[#197] Add a leading slash to the FilePath attribute

According to the frostfs api specification,
the File Path attribute must start with a
leading slash. More info:
https://git.frostfs.info/TrueCloudLab/frostfs-api

Signed-off-by: Roman Loginov <r.loginov@yadro.com>

internal/handler/handler.go

@@ -253,9 +253,7 @@ func (h *Handler) byAttribute(c *fasthttp.RequestCtx, handler func(context.Conte
 		return
 	}
 
-	if key == attrFileName {
-		val = prepareFileName(val)
-	}
+	val = prepareAtribute(key, val)
 
 	log = log.With(zap.String("cid", cidParam), zap.String("attr_key", key), zap.String("attr_val", val))
 
@@ -298,7 +296,8 @@ func (h *Handler) findObjectByAttribute(ctx context.Context, log *zap.Logger, cn
 		switch {
 		case errors.Is(err, io.EOF) && h.needSearchByFileName(attrKey, attrVal):
 			log.Debug(logs.ObjectNotFoundByFilePathTrySearchByFileName, logs.TagField(logs.TagExternalStorage))
-			return h.findObjectByAttribute(ctx, log, cnrID, attrFileName, prepareFileName(attrVal))
+			attrVal = prepareAtribute(attrFileName, attrVal)
+			return h.findObjectByAttribute(ctx, log, cnrID, attrFileName, attrVal)
 		case errors.Is(err, io.EOF):
 			log.Error(logs.ObjectNotFound, zap.Error(err), logs.TagField(logs.TagExternalStorage))
 			return oid.ID{}, fmt.Errorf("object not found: %w", err)
@@ -319,6 +318,18 @@ func (h *Handler) needSearchByFileName(key, val string) bool {
 	return strings.HasPrefix(val, "/") && strings.Count(val, "/") == 1 || !strings.Contains(val, "/")
 }
 
+func prepareAtribute(attrKey, attrVal string) string {
+	if attrKey == attrFileName {
+		return prepareFileName(attrVal)
+	}
+
+	if attrKey == attrFilePath {
+		return prepareFilePath(attrVal)
+	}
+
+	return attrVal
+}
+
 func prepareFileName(fileName string) string {
 	if strings.HasPrefix(fileName, "/") {
 		return fileName[1:]
@@ -327,6 +338,14 @@ func prepareFileName(fileName string) string {
 	return fileName
 }
 
+func prepareFilePath(filePath string) string {
+	if !strings.HasPrefix(filePath, "/") {
+		return "/" + filePath
+	}
+
+	return filePath
+}
+
 // resolveContainer decode container id, if it's not a valid container id
 // then trey to resolve name using provided resolver.
 func (h *Handler) resolveContainer(ctx context.Context, containerID string) (*cid.ID, error) {