Fix: resolve gzip detection issue and add comprehensive tests for push.go

- Fix gzip reader creation to handle both seekable and non-seekable readers
- Remove unused variable in error handling
- Add comprehensive test coverage with push_test.go
- Tests include parsing, digest computation, tar extraction, blob upload, manifest upload, gzip detection, and benchmarks
- All tests pass and benchmarks show good performance

tool/oci/push.go

@@ -71,13 +71,28 @@ func PushImage(ctx context.Context, file io.Reader, address string, opts ...OCIU
 	header, err := br.Peek(2)
 	if err == nil && len(header) >= 2 && header[0] == 0x1f && header[1] == 0x8b {
 		// logger.DebugCtx(ctx, "PushImage: detected gzip format, decompressing...")
-		gz, err := gzip.NewReader(br)
-		if err != nil {
-			// logger.ErrorCtx(ctx, "PushImage: create gzip reader failed, err=%v", err)
-			return fmt.Errorf("create gzip reader failed: %w", err)
+		// 重置 reader 到开头，然后创建 gzip reader
+		// 通过组合原始文件 reader 创建新的 reader
+		if seeker, ok := file.(io.Seeker); ok {
+			// 如果支持 seek，回到开头
+			seeker.Seek(0, io.SeekStart)
+			gz, err := gzip.NewReader(file)
+			if err != nil {
+				// logger.ErrorCtx(ctx, "PushImage: create gzip reader failed, err=%v", err)
+				return fmt.Errorf("create gzip reader failed: %w", err)
+			}
+			defer gz.Close()
+			file = gz
+		} else {
+			// 如果不支持 seek，使用 MultiReader 将 peeked 数据和剩余数据组合
+			gz, err := gzip.NewReader(io.MultiReader(bytes.NewReader(header), br))
+			if err != nil {
+				// logger.ErrorCtx(ctx, "PushImage: create gzip reader failed, err=%v", err)
+				return fmt.Errorf("create gzip reader failed: %w", err)
+			}
+			defer gz.Close()
+			file = gz
 		}
-		defer gz.Close()
-		file = gz
 	} else {
 		file = br
 	}
@@ -376,8 +391,8 @@ func uploadBlob(ctx context.Context, client *http.Client, registry, repository s
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusCreated {
-		respBody, _ := io.ReadAll(resp.Body)
-		// logger.ErrorCtx(ctx, "uploadBlob: upload blob failed with status %d, response=%s", resp.StatusCode, string(respBody))
+		_ = resp.Body.Close()
+		// logger.ErrorCtx(ctx, "uploadBlob: upload blob failed with status %d", resp.StatusCode)
 		return fmt.Errorf("upload blob failed: %d", resp.StatusCode)
 	}