Introduce pgproto3 package

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

backend_key_data.go

@@ -0,0 +1,47 @@
+package pgproto3
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+)
+
+type BackendKeyData struct {
+	ProcessID uint32
+	SecretKey uint32
+}
+
+func (*BackendKeyData) Backend() {}
+
+func (dst *BackendKeyData) UnmarshalBinary(src []byte) error {
+	if len(src) != 8 {
+		return &invalidMessageLenErr{messageType: "BackendKeyData", expectedLen: 8, actualLen: len(src)}
+	}
+
+	dst.ProcessID = binary.BigEndian.Uint32(src[:4])
+	dst.SecretKey = binary.BigEndian.Uint32(src[4:])
+
+	return nil
+}
+
+func (src *BackendKeyData) MarshalBinary() ([]byte, error) {
+	var bigEndian BigEndianBuf
+	buf := &bytes.Buffer{}
+	buf.WriteByte('K')
+	buf.Write(bigEndian.Uint32(12))
+	buf.Write(bigEndian.Uint32(src.ProcessID))
+	buf.Write(bigEndian.Uint32(src.SecretKey))
+	return buf.Bytes(), nil
+}
+
+func (src *BackendKeyData) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type      string
+		ProcessID uint32
+		SecretKey uint32
+	}{
+		Type:      "BackendKeyData",
+		ProcessID: src.ProcessID,
+		SecretKey: src.SecretKey,
+	})
+}