bbr Enable BBR

#!/usr/bin/env bash
# Served by xyz.sh/bbr
# Human-readable page: https://xyz.sh/bbr
# This file is the common library followed by the script body.
# No telemetry is added by xyz.sh.
# =============================================================================
# xyz.sh common library
# Shared helpers for every script served by xyz.sh.
#
# Promises:
#   - No telemetry, analytics, or background "phone-home" calls
#   - No hidden installs or config changes beyond what the script announces
#   - Official upstream URLs are printed before any remote code is executed
#   - Destructive or system-changing steps ask for confirmation (or YES=1 / -y)
# =============================================================================

if [[ -n "${XYZ_COMMON_LOADED:-}" ]]; then
  # When sourced a second time, return. When executed as a file, return fails.
  # shellcheck disable=SC2317
  return 0 2>/dev/null || true
fi
# shellcheck disable=SC2034
XYZ_COMMON_LOADED=1

set -euo pipefail

XYZ_VERSION="1.3.0"
XYZ_BASE="${XYZ_BASE:-https://xyz.sh}"
XYZ_NAME="${XYZ_NAME:-unknown}"

# --- language ---------------------------------------------------------------
# Override with XYZ_LANG=zh or XYZ_LANG=en.
if [[ -z "${XYZ_LANG:-}" ]]; then
  case "${LC_ALL:-${LC_MESSAGES:-${LANG:-}}}" in
    zh*|ZH*|cmn*|CMN*) XYZ_LANG="zh" ;;
    *) XYZ_LANG="en" ;;
  esac
fi

xyz_t() {
  # xyz_t "English text" "中文文本"
  if [[ "${XYZ_LANG}" == "zh" ]]; then
    printf '%s' "${2:-$1}"
  else
    printf '%s' "$1"
  fi
}

# --- colors (TTY only) ------------------------------------------------------
# XYZ_COLOR=always|never|auto (default auto: TTY and no NO_COLOR); --no-color.
_xyz_color=0
case "${XYZ_COLOR:-auto}" in
  always) _xyz_color=1 ;;
  never) _xyz_color=0 ;;
  *) [[ -t 1 && -z "${NO_COLOR:-}" ]] && _xyz_color=1 ;;
esac
[[ "${XYZ_NO_COLOR:-0}" == "1" ]] && _xyz_color=0
if [[ "${_xyz_color}" == "1" ]]; then
  XYZ_C_RESET=$'\033[0m'
  XYZ_C_BOLD=$'\033[1m'
  XYZ_C_DIM=$'\033[2m'
  XYZ_C_RED=$'\033[31m'
  XYZ_C_GREEN=$'\033[32m'
  XYZ_C_YELLOW=$'\033[33m'
  XYZ_C_CYAN=$'\033[36m'
else
  XYZ_C_RESET=""
  XYZ_C_BOLD=""
  XYZ_C_DIM=""
  XYZ_C_RED=""
  XYZ_C_GREEN=""
  XYZ_C_YELLOW=""
  XYZ_C_CYAN=""
fi

xyz_info()  { printf '%s[INFO]%s %s\n'  "${XYZ_C_GREEN}"  "${XYZ_C_RESET}" "$*"; }
xyz_warn()  { printf '%s[WARN]%s %s\n'  "${XYZ_C_YELLOW}" "${XYZ_C_RESET}" "$*" >&2; }
xyz_error() { printf '%s[ERROR]%s %s\n' "${XYZ_C_RED}"    "${XYZ_C_RESET}" "$*" >&2; }
xyz_step()  { printf '%s==>%s %s\n'     "${XYZ_C_CYAN}"   "${XYZ_C_RESET}" "$*"; }

