lnd: if using btcd backend, ensure that --txindex is active

In this commit, we add a new runtime assertion to ensure that the
backed btcd node (if this mode is active) has the proper indexes set
up. Atm, if btcd isn’t running with the txindex active, then the
current ChainNotifier implementation will be unable to properly handle
certain classes of historical notification dispatches.

In order to test that the running btcd node is configured properly,
we’ll fetch the latest block, then try to query a transaction within
that block using the txindex. If btcd isn’t running with this mode
active, then the request will fail. In this case, we’ll then fail to
start lnd with an error.

Fixes #525.

chainregistry.go

@@ -142,8 +142,9 @@ func newChainControlFromConfig(cfg *config, chanDB *channeldb.DB,
 	}
 
 	var (
-		err     error
-		cleanUp func()
+		err        error
+		cleanUp    func()
+		rawRPCConn *chain.RPCClient
 	)
 
 	// If spv mode is active, then we'll be using a distinct set of
@@ -269,6 +270,7 @@ func newChainControlFromConfig(cfg *config, chanDB *channeldb.DB,
 		}
 
 		walletConfig.ChainSource = chainRPC
+		rawRPCConn = chainRPC
 
 		// If we're not in simnet or regtest mode, then we'll attempt
 		// to use a proper fee estimator for testnet.
@@ -330,6 +332,35 @@ func newChainControlFromConfig(cfg *config, chanDB *channeldb.DB,
 
 	cc.wallet = wallet
 
+	// As a final check, if we're using the RPC backend, we'll ensure that
+	// the btcd node has the txindex set. Atm, this is required in order to
+	// properly perform historical confirmation+spend dispatches.
+	if !cfg.NeutrinoMode.Active {
+		// In order to check to see if we have the txindex up to date
+		// and active, we'll try to fetch the first transaction in the
+		// latest block via the index. If this doesn't succeed, then we
+		// know it isn't active (or just not yet up to date).
+		bestHash, _, err := cc.chainIO.GetBestBlock()
+		if err != nil {
+			return nil, nil, fmt.Errorf("unable to get current "+
+				"best hash: %v", err)
+		}
+		bestBlock, err := cc.chainIO.GetBlock(bestHash)
+		if err != nil {
+			return nil, nil, fmt.Errorf("unable to get current "+
+				"block hash: %v", err)
+		}
+
+		firstTxHash := bestBlock.Transactions[0].TxHash()
+		_, err = rawRPCConn.GetRawTransaction(&firstTxHash)
+		if err != nil {
+			// If the node doesn't have the txindex set, then we'll
+			// halt startup, as we can't proceed in this state.
+			return nil, nil, fmt.Errorf("btcd detected to not " +
+				"have --txindex active, cannot proceed")
+		}
+	}
+
 	return cc, cleanUp, nil
 }