {
+		for i, url := range s.Url {
+			ui.Message(fmt.Sprintf("Downloading or copying: %s", url))
+
+			config := downloadConfigs[i]
 
 			path, err, retry := s.download(config, state)
 			if err != nil {
@@ -105,6 +121,7 @@ func (s *StepDownload) Run(state multistep.StateBag) multistep.StepAction {
 				break
 			}
 		}
+	}
 
 	if finalPath == "" {
 		err := fmt.Errorf("%s download failed.", s.Description)