lnd: implement the sendcoins RPC request

This commit implements the “send coins” RPC request which was
introduced at both the lnrpc and command line level in a prior commit.

A small refactoring has taken place w.r.t to sendmany+sendcoins in
order to eliminate some code duplication.

lnwallet/script_utils_test.go

@@ -164,6 +164,10 @@ func TestRevocationKeyDerivation(t *testing.T) {
 	}
 }
 
+// makeWitnessTestCase is a helper function used within test cases involving
+// the validity of a crafted witness. This function is a wrapper function which
+// allows constructing table-driven tests. In the case of an error while
+// constructing the witness, the test fails fataly.
 func makeWitnessTestCase(t *testing.T, f func() (wire.TxWitness, error)) func() wire.TxWitness {
 	return func() wire.TxWitness {
 		witness, err := f()
@@ -190,6 +194,8 @@ func makeWitnessTestCase(t *testing.T, f func() (wire.TxWitness, error)) func()
 //    * invalid sequence for CSV
 //    * valid lock-time+sequence, valid sig
 func TestHTLCSenderSpendValidation(t *testing.T) {
+	// TODO(roasbeef): eliminate duplication with other HTLC tests.
+
 	// We generate a fake output, and the coresponding txin. This output
 	// doesn't need to exist, as we'll only be validating spending from the
 	// transaction that references this.
@@ -199,13 +205,15 @@ func TestHTLCSenderSpendValidation(t *testing.T) {
 	}
 	fakeFundingTxIn := wire.NewTxIn(fundingOut, nil, nil)
 
+	// Generate a payment and revocation pre-image to be used below.
 	revokePreimage := testHdSeed[:]
 	revokeHash := fastsha256.Sum256(revokePreimage)
-
 	paymentPreimage := revokeHash
 	paymentPreimage[0] ^= 1
 	paymentHash := fastsha256.Sum256(paymentPreimage[:])
 
+	// We'll also need some tests keys for alice and bob, and meta-data of
+	// the HTLC output.
 	aliceKeyPriv, aliceKeyPub := btcec.PrivKeyFromBytes(btcec.S256(),
 		testWalletPrivKey)
 	bobKeyPriv, bobKeyPub := btcec.PrivKeyFromBytes(btcec.S256(),
@@ -214,6 +222,7 @@ func TestHTLCSenderSpendValidation(t *testing.T) {
 	cltvTimeout := uint32(8)
 	csvTimeout := uint32(5)
 
+	// Generate the raw HTLC redemption scripts, and its p2wsh counterpart.
 	htlcScript, err := senderHTLCScript(cltvTimeout, csvTimeout,
 		aliceKeyPub, bobKeyPub, revokeHash[:], paymentHash[:])
 	if err != nil {
@@ -318,6 +327,8 @@ func TestHTLCSenderSpendValidation(t *testing.T) {
 			t.Fatalf("unable to create engine: %v", err)
 		}
 
+		// This buffer will trace execution of the Script, only dumping
+		// out to stdout in the case that a test fails.
 		var debugBuf bytes.Buffer
 
 		done := false
@@ -366,13 +377,15 @@ func TestHTLCReceiverSpendValidation(t *testing.T) {
 	}
 	fakeFundingTxIn := wire.NewTxIn(fundingOut, nil, nil)
 
+	// Generate a payment and revocation pre-image to be used below.
 	revokePreimage := testHdSeed[:]
 	revokeHash := fastsha256.Sum256(revokePreimage)
-
 	paymentPreimage := revokeHash
 	paymentPreimage[0] ^= 1
 	paymentHash := fastsha256.Sum256(paymentPreimage[:])
 
+	// We'll also need some tests keys for alice and bob, and meta-data of
+	// the HTLC output.
 	aliceKeyPriv, aliceKeyPub := btcec.PrivKeyFromBytes(btcec.S256(),
 		testWalletPrivKey)
 	bobKeyPriv, bobKeyPub := btcec.PrivKeyFromBytes(btcec.S256(),
@@ -381,6 +394,7 @@ func TestHTLCReceiverSpendValidation(t *testing.T) {
 	cltvTimeout := uint32(8)
 	csvTimeout := uint32(5)
 
