add error checking for nil keys

Checks in:
- blockstore
- blockservice
- dagservice
- bitswap

Do not anger the pokemans #2715

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

blockservice.go

@@ -72,6 +72,11 @@ func (s *BlockService) AddBlocks(bs []blocks.Block) ([]key.Key, error) {
 // GetBlock retrieves a particular block from the service,
 // Getting it from the datastore using the key (hash).
 func (s *BlockService) GetBlock(ctx context.Context, k key.Key) (blocks.Block, error) {
+	if k == "" {
+		log.Debug("BlockService GetBlock: Nil Key")
+		return nil, ErrNotFound
+	}
+
 	log.Debugf("BlockService GetBlock: '%s'", k)
 	block, err := s.Blockstore.Get(k)
 	if err == nil {

test/blocks_test.go

@@ -22,6 +22,11 @@ func TestBlocks(t *testing.T) {
 	bs := New(bstore, offline.Exchange(bstore))
 	defer bs.Close()
 
+	_, err := bs.GetBlock(context.Background(), key.Key(""))
+	if err != ErrNotFound {
+		t.Error("Empty String Key should error", err)
+	}
+
 	b := blocks.NewBlock([]byte("beep boop"))
 	h := u.Hash([]byte("beep boop"))
 	if !bytes.Equal(b.Multihash(), h) {