# --- args / init ------------------------------------------------------------
XYZ_ARGS=()
XYZ_YES=0
XYZ_DRY_RUN=0

xyz_parse_global_args() {
  local filtered=()
  local arg
  for arg in "$@"; do
    case "${arg}" in
      -y|--yes)
        XYZ_YES=1
        ;;
      --lang=zh|zh)
        XYZ_LANG="zh"
        ;;
      --lang=en|en)
        XYZ_LANG="en"
        ;;
      --dry-run)
        XYZ_DRY_RUN=1
        ;;
      --no-color)
        XYZ_NO_COLOR=1
        XYZ_C_RESET=""; XYZ_C_BOLD=""; XYZ_C_DIM=""; XYZ_C_RED=""
        XYZ_C_GREEN=""; XYZ_C_YELLOW=""; XYZ_C_CYAN=""
        ;;
      --help|-h)
        XYZ_HELP=1
        filtered+=("${arg}")
        ;;
      *)
        filtered+=("${arg}")
        ;;
    esac
  done
  XYZ_ARGS=("${filtered[@]+"${filtered[@]}"}")
  if [[ "${YES:-}" =~ ^(1|yes|true|YES)$ || "${XYZ_ASSUME_YES:-}" == "1" ]]; then
    XYZ_YES=1
  fi
  # Exported so individual scripts can read flags set here.
  export XYZ_ARGS XYZ_YES XYZ_LANG XYZ_HELP="${XYZ_HELP:-}" XYZ_DRY_RUN="${XYZ_DRY_RUN:-0}"
  export XYZ_NO_COLOR="${XYZ_NO_COLOR:-0}"
  if declare -F xyz_ui_init >/dev/null; then xyz_ui_init; fi
}

xyz_banner() {
  local title="${XYZ_TITLE:-$XYZ_NAME}"
  printf '\n%s%sxyz.sh/%s%s  v%s\n' "${XYZ_C_BOLD}" "${XYZ_C_CYAN}" "${XYZ_NAME}" "${XYZ_C_RESET}" "${XYZ_VERSION}"
  printf '%s\n' "${XYZ_C_DIM}----------------------------------------${XYZ_C_RESET}"
  printf '  %s: %s/%s\n' "$(xyz_t "Page" "页面")" "${XYZ_BASE}" "${XYZ_NAME}"
  printf '  %s: %s/%s.sh\n' "$(xyz_t "Raw" "源码")" "${XYZ_BASE}" "${XYZ_NAME}"
  if [[ -n "${XYZ_UPSTREAM:-}" ]]; then
    printf '  %s: %s\n' "$(xyz_t "Upstream" "上游来源")" "${XYZ_UPSTREAM}"
  fi
  printf '  %s\n' "$(xyz_t "No telemetry, no hidden actions." "无遥测、无隐藏操作。")"
  printf '%s\n\n' "${XYZ_C_DIM}----------------------------------------${XYZ_C_RESET}"
  if [[ -n "${title}" && "${title}" != "${XYZ_NAME}" ]]; then
    xyz_step "${title}"
  fi
}

xyz_init() {
  xyz_parse_global_args "$@"
  xyz_detect_os
  xyz_banner
}

# --- root / OS --------------------------------------------------------------
xyz_is_root() {
  [[ "${EUID:-$(id -u)}" -eq 0 ]]
}

xyz_require_root() {
  if ! xyz_is_root; then
    xyz_error "$(xyz_t \
      "This script must be run as root. Try: sudo bash" \
      "请使用 root 运行。可尝试：sudo bash")"
    exit 1
  fi
}

xyz_prefer_root() {
  if ! xyz_is_root; then
    xyz_warn "$(xyz_t \
      "Not running as root; some information or tests may be limited." \
      "当前不是 root，部分信息或测试可能不完整。")"
  fi
}

XYZ_OS_ID=""
XYZ_OS_LIKE=""
XYZ_OS_VERSION=""
XYZ_OS_FAMILY=""   # debian | rhel | unknown
XYZ_OS_PRETTY=""

