add minecraft server monitor

cmd/servermon/main.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/peterbourgon/ff/v3"
+	"github.com/spacechunks/explorer/servermon"
+)
+
+func main() {
+	var (
+		logger                   = slog.New(slog.NewJSONHandler(os.Stdout, nil))
+		ctx, cancel              = context.WithCancel(context.Background())
+		fs                       = flag.NewFlagSet("servermon", flag.ContinueOnError)
+		playerCountCheckInterval = fs.Duration("player-count-check-interval", 2*time.Minute, "in what interval the player count of the server will be checked")                       //nolint:lll
+		mgmtEndpoint             = fs.String("mc-server-management-api-endpoint", "http://localhost:26656", "the endpoint at which the minecraft server management api is available") //nolint:lll
+		mgmtAPIToken             = fs.String("mc-server-management-api-token", "", "token to use for the minecraft server management api")                                            //nolint:lll
+	)
+
+	if err := ff.Parse(fs, os.Args[1:],
+		ff.WithEnvVarPrefix("SERVERMON"),
+		ff.WithConfigFileFlag("config"),
+		ff.WithConfigFileParser(ff.JSONParser),
+	); err != nil {
+		logger.ErrorContext(ctx, "failed to parse config", "err", err)
+		os.Exit(1)
+	}
+
+	var (
+		cfg = servermon.Config{
+			PlayerCountCheckInterval:      *playerCountCheckInterval,
+			MCServerManagementAPIEndpoint: *mgmtEndpoint,
+			MCServerManagementAPIToken:    *mgmtAPIToken,
+		}
+		mon = servermon.New(logger, cfg)
+	)
+
+	go func() {
+		c := make(chan os.Signal, 1)
+		signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)
+		s := <-c
+		logger.Info("received shutdown signal", "signal", s.String())
+		cancel()
+	}()
+
+	if err := mon.Run(ctx); err != nil {
+		logger.ErrorContext(ctx, "error running servermon", "err", err)
+		os.Exit(1)
+	}
+}

servermon/monitor.go

@@ -0,0 +1,84 @@
+package servermon
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"time"
+
+	gorilla "github.com/gorilla/websocket"
+	"github.com/sourcegraph/jsonrpc2"
+	"github.com/sourcegraph/jsonrpc2/websocket"
+)
+
+type Config struct {
+	PlayerCountCheckInterval      time.Duration
+	MCServerManagementAPIEndpoint string
+	MCServerManagementAPIToken    string
+}
+
+type Monitor struct {
+	logger *slog.Logger
+	conf   Config
+}
+
+func New(logger *slog.Logger, cfg Config) Monitor {
+	return Monitor{
+		logger: logger,
+		conf:   cfg,
+	}
+}
+
+type player struct {
+	ID   string `json:"id"`
+	Name string `json:"name"`
+}
+
+func (m Monitor) Run(ctx context.Context) error {
+	wsConn, _, err := gorilla.DefaultDialer.Dial(m.conf.MCServerManagementAPIEndpoint, map[string][]string{
+		"Authorization": {"Bearer " + m.conf.MCServerManagementAPIToken},
+	})
+	if err != nil {
+		return fmt.Errorf("dial: %w", err)
+	}
+
+	rpcConn := jsonrpc2.NewConn(ctx, websocket.NewObjectStream(wsConn), &m)
+	defer rpcConn.Close()
+
+	listTicker := time.NewTicker(1 * time.Second)
+	defer listTicker.Stop()
+
+	checkTicker := time.NewTicker(m.conf.PlayerCountCheckInterval)
+	defer checkTicker.Stop()
+
+	joined := false
+
+	for {
+		select {
+		case <-listTicker.C:
+			players := make([]player, 0)
+
+			if err := rpcConn.Call(ctx, "minecraft:players", nil, &players); err != nil {
+				return fmt.Errorf("call players: %w", err)
+			}
+
+			if len(players) > 0 {
+				joined = true
+			}
+		case <-checkTicker.C:
+			if joined {
+				m.logger.Info("JOINED")
+				joined = false
+			} else {
+				m.logger.Info("KILL")
+			}
+
+		case <-ctx.Done():
+			return nil
+		}
+	}
+}
+
+// Handle is present, because jsonrpc2 crashes if we pass a nil handler to jsonrpc2.NewConn
+// and receive a message afterward.
+func (m Monitor) Handle(_ context.Context, _ *jsonrpc2.Conn, _ *jsonrpc2.Request) {}