func (s *sniffingRouter) RouteBackend() error {
	// route the next message from backend to frotnend,
	// blocking and flushing if necessary
	err := s.be.Next(&s.beBuf)
	if err != nil {
		return err
	}
	if proto.IsBackendKeyData(&s.beBuf) {
		beInfo, err := proto.ReadBackendKeyData(&s.beBuf)
		if err != nil {
			return err
		}
		s.backendPid = beInfo.BackendPid
		s.secretKey = beInfo.SecretKey
	}

	var clone core.Message
	clone.InitFromMessage(&s.beBuf)
	s.beCh <- &clone

	err = s.fe.Send(&s.beBuf)
	if !s.be.HasNext() {
		return s.fe.Flush()
	}
	return nil
}

func RejectFrontendConnection(c net.Conn) {
	var message fbcore.Message
	initFatalMessage(&message, "57A01", "no server connection available")

	_, _ = message.WriteTo(c)
	_ = c.Close()
}

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 initFatalMessage(message *fbcore.Message, sqlstate, errorMessage string) {
	buf := &bytes.Buffer{}
	buf.WriteByte('S')
	fbbuf.WriteCString(buf, "FATAL")
	buf.WriteByte('C')
	fbbuf.WriteCString(buf, sqlstate)
	buf.WriteByte('M')
	fbbuf.WriteCString(buf, errorMessage)
	buf.WriteByte('\x00')

	message.InitFromBytes(fbproto.MsgErrorResponseE, buf.Bytes())
}

func (c *FrontendConnection) readExecuteMessage(msg *fbcore.Message) error {
	statementName, err := fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return err
	}
	if statementName != "" {
		return fmt.Errorf("attempted to use statement name %q; only unnamed statements are supported")
	}
	// ignore maxRowCount
	_, err = fbbuf.ReadInt32(msg.Payload())
	// TODO: ensure we're at the end of the packet
	return err
}

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) readBindMessage(msg *fbcore.Message) error {
	portalName, err := fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return err
	}
	if portalName != "" {
		return fmt.Errorf("attempted to bind to a named portal %q; only the unnamed portal is supported")
	}
	statementName, err := fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return err
	}
	if statementName != "" {
		return fmt.Errorf("attempted to bind statement %q, even though it has not been parsed yet", statementName)
	}
	numParamFormats, err := fbbuf.ReadInt16(msg.Payload())
	if err != nil {
		return err
	}
	if numParamFormats != 0 {
		return fmt.Errorf("the number of parameter formats (%d) does not match the number of parameters in the query (0)", numParamFormats)
	}
	numParameters, err := fbbuf.ReadInt16(msg.Payload())
	if err != nil {
		return err
	}
	if numParameters != 0 {
		return fmt.Errorf("the number of parameters provided by the client (%d) does not match the number of parameters in the query (0)", numParameters)
	}
	// TODO: ensure we're at the end of the packet
	return nil
}

func (c *FrontendConnection) readDescribeMessage(msg *fbcore.Message) (byte, error) {
	typ, err := fbbuf.ReadByte(msg.Payload())
	if err != nil {
		return 0, err
	}
	if typ != 'S' && typ != 'P' {
		return 0, fmt.Errorf("invalid type %q", typ)
	}
	statementName, err := fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return 0, err
	}
	if statementName != "" {
		return 0, fmt.Errorf("tried to use statement/portal name %q; only unnamed statements and portals are supported")
	}
	// TODO: ensure we're at the end of the packet
	return typ, nil
}

func (s *sniffingRouter) RouteFrontend() (err error) {
	// route the next message from frontend to backend,
	// blocking and flushing if necessary
	err = s.fe.Next(&s.feBuf)
	if err != nil {
		return
	}

	var clone core.Message
	clone.InitFromMessage(&s.feBuf)
	s.feCh <- &clone

	err = s.be.Send(&s.feBuf)
	if err != nil {
		return
	}
	if !s.fe.HasNext() {
		return s.be.Flush()
	}
	return
}

// Process a log message, sending it to the client.
func processLogMsg(die dieCh, primary *logplexc.Client, audit *logplexc.Client,
	msgInit msgInit, sr *serveRecord, exit exitFn) {
	var m core.Message

	for {
		// Poll request to exit
		select {
		case <-die:
			return
		default:
			break
		}

		msgInit(&m, exit)