xyz_detect_os() {
  XYZ_OS_ID=""
  XYZ_OS_LIKE=""
  XYZ_OS_VERSION=""
  XYZ_OS_FAMILY="unknown"
  XYZ_OS_PRETTY="unknown"
  if [[ -r /etc/os-release ]]; then
    # shellcheck disable=SC1091
    . /etc/os-release
    XYZ_OS_ID="${ID:-}"
    XYZ_OS_LIKE="${ID_LIKE:-}"
    XYZ_OS_VERSION="${VERSION_ID:-}"
    XYZ_OS_PRETTY="${PRETTY_NAME:-$XYZ_OS_ID}"
    export XYZ_OS_ID XYZ_OS_LIKE XYZ_OS_VERSION XYZ_OS_FAMILY XYZ_OS_PRETTY
  fi
  case "${XYZ_OS_ID}" in
    debian|ubuntu)
      XYZ_OS_FAMILY="debian"
      ;;
    centos|rhel|rocky|almalinux|alma|fedora)
      XYZ_OS_FAMILY="rhel"
      ;;
    *)
      case " ${XYZ_OS_ID} ${XYZ_OS_LIKE} " in
        *debian*|*ubuntu*) XYZ_OS_FAMILY="debian" ;;
        *rhel*|*centos*|*fedora*|*rocky*|*alma*) XYZ_OS_FAMILY="rhel" ;;
        *) : ;;
      esac
      ;;
  esac
}

xyz_os_supported() {
  case "${XYZ_OS_ID}" in
    debian|ubuntu|centos|rocky|almalinux) return 0 ;;
    *) : ;;
  esac
  case " ${XYZ_OS_LIKE} " in
    *debian*|*ubuntu*|*rhel*|*centos*|*rocky*|*alma*) return 0 ;;
    *) : ;;
  esac
  return 1
}

xyz_require_supported_os() {
  xyz_detect_os
  if ! xyz_os_supported; then
    xyz_warn "$(xyz_t \
      "Unrecognized distribution: ${XYZ_OS_ID:-unknown} (${XYZ_OS_PRETTY}). Officially supported: Debian, Ubuntu, CentOS, Rocky, AlmaLinux." \
      "未能识别的发行版：${XYZ_OS_ID:-unknown}（${XYZ_OS_PRETTY}）。官方支持：Debian、Ubuntu、CentOS、Rocky、AlmaLinux。")"
    if ! xyz_confirm "$(xyz_t "Continue anyway?" "仍然继续？")"; then
      exit 1
    fi
  else
    xyz_info "$(xyz_t "Detected OS:" "检测到系统：") ${XYZ_OS_PRETTY} (${XYZ_OS_FAMILY})"
  fi
}

# --- packages / commands ----------------------------------------------------
xyz_need_cmd() {
  command -v "$1" >/dev/null 2>&1
}

xyz_pkg_install() {
  xyz_detect_os
  if (( $# == 0 )); then
    return 0
  fi
  case "${XYZ_OS_FAMILY}" in
    debian)
      export DEBIAN_FRONTEND=noninteractive
      apt-get update -y || xyz_warn "$(xyz_t "apt-get update reported errors (a repository may be unreachable); trying to install anyway." "apt-get update 报错（可能有软件源无法访问），仍尝试安装。")"
      apt-get install -y --no-install-recommends "$@"
      ;;
    rhel)
      if xyz_need_cmd dnf; then
        dnf install -y "$@"
      elif xyz_need_cmd yum; then
        yum install -y "$@"
      else
        xyz_error "$(xyz_t "Neither dnf nor yum is available." "找不到 dnf 或 yum。")"
        exit 1
      fi
      ;;
    *)
      xyz_error "$(xyz_t "Cannot install packages on this OS automatically." "无法在此系统上自动安装软件包。")"
      exit 1
      ;;
  esac
}

xyz_ensure_cmds() {
  local pkg
  local missing=()
  for pkg in "$@"; do
    if ! xyz_need_cmd "${pkg}"; then
      missing+=("${pkg}")
    fi
  done
  if ((${#missing[@]} > 0)); then
    xyz_info "$(xyz_t "Installing missing commands:" "正在安装缺失命令：") ${missing[*]}"
    xyz_pkg_install "${missing[@]}"
  fi
}

