Adding append storage driver

pkgs/storage/appendstorage/append_storage.go

@@ -0,0 +1,99 @@
+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
+}