feat: implement logreceiver for kernel logs

Related to: siderolabs/sidero#527

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

cmd/siderolink-agent/log_receiver.go

@@ -0,0 +1,46 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package main
+
+import (
+	"context"
+
+	"go.uber.org/zap"
+	"golang.org/x/sync/errgroup"
+	"inet.af/netaddr"
+
+	"github.com/talos-systems/siderolink/pkg/logreceiver"
+)
+
+var logReceiverFlags struct {
+	endpoint string
+}
+
+func logHandler(logger *zap.Logger) logreceiver.Handler {
+	return func(srcAddress netaddr.IP, msg map[string]interface{}) {
+		logger.Info("kernel log message", zap.Stringer("src_address", srcAddress), zap.Any("msg", msg))
+	}
+}
+
+func logReceiver(ctx context.Context, eg *errgroup.Group, logger *zap.Logger) error {
+	srv, err := logreceiver.NewServer(logger, logReceiverFlags.endpoint, logHandler(logger))
+	if err != nil {
+		return err
+	}
+
+	eg.Go(func() error {
+		return srv.Serve()
+	})
+
+	eg.Go(func() error {
+		<-ctx.Done()
+
+		srv.Stop()
+
+		return nil
+	})
+
+	return nil
+}

cmd/siderolink-agent/main.go

@@ -21,6 +21,7 @@ func main() {
 	flag.StringVar(&sideroLinkFlags.wireguardEndpoint, "sidero-link-wireguard-endpoint", "172.20.0.1:51821", "advertised Wireguard endpoint")
 	flag.StringVar(&sideroLinkFlags.apiEndpoint, "sidero-link-api-endpoint", ":4000", "gRPC API endpoint for the SideroLink")
 	flag.StringVar(&eventSinkFlags.apiEndpoint, "event-sink-endpoint", ":8080", "gRPC API endpoint for the Event Sink")
+	flag.StringVar(&logReceiverFlags.endpoint, "log-receiver-endpoint", ":4001", "TCP log receiver endpoint")
 	flag.Parse()
 
 	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
@@ -44,7 +45,11 @@ func run(ctx context.Context) error {
 	}
 
 	if err := eventSink(ctx, eg); err != nil {
-		return fmt.Errorf("SideroLink: %w", err)
+		return fmt.Errorf("event sink: %w", err)
+	}
+
+	if err := logReceiver(ctx, eg, logger); err != nil {
+		return fmt.Errorf("log receiver: %w", err)
 	}
 
 	if err := eg.Wait(); err != nil && !errors.Is(err, grpc.ErrServerStopped) {

pkg/logreceiver/logreceiver.go

@@ -0,0 +1,6 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// Package logreceiver implements JSON-over-TCP log receiver.
+package logreceiver

pkg/logreceiver/server.go

@@ -0,0 +1,90 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package logreceiver
+
+import (
+	"bufio"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+
+	"go.uber.org/zap"
+	"inet.af/netaddr"
+)
+
+// Server implements TCP server to receive JSON logs.
+type Server struct {
+	listener net.Listener
+	logger   *zap.Logger
+	handler  Handler
+}
+
+// Handler is called for each received message.
+type Handler func(srcAddress netaddr.IP, msg map[string]interface{})
+
+// NewServer initializes new Server and starts listening.
+func NewServer(logger *zap.Logger, listenAddress string, handler Handler) (*Server, error) {
+	lis, err := net.Listen("tcp", listenAddress)
+	if err != nil {
+		return nil, fmt.Errorf("error listening: %w", err)
+	}
+
+	return &Server{
+		listener: lis,
+		logger:   logger,
+		handler:  handler,
+	}, nil
+}
+
+// Serve runs the TCP server loop.
+func (srv *Server) Serve() error {
+	for {
+		conn, err := srv.listener.Accept()
+		if err != nil {
+			return fmt.Errorf("error accepting connection: %w", err)
+		}
+
+		go srv.handleConnection(conn)
+	}
+}
+
+// Stop serving.
+//
+// This has a bug that it doesn't close the connections.
+func (srv *Server) Stop() {
+	srv.listener.Close() //nolint:errcheck
+}
+
+func (srv *Server) handleConnection(conn net.Conn) {
+	defer conn.Close() //nolint:errcheck
+
+	bufReader := bufio.NewReader(conn)
+	decoder := json.NewDecoder(bufReader)
+
+	srcAddr, ok := conn.RemoteAddr().(*net.TCPAddr)
+	if !ok {
+		srv.logger.Error("error getting remote IP address")
+
+		return
+	}
+
+	srcAddress, _ := netaddr.FromStdIP(srcAddr.IP)
+
+	for {
+		msg := map[string]interface{}{}
+
+		if err := decoder.Decode(&msg); err != nil {
+			if !errors.Is(err, net.ErrClosed) && !errors.Is(err, io.EOF) {
+				srv.logger.Error("error decoding message", zap.Error(err))
+			}
+
+			return
+		}
+
+		srv.handler(srcAddress, msg)
+	}
+}