# --- confirmation (safe with curl | bash) -----------------------------------
# A readable /dev/tty node is not enough: in containers or curl|bash without a
# controlling terminal, open() fails with ENXIO ("No such device or address").
# [[ -r /dev/tty ]] is true in that case and must not be used as the check.
xyz_open_tty() {
  # Opens /dev/tty into XYZ_TTY_FD if it is a real terminal. Caller must close.
  local fd
  XYZ_TTY_FD=""
  # Brace group so a failed open cannot leak "No such device or address".
  if { exec {fd}<>/dev/tty; } 2>/dev/null && [[ -t "${fd}" ]]; then
    XYZ_TTY_FD="${fd}"
    return 0
  fi
  if [[ -n "${fd:-}" ]]; then
    exec {fd}>&- 2>/dev/null || true
  fi
  return 1
}

xyz_close_tty() {
  if [[ -n "${XYZ_TTY_FD:-}" ]]; then
    exec {XYZ_TTY_FD}>&- 2>/dev/null || true
    XYZ_TTY_FD=""
  fi
}

xyz_confirm() {
  local prompt="$1"
  if [[ "${XYZ_YES}" == "1" ]]; then
    xyz_info "$(xyz_t "Auto-confirmed (-y / YES=1):" "已自动确认（-y / YES=1）：") ${prompt}"
    return 0
  fi
  local reply=""
  if xyz_open_tty; then
    printf '%s [y/N] ' "${prompt}" >&"${XYZ_TTY_FD}"
    # shellcheck disable=SC2162
    read -r reply <&"${XYZ_TTY_FD}" || true
    xyz_close_tty
  else
    xyz_warn "$(xyz_t \
      "No TTY available for confirmation. Re-run with -y or YES=1 if you accept." \
      "没有可用的终端来确认。若你已了解并同意，请加 -y 或 YES=1 重试。")"
    return 1
  fi
  case "${reply}" in
    y|Y|yes|YES|Yes) return 0 ;;
    *) return 1 ;;
  esac
}

# --- download helpers -------------------------------------------------------
# Create the temp dir in the main shell. xyz_tmpdir is usually called inside
# $(...), a subshell, so creating it (and its EXIT trap) there would delete the
# directory as soon as the subshell returned.
xyz_init_tmpdir() {
  if [[ -z "${XYZ_TMPDIR:-}" || ! -d "${XYZ_TMPDIR}" ]]; then
    XYZ_TMPDIR="$(mktemp -d "${TMPDIR:-/tmp}/xyzsh.XXXXXX")"
    # shellcheck disable=SC2064
    trap "rm -rf '${XYZ_TMPDIR}'" EXIT
  fi
}

xyz_tmpdir() {
  if [[ -z "${XYZ_TMPDIR:-}" || ! -d "${XYZ_TMPDIR}" ]]; then
    xyz_error "internal: temp dir not initialised"
    exit 1
  fi
  printf '%s' "${XYZ_TMPDIR}"
}

xyz_fetch() {
  # xyz_fetch URL DEST
  local url="$1"
  local dest="$2"
  xyz_info "$(xyz_t "Downloading" "正在下载"): ${url}"
  xyz_info "$(xyz_t "Saving to" "保存到"): ${dest}"
  if xyz_need_cmd curl; then
    curl -fsSL --connect-timeout 20 --max-time 180 --retry 2 --retry-delay 1 \
      -o "${dest}" "${url}"
  elif xyz_need_cmd wget; then
    wget -q --timeout=60 -O "${dest}" "${url}"
  else
    xyz_error "$(xyz_t "Need curl or wget to download files." "需要 curl 或 wget 才能下载文件。")"
    exit 1
  fi
  if [[ ! -s "${dest}" ]]; then
    xyz_error "$(xyz_t "Download failed or file is empty:" "下载失败或文件为空：") ${url}"
    exit 1
  fi
  if xyz_need_cmd sha256sum; then
    xyz_info "SHA256: $(sha256sum "${dest}" | awk '{print $1}')"
  elif xyz_need_cmd shasum; then
    xyz_info "SHA256: $(shasum -a 256 "${dest}" | awk '{print $1}')"
  fi
}

