lnwire: use write buffer in Encode methods

This commit changes the WriteElement and WriteElements methods to take a
write buffer instead of io.Writer. The corresponding Encode methods are
changed to use the write buffer.

lnwire/lnwire.go

@@ -75,13 +75,8 @@ func (a addressType) AddrLen() uint16 {
 }
 
 // WriteElement is a one-stop shop to write the big endian representation of
-// any element which is to be serialized for the wire protocol. The passed
-// io.Writer should be backed by an appropriately sized byte slice, or be able
-// to dynamically expand to accommodate additional data.
-//
-// TODO(roasbeef): this should eventually draw from a buffer pool for
-// serialization.
-func WriteElement(w io.Writer, element interface{}) error {
+// any element which is to be serialized for the wire protocol.
+func WriteElement(w *bytes.Buffer, element interface{}) error {
 	switch e := element.(type) {
 	case NodeAlias:
 		if _, err := w.Write(e[:]); err != nil {
@@ -437,10 +432,10 @@ func WriteElement(w io.Writer, element interface{}) error {
 }
 
 // WriteElements is writes each element in the elements slice to the passed
-// io.Writer using WriteElement.
-func WriteElements(w io.Writer, elements ...interface{}) error {
+// buffer using WriteElement.
+func WriteElements(buf *bytes.Buffer, elements ...interface{}) error {
 	for _, element := range elements {
-		err := WriteElement(w, element)
+		err := WriteElement(buf, element)
 		if err != nil {
 			return err
 		}