rework dagreader to have a dagservice for node resolution

dagreader.go

@@ -5,20 +5,22 @@ import (
 	"errors"
 	"io"
 
-	"code.google.com/p/goprotobuf/proto"
+	proto "code.google.com/p/goprotobuf/proto"
+	u "github.com/jbenet/go-ipfs/util"
 )
 
 var ErrIsDir = errors.New("this dag node is a directory.")
 
 // DagReader provides a way to easily read the data contained in a dag.
 type DagReader struct {
+	serv     *DAGService
 	node     *Node
 	position int
 	buf      *bytes.Buffer
 	thisData []byte
 }
 
-func NewDagReader(n *Node) (io.Reader, error) {
+func NewDagReader(n *Node, serv *DAGService) (io.Reader, error) {
 	pb := new(PBData)
 	err := proto.Unmarshal(n.Data, pb)
 	if err != nil {
@@ -31,6 +33,7 @@ func NewDagReader(n *Node) (io.Reader, error) {
 		return &DagReader{
 			node:     n,
 			thisData: pb.GetData(),
+			serv:     serv,
 		}, nil
 	case PBData_Raw:
 		return bytes.NewBuffer(pb.GetData()), nil
@@ -46,8 +49,11 @@ func (dr *DagReader) precalcNextBuf() error {
 	nxtLink := dr.node.Links[dr.position]
 	nxt := nxtLink.Node
 	if nxt == nil {
-		//TODO: should use dagservice or something to get needed block
-		return errors.New("Link to nil node! Tree not fully expanded!")
+		nxtNode, err := dr.serv.Get(u.Key(nxtLink.Hash))
+		if err != nil {
+			return err
+		}
+		nxt = nxtNode
 	}
 	pb := new(PBData)
 	err := proto.Unmarshal(nxt.Data, pb)
@@ -96,3 +102,29 @@ func (dr *DagReader) Read(b []byte) (int, error) {
 		}
 	}
 }
+
+/*
+func (dr *DagReader) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	case os.SEEK_SET:
+		for i := 0; i < len(dr.node.Links); i++ {
+			nsize := dr.node.Links[i].Size - 8
+			if offset > nsize {
+				offset -= nsize
+			} else {
+				break
+			}
+		}
+		dr.position = i
+		err := dr.precalcNextBuf()
+		if err != nil {
+			return 0, err
+		}
+	case os.SEEK_CUR:
+	case os.SEEK_END:
+	default:
+		return 0, errors.New("invalid whence")
+	}
+	return 0, nil
+}
+*/

merkledag.go

@@ -96,6 +96,8 @@ func (n *Node) Key() (u.Key, error) {
 // DAGService is an IPFS Merkle DAG service.
 // - the root is virtual (like a forest)
 // - stores nodes' data in a BlockService
+// TODO: should cache Nodes that are in memory, and be
+//       able to free some of them when vm pressure is high
 type DAGService struct {
 	Blocks *bserv.BlockService
 }