xyz_run_upstream() {
  # xyz_run_upstream URL [args...]
  # Downloads an official installer, shows the URL and a short preview, then
  # runs it only after confirmation (unless -y / YES=1).
  local url="$1"
  shift
  local dest
  xyz_init_tmpdir
  dest="$(xyz_tmpdir)/upstream.sh"
  xyz_fetch "${url}" "${dest}"
  chmod +x "${dest}"
  xyz_info "$(xyz_t "Preview (first 20 lines):" "预览（前 20 行）：")"
  sed -n '1,20p' "${dest}" || true
  printf '%s\n' "${XYZ_C_DIM}...${XYZ_C_RESET}"
  # Default --dry-run: verify the download and preview, do not execute.
  # Scripts that forward --dry-run to upstream (e.g. docker) set
  # XYZ_FORWARD_DRY_RUN=1 so the official script still runs with that flag.
  if [[ "${XYZ_DRY_RUN:-0}" == "1" && "${XYZ_FORWARD_DRY_RUN:-0}" != "1" ]]; then
    xyz_info "$(xyz_t \
      "Dry-run: official script downloaded and previewed; not executing it." \
      "演练模式：已下载并预览官方脚本，不会执行。")"
    return 0
  fi
  if ! xyz_confirm "$(xyz_t \
    "Run this official upstream script?" \
    "运行这份官方上游脚本？")"; then
    xyz_error "$(xyz_t "Aborted by user." "已取消。")"
    exit 1
  fi
  xyz_step "$(xyz_t "Executing upstream script" "正在执行上游脚本")"
  # Never let the upstream script inherit our stdin: under `curl | bash` that
  # is the rest of this very script. Give it the terminal if there is one,
  # otherwise /dev/null. Interactive installers set XYZ_UPSTREAM_NEEDS_TTY=1.
  if xyz_open_tty; then
    local tty_fd="${XYZ_TTY_FD}"
    XYZ_TTY_FD=""
    bash "${dest}" "$@" <&"${tty_fd}"
    local rc=$?
    exec {tty_fd}>&- 2>/dev/null || true
    return "${rc}"
  fi
  if [[ "${XYZ_UPSTREAM_NEEDS_TTY:-0}" == "1" ]]; then
    xyz_error "$(xyz_t \
      "This official installer is interactive and needs a terminal. Log in with SSH and run: bash <(curl -fsSL ${XYZ_BASE}/${XYZ_NAME})" \
      "这个官方安装脚本需要交互，必须在终端里运行。请用 SSH 登录后执行：bash <(curl -fsSL ${XYZ_BASE}/${XYZ_NAME})")"
    exit 1
  fi
  bash "${dest}" "$@" </dev/null
}

# --- small shared helpers ----------------------------------------------------
xyz_strip_ansi() {
  sed -e 's/\x1b\[[0-9;?]*[A-Za-z]//g' -e 's/\r//g'
}

# Effective SSH port: sshd -T (what sshd really uses) > config files > env > 22.
xyz_effective_ssh_port() {
  local port=""
  if xyz_need_cmd sshd; then
    port="$(sshd -T 2>/dev/null | awk '$1=="port" {print $2; exit}' || true)"
  fi
  if [[ -z "${port}" && -d /etc/ssh/sshd_config.d ]]; then
    port="$(cat /etc/ssh/sshd_config.d/*.conf 2>/dev/null | awk 'tolower($1)=="port" {print $2; exit}' || true)"
  fi
  if [[ -z "${port}" && -f /etc/ssh/sshd_config ]]; then
    port="$(awk 'tolower($1)=="port" {print $2; exit}' /etc/ssh/sshd_config || true)"
  fi
  if [[ -z "${port}" && -n "${SSH_CONNECTION:-}" ]]; then
    port="$(printf '%s' "${SSH_CONNECTION}" | awk '{print $4}')"
  fi
  printf '%s' "${port:-22}"
}

xyz_has_systemd() {
  [[ -d /run/systemd/system ]] && xyz_need_cmd systemctl
}

# Back up a file once per run as FILE.xyz-bak-YYYYmmddHHMMSS and print the path.
xyz_backup_file() {
  local f="$1"
  local bak
  bak="${f}.xyz-bak-$(date +%Y%m%d%H%M%S)"
  if [[ -e "${f}" ]]; then
    cp -a "${f}" "${bak}"
    printf '%s' "${bak}"
  fi
}

# --- misc -------------------------------------------------------------------
xyz_usage_exit() {
  if [[ "${1:-}" != "" ]]; then
    printf '%s\n' "$1"
  fi
  exit 0
}

XYZ_NAME="bbr"

