[#472] blobstor: move fsTree to a separate package

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/blobstor/fstree/fstree.go

@@ -0,0 +1,106 @@
+package fstree
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"io/ioutil"
+	"os"
+	"path"
+
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+)
+
+// FSTree represents object storage as filesystem tree.
+type FSTree struct {
+	Info
+
+	Depth      int
+	DirNameLen int
+}
+
+// Info groups the information about file storage.
+type Info struct {
+	// Permission bits of the root directory.
+	Permissions os.FileMode
+
+	// Full path to the root directory.
+	RootPath string
+}
+
+const (
+	// DirNameLen is how many bytes is used to group keys into directories.
+	DirNameLen = 1 // in bytes
+	// MaxDepth is maximum depth of nested directories.
+	MaxDepth = (sha256.Size - 1) / DirNameLen
+)
+
+// ErrFileNotFound is returned when file is missing.
+var ErrFileNotFound = errors.New("file not found")
+
+func stringifyAddress(addr *objectSDK.Address) string {
+	h := sha256.Sum256([]byte(addr.String()))
+
+	return hex.EncodeToString(h[:])
+}
+
+func (t *FSTree) treePath(addr *objectSDK.Address) string {
+	sAddr := stringifyAddress(addr)
+
+	dirs := make([]string, 0, t.Depth+1+1) // 1 for root, 1 for file
+	dirs = append(dirs, t.RootPath)
+
+	for i := 0; i < t.Depth; i++ {
+		dirs = append(dirs, sAddr[:t.DirNameLen])
+		sAddr = sAddr[t.DirNameLen:]
+	}
+
+	dirs = append(dirs, sAddr)
+
+	return path.Join(dirs...)
+}
+
+// Delete removes object with the specified address from storage.
+func (t *FSTree) Delete(addr *objectSDK.Address) error {
+	p, err := t.Exists(addr)
+	if err != nil {
+		return err
+	}
+
+	return os.Remove(p)
+}
+
+// Exists returns path to file with object contents if it exists in storage
+// and an error otherwise.
+func (t *FSTree) Exists(addr *objectSDK.Address) (string, error) {
+	p := t.treePath(addr)
+
+	_, err := os.Stat(p)
+	if os.IsNotExist(err) {
+		err = ErrFileNotFound
+	}
+
+	return p, err
+}
+
+// Put puts object in storage.
+func (t *FSTree) Put(addr *objectSDK.Address, data []byte) error {
+	p := t.treePath(addr)
+
+	if err := os.MkdirAll(path.Dir(p), t.Permissions); err != nil {
+		return err
+	}
+
+	return ioutil.WriteFile(p, data, t.Permissions)
+}
+
+// Get returns object from storage by address.
+func (t *FSTree) Get(addr *objectSDK.Address) ([]byte, error) {
+	p := t.treePath(addr)
+
+	if _, err := os.Stat(p); os.IsNotExist(err) {
+		return nil, ErrFileNotFound
+	}
+
+	return ioutil.ReadFile(p)
+}