MessageWriter needs to be public for custom value transcoders

connection.go

@@ -267,11 +267,11 @@ func (c *Connection) Prepare(name, sql string) (err error) {
 	// parse
 	buf := c.getBuf()
 	w := newMessageWriter(buf)
-	w.writeCString(name)
-	w.writeCString(sql)
-	w.write(int16(0))
-	if w.err != nil {
-		return w.err
+	w.WriteCString(name)
+	w.WriteCString(sql)
+	w.Write(int16(0))
+	if w.Err != nil {
+		return w.Err
 	}
 	err = c.txMsg('P', buf)
 	if err != nil {
@@ -281,10 +281,10 @@ func (c *Connection) Prepare(name, sql string) (err error) {
 	// describe
 	buf = c.getBuf()
 	w = newMessageWriter(buf)
-	w.writeByte('S')
-	w.writeCString(name)
-	if w.err != nil {
-		return w.err
+	w.WriteByte('S')
+	w.WriteCString(name)
+	if w.Err != nil {
+		return w.Err
 	}
 
 	err = c.txMsg('D', buf)
@@ -371,18 +371,18 @@ func (c *Connection) sendPreparedQuery(ps *preparedStatement, arguments ...inter
 	// bind
 	buf := c.getBuf()
 	w := newMessageWriter(buf)
-	w.writeCString("")
-	w.writeCString(ps.Name)
-	w.write(int16(len(ps.ParameterOids)))
+	w.WriteCString("")
+	w.WriteCString(ps.Name)
+	w.Write(int16(len(ps.ParameterOids)))
 	for _, oid := range ps.ParameterOids {
 		transcoder := ValueTranscoders[oid]
 		if transcoder == nil {
 			transcoder = defaultTranscoder
 		}
-		w.write(transcoder.EncodeFormat)
+		w.Write(transcoder.EncodeFormat)
 	}
 
-	w.write(int16(len(arguments)))
+	w.Write(int16(len(arguments)))
 	for i, oid := range ps.ParameterOids {
 		transcoder := ValueTranscoders[oid]
 		if transcoder == nil {
@@ -391,17 +391,17 @@ func (c *Connection) sendPreparedQuery(ps *preparedStatement, arguments ...inter
 		transcoder.EncodeTo(w, arguments[i])
 	}
 
-	w.write(int16(len(ps.FieldDescriptions)))
+	w.Write(int16(len(ps.FieldDescriptions)))
 	for _, fd := range ps.FieldDescriptions {
 		transcoder := ValueTranscoders[fd.DataType]
 		if transcoder != nil && transcoder.DecodeBinary != nil {
-			w.write(int16(1))
+			w.Write(int16(1))
 		} else {
-			w.write(int16(0))
+			w.Write(int16(0))
 		}
 	}
-	if w.err != nil {
-		return w.err
+	if w.Err != nil {
+		return w.Err
 	}
 
 	err = c.txMsg('B', buf)
@@ -412,11 +412,11 @@ func (c *Connection) sendPreparedQuery(ps *preparedStatement, arguments ...inter
 	// execute
 	buf = c.getBuf()
 	w = newMessageWriter(buf)
-	w.writeCString("")
-	w.write(int32(0))
+	w.WriteCString("")
+	w.Write(int32(0))
 
-	if w.err != nil {
-		return w.err
+	if w.Err != nil {
+		return w.Err
 	}
 
 	err = c.txMsg('E', buf)

message_writer.go

@@ -5,46 +5,54 @@ import (
 	"encoding/binary"
 )
 
-type messageWriter struct {
+// MessageWriter is a helper for producing messages to send to PostgreSQL.
+// To avoid verbose error handling it internally records errors and no-ops
+// any calls that occur after an error. At the end of a sequence of writes
+// the Err field should be checked to see if any errors occurred.
+type MessageWriter struct {
 	buf *bytes.Buffer
-	err error
+	Err error
 }
 
-func newMessageWriter(buf *bytes.Buffer) *messageWriter {
-	return &messageWriter{buf: buf}
+func newMessageWriter(buf *bytes.Buffer) *MessageWriter {
+	return &MessageWriter{buf: buf}
 }
 
-func (w *messageWriter) writeCString(s string) {
-	if w.err != nil {
+// WriteCString writes a null-terminated string.
+func (w *MessageWriter) WriteCString(s string) {
+	if w.Err != nil {
 		return
 	}
-	if _, w.err = w.buf.WriteString(s); w.err != nil {
+	if _, w.Err = w.buf.WriteString(s); w.Err != nil {
 		return
 	}
-	w.err = w.buf.WriteByte(0)
+	w.Err = w.buf.WriteByte(0)
 }
 
-func (w *messageWriter) writeString(s string) {
-	if w.err != nil {
+// WriteString writes a string without a null terminator.
+func (w *MessageWriter) WriteString(s string) {
+	if w.Err != nil {
 		return
 	}
-	if _, w.err = w.buf.WriteString(s); w.err != nil {
+	if _, w.Err = w.buf.WriteString(s); w.Err != nil {
 		return
 	}
 }
 
