Uses GET to get download file size

(instead of HEAD, since servers might not respond to HEAD)

downloader.go

@@ -167,7 +167,7 @@ func (d *Downloader) getDownloadSize(ctx context.Context, u string) (int64, erro
 	defer close(ch)
 	err := retry.Do(
 		func() error {
-			req, err := http.NewRequestWithContext(ctx, http.MethodHead, u, nil)
+			req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
 			if err != nil {
 				return fmt.Errorf("creating the request for %s: %w", u, err)
 			}

downloader_test.go

@@ -27,9 +27,10 @@ func TestDownload_Error(t *testing.T) {
 		{"timeout", func(w http.ResponseWriter) { time.Sleep(10 * timeout) }},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
+			var firstReq int32
 			s := httptest.NewServer(http.HandlerFunc(
 				func(w http.ResponseWriter, r *http.Request) {
-					if r.Method == http.MethodHead {
+					if atomic.CompareAndSwapInt32(&firstReq, 0, 1) {
 						w.Header().Add("Content-Length", "2")
 						return
 					}
@@ -62,9 +63,10 @@ func TestDownload_Error(t *testing.T) {
 }
 
 func TestDownload_OkWithDefaultDownloader(t *testing.T) {
+	var firstReq int32
 	s := httptest.NewServer(http.HandlerFunc(
 		func(w http.ResponseWriter, r *http.Request) {
-			if r.Method == http.MethodHead {
+			if atomic.CompareAndSwapInt32(&firstReq, 0, 1) {
 				w.Header().Add("Content-Length", "2")
 				return
 			}
@@ -271,9 +273,10 @@ func TestDownload_ReportPreviouslyDownloadedBytes(t *testing.T) {
 func TestDownloadWithContext_ErrorUserTimeout(t *testing.T) {
 	userTimeout := 250 * time.Millisecond // please note that the user timeout is less than the timeout per chunk.
 	timeout := 10 * userTimeout
+	var firstReq int32
 	s := httptest.NewServer(http.HandlerFunc(
 		func(w http.ResponseWriter, r *http.Request) {
-			if r.Method == http.MethodHead {
+			if atomic.CompareAndSwapInt32(&firstReq, 0, 1) {
 				w.Header().Add("Content-Length", "2")
 				return
 			}