lnwire: add new type OpaqueAddrs

In this commit, a new net.Addr implementation called OpaqueAddrs is
added along with a WriteOpaqueAddrs func that is called in
WriteNetAddrs. It will be used to store any address bytes that we cannot
parse due to us not being aware of the address type.

lnwire/lnwire_test.go

@@ -230,43 +230,33 @@ func TestChanUpdateChanFlags(t *testing.T) {
 // TestDecodeUnknownAddressType shows that an unknown address type is currently
 // incorrectly dealt with.
 func TestDecodeUnknownAddressType(t *testing.T) {
-	// First, we'll encode all the addresses into an intermediate
-	// buffer. We need to do this in order to compute the total
-	// length of the addresses.
-	addrBuf := bytes.NewBuffer(make([]byte, 0, MaxMsgBody))
-
 	// Add a normal, clearnet address.
 	tcpAddr := &net.TCPAddr{
 		IP:   net.IP{127, 0, 0, 1},
 		Port: 8080,
 	}
 
-	err := WriteTCPAddr(addrBuf, tcpAddr)
-	require.NoError(t, err)
-
 	// Add an onion address.
 	onionAddr := &tor.OnionAddr{
 		OnionService: "abcdefghijklmnop.onion",
 		Port:         9065,
 	}
 
-	err = WriteOnionAddr(addrBuf, onionAddr)
-	require.NoError(t, err)
-
 	// Now add an address with an unknown type.
 	var newAddrType addressType = math.MaxUint8
 	data := make([]byte, 0, 16)
 	data = append(data, uint8(newAddrType))
-	_, err = addrBuf.Write(data)
-	require.NoError(t, err)
+	opaqueAddrs := &OpaqueAddrs{
+		Payload: data,
+	}
 
-	// Now that we have all the addresses, we can append the length.
 	buffer := bytes.NewBuffer(make([]byte, 0, MaxMsgBody))
-	err = writeDataWithLength(buffer, addrBuf.Bytes())
+	err := WriteNetAddrs(
+		buffer, []net.Addr{tcpAddr, onionAddr, opaqueAddrs},
+	)
 	require.NoError(t, err)
 
-	// Now we attempt to parse the bytes and we assert that we get an
-	// error.
+	// Now we attempt to parse the bytes and assert that we get an error.
 	var addrs []net.Addr
 	err = ReadElement(buffer, &addrs)
 	require.Error(t, err)