Introduce pgproto3 package

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

ready_for_query.go

@@ -0,0 +1,35 @@
+package pgproto3
+
+import (
+	"encoding/json"
+)
+
+type ReadyForQuery struct {
+	TxStatus byte
+}
+
+func (*ReadyForQuery) Backend() {}
+
+func (dst *ReadyForQuery) UnmarshalBinary(src []byte) error {
+	if len(src) != 1 {
+		return &invalidMessageLenErr{messageType: "ReadyForQuery", expectedLen: 1, actualLen: len(src)}
+	}
+
+	dst.TxStatus = src[0]
+
+	return nil
+}
+
+func (src *ReadyForQuery) MarshalBinary() ([]byte, error) {
+	return []byte{'Z', 0, 0, 0, 5, src.TxStatus}, nil
+}
+
+func (src *ReadyForQuery) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type     string
+		TxStatus string
+	}{
+		Type:     "ReadyForQuery",
+		TxStatus: string(src.TxStatus),
+	})
+}