lnwire: Add upfront shutdown messages and feature bit

This commit adds the feature bit and additional fields
required in `open_channel` and `accept_channel` wire
messages for `option_upfront_shutdown_script`.

lnwire/accept_channel_test.go

@@ -0,0 +1,71 @@
+package lnwire
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/btcsuite/btcd/btcec"
+)
+
+// TestDecodeAcceptChannel tests decoding of an accept channel wire message with
+// and without the optional upfront shutdown script.
+func TestDecodeAcceptChannel(t *testing.T) {
+	tests := []struct {
+		name           string
+		shutdownScript DeliveryAddress
+	}{
+		{
+			name:           "no upfront shutdown script",
+			shutdownScript: nil,
+		},
+		{
+			name:           "empty byte array",
+			shutdownScript: []byte{},
+		},
+		{
+			name:           "upfront shutdown script set",
+			shutdownScript: []byte("example"),
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+
+		t.Run(test.name, func(t *testing.T) {
+			priv, err := btcec.NewPrivateKey(btcec.S256())
+			if err != nil {
+				t.Fatalf("cannot create privkey: %v", err)
+			}
+			pk := priv.PubKey()
+
+			encoded := &AcceptChannel{
+				PendingChannelID:      [32]byte{},
+				FundingKey:            pk,
+				RevocationPoint:       pk,
+				PaymentPoint:          pk,
+				DelayedPaymentPoint:   pk,
+				HtlcPoint:             pk,
+				FirstCommitmentPoint:  pk,
+				UpfrontShutdownScript: test.shutdownScript,
+			}
+
+			buf := &bytes.Buffer{}
+			if _, err := WriteMessage(buf, encoded, 0); err != nil {
+				t.Fatalf("cannot write message: %v", err)
+			}
+
+			msg, err := ReadMessage(buf, 0)
+			if err != nil {
+				t.Fatalf("cannot read message: %v", err)
+			}
+
+			decoded := msg.(*AcceptChannel)
+			if !bytes.Equal(
+				decoded.UpfrontShutdownScript, encoded.UpfrontShutdownScript,
+			) {
+				t.Fatalf("decoded script: %x does not equal encoded script: %x",
+					decoded.UpfrontShutdownScript, encoded.UpfrontShutdownScript)
+			}
+		})
+	}
+}