merkledag: change 'Node' to be an interface

Also change existing 'Node' type to 'ProtoNode' and use that most
everywhere for now. As we move forward with the integration we will try
and use the Node interface in more places that we're currently using
ProtoNode.

License: MIT
Signed-off-by: Jeromy <why@ipfs.io>

test/blocks_test.go

@@ -18,18 +18,8 @@ import (
 	dssync "gx/ipfs/QmbzuUusHqaLLoNTDEVLcSF6vZDHZDLPC7p4bztRvvkXxU/go-datastore/sync"
 )
 
-func newObject(data []byte) *testObject {
-	return &testObject{
-		Block: blocks.NewBlock(data),
-	}
-}
-
-type testObject struct {
-	blocks.Block
-}
-
-func (o *testObject) Cid() *cid.Cid {
-	return cid.NewCidV0(o.Block.Multihash())
+func newObject(data []byte) blocks.Block {
+	return blocks.NewBlock(data)
 }
 
 func TestBlocks(t *testing.T) {
@@ -38,12 +28,8 @@ func TestBlocks(t *testing.T) {
 	defer bs.Close()
 
 	o := newObject([]byte("beep boop"))
-	h := u.Hash([]byte("beep boop"))
-	if !bytes.Equal(o.Multihash(), h) {
-		t.Error("Block Multihash and data multihash not equal")
-	}
-
-	if !o.Cid().Equals(cid.NewCidV0(h)) {
+	h := cid.NewCidV0(u.Hash([]byte("beep boop")))
+	if !o.Cid().Equals(h) {
 		t.Error("Block key and data multihash key not equal")
 	}
 
@@ -74,8 +60,8 @@ func TestBlocks(t *testing.T) {
 	}
 }
 
-func makeObjects(n int) []*testObject {
-	var out []*testObject
+func makeObjects(n int) []blocks.Block {
+	var out []blocks.Block
 	for i := 0; i < n; i++ {
 		out = append(out, newObject([]byte(fmt.Sprintf("object %d", i))))
 	}