jackc/pgx · error

unknown message type: %c

Error message

unknown message type: %c

What it means

The frontend received a message from the server with a type byte not defined in the PostgreSQL protocol. The %c shows the unknown type character. Likely a non-PostgreSQL server or corrupted stream.

Solutions

1. Confirm you are connecting to a PostgreSQL server
2. Check port number — connecting to a non-PostgreSQL service produces this
3. Inspect for middleboxes altering traffic
4. Reconnect to rule out transient corruption

When it happens

Trigger: Thrown at pgproto3/frontend.go:394 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jackc/pgx@ec1a0befd2 (2026-08-04). Data as JSON: /api/errors/f223bd7013bcb100. Report an issue: GitHub.

Appendix: source

Thrown at pgproto3/frontend.go:394

		}
	case 's':
		msg = &f.portalSuspended
	case 'S':
		msg = &f.parameterStatus
	case 't':
		msg = &f.parameterDescription
	case 'T':
		msg = &f.rowDescription
	case 'V':
		msg = &f.functionCallResponse
	case 'W':
		msg = &f.copyBothResponse
	case 'Z':
		msg = &f.readyForQuery
	case 'v':
		msg = &f.negotiateProtocolVersion
	default:
		return nil, fmt.Errorf("unknown message type: %c", f.msgType)
	}

	err = msg.Decode(msgBody)
	if err != nil {
		return nil, err
	}

	if f.tracer != nil {
		f.tracer.traceMessage('B', int32(5+len(msgBody)), msg)
	}

	return msg, nil
}

// Authentication message type constants.
// See src/include/libpq/pqcomm.h for all
// constants.
const (

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