HTTP: add handlers to allow object creation and modification

path/resolver.go

@@ -11,16 +11,26 @@ import (
 
 var log = u.Logger("path")
 
+// ErrNoLink is returned when a link is not found in a path
+type ErrNoLink struct {
+	name string
+	node mh.Multihash
+}
+
+func (e ErrNoLink) Error() string {
+	return fmt.Sprintf("no link named %q under %s", e.name, e.node.B58String())
+}
+
 // Resolver provides path resolution to IPFS
 // It has a pointer to a DAGService, which is uses to resolve nodes.
 type Resolver struct {
 	DAG merkledag.DAGService
 }
 
-// ResolvePath fetches the node for given path. It uses the first
-// path component as a hash (key) of the first node, then resolves
-// all other components walking the links, with ResolveLinks.
-func (s *Resolver) ResolvePath(fpath Path) (*merkledag.Node, error) {
+// SplitAbsPath clean up and split fpath. It extracts the first component (which
+// must be a Multihash) and return it separately.
+func SplitAbsPath(fpath Path) (mh.Multihash, []string, error) {
+
 	log.Debugf("Resolve: '%s'", fpath)
 
 	parts := fpath.Segments()
@@ -30,13 +40,36 @@ func (s *Resolver) ResolvePath(fpath Path) (*merkledag.Node, error) {
 
 	// if nothing, bail.
 	if len(parts) == 0 {
-		return nil, fmt.Errorf("ipfs path must contain at least one component")
+		return nil, nil, fmt.Errorf("ipfs path must contain at least one component")
 	}
 
 	// first element in the path is a b58 hash (for now)
 	h, err := mh.FromB58String(parts[0])
 	if err != nil {
 		log.Debug("given path element is not a base58 string.\n")
+		return nil, nil, err
+	}
+
+	return h, parts[1:], nil
+}
+
+// ResolvePath fetches the node for given path. It returns the last item
+// returned by ResolvePathComponents.
+func (s *Resolver) ResolvePath(fpath Path) (*merkledag.Node, error) {
+	nodes, err := s.ResolvePathComponents(fpath)
+	if err != nil || nodes == nil {
+		return nil, err
+	} else {
+		return nodes[len(nodes)-1], err
+	}
+}
+
+// ResolvePathComponents fetches the nodes for each segment of the given path.
+// It uses the first path component as a hash (key) of the first node, then
+// resolves all other components walking the links, with ResolveLinks.
+func (s *Resolver) ResolvePathComponents(fpath Path) ([]*merkledag.Node, error) {
+	h, parts, err := SplitAbsPath(fpath)
+	if err != nil {
 		return nil, err
 	}
 
@@ -46,19 +79,22 @@ func (s *Resolver) ResolvePath(fpath Path) (*merkledag.Node, error) {
 		return nil, err
 	}
 
-	return s.ResolveLinks(nd, parts[1:])
+	return s.ResolveLinks(nd, parts)
 }
 
 // ResolveLinks iteratively resolves names by walking the link hierarchy.
 // Every node is fetched from the DAGService, resolving the next name.
-// Returns the last node found.
+// Returns the list of nodes forming the path, starting with ndd. This list is
+// guaranteed never to be empty.
 //
 // ResolveLinks(nd, []string{"foo", "bar", "baz"})
 // would retrieve "baz" in ("bar" in ("foo" in nd.Links).Links).Links
 func (s *Resolver) ResolveLinks(ndd *merkledag.Node, names []string) (
-	nd *merkledag.Node, err error) {
+	result []*merkledag.Node, err error) {
 
-	nd = ndd // dup arg workaround
+	result = make([]*merkledag.Node, 0, len(names)+1)
+	result = append(result, ndd)
+	nd := ndd // dup arg workaround
 
 	// for each of the path components
 	for _, name := range names {
@@ -75,21 +111,22 @@ func (s *Resolver) ResolveLinks(ndd *merkledag.Node, names []string) (
 		}
 
 		if next == "" {
-			h1, _ := nd.Multihash()
-			h2 := h1.B58String()
-			return nil, fmt.Errorf("no link named %q under %s", name, h2)
+			n, _ := nd.Multihash()
+			return result, ErrNoLink{name: name, node: n}
 		}
 
 		if nlink.Node == nil {
 			// fetch object for link and assign to nd
 			nd, err = s.DAG.Get(next)
 			if err != nil {
-				return nd, err
+				return append(result, nd), err
 			}
 			nlink.Node = nd
 		} else {
 			nd = nlink.Node
 		}
+
+		result = append(result, nlink.Node)
 	}
 	return
 }