some cleanup, and fix minor bug in dagreader from previous commit

blockservice/blockservice.go

@@ -95,6 +95,9 @@ func (s *BlockService) GetBlock(ctx context.Context, k u.Key) (*blocks.Block, er
 	}
 }
 
+// GetBlocks gets a list of blocks asynchronously and returns through
+// the returned channel.
+// NB: No guarantees are made about order.
 func (s *BlockService) GetBlocks(ctx context.Context, ks []u.Key) <-chan *blocks.Block {
 	out := make(chan *blocks.Block, 32)
 	go func() {

merkledag/merkledag.go

@@ -288,9 +288,8 @@ func FetchGraph(ctx context.Context, root *Node, serv DAGService) chan struct{}
 }
 
 // BatchFetch will fill out all of the links of the given Node.
-// It returns a channel of indicies, which will be returned in order
-// from 0 to len(root.Links) - 1, signalling that the link specified by
-// the index has been filled out.
+// It returns a channel of nodes, which the caller can receive
+// all the child nodes of 'root' on, in proper order.
 func (ds *dagService) BatchFetch(ctx context.Context, root *Node) <-chan *Node {
 	sig := make(chan *Node)
 	go func() {
@@ -299,7 +298,6 @@ func (ds *dagService) BatchFetch(ctx context.Context, root *Node) <-chan *Node {
 
 		//
 		next := 0
-		seen := make(map[int]struct{})
 		//
 
 		for _, lnk := range root.Links {
@@ -314,10 +312,6 @@ func (ds *dagService) BatchFetch(ctx context.Context, root *Node) <-chan *Node {
 					continue
 				}
 
-				//
-				seen[i] = struct{}{}
-				//
-
 				nd, err := Decoded(blk.Data)
 				if err != nil {
 					log.Error("Got back bad block!")

unixfs/io/dagreader.go

@@ -61,12 +61,8 @@ func NewDagReader(n *mdag.Node, serv mdag.DAGService) (io.Reader, error) {
 func (dr *DagReader) precalcNextBuf() error {
 	var nxt *mdag.Node
 	var ok bool
-	select {
-	case nxt, ok = <-dr.fetchChan:
-		if !ok {
-			return io.EOF
-		}
-	default:
+
+	if dr.serv == nil {
 		// Only used when fetchChan is nil,
 		// which only happens when passed in a nil dagservice
 		// TODO: this logic is hard to follow, do it better.
@@ -76,7 +72,18 @@ func (dr *DagReader) precalcNextBuf() error {
 			return io.EOF
 		}
 		nxt = dr.node.Links[dr.linkPosition].Node
+		if nxt == nil {
+			return errors.New("Got nil node back from link! and no DAGService!")
+		}
 		dr.linkPosition++
+
+	} else {
+		select {
+		case nxt, ok = <-dr.fetchChan:
+			if !ok {
+				return io.EOF
+			}
+		}
 	}
 
 	pb := new(ftpb.Data)