Started refactor to messageWriter

connection.go

@@ -219,27 +219,13 @@ func (c *Connection) SelectValues(sql string, arguments ...interface{}) (values
 func (c *Connection) Prepare(name, sql string) (err error) {
 	// parse
 	buf := c.getBuf()
-	_, err = buf.WriteString(name)
-	if err != nil {
-		return
+	w := newMessageWriter(buf)
+	w.writeStringNull(name)
+	w.writeStringNull(sql)
+	w.write(int16(0))
+	if w.err != nil {
+		return w.err
 	}
-	err = buf.WriteByte(0)
-	if err != nil {
-		return
-	}
-	_, err = buf.WriteString(sql)
-	if err != nil {
-		return
-	}
-	err = buf.WriteByte(0)
-	if err != nil {
-		return
-	}
-	err = binary.Write(buf, binary.BigEndian, int16(0))
-	if err != nil {
-		return
-	}
-
 	err = c.txMsg('P', buf)
 	if err != nil {
 		return
@@ -247,18 +233,9 @@ func (c *Connection) Prepare(name, sql string) (err error) {
 
 	// describe
 	buf = c.getBuf()
-	err = buf.WriteByte('S')
-	if err != nil {
-		return
-	}
-	_, err = buf.WriteString(name)
-	if err != nil {
-		return
-	}
-	err = buf.WriteByte(0)
-	if err != nil {
-		return
-	}
+	w = newMessageWriter(buf)
+	w.writeByte('S')
+	w.writeStringNull(name)
 
 	err = c.txMsg('D', buf)
 	if err != nil {

message_writer.go

@@ -0,0 +1,41 @@
+package pgx
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+type messageWriter struct {
+	buf *bytes.Buffer
+	err error
+}
+
+func newMessageWriter(buf *bytes.Buffer) *messageWriter {
+	return &messageWriter{buf: buf}
+}
+
+func (w *messageWriter) writeStringNull(s string) {
+	if w.err != nil {
+		return
+	}
+	if _, w.err = w.buf.WriteString(s); w.err != nil {
+		return
+	}
+	w.err = w.buf.WriteByte(0)
+}
+
+func (w *messageWriter) writeByte(b byte) {
+	if w.err != nil {
+		return
+	}
+
+	w.err = w.buf.WriteByte(b)
+}
+
+func (w *messageWriter) write(data interface{}) {
+	if w.err != nil {
+		return
+	}
+
+	w.err = binary.Write(w.buf, binary.BigEndian, data)
+}