Add *Conn. CopyFromTextual, CopyToTextual, which use textual format for copying data

copy_done.go

@@ -0,0 +1,30 @@
+package pgproto3
+
+import (
+	"encoding/json"
+)
+
+type CopyDone struct {
+}
+
+func (*CopyDone) Backend() {}
+
+func (dst *CopyDone) Decode(src []byte) error {
+	if len(src) != 0 {
+		return &invalidMessageLenErr{messageType: "CopyDone", expectedLen: 0, actualLen: len(src)}
+	}
+
+	return nil
+}
+
+func (src *CopyDone) Encode(dst []byte) []byte {
+	return append(dst, 'c', 0, 0, 0, 4)
+}
+
+func (src *CopyDone) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+	}{
+		Type: "CopyDone",
+	})
+}