-func (w *messageWriter) writeByte(b byte) {
-	if w.err != nil {
+func (w *MessageWriter) WriteByte(b byte) {
+	if w.Err != nil {
 		return
 	}
 
-	w.err = w.buf.WriteByte(b)
+	w.Err = w.buf.WriteByte(b)
 }
 
-func (w *messageWriter) write(data interface{}) {
-	if w.err != nil {
+// Write writes data in the network byte order. data can be an integer type,
+// float type, or byte slice.
+func (w *MessageWriter) Write(data interface{}) {
+	if w.Err != nil {
 		return
 	}
 
-	w.err = binary.Write(w.buf, binary.BigEndian, data)
+	w.Err = binary.Write(w.buf, binary.BigEndian, data)
 }

value_transcoder.go

@@ -15,7 +15,7 @@ type ValueTranscoder struct {
 	// DecodeBinary decodes values returned from the server in binary format
 	DecodeBinary func(*MessageReader, int32) interface{}
 	// EncodeTo encodes values to send to the server
-	EncodeTo func(*messageWriter, interface{})
+	EncodeTo func(*MessageWriter, interface{})
 	// EncodeFormat is the format values are encoded for transmission.
 	// 0 = text
 	// 1 = binary
@@ -112,13 +112,13 @@ func decodeBoolFromBinary(mr *MessageReader, size int32) interface{} {
 	return b != 0
 }
 
-func encodeBool(w *messageWriter, value interface{}) {
+func encodeBool(w *MessageWriter, value interface{}) {
 	v := value.(bool)
-	w.write(int32(1))
+	w.Write(int32(1))
 	if v {
-		w.writeByte(1)
+		w.WriteByte(1)
 	} else {
-		w.writeByte(0)
+		w.WriteByte(0)
 	}
 }
 
@@ -138,10 +138,10 @@ func decodeInt8FromBinary(mr *MessageReader, size int32) interface{} {
 	return mr.ReadInt64()
 }
 
-func encodeInt8(w *messageWriter, value interface{}) {
+func encodeInt8(w *MessageWriter, value interface{}) {
 	v := value.(int64)
-	w.write(int32(8))
-	w.write(v)
+	w.Write(int32(8))
+	w.Write(v)
 }
 
 func decodeInt2FromText(mr *MessageReader, size int32) interface{} {
@@ -160,10 +160,10 @@ func decodeInt2FromBinary(mr *MessageReader, size int32) interface{} {
 	return mr.ReadInt16()
 }
 
-func encodeInt2(w *messageWriter, value interface{}) {
+func encodeInt2(w *MessageWriter, value interface{}) {
 	v := value.(int16)
-	w.write(int32(2))
-	w.write(v)
+	w.Write(int32(2))
+	w.Write(v)
 }
 
 func decodeInt4FromText(mr *MessageReader, size int32) interface{} {
@@ -182,10 +182,10 @@ func decodeInt4FromBinary(mr *MessageReader, size int32) interface{} {
 	return mr.ReadInt32()
 }
 
-func encodeInt4(w *messageWriter, value interface{}) {
+func encodeInt4(w *MessageWriter, value interface{}) {
 	v := value.(int32)
-	w.write(int32(4))
-	w.write(v)
+	w.Write(int32(4))
+	w.Write(v)
 }
 
 func decodeFloat4FromText(mr *MessageReader, size int32) interface{} {
@@ -207,10 +207,10 @@ func decodeFloat4FromBinary(mr *MessageReader, size int32) interface{} {
 	return *(*float32)(p)
 }
 
-func encodeFloat4(w *messageWriter, value interface{}) {
+func encodeFloat4(w *MessageWriter, value interface{}) {
 	v := value.(float32)
-	w.write(int32(4))
-	w.write(v)
+	w.Write(int32(4))
+	w.Write(v)
 }
 
 func decodeFloat8FromText(mr *MessageReader, size int32) interface{} {
@@ -232,20 +232,20 @@ func decodeFloat8FromBinary(mr *MessageReader, size int32) interface{} {
 	return *(*float64)(p)
 }
 
-func encodeFloat8(w *messageWriter, value interface{}) {
+func encodeFloat8(w *MessageWriter, value interface{}) {
 	v := value.(float64)
-	w.write(int32(8))
-	w.write(v)
+	w.Write(int32(8))
+	w.Write(v)
 }
 
 func decodeTextFromText(mr *MessageReader, size int32) interface{} {
 	return mr.ReadByteString(size)
 }
 
-func encodeText(w *messageWriter, value interface{}) {
+func encodeText(w *MessageWriter, value interface{}) {
 	s := value.(string)
-	w.write(int32(len(s)))
-	w.writeString(s)
+	w.Write(int32(len(s)))
+	w.WriteString(s)
 }
 
 func decodeByteaFromText(mr *MessageReader, size int32) interface{} {
@@ -257,8 +257,8 @@ func decodeByteaFromText(mr *MessageReader, size int32) interface{} {
 	return b
 }
 
-func encodeBytea(w *messageWriter, value interface{}) {
+func encodeBytea(w *MessageWriter, value interface{}) {
 	b := value.([]byte)
-	w.write(int32(len(b)))
-	w.write(b)
+	w.Write(int32(len(b)))
+	w.Write(b)
 }