add error checking for nil keys

Checks in:
- blockstore
- blockservice
- dagservice
- bitswap

Do not anger the pokemans ipfs#2715

License: MIT
Signed-off-by: Juan Benet <juan@benet.ai>

merkledag.go

@@ -68,6 +68,9 @@ func (n *dagService) Batch() *Batch {
 
 // Get retrieves a node from the dagService, fetching the block in the BlockService
 func (n *dagService) Get(ctx context.Context, k key.Key) (*Node, error) {
+	if k == "" {
+		return nil, ErrNotFound
+	}
 	if n == nil {
 		return nil, fmt.Errorf("dagService is nil")
 	}

merkledag_test.go

@@ -32,6 +32,13 @@ type dagservAndPinner struct {
 	mp pin.Pinner
 }
 
+func getDagserv(t *testing.T) DAGService {
+	db := dssync.MutexWrap(ds.NewMapDatastore())
+	bs := bstore.NewBlockstore(db)
+	blockserv := bserv.New(bs, offline.Exchange(bs))
+	return NewDAGService(blockserv)
+}
+
 func getDagservAndPinner(t *testing.T) dagservAndPinner {
 	db := dssync.MutexWrap(ds.NewMapDatastore())
 	bs := bstore.NewBlockstore(db)
@@ -245,6 +252,14 @@ func assertCanGet(t *testing.T, ds DAGService, n *Node) {
 	}
 }
 
+func TestEmptyKey(t *testing.T) {
+	ds := getDagserv(t)
+	_, err := ds.Get(context.Background(), key.Key(""))
+	if err != ErrNotFound {
+		t.Error("dag service should error when key is nil", err)
+	}
+}
+
 func TestCantGet(t *testing.T) {
 	dsp := getDagservAndPinner(t)
 	a := &Node{Data: []byte("A")}