[#151] index page: Add browse via native protocol

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

tree/tree.go

@@ -30,6 +30,11 @@ type (
 		Meta  map[string]string
 	}
 
+	multiSystemNode struct {
+		// the first element is latest
+		nodes []*treeNode
+	}
+
 	GetNodesParams struct {
 		CnrID      cid.ID
 		BktInfo    *data.BucketInfo
@@ -50,18 +55,19 @@ var (
 )
 
 const (
-	FileNameKey = "FileName"
-)
+	FileNameKey      = "FileName"
+	settingsFileName = "bucket-settings"
 
-const (
-	oidKV = "OID"
+	oidKV      = "OID"
+	uploadIDKV = "UploadId"
+	sizeKV     = "Size"
 
 	// keys for delete marker nodes.
 	isDeleteMarkerKV = "IsDeleteMarker"
-	sizeKV           = "Size"
 
 	// versionTree -- ID of a tree with object versions.
 	versionTree = "version"
+	systemTree  = "system"
 
 	separator = "/"
 )
@@ -135,6 +141,45 @@ func newNodeVersionFromTreeNode(treeNode *treeNode) *api.NodeVersion {
 	return version
 }
 
+func newMultiNode(nodes []NodeResponse) (*multiSystemNode, error) {
+	var (
+		err          error
+		index        int
+		maxTimestamp uint64
+	)
+
+	if len(nodes) == 0 {
+		return nil, errors.New("multi node must have at least one node")
+	}
+
+	treeNodes := make([]*treeNode, len(nodes))
+
+	for i, node := range nodes {
+		if treeNodes[i], err = newTreeNode(node); err != nil {
+			return nil, fmt.Errorf("parse system node response: %w", err)
+		}
+
+		if timestamp := getMaxTimestamp(node); timestamp > maxTimestamp {
+			index = i
+			maxTimestamp = timestamp
+		}
+	}
+
+	treeNodes[0], treeNodes[index] = treeNodes[index], treeNodes[0]
+
+	return &multiSystemNode{
+		nodes: treeNodes,
+	}, nil
+}
+
+func (m *multiSystemNode) Latest() *treeNode {
+	return m.nodes[0]
+}
+
+func (m *multiSystemNode) Old() []*treeNode {
+	return m.nodes[1:]
+}
+
 func (c *Tree) GetLatestVersion(ctx context.Context, cnrID *cid.ID, objectName string) (*api.NodeVersion, error) {
 	nodes, err := c.GetVersions(ctx, cnrID, objectName)
 	if err != nil {
@@ -165,6 +210,55 @@ func (c *Tree) GetVersions(ctx context.Context, cnrID *cid.ID, objectName string
 	return c.service.GetNodes(ctx, p)
 }
 
+func (c *Tree) CheckSettingsNodeExist(ctx context.Context, bktInfo *data.BucketInfo) error {
+	_, err := c.getSystemNode(ctx, bktInfo, settingsFileName)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *Tree) getSystemNode(ctx context.Context, bktInfo *data.BucketInfo, name string) (*multiSystemNode, error) {
+	p := &GetNodesParams{
+		CnrID:      bktInfo.CID,
+		BktInfo:    bktInfo,
+		TreeID:     systemTree,
+		Path:       []string{name},
+		LatestOnly: false,
+		AllAttrs:   true,
+	}
+	nodes, err := c.service.GetNodes(ctx, p)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes = filterMultipartNodes(nodes)
+
+	if len(nodes) == 0 {
+		return nil, ErrNodeNotFound
+	}
+
+	return newMultiNode(nodes)
+}
+
+func filterMultipartNodes(nodes []NodeResponse) []NodeResponse {
+	res := make([]NodeResponse, 0, len(nodes))
+
+LOOP:
+	for _, node := range nodes {
+		for _, meta := range node.GetMeta() {
+			if meta.GetKey() == uploadIDKV {
+				continue LOOP
+			}
+		}
+
+		res = append(res, node)
+	}
+
+	return res
+}
+
 func getLatestVersionNode(nodes []NodeResponse) (NodeResponse, error) {
 	var (
 		maxCreationTime uint64