UPDATE: Add ldiff

pkg/firefly/ldiff.go

@@ -0,0 +1,94 @@
+package firefly
+
+import (
+	"firefly-launcher/pkg/firefly/pb"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/exp/mmap"
+)
+
+
+func LDiffFile(data *pb.AssetManifest, assetName string, assetSize int64, ldiffsDir, outputDir string) error {
+	path := filepath.Join(ldiffsDir, data.ChunkFileName)
+
+	info, err := os.Stat(path)
+	if err != nil {
+		return fmt.Errorf("%s does not exist: %w", path, err)
+	}
+
+	fileSize := info.Size()
+	var buffer []byte
+
+	if fileSize > 10*1024*1024 && data.HdiffFileSize > 1*1024*1024 {
+		// mmap for large files using x/exp/mmap
+		reader, err := mmap.Open(path)
+		if err != nil {
+			// fallback to buffered read
+			file, err := os.Open(path)
+			if err != nil {
+				return fmt.Errorf("error opening file %s: %w", path, err)
+			}
+			defer file.Close()
+			buffer, err = ReadBuffer(file, data.HdiffFileInChunkOffset, data.HdiffFileSize)
+			if err != nil {
+				return err
+			}
+		} else {
+			defer reader.Close()
+			buffer = make([]byte, data.HdiffFileSize)
+			_, err := reader.ReadAt(buffer, data.HdiffFileInChunkOffset)
+			if err != nil {
+				return fmt.Errorf("error reading mmap data: %w", err)
+			}
+		}
+	} else {
+		// small files, buffered read
+		file, err := os.Open(path)
+		if err != nil {
+			return fmt.Errorf("error opening file %s: %w", path, err)
+		}
+		defer file.Close()
+
+		buffer, err = ReadBuffer(file, data.HdiffFileInChunkOffset, data.HdiffFileSize)
+		if err != nil {
+			return err
+		}
+	}
+
+	extension := ""
+	if data.OriginalFileSize != 0 || assetSize != data.HdiffFileSize {
+		extension = ".hdiff"
+	}
+	assetPath := filepath.Join(outputDir, assetName+extension)
+	parentDir := filepath.Dir(assetPath)
+	if _, err := os.Stat(parentDir); os.IsNotExist(err) {
+		if err := os.MkdirAll(parentDir, 0o755); err != nil {
+			return fmt.Errorf("error creating directory %s: %w", parentDir, err)
+		}
+	}
+
+	if err := os.WriteFile(assetPath, buffer, 0o644); err != nil {
+		return fmt.Errorf("error writing file %s: %w", assetPath, err)
+	}
+
+	return nil
+}
+
+
+
+func ReadBuffer(file *os.File, offset int64, size int64) ([]byte, error) {
+	buffer := make([]byte, size)
+
+	n, err := file.ReadAt(buffer, offset)
+	if err != nil {
+		return nil, fmt.Errorf("error reading data: %w", err)
+	}
+	if int64(n) != size {
+		return nil, fmt.Errorf("expected %d bytes, but read %d bytes", size, n)
+	}
+
+	return buffer, nil
+}
+