+	// Generate the raw HTLC redemption scripts, and its p2wsh counterpart.
 	htlcScript, err := receiverHTLCScript(cltvTimeout, csvTimeout,
 		aliceKeyPub, bobKeyPub, revokeHash[:], paymentHash[:])
 	if err != nil {
@@ -486,6 +500,8 @@ func TestHTLCReceiverSpendValidation(t *testing.T) {
 			t.Fatalf("unable to create engine: %v", err)
 		}
 
+		// This buffer will trace execution of the Script, only dumping
+		// out to stdout in the case that a test fails.
 		var debugBuf bytes.Buffer
 
 		done := false

rpcserver.go

@@ -62,13 +62,13 @@ func (r *rpcServer) Stop() error {
 	return nil
 }
 
-// SendMany handles a request for a transaction create multiple specified
+// addrPairsToOutputs converts a map describing a set of outputs to be created,
-// outputs in parallel.
+// the outputs themselves. The passed map pairs up an address, to a desired
-func (r *rpcServer) SendMany(ctx context.Context,
+// output value amount. Each address is converted to its corresponding pkScript
-	in *lnrpc.SendManyRequest) (*lnrpc.SendManyResponse, error) {
+// to be used within the constructed output(s).
-
+func addrPairsToOutputs(addrPairs map[string]int64) ([]*wire.TxOut, error) {
-	outputs := make([]*wire.TxOut, 0, len(in.AddrToAmount))
+	outputs := make([]*wire.TxOut, 0, len(addrPairs))
-	for addr, amt := range in.AddrToAmount {
+	for addr, amt := range addrPairs {
 		addr, err := btcutil.DecodeAddress(addr, activeNetParams)
 		if err != nil {
 			return nil, err
@@ -82,14 +82,50 @@ func (r *rpcServer) SendMany(ctx context.Context,
 		outputs = append(outputs, wire.NewTxOut(amt, pkscript))
 	}
 
-	// Instruct the wallet to create an transaction paying to the specified
+	return outputs, nil
-	// outputs, selecting any coins with at least one confirmation.
+}
-	txid, err := r.server.lnwallet.SendOutputs(outputs, defaultAccount, 1)
+
+// sendCoinsOnChain makes an on-chain transaction in or to send coins to one or
+// more addresses specified in the passed payment map. The payment map maps an
+// address to a specified output value to be sent to that address.
+func (r *rpcServer) sendCoinsOnChain(paymentMap map[string]int64) (*wire.ShaHash, error) {
+	outputs, err := addrPairsToOutputs(paymentMap)
 	if err != nil {
 		return nil, err
 	}
 
-	rpcsLog.Infof("Generated txid: %v", txid.String())
+	return r.server.lnwallet.SendOutputs(outputs, defaultAccount, 1)
+}
+
+// SendCoins executes a request to send coins to a particular address. Unlike
+// SendMany, this RPC call only allows creating a single output at a time.
+func (r *rpcServer) SendCoins(ctx context.Context,
+	in *lnrpc.SendCoinsRequest) (*lnrpc.SendCoinsResponse, error) {
+
+	rpcsLog.Infof("[sendcoins] addr=%v, amt=%v", in.Addr, btcutil.Amount(in.Amount))
+
+	paymentMap := map[string]int64{in.Addr: in.Amount}
+	txid, err := r.sendCoinsOnChain(paymentMap)
+	if err != nil {
+		return nil, err
+	}
+
+	rpcsLog.Infof("[sendcoins] spend generated txid: %v", txid.String())
+
+	return &lnrpc.SendCoinsResponse{Txid: txid.String()}, nil
+}
+
+// SendMany handles a request for a transaction create multiple specified
+// outputs in parallel.
+func (r *rpcServer) SendMany(ctx context.Context,
+	in *lnrpc.SendManyRequest) (*lnrpc.SendManyResponse, error) {
+
+	txid, err := r.sendCoinsOnChain(in.AddrToAmount)
+	if err != nil {
+		return nil, err
+	}
+
+	rpcsLog.Infof("[sendmany] spend generated txid: %v", txid.String())
 
 	return &lnrpc.SendManyResponse{Txid: txid.String()}, nil
 }
@@ -119,7 +155,7 @@ func (r *rpcServer) NewAddress(ctx context.Context,
 		return nil, err
 	}
 
