Error gracefully when an image is not found on pull. Addresses #50 and comments from #49

future/future.go

@@ -89,7 +89,7 @@ func Pv(src io.Reader, info io.Writer) io.Reader {
 // the body of the response. If `stderr` is not nil, a progress bar will be
 // written to it.
 func Curl(url string, stderr io.Writer) (io.Reader, error) {
-	curl := exec.Command("curl", "-#", "-L", url)
+	curl := exec.Command("curl", "-#", "-L", "--fail", url)
 	output, err := curl.StdoutPipe()
 	if err != nil {
 		return nil, err
@@ -98,5 +98,8 @@ func Curl(url string, stderr io.Writer) (io.Reader, error) {
 	if err := curl.Start(); err != nil {
 		return nil, err
 	}
+	if err := curl.Wait(); err != nil {
+		return nil, err
+	}
 	return output, nil
 }