gopacker/data/data.go

package data

import (
	"bytes"
	"compress/flate"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"io"
	"os"
)

type File struct {
	Size   int64 `json:"size"`
	ZSize  int64 `json:"zsize"`
	Offset int64 `json:"offset"`
}

func (f *File) Read(pf *os.File, b []byte) (int, error) {
	if f.ZSize > 0 {
		compressed := make([]byte, f.ZSize)
		_, err := pf.ReadAt(compressed, f.Offset)
		if err != nil {
			return 0, err
		}
		// Decompress
		reader := flate.NewReader(bytes.NewReader(compressed))
		defer reader.Close()
		n, err := reader.Read(b)
		if err != nil && err != io.EOF {
			fmt.Println("Error reading file:", err, n, compressed)
			return 0, err
		}
		return n, nil
	}

	return pf.ReadAt(b, f.Offset)
}

type FileSystem struct {
	Files map[string]File `json:"files"`
	fp    *os.File
}

func (fs *FileSystem) ToJSON() (string, error) {
	data, err := json.Marshal(fs)
	if err != nil {
		return "", fmt.Errorf("failed to marshal FileSystem to JSON: %v", err)
	}
	return string(data), nil
}

func FromJSON(jsonStr string) (*FileSystem, error) {
	var fs FileSystem
	err := json.Unmarshal([]byte(jsonStr), &fs)
	if err != nil {
		return nil, fmt.Errorf("failed to unmarshal JSON to FileSystem: %v", err)
	}
	return &fs, nil
}

func (fs *FileSystem) AddFile(name string, size int64, offset int64) {
	if fs.Files == nil {
		fs.Files = make(map[string]File)
	}
	fs.Files[name] = File{Size: size, Offset: offset}
}

func (fs *FileSystem) GetFile(name string) (File, bool) {
	file, exists := fs.Files[name]
	return file, exists
}

func (fs *FileSystem) ListFiles() []string {
	keys := make([]string, 0, len(fs.Files))
	for k := range fs.Files {
		keys = append(keys, k)
	}
	return keys
}

func (fs *FileSystem) ReadFile(name string) ([]byte, int, error) {
	err := fs.openContainerFile()
	if err != nil {
		return []byte{}, 0, fmt.Errorf("failed to open container file: %v", err)
	}
	file, exists := fs.GetFile(name)
	if !exists {
		return []byte{}, 0, fmt.Errorf("file %s not found", name)
	}

	b := make([]byte, file.Size)
	len, err := file.Read(fs.fp, b)
	return b, len, err
}
func (fs *FileSystem) openContainerFile() error {
	if fs.fp != nil {
		return nil
	}
	exePath, err := os.Executable()
	if err != nil {
		return fmt.Errorf("failed to get executable path: %v", err)
	}
	fp, err := os.Open(exePath)
	if err != nil {
		return fmt.Errorf("failed to open executable file: %v", err)
	}
	fs.fp = fp
	return nil
}
func (fs *FileSystem) Close() error {
	if fs.fp != nil {
		err := fs.fp.Close()
		fs.fp = nil
		return err
	}
	return nil
}

func GetFileSystem() (*FileSystem, error) {
	exePath, err := os.Executable()
	if err != nil {
		return nil, fmt.Errorf("failed to get executable path: %v", err)
	}
	fp, err := os.Open(exePath)
	if err != nil {
		return nil, fmt.Errorf("failed to open executable file: %v", err)
	}
	defer fp.Close()
	// Seek to the end to find the JSON metadata
	stat, err := fp.Stat()
	if err != nil {
		return nil, fmt.Errorf("failed to stat executable file: %v", err)
	}
	size := stat.Size()
	if size < 8 {
		return nil, fmt.Errorf("executable file is too small to contain metadata")
	}
	_, err = fp.Seek(-8, io.SeekEnd)
	if err != nil {
		return nil, fmt.Errorf("failed to seek to end of executable file: %v", err)
	}
	var fsSize uint64
	err = binary.Read(fp, binary.LittleEndian, &fsSize)
	if err != nil {
		return nil, fmt.Errorf("failed to decode metadata size: %v", err)
	}
	fmt.Println("fsSize:", fsSize)
	if fsSize == 0 || fsSize > uint64(size-8) {
		return nil, fmt.Errorf("invalid metadata size: %d", fsSize)
	}
	_, err = fp.Seek(-(8 + int64(fsSize)), io.SeekEnd)
	if err != nil {
		return nil, fmt.Errorf("failed to seek to metadata position: %v", err)
	}
	jsonData := make([]byte, fsSize)
	_, err = fp.Read(jsonData)
	if err != nil {
		return nil, fmt.Errorf("failed to read metadata: %v", err)
	}
	var fs FileSystem
	err = json.Unmarshal(jsonData, &fs)
	if err != nil {
		return nil, fmt.Errorf("failed to decode JSON metadata: %v", err)
	}
	return &fs, nil
}