minio/pkgs/storage/appendstorage/append_storage.go

package appendstorage

import (
	"bytes"
	"encoding/gob"
	"io/ioutil"
	"os"
	"path"
	"strconv"

	"github.com/minio-io/minio/pkgs/storage"
)

type appendStorage struct {
	RootDir     string
	file        *os.File
	objects     map[string]Header
	objectsFile string
}

type Header struct {
	Path   string
	Offset int64
	Length int
	Crc    []byte
}

func NewStorage(rootDir string, slice int) (storage.ObjectStorage, error) {
	rootPath := path.Join(rootDir, strconv.Itoa(slice))
	// TODO verify and fix partial writes
	file, err := os.OpenFile(rootPath, os.O_APPEND|os.O_CREATE|os.O_RDWR, 0600)
	if err != nil {
		return &appendStorage{}, err
	}
	objectsFile := path.Join(rootDir, strconv.Itoa(slice)+".map")
	objects := make(map[string]Header)
	if _, err := os.Stat(objectsFile); err == nil {
		mapFile, err := os.Open(objectsFile)
		defer mapFile.Close()
		if err != nil {
			return &appendStorage{}, nil
		}
		dec := gob.NewDecoder(mapFile)
		err = dec.Decode(&objects)
		if err != nil {
			return &appendStorage{}, nil
		}
	}
	if err != nil {
		return &appendStorage{}, err
	}
	return &appendStorage{
		RootDir:     rootDir,
		file:        file,
		objects:     objects,
		objectsFile: objectsFile,
	}, nil
}

func (storage *appendStorage) Get(objectPath string) ([]byte, error) {
	header, ok := storage.objects[objectPath]
	if ok == false {
		return nil, nil
	}

	offset := header.Offset
	length := header.Length

	object := make([]byte, length)
	_, err := storage.file.ReadAt(object, offset)
	if err != nil {
		return nil, err
	}
	return object, nil
}

func (storage *appendStorage) Put(objectPath string, object []byte) error {
	header := Header{
		Path:   objectPath,
		Offset: 0,
		Length: 0,
		Crc:    nil,
	}
	offset, err := storage.file.Seek(0, os.SEEK_END)
	if err != nil {
		return err
	}
	if _, err := storage.file.Write(object); err != nil {
		return err
	}
	header.Offset = offset
	header.Length = len(object)
	storage.objects[objectPath] = header
	var mapBuffer bytes.Buffer
	encoder := gob.NewEncoder(&mapBuffer)
	encoder.Encode(storage.objects)
	ioutil.WriteFile(storage.objectsFile, mapBuffer.Bytes(), 0600)
	return nil
}