		// Refuse to handle any log message above an arbitrary
		// size.  Furthermore, exit the worker, closing the0
		// connection, so that the client doesn't even bother
		// to wait for this process to drain the oversized
		// item and anything following it; these will be
		// dropped.  It's on the client to gracefully handle
		// the error and re-connect after this happens.
		if m.Size() > 1*MB {
			exit("client %q sent oversized log record")
		}

		payload, err := m.Force()
		if err != nil {
			exit("could not retrieve payload of message: %v",
				err)
		}

		var lr logRecord
		parseLogRecord(&lr, payload, exit)
		routeLogRecord(&lr, primary, audit, sr, exit)
	}
}

func (c *FrontendConnection) discardUntilSync() error {
	var message fbcore.Message

	for {
		err := c.stream.Next(&message)
		if err != nil {
			return err
		}

		switch message.MsgType() {
		case fbproto.MsgSyncS:
			_, err = message.Force()
			return nil
		default:
			_, err = message.Force()
		}
		if err != nil {
			return err
		}
	}
}

func (c *FrontendConnection) readParseMessage(msg *fbcore.Message) (queryString string, err error) {
	statementName, err := fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return "", err
	}
	if statementName != "" {
		return "", fmt.Errorf("attempted to use statement name %q; only unnamed statements are supported")
	}
	queryString, err = fbbuf.ReadCString(msg.Payload())
	if err != nil {
		return "", err
	}
	numParamTypes, err := fbbuf.ReadInt16(msg.Payload())
	if err != nil {
		return "", err
	}
	if numParamTypes != 0 {
		return "", fmt.Errorf("attempted to prepare a statement with %d param types", numParamTypes)
	}
	// TODO: ensure we're at the end of the packet
	return queryString, nil
}

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
}

// This is the main loop for processing messages from the frontend.  Note that
// we must *never* send anything directly to the connection; all communication
// must go through queryResultCh.  We're also not responsible for doing any
// cleanup in any case; that'll all be handled by mainLoop.
func (c *FrontendConnection) queryProcessingMainLoop() {
	var unnamedStatement FrontendQuery

	var queryResult QueryResult
	var sendReadyForQuery bool

sessionLoop:
	for {
		var message fbcore.Message

		err := c.stream.Next(&message)
		if err != nil {
			c.setSessionError(err)
			break sessionLoop
		}

		queryResult = nil
		sendReadyForQuery = false

		switch message.MsgType() {
		case fbproto.MsgParseP:
			queryString, err := c.readParseMessage(&message)
			if err != nil {
				c.setSessionError(err)
				break sessionLoop
			}
			unnamedStatement, err = ParseQuery(queryString)
			if err != nil {
				queryResult = NewErrorResponse("42601", err.Error())
				c.queryResultCh <- queryResultSync{queryResult, false}

				err = c.discardUntilSync()
				if err != nil {
					c.setSessionError(err)
					break sessionLoop
				}

				queryResult = NewNopResponder()
				sendReadyForQuery = true
			} else {
				queryResult = NewParseComplete()
				sendReadyForQuery = false
			}

		case fbproto.MsgExecuteE:
			err = c.readExecuteMessage(&message)
			if unnamedStatement == nil {
				err = fmt.Errorf("attempted to execute the unnamed prepared statement when one does not exist")
				c.setSessionError(err)
				break sessionLoop
			}
			queryResult, err = unnamedStatement.Process(c)
			if err != nil {
				c.setSessionError(err)
				break sessionLoop
			}
			sendReadyForQuery = false
			// Disallow reuse; not exactly following the protocol to the letter,
			// but apps reusing the unnamed statement should not exist, either.
			unnamedStatement = nil

		case fbproto.MsgDescribeD:
			_, err = c.readDescribeMessage(&message)
			if err != nil {
				c.setSessionError(err)
				break sessionLoop
			}
			if unnamedStatement == nil {
				err = fmt.Errorf("attempted to describe the unnamed prepared statement when one does not exist")
				c.setSessionError(err)
				break sessionLoop
			}
			queryResult = unnamedStatement.Describe()
			sendReadyForQuery = false

		case fbproto.MsgBindB:
			err = c.readBindMessage(&message)
			if err != nil {
				c.setSessionError(err)
				break sessionLoop
			}
			queryResult = NewBindComplete()
			sendReadyForQuery = false

		case fbproto.MsgSyncS:
			queryResult = NewNopResponder()
			sendReadyForQuery = true

		case fbproto.MsgQueryQ:
			query, err := fbproto.ReadQuery(&message)
			if err != nil {
				c.setSessionError(err)
				break sessionLoop
			}
			q, err := ParseQuery(query.Query)
			if err != nil {
//.........这里部分代码省略.........