# xyz.sh/bbr — enable TCP BBR congestion control via sysctl.
#
# This script only loads the in-tree kernel module and writes sysctl settings.
# It does not download or compile a third-party kernel, and it does not change
# any other network parameters.
#
# Usage:
#   curl -fsSL xyz.sh/bbr | bash
#   curl -fsSL xyz.sh/bbr | bash -s -- -y
#   curl -fsSL xyz.sh/bbr | bash -s -- --status
#
# Supported: Debian, Ubuntu, CentOS, Rocky, AlmaLinux (kernel 4.9+).
# Requires root. No telemetry.

set -euo pipefail

if [[ -z "${XYZ_COMMON_LOADED:-}" ]]; then
  _xyz_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
  if [[ -f "${_xyz_dir}/lib/common.sh" ]]; then
    # shellcheck source=lib/common.sh
    source "${_xyz_dir}/lib/common.sh"
  else
    echo "xyz.sh: missing lib/common.sh" >&2
    exit 1
  fi
fi

XYZ_NAME="bbr"
XYZ_TITLE="$(xyz_t "Enable TCP BBR" "启用 TCP BBR")"
XYZ_UPSTREAM=""
xyz_init "$@"
xyz_require_root
xyz_require_supported_os

SYSCTL_FILE="/etc/sysctl.d/99-xyz-bbr.conf"

xyz_bbr_status() {
  echo
  xyz_step "$(xyz_t "Current congestion control" "当前拥塞控制")"
  printf '  net.ipv4.tcp_congestion_control = %s\n' \
    "$(sysctl -n net.ipv4.tcp_congestion_control 2>/dev/null || echo n/a)"
  printf '  net.core.default_qdisc           = %s\n' \
    "$(sysctl -n net.core.default_qdisc 2>/dev/null || echo n/a)"
  if [[ -r /proc/sys/net/ipv4/tcp_available_congestion_control ]]; then
    printf '  available                        = %s\n' \
      "$(cat /proc/sys/net/ipv4/tcp_available_congestion_control)"
  fi
  if lsmod 2>/dev/null | grep -q '^tcp_bbr'; then
    printf '  tcp_bbr module                   = loaded\n'
  else
    printf '  tcp_bbr module                   = not loaded\n'
  fi
  echo
}

if [[ "${XYZ_HELP:-}" == "1" ]]; then
  cat <<EOF
$(xyz_t "Usage:" "用法：")
  curl -fsSL xyz.sh/bbr | bash
  curl -fsSL xyz.sh/bbr | bash -s -- -y
  curl -fsSL xyz.sh/bbr | bash -s -- --status
  curl -fsSL xyz.sh/bbr | bash -s -- --dry-run

$(xyz_t "Writes:" "将写入：")
  net.core.default_qdisc = fq
  net.ipv4.tcp_congestion_control = bbr
  ${SYSCTL_FILE}
EOF
  exit 0
fi

if [[ "${XYZ_ARGS[0]:-}" == "--status" ]]; then
  xyz_bbr_status
  exit 0
fi

KERNEL="$(uname -r)"
xyz_info "$(xyz_t "Kernel:" "内核：") ${KERNEL}"