-	rpcsLog.Infof("Generated new address: %v", addr.String())
+	rpcsLog.Infof("[newaddress] addr=%v", addr.String())
 	return &lnrpc.NewAddressResponse{Address: addr.String()}, nil
 }
 
@@ -132,7 +168,7 @@ func (r *rpcServer) ConnectPeer(ctx context.Context,
 	}
 
 	idAtHost := fmt.Sprintf("%v@%v", in.Addr.PubKeyHash, in.Addr.Host)
-	rpcsLog.Debugf("Attempting to connect to peer %v", idAtHost)
+	rpcsLog.Debugf("[connectpeer] peer=%v", idAtHost)
 
 	peerAddr, err := lndc.LnAddrFromString(idAtHost)
 	if err != nil {
@@ -155,7 +191,7 @@ func (r *rpcServer) ConnectPeer(ctx context.Context,
 func (r *rpcServer) OpenChannel(ctx context.Context,
 	in *lnrpc.OpenChannelRequest) (*lnrpc.OpenChannelResponse, error) {
 
-	rpcsLog.Tracef("Recieved request to openchannel to peerid(%v) "+
+	rpcsLog.Tracef("[openchannel] request to peerid(%v) "+
 		"allocation(us=%v, them=%v) numconfs=%v", in.TargetPeerId,
 		in.LocalFundingAmount, in.RemoteFundingAmount, in.NumConfs)
 
@@ -171,7 +207,7 @@ func (r *rpcServer) OpenChannel(ctx context.Context,
 		return nil, err
 	}
 
-	rpcsLog.Tracef("Opened channel with peerid(%v), ChannelPoint(%v)",
+	rpcsLog.Tracef("[openchannel] success peerid(%v), ChannelPoint(%v)",
 		in.TargetPeerId, resp)
 
 	return &lnrpc.OpenChannelResponse{
@@ -191,12 +227,12 @@ func (r *rpcServer) CloseChannel(ctx context.Context,
 	index := in.ChannelPoint.OutputIndex
 	txid, err := wire.NewShaHash(in.ChannelPoint.FundingTxid)
 	if err != nil {
-		rpcsLog.Errorf("(closechannel) invalid txid: %v", err)
+		rpcsLog.Errorf("[closechannel] invalid txid: %v", err)
 		return nil, err
 	}
 	targetChannelPoint := wire.NewOutPoint(txid, index)
 
-	rpcsLog.Tracef("Recieved closechannel request for ChannelPoint(%v)",
+	rpcsLog.Tracef("[closechannel] request for ChannelPoint(%v)",
 		targetChannelPoint)
 
 	resp, err := r.server.CloseChannel(targetChannelPoint)
@@ -213,7 +249,7 @@ func (r *rpcServer) CloseChannel(ctx context.Context,
 func (r *rpcServer) ListPeers(ctx context.Context,
 	in *lnrpc.ListPeersRequest) (*lnrpc.ListPeersResponse, error) {
 
-	rpcsLog.Tracef("recieved listpeers request")
+	rpcsLog.Tracef("[listpeers] request")
 
 	serverPeers := r.server.Peers()
 	resp := &lnrpc.ListPeersResponse{
@@ -250,7 +286,7 @@ func (r *rpcServer) ListPeers(ctx context.Context,
 		resp.Peers = append(resp.Peers, peer)
 	}
 
-	rpcsLog.Tracef("listpeers yielded %v peers", serverPeers)
+	rpcsLog.Debugf("[listpeers] yielded %v peers", serverPeers)
 
 	return resp, nil
 }
@@ -288,7 +324,7 @@ func (r *rpcServer) WalletBalance(ctx context.Context,
 		balance = outputSum.ToBTC()
 	}
 
-	rpcsLog.Debugf("walletbalance query response: %v", balance)
+	rpcsLog.Debugf("[walletbalance] balance=%v", balance)
 
 	return &lnrpc.WalletBalanceResponse{balance}, nil
 }