feat(core): add naming, RCON, store, config, and image-build libraries

Foundational libraries: deterministic resource naming, the RCON client, the Postgres store with embedded SQL migrations, configuration loading, and container image-build helpers.

internal/rcon/rcon.go

@@ -0,0 +1,188 @@
+// Package rcon implements a minimal Source RCON client (spec §5, §7).
+//
+// The operator uses it for two purposes:
+//   - Readiness probing: a successful Dial (TCP connect + auth) is the
+//     loader-agnostic "RCON 探通" gate. A status ping is never sufficient.
+//   - Graceful shutdown: Execute("save-all flush") then Execute("stop") from
+//     the operator-injected preStop hook.
+//
+// Multi-packet responses (a single command whose reply exceeds one ~4 KiB
+// packet) are not reassembled; Phase-1 commands ("list", "save-all", "stop")
+// always fit in one packet. This is intentional and documented rather than
+// silently truncating large replies.
+package rcon
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"time"
+)
+
+// Source RCON packet types.
+const (
+	typeResponseValue = 0 // SERVERDATA_RESPONSE_VALUE
+	typeExecCommand   = 2 // SERVERDATA_EXECCOMMAND
+	typeAuthResponse  = 2 // SERVERDATA_AUTH_RESPONSE (same id as EXECCOMMAND)
+	typeAuth          = 3 // SERVERDATA_AUTH
+)
+
+// authFailedID is the request id a server returns when auth fails.
+const authFailedID int32 = -1
+
+// Packet length bounds. minPacketLen is 4 (id) + 4 (type) + 2 (terminators).
+const (
+	minPacketLen = 10
+	maxPacketLen = 4096
+)
+
+// ErrAuthFailed is returned by Dial when the RCON password is rejected.
+var ErrAuthFailed = errors.New("rcon: authentication failed")
+
+// DefaultPort is the conventional RCON port.
+const DefaultPort = 25575
+
+// Conn is an authenticated RCON connection. It is not safe for concurrent use.
+type Conn struct {
+	conn  net.Conn
+	reqID int32
+}
+
+// Dial opens a TCP connection to addr and authenticates with password. The
+// timeout, if > 0, bounds the whole connect+auth handshake; it is cleared on
+// the returned Conn so subsequent calls block unless SetDeadline is used.
+func Dial(addr, password string, timeout time.Duration) (*Conn, error) {
+	var (
+		netConn net.Conn
+		err     error
+	)
+	if timeout > 0 {
+		netConn, err = net.DialTimeout("tcp", addr, timeout)
+	} else {
+		netConn, err = net.Dial("tcp", addr)
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	c := &Conn{conn: netConn}
+	if timeout > 0 {
+		if err := netConn.SetDeadline(time.Now().Add(timeout)); err != nil {
+			netConn.Close()
+			return nil, err
+		}
+	}
+	if err := c.auth(password); err != nil {
+		netConn.Close()
+		return nil, err
+	}
+	// Clear the handshake deadline so the connection is reusable.
+	if err := netConn.SetDeadline(time.Time{}); err != nil {
+		netConn.Close()
+		return nil, err
+	}
+	return c, nil
+}
+
+// SetDeadline sets an absolute deadline for subsequent Execute calls.
+func (c *Conn) SetDeadline(t time.Time) error { return c.conn.SetDeadline(t) }
+
+// Close closes the underlying connection.
+func (c *Conn) Close() error { return c.conn.Close() }
+
+// Execute runs a single command and returns the server's reply body.
+func (c *Conn) Execute(cmd string) (string, error) {
+	id := c.nextID()
+	if err := writePacket(c.conn, id, typeExecCommand, cmd); err != nil {
+		return "", err
+	}
+	respID, _, body, err := readPacket(c.conn)
+	if err != nil {
+		return "", err
+	}
+	if respID != id {
+		return "", fmt.Errorf("rcon: response id mismatch: got %d want %d", respID, id)
+	}
+	return body, nil
+}
+
+// auth performs the SERVERDATA_AUTH handshake. Some servers emit an empty
+// RESPONSE_VALUE before the auth response, so non-auth packets are skipped.
+func (c *Conn) auth(password string) error {
+	id := c.nextID()
+	if err := writePacket(c.conn, id, typeAuth, password); err != nil {
+		return err
+	}
+	for {
+		respID, respType, _, err := readPacket(c.conn)
+		if err != nil {
+			return err
+		}
+		if respType != typeAuthResponse {
+			// Empty RESPONSE_VALUE echo; keep reading for the real answer.
+			continue
+		}
+		if respID == authFailedID {
+			return ErrAuthFailed
+		}
+		if respID != id {
+			return fmt.Errorf("rcon: auth id mismatch: got %d want %d", respID, id)
+		}
+		return nil
+	}
+}
+
+func (c *Conn) nextID() int32 {
+	c.reqID++
+	if c.reqID < 0 {
+		c.reqID = 1
+	}
+	return c.reqID
+}
+
+// writePacket encodes one RCON packet: little-endian length, id, type, the
+// null-terminated body, and a trailing null byte.
+func writePacket(w io.Writer, id, typ int32, body string) error {
+	bodyBytes := []byte(body)
+	length := int32(4 + 4 + len(bodyBytes) + 2)
+	if length > maxPacketLen {
+		return fmt.Errorf("rcon: outgoing packet too large: %d bytes", length)
+	}
+	buf := make([]byte, 0, 4+length)
+	buf = appendInt32(buf, length)
+	buf = appendInt32(buf, id)
+	buf = appendInt32(buf, typ)
+	buf = append(buf, bodyBytes...)
+	buf = append(buf, 0, 0)
+	_, err := w.Write(buf)
+	return err
+}
+
+// readPacket decodes one RCON packet.
+func readPacket(r io.Reader) (id, typ int32, body string, err error) {
+	var lenBuf [4]byte
+	if _, err = io.ReadFull(r, lenBuf[:]); err != nil {
+		return 0, 0, "", err
+	}
+	length := int32(binary.LittleEndian.Uint32(lenBuf[:]))
+	if length < minPacketLen || length > maxPacketLen {
+		return 0, 0, "", fmt.Errorf("rcon: invalid packet length %d", length)
+	}
+	payload := make([]byte, length)
+	if _, err = io.ReadFull(r, payload); err != nil {
+		return 0, 0, "", err
+	}
+	id = int32(binary.LittleEndian.Uint32(payload[0:4]))
+	typ = int32(binary.LittleEndian.Uint32(payload[4:8]))
+	// Strip the two trailing null bytes from the body.
+	body = string(payload[8 : length-2])
+	return id, typ, body, nil
+}
+
+func appendInt32(buf []byte, v int32) []byte {
+	var b [4]byte
+	binary.LittleEndian.PutUint32(b[:], uint32(v))
+	return append(buf, b[:]...)
+}