Introduce pgproto3 package

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

query.go

@@ -0,0 +1,43 @@
+package pgproto3
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+type Query struct {
+	String string
+}
+
+func (*Query) Frontend() {}
+
+func (dst *Query) UnmarshalBinary(src []byte) error {
+	i := bytes.IndexByte(src, 0)
+	if i != len(src)-1 {
+		return &invalidMessageFormatErr{messageType: "Query"}
+	}
+
+	dst.String = string(src[:i])
+
+	return nil
+}
+
+func (src *Query) MarshalBinary() ([]byte, error) {
+	var bigEndian BigEndianBuf
+	buf := &bytes.Buffer{}
+	buf.WriteByte('Q')
+	buf.Write(bigEndian.Uint32(uint32(4 + len(src.String) + 1)))
+	buf.WriteString(src.String)
+	buf.WriteByte(0)
+	return buf.Bytes(), nil
+}
+
+func (src *Query) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type   string
+		String string
+	}{
+		Type:   "Query",
+		String: src.String,
+	})
+}