Extract content type detection to its own method.

Signed-off-by: David Calavera <david.calavera@gmail.com>

tq/basic_upload.go

@@ -72,23 +72,8 @@ func (a *basicUploadAdapter) DoTransfer(ctx interface{}, t *Transfer, cb Progres
 	}
 	defer f.Close()
 
-	if len(req.Header.Get("Content-Type")) == 0 {
-		buffer := make([]byte, 512)
-		n, err := f.Read(buffer)
-		if err != nil && err != io.EOF {
-			return errors.Wrap(err, "basic upload")
-		}
-
-		contentType := http.DetectContentType(buffer[:n])
-		if _, err := f.Seek(0, 0); err != nil {
-			return errors.Wrap(err, "basic upload")
-		}
-
-		if contentType == "" {
-			contentType = defaultContentType
-		}
-
-		req.Header.Set("Content-Type", contentType)
+	if err := setContentTypeFor(req, f); err != nil {
+		return err
 	}
 
 	// Ensure progress callbacks made while uploading
@@ -188,3 +173,27 @@ func configureBasicUploadAdapter(m *Manifest) {
 		return nil
 	})
 }
+
+func setContentTypeFor(req *http.Request, r io.ReadSeeker) error {
+	if len(req.Header.Get("Content-Type")) != 0 {
+		return nil
+	}
+
+	buffer := make([]byte, 512)
+	n, err := r.Read(buffer)
+	if err != nil && err != io.EOF {
+		return errors.Wrap(err, "content type detect")
+	}
+
+	contentType := http.DetectContentType(buffer[:n])
+	if _, err := r.Seek(0, 0); err != nil {
+		return errors.Wrap(err, "content type rewind")
+	}
+
+	if contentType == "" {
+		contentType = defaultContentType
+	}
+
+	req.Header.Set("Content-Type", contentType)
+	return nil
+}