if [[ -r /proc/sys/net/ipv4/tcp_available_congestion_control ]] \
  && grep -qw bbr /proc/sys/net/ipv4/tcp_available_congestion_control; then
  xyz_info "$(xyz_t "Kernel already lists BBR as available." "内核已提供 BBR。")"
else
  if [[ -e /lib/modules/${KERNEL}/kernel/net/ipv4/tcp_bbr.ko \
     || -e /lib/modules/${KERNEL}/kernel/net/ipv4/tcp_bbr.ko.xz \
     || -e /lib/modules/${KERNEL}/kernel/net/ipv4/tcp_bbr.ko.zst ]]; then
    if [[ "${XYZ_DRY_RUN:-0}" == "1" ]]; then
      xyz_info "$(xyz_t "Dry-run: would load tcp_bbr via modprobe." "演练模式：将通过 modprobe 加载 tcp_bbr。")"
    else
      xyz_step "$(xyz_t "Loading tcp_bbr module" "正在加载 tcp_bbr 模块")"
      if ! modprobe tcp_bbr; then
        xyz_error "$(xyz_t \
          "modprobe tcp_bbr failed. This environment may not allow loading kernel modules (common in containers)." \
          "modprobe tcp_bbr 失败。当前环境可能不允许加载内核模块（容器中常见）。")"
        exit 1
      fi
    fi
  else
    xyz_error "$(xyz_t \
      "This kernel does not appear to include tcp_bbr. BBR needs Linux 4.9 or later with the module enabled. No kernel will be replaced." \
      "当前内核似乎不包含 tcp_bbr。BBR 需要 Linux 4.9 及以上且启用了该模块。本脚本不会更换内核。")"
    if [[ "${XYZ_DRY_RUN:-0}" == "1" ]]; then
      xyz_info "$(xyz_t "Dry-run: planned sysctl (not applied): net.core.default_qdisc=fq, net.ipv4.tcp_congestion_control=bbr." "演练模式：计划的 sysctl（未应用）：net.core.default_qdisc=fq, net.ipv4.tcp_congestion_control=bbr。")"
    fi
    exit 1
  fi
fi

CURRENT_CC="$(sysctl -n net.ipv4.tcp_congestion_control 2>/dev/null || true)"
if [[ "${CURRENT_CC}" == "bbr" ]]; then
  xyz_info "$(xyz_t "BBR is already the active congestion control." "当前已在使用 BBR。")"
  xyz_bbr_status
  if [[ ! -f "${SYSCTL_FILE}" ]]; then
    if [[ "${XYZ_DRY_RUN:-0}" == "1" ]]; then
      xyz_info "$(xyz_t "Dry-run: would persist settings to ${SYSCTL_FILE}." "演练模式：将把设置写入 ${SYSCTL_FILE}。")"
    elif xyz_confirm "$(xyz_t "Persist settings to ${SYSCTL_FILE}?" "将设置写入 ${SYSCTL_FILE} 以便开机保持？")"; then
      printf '%s\n' \
        "# Written by xyz.sh/bbr — TCP BBR + fq qdisc" \
        "net.core.default_qdisc = fq" \
        "net.ipv4.tcp_congestion_control = bbr" \
        > "${SYSCTL_FILE}"
      xyz_info "$(xyz_t "Persisted." "已持久化。")"
    fi
  fi
  exit 0
fi

xyz_info "$(xyz_t "Planned sysctl changes:" "将应用的 sysctl 变更：")"
printf '  net.core.default_qdisc = fq\n'
printf '  net.ipv4.tcp_congestion_control = bbr\n'
printf '  persist file: %s\n' "${SYSCTL_FILE}"

if [[ "${XYZ_DRY_RUN:-0}" == "1" ]]; then
  xyz_info "$(xyz_t "Dry-run: no sysctl changes were applied." "演练模式：未应用任何 sysctl 变更。")"
  exit 0
fi

if ! xyz_confirm "$(xyz_t "Apply and persist these settings?" "应用并持久化这些设置？")"; then
  xyz_error "$(xyz_t "Aborted by user." "已取消。")"
  exit 1
fi

# Persist first, then apply, so a mid-way failure can still be retried.
printf '%s\n' \
  "# Written by xyz.sh/bbr — TCP BBR + fq qdisc" \
  "# Safe to delete this file and run sysctl --system to revert persistence." \
  "net.core.default_qdisc = fq" \
  "net.ipv4.tcp_congestion_control = bbr" \
  > "${SYSCTL_FILE}"

if ! sysctl -p "${SYSCTL_FILE}"; then
  xyz_error "$(xyz_t \
    "Failed to apply sysctl settings. This is common in unprivileged containers, or when the host network namespace is read-only." \
    "无法应用 sysctl 设置。在无特权容器中，或主机网络命名空间只读时，这很常见。")"
  exit 1
fi

xyz_bbr_status
if [[ "$(sysctl -n net.ipv4.tcp_congestion_control)" == "bbr" ]]; then
  xyz_info "$(xyz_t "BBR is now enabled." "BBR 已启用。")"
else
  xyz_error "$(xyz_t "Failed to switch congestion control to BBR." "未能将拥塞控制切换为 BBR。")"
  exit 1
fi