tapgarden: add GetBlockHash to ChainBridge interface and implementations

GetBlockHash accepts a block height and, if successful, returns the
corresponding block hash.

chain_bridge.go

@@ -67,6 +67,20 @@ func (l *LndRpcChainBridge) GetBlock(ctx context.Context,
 	return block, nil
 }
 
+// GetBlockHash returns the hash of the block in the best blockchain at the
+// given height.
+func (l *LndRpcChainBridge) GetBlockHash(ctx context.Context,
+	blockHeight int64) (chainhash.Hash, error) {
+
+	blockHash, err := l.lnd.ChainKit.GetBlockHash(ctx, blockHeight)
+	if err != nil {
+		return chainhash.Hash{}, fmt.Errorf("unable to retrieve "+
+			"block hash: %w", err)
+	}
+
+	return blockHash, nil
+}
+
 // CurrentHeight return the current height of the main chain.
 func (l *LndRpcChainBridge) CurrentHeight(ctx context.Context) (uint32, error) {
 	info, err := l.lnd.Client.GetInfo(ctx)

tapgarden/interface.go

@@ -252,6 +252,10 @@ type ChainBridge interface {
 	// GetBlock returns a chain block given its hash.
 	GetBlock(context.Context, chainhash.Hash) (*wire.MsgBlock, error)
 
+	// GetBlockHash returns the hash of the block in the best blockchain at
+	// the given height.
+	GetBlockHash(context.Context, int64) (chainhash.Hash, error)
+
 	// CurrentHeight return the current height of the main chain.
 	CurrentHeight(context.Context) (uint32, error)
 

tapgarden/mock.go

@@ -298,6 +298,14 @@ func (m *MockChainBridge) GetBlock(ctx context.Context,
 	return &wire.MsgBlock{}, nil
 }
 
+// GetBlockHash returns the hash of the block in the best blockchain at the
+// given height.
+func (m *MockChainBridge) GetBlockHash(ctx context.Context,
+	blockHeight int64) (chainhash.Hash, error) {
+
+	return chainhash.Hash{}, nil
+}
+
 func (m *MockChainBridge) CurrentHeight(_ context.Context) (uint32, error) {
 	return 0, nil
 }