package server import ( "bytes" "context" "github.com/go-kit/kit/metrics" "github.com/itzg/mc-router/mcproto" "github.com/juju/ratelimit" "github.com/sirupsen/logrus" "io" "net" "time" ) const ( handshakeTimeout = 5 * time.Second ) var noDeadline time.Time type Connector interface { StartAcceptingConnections(ctx context.Context, listenAddress string, connRateLimit int) error } type ConnectorMetrics struct { Errors metrics.Counter BytesTransmitted metrics.Counter Connections metrics.Counter ActiveConnections metrics.Gauge } func NewConnector(metrics *ConnectorMetrics) Connector { return &connectorImpl{ metrics: metrics, } } type connectorImpl struct { state mcproto.State metrics *ConnectorMetrics } func (c *connectorImpl) StartAcceptingConnections(ctx context.Context, listenAddress string, connRateLimit int) error { ln, err := net.Listen("tcp", listenAddress) if err != nil { logrus.WithError(err).Fatal("Unable to start listening") return err } logrus.WithField("listenAddress", listenAddress).Info("Listening for Minecraft client connections") go c.acceptConnections(ctx, ln, connRateLimit) return nil } func (c *connectorImpl) acceptConnections(ctx context.Context, ln net.Listener, connRateLimit int) { //noinspection GoUnhandledErrorResult defer ln.Close() bucket := ratelimit.NewBucketWithRate(float64(connRateLimit), int64(connRateLimit*2)) for { select { case <-ctx.Done(): return case <-time.After(bucket.Take(1)): conn, err := ln.Accept() if err != nil { logrus.WithError(err).Error("Failed to accept connection") } else { go c.HandleConnection(ctx, conn) } } } } func (c *connectorImpl) HandleConnection(ctx context.Context, frontendConn net.Conn) { c.metrics.Connections.With("side", "frontend").Add(1) //noinspection GoUnhandledErrorResult defer frontendConn.Close() clientAddr := frontendConn.RemoteAddr() logrus. WithField("client", clientAddr). Info("Got connection") defer logrus.WithField("client", clientAddr).Debug("Closing frontend connection") inspectionBuffer := new(bytes.Buffer) inspectionReader := io.TeeReader(frontendConn, inspectionBuffer) if err := frontendConn.SetReadDeadline(time.Now().Add(handshakeTimeout)); err != nil { logrus. WithError(err). WithField("client", clientAddr). Error("Failed to set read deadline") c.metrics.Errors.With("type", "read_deadline").Add(1) return } packet, err := mcproto.ReadPacket(inspectionReader, clientAddr, c.state) if err != nil { logrus.WithError(err).WithField("clientAddr", clientAddr).Error("Failed to read packet") c.metrics.Errors.With("type", "read").Add(1) return } logrus. WithField("client", clientAddr). WithField("length", packet.Length). WithField("packetID", packet.PacketID). Debug("Got packet") if packet.PacketID == mcproto.PacketIdHandshake { handshake, err := mcproto.ReadHandshake(packet.Data) if err != nil { logrus.WithError(err).WithField("clientAddr", clientAddr). Error("Failed to read handshake") c.metrics.Errors.With("type", "read").Add(1) return } logrus. WithField("client", clientAddr). WithField("handshake", handshake). Debug("Got handshake") serverAddress := handshake.ServerAddress c.findAndConnectBackend(ctx, frontendConn, clientAddr, inspectionBuffer, serverAddress) } else if packet.PacketID == mcproto.PacketIdLegacyServerListPing { handshake, ok := packet.Data.(*mcproto.LegacyServerListPing) if !ok { logrus. WithField("client", clientAddr). WithField("packet", packet). Warn("Unexpected data type for PacketIdLegacyServerListPing") c.metrics.Errors.With("type", "unexpected_content").Add(1) return } logrus. WithField("client", clientAddr). WithField("handshake", handshake). Debug("Got legacy server list ping") serverAddress := handshake.ServerAddress c.findAndConnectBackend(ctx, frontendConn, clientAddr, inspectionBuffer, serverAddress) } else { logrus. WithField("client", clientAddr). WithField("packetID", packet.PacketID). Error("Unexpected packetID, expected handshake") c.metrics.Errors.With("type", "unexpected_content").Add(1) return } } func (c *connectorImpl) findAndConnectBackend(ctx context.Context, frontendConn net.Conn, clientAddr net.Addr, preReadContent io.Reader, serverAddress string) { backendHostPort, resolvedHost := Routes.FindBackendForServerAddress(serverAddress) if backendHostPort == "" { logrus.WithField("serverAddress", serverAddress).Warn("Unable to find registered backend") c.metrics.Errors.With("type", "missing_backend").Add(1) return } logrus. WithField("client", clientAddr). WithField("server", serverAddress). WithField("backendHostPort", backendHostPort). Info("Connecting to backend") backendConn, err := net.Dial("tcp", backendHostPort) if err != nil { logrus. WithError(err). WithField("client", clientAddr). WithField("serverAddress", serverAddress). WithField("backend", backendHostPort). Warn("Unable to connect to backend") c.metrics.Errors.With("type", "backend_failed").Add(1) return } c.metrics.Connections.With("side", "backend", "host", resolvedHost).Add(1) c.metrics.ActiveConnections.Add(1) defer c.metrics.ActiveConnections.Add(-1) amount, err := io.Copy(backendConn, preReadContent) if err != nil { logrus.WithError(err).Error("Failed to write handshake to backend connection") c.metrics.Errors.With("type", "backend_failed").Add(1) return } logrus.WithField("amount", amount).Debug("Relayed handshake to backend") if err = frontendConn.SetReadDeadline(noDeadline); err != nil { logrus. WithError(err). WithField("client", clientAddr). Error("Failed to clear read deadline") c.metrics.Errors.With("type", "read_deadline").Add(1) return } c.pumpConnections(ctx, frontendConn, backendConn) return } func (c *connectorImpl) pumpConnections(ctx context.Context, frontendConn, backendConn net.Conn) { //noinspection GoUnhandledErrorResult defer backendConn.Close() clientAddr := frontendConn.RemoteAddr() defer logrus.WithField("client", clientAddr).Debug("Closing backend connection") errors := make(chan error, 2) go c.pumpFrames(backendConn, frontendConn, errors, "backend", "frontend", clientAddr) go c.pumpFrames(frontendConn, backendConn, errors, "frontend", "backend", clientAddr) select { case err := <-errors: if err != io.EOF { logrus.WithError(err). WithField("client", clientAddr). Error("Error observed on connection relay") c.metrics.Errors.With("type", "relay").Add(1) } case <-ctx.Done(): logrus.Debug("Observed context cancellation") } } func (c *connectorImpl) pumpFrames(incoming io.Reader, outgoing io.Writer, errors chan<- error, from, to string, clientAddr net.Addr) { amount, err := io.Copy(outgoing, incoming) logrus. WithField("client", clientAddr). WithField("amount", amount). Infof("Finished relay %s->%s", from, to) c.metrics.BytesTransmitted.Add(float64(amount)) if err != nil { errors <- err } else { // successful io.Copy return nil error, not EOF...to simulate that to trigger outer handling errors <- io.EOF } }