Introduce pgproto3 package

pgproto3 will wrap the message encoding and decoding for the PostgreSQL
frontend/backend protocol version 3.

copy_data.go

@@ -0,0 +1,41 @@
+package pgproto3
+
+import (
+	"bytes"
+	"encoding/hex"
+	"encoding/json"
+)
+
+type CopyData struct {
+	Data []byte
+}
+
+func (*CopyData) Backend()  {}
+func (*CopyData) Frontend() {}
+
+func (dst *CopyData) UnmarshalBinary(src []byte) error {
+	dst.Data = make([]byte, len(src))
+	copy(dst.Data, src)
+	return nil
+}
+
+func (src *CopyData) MarshalBinary() ([]byte, error) {
+	var bigEndian BigEndianBuf
+	buf := &bytes.Buffer{}
+
+	buf.WriteByte('d')
+	buf.Write(bigEndian.Uint32(uint32(4 + len(src.Data))))
+	buf.Write(src.Data)
+
+	return buf.Bytes(), nil
+}
+
+func (src *CopyData) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Data string
+	}{
+		Type: "CopyData",
+		Data: hex.EncodeToString(src.Data),
+	})
+}