| Value | Meaning |
|---|---|
| Authentication'R' | |
| BackendKeyData'K' | |
| BindComplete'2' | |
| CloseComplete'3' | |
| CommandComplete'C' | |
| CopyData'd' | |
| CopyDone'c' | |
| CopyInResponse'G' | |
| CopyOutResponse'H' | |
| CopyBothResponse'W' | |
| DataRow'D' | |
| EmptyQueryResponse'I' | |
| ErrorResponse'E' | |
| FunctionCallResponse'V' | |
| NoData'n' | |
| NoticeResponse'N' | |
| NotificationResponse'A' | |
| ParameterDescription't' | |
| ParameterStatus'S' | |
| ParseComplete'1' | |
| PortalSuspended's' | |
| ReadyForQuery'Z' | |
| RowDescription'T' |
https://www.postgresql.org/docs/9.5/static/protocol-message-formats.html