Megalodon: manage ARK servers over RCON from a web dashboard

Watches any number of ARK:SE servers (RCON for players and chat, the query
port for map, version and player cap), records joins, leaves, chat and an
audit trail, and keeps a player database across servers.

Control: save, broadcast, chat, whisper, kick, time of day, MOTD, wild dino
wipe, a raw console with history and macros, restarts with timed warnings and
a world save, optional start command and auto-start. Bans are kept by
Megalodon: timed, cluster-wide and re-enforced when the player returns.

Automation: schedules (every N or at times of day), Discord/ntfy/webhook
notifications, welcome message, chat word filter.

Access: viewer, moderator and admin roles, API tokens, Prometheus metrics.
cmd/fakeark simulates a server for trying it out.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ark/query.go

@@ -0,0 +1,92 @@
+package ark
+
+import (
+	"bytes"
+	"errors"
+	"net"
+	"regexp"
+	"time"
+)
+
+// Info is what a server tells the Steam server browser (A2S_INFO).
+type Info struct {
+	Name       string `json:"name"`
+	Map        string `json:"map"`
+	Game       string `json:"game"`
+	Version    string `json:"version,omitempty"`
+	Players    int    `json:"players"`
+	MaxPlayers int    `json:"max_players"`
+	PingMS     int64  `json:"ping_ms"`
+}
+
+var a2sRequest = []byte("\xff\xff\xff\xffTSource Engine Query\x00")
+
+// ARK puts its version in the server name: "My Server - (v349.7)".
+var nameVersion = regexp.MustCompile(`\(v(\d+(?:\.\d+)*)\)`)
+
+// Query asks the game's query port (UDP, usually 27015) who is on the server, without needing the
+// RCON password.
+func Query(addr string, timeout time.Duration) (*Info, error) {
+	conn, err := net.Dial("udp", addr)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+	start := time.Now()
+	conn.SetDeadline(start.Add(timeout))
+	if _, err := conn.Write(a2sRequest); err != nil {
+		return nil, err
+	}
+	buf := make([]byte, 1400)
+	n, err := conn.Read(buf)
+	if err != nil {
+		return nil, err
+	}
+	if n >= 9 && buf[4] == 0x41 { // challenge: ask again with the number it gave
+		req := append(append([]byte{}, a2sRequest...), buf[5:9]...)
+		if _, err := conn.Write(req); err != nil {
+			return nil, err
+		}
+		if n, err = conn.Read(buf); err != nil {
+			return nil, err
+		}
+	}
+	info, err := parseInfo(buf[:n])
+	if err != nil {
+		return nil, err
+	}
+	info.PingMS = time.Since(start).Milliseconds()
+	return info, nil
+}
+
+func parseInfo(b []byte) (*Info, error) {
+	if len(b) < 6 || !bytes.Equal(b[:4], []byte{0xff, 0xff, 0xff, 0xff}) || b[4] != 0x49 {
+		return nil, errors.New("not an A2S_INFO reply")
+	}
+	r := b[6:] // skip the header and the protocol byte
+	str := func() string {
+		i := bytes.IndexByte(r, 0)
+		if i < 0 {
+			s := string(r)
+			r = nil
+			return s
+		}
+		s := string(r[:i])
+		r = r[i+1:]
+		return s
+	}
+	var in Info
+	in.Name, in.Map = str(), str()
+	str() // folder
+	in.Game = str()
+	if len(r) < 9 {
+		return nil, errors.New("short A2S_INFO reply")
+	}
+	in.Players, in.MaxPlayers = int(r[2]), int(r[3])
+	r = r[9:] // app id (2), players, max, bots, type, environment, visibility, VAC
+	in.Version = str()
+	if m := nameVersion.FindStringSubmatch(in.Name); m != nil {
+		in.Version = m[1]
+	}
+	return &in, nil
+}