error handling inside goroutines

pkg/ecload/ecload.go

@@ -41,6 +41,10 @@ func DownloadBook(outDir string, size string, id string, logger Logger) error {
 	semaphore := make(chan struct{}, MAX_DOWNLOADS)
 
 	logger.Info.Println("downloading pages...")
+
+	ec := make(chan error)
+	finished := make(chan bool, 1)
+
 	for index, pageUrl := range pageUrls {
 		wg.Add(1)
 
@@ -52,18 +56,31 @@ func DownloadBook(outDir string, size string, id string, logger Logger) error {
 				<-semaphore
 			}()
 
-			downloadUrl, err:= getSizeLink(pageUrl, size)
+			downloadUrl, err := getSizeLink(pageUrl, size)
 			if err != nil {
-				//return err
+				ec <- err
 			}
 
 			filename := fmt.Sprintf("%06d.jpg", index)
-			downloadToFile(filename, dir, downloadUrl)
+			err = downloadToFile(filename, dir, downloadUrl)
-
+			if err != nil {
+				ec <- err
+			}
 		}(index, pageUrl)
 	}
 
-	wg.Wait()
+	go func() {
+		wg.Wait()
+		close(finished)
+	}()
+
+	select {
+	case <-finished:
+	case err := <-ec:
+		if err != nil {
+			return err
+		}
+	}
 
 	err = os.MkdirAll(outDir, os.ModePerm)
 	if err != nil {
@@ -77,7 +94,7 @@ func DownloadBook(outDir string, size string, id string, logger Logger) error {
 }
 
 // Find the download link for a page of a specific size.
-func getSizeLink(pageUrl string , size string) (string, error) {
+func getSizeLink(pageUrl string, size string) (string, error) {
 	doc, err := fetchDocument(pageUrl)
 	if err != nil {
 		return "", err