func (c *FrontendConnection) sendNotification(n *pq.Notification) error {
	var message fbcore.Message

	buf := &bytes.Buffer{}
	fbbuf.WriteInt32(buf, int32(n.BePid))
	fbbuf.WriteCString(buf, n.Channel)
	fbbuf.WriteCString(buf, n.Extra)
	message.InitFromBytes(fbproto.MsgNotificationResponseA, buf.Bytes())

	return c.WriteAndFlush(&message)
}
func (r trivialSelectResult) Respond(f Frontend) error {
	var msg fbcore.Message

	buf := &bytes.Buffer{}
	fbbuf.WriteInt16(buf, 1)
	fbbuf.WriteInt32(buf, 1)
	buf.WriteByte('1')
	msg.InitFromBytes(fbproto.MsgDataRowD, buf.Bytes())
	err := f.WriteMessage(&msg)
	if err != nil {
		return err
	}
	return commandComplete("SELECT").Respond(f)
}
func (c *FrontendConnection) auth(dbcfg VirtualDatabaseConfiguration, sm *fbproto.StartupMessage) bool {
	authFailed := func(sqlstate, format string, v ...interface{}) bool {
		var msg fbcore.Message
		message := fmt.Sprintf(format, v...)
		initFatalMessage(&msg, sqlstate, message)
		_ = c.WriteMessage(&msg)
		_ = c.FlushStream()
		return false
	}

	username, ok := sm.Params["user"]
	if !ok {
		return authFailed("08P01", `required startup parameter "user" nor present in startup packet`)
	}
	dbname, ok := sm.Params["database"]
	if !ok {
		dbname = username
	}
	authMethod, ok := dbcfg.FindDatabase(dbname)
	if !ok {
		return authFailed("3D000", "database %q does not exist", dbname)
	}

	switch authMethod {
	case "trust":
		return true
	case "md5":
		// handled below
	default:
		elog.Errorf("unrecognized authentication method %q", authMethod)
		return authFailed("XX000", "internal error")
	}

	salt := make([]byte, 4)
	_, err := rand.Read(salt)
	if err != nil {
		elog.Errorf("could not generate random salt: %s", err)
		return authFailed("XX000", "internal error")
	}

	var msg fbcore.Message
	buf := &bytes.Buffer{}
	fbbuf.WriteInt32(buf, 5)
	buf.Write(salt)
	msg.InitFromBytes(fbproto.MsgAuthenticationMD5PasswordR, buf.Bytes())
	err = c.WriteAndFlush(&msg)
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}
	err = c.stream.Next(&msg)
	if err == io.EOF {
		elog.Debugf("EOF during startup sequence")
		return false
	} else if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}
	if msg.MsgType() != fbproto.MsgPasswordMessageP {
		return authFailed("08P01", "unexpected response %x", msg.MsgType())
	}
	// don't bother with messages which are clearly too big
	if msg.Size() > 100 {
		return authFailed("28001", "password authentication failed for user %q", username)
	}
	password, err := msg.Force()
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}
	success, err := dbcfg.MD5Auth(dbname, username, salt, password)
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}
	if !success {
		return authFailed("28001", "password authentication failed for user %q", username)
	}
	return true
}