[#176] localstore: Implement primary BlobStor

Implement primary local BLOB storage based on filesystem tree.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/blobstor/fstree.go

@@ -0,0 +1,49 @@
+package blobstor
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"os"
+	"path"
+
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+)
+
+type fsTree struct {
+	depth int
+
+	dirNameLen int
+
+	perm os.FileMode
+
+	rootDir string
+}
+
+const dirNameLen = 2 // in bytes
+
+var maxDepth = (hex.EncodedLen(sha256.Size) - 1) / dirNameLen
+
+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.rootDir)
+
+	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...)
+}