func (c *FrontendConnection) startup(startupParameters map[string]string, dbcfg VirtualDatabaseConfiguration) bool {
	var message fbcore.Message
	var err error

	for {
		err = c.stream.Next(&message)
		if err != nil {
			elog.Logf("error while reading startup packet: %s", err)
			return false
		}
		if fbproto.IsStartupMessage(&message) {
			break
		} else if fbproto.IsSSLRequest(&message) {
			_, err = message.Force()
			if err != nil {
				elog.Logf("error while reading SSLRequest: %s", err)
				return false
			}
			err = c.stream.SendSSLRequestResponse(fbcore.RejectSSLRequest)
			if err != nil {
				elog.Logf("error during startup sequence: %s", err)
				return false
			}
			err = c.FlushStream()
			if err != nil {
				elog.Logf("error during startup sequence: %s", err)
			}
		} else if fbproto.IsCancelRequest(&message) {
			_ = c.stream.Close()
			return false
		} else {
			elog.Warningf("unrecognized frontend message type 0x%x during startup", message.MsgType())
			return false
		}
	}
	sm, err := fbproto.ReadStartupMessage(&message)
	if err != nil {
		elog.Logf("error while reading startup packet: %s", err)
		return false
	}

	if !c.auth(dbcfg, sm) {
		// error already logged
		_ = c.stream.Close()
		return false
	}

	fbproto.InitAuthenticationOk(&message)
	err = c.WriteMessage(&message)
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}

	for k, v := range startupParameters {
		buf := &bytes.Buffer{}
		fbbuf.WriteCString(buf, k)
		fbbuf.WriteCString(buf, v)
		message.InitFromBytes(fbproto.MsgParameterStatusS, buf.Bytes())
		err = c.WriteMessage(&message)
		if err != nil {
			elog.Logf("error during startup sequence: %s", err)
			return false
		}
	}

	fbproto.InitReadyForQuery(&message, fbproto.RfqIdle)
	err = c.WriteMessage(&message)
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}

	err = c.FlushStream()
	if err != nil {
		elog.Logf("error during startup sequence: %s", err)
		return false
	}
	return true
}

// Process the identity ('I') message, reporting the identity therein.
func processIdentMsg(msgInit msgInit, exit exitFn) string {
	var m core.Message

	msgInit(&m, exit)

	// Read the remote system identifier string
	if m.MsgType() != 'I' {
		exit("expected identification ('I') message, "+
			"but received %c", m.MsgType())
	}

	// hard-coded lengh limit, but it's very generous
	if m.Size() > 10*KB {
		log.Printf("oversized message string, msg size is %d",
			m.Size())
	}

	s, err := buf.ReadCString(m.Payload())
	if err != nil {
		exit("couldn't read identification string: %v",
			err)
	}

	return s
}

// Read the version message, calling exit if this is not a supported
// version.
func processVerMsg(msgInit msgInit, exit exitFn) {
	var m core.Message

	msgInit(&m, exit)

	if m.MsgType() != 'V' {
		exit("expected version ('V') message, "+
			"but received %c", m.MsgType())
	}

	// hard-coded lengh limit, but it's very generous
	if m.Size() > 10*KB {
		log.Printf("oversized message string, msg size is %d",
			m.Size())
	}

	s, err := buf.ReadCString(m.Payload())
	if err != nil {
		exit("couldn't read version string: %v", err)
	}

	if !(strings.HasPrefix(s, "PG-9.0") ||
		strings.HasPrefix(s, "PG-9.1") ||
		strings.HasPrefix(s, "PG-9.2") ||
		strings.HasPrefix(s, "PG-9.3") ||
		strings.HasPrefix(s, "PG-9.4") ||
		strings.HasPrefix(s, "PG-9.5")) ||
		!strings.HasSuffix(s, "/logfebe-1") {
		exit("protocol version not supported: %s", s)
	}
}