#!/bin/bash
# MSS 值扫描：1360 可能不是最优。
#
# 现状：MTU 修复后 15 分钟长测 78%（最长连续失败从 68 秒降到 15 秒）。
#       失败是孤立单次超时，不是持续中断。
#       MSS 夹多少最合适需要实测 —— 夹太小包变小、来回变多；
#       夹太大又超出路径能过的尺寸。
set -u

URL=https://relay.xxmxxs.top
RELAY_DIR=/root/lanremote-relay
PROBE=24

clear_mss() {
    for chain in OUTPUT POSTROUTING; do
        while iptables -t mangle -C "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1360 2>/dev/null; do
            iptables -t mangle -D "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1360 2>/dev/null || break
        done
        while iptables -t mangle -C "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1300 2>/dev/null; do
            iptables -t mangle -D "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1300 2>/dev/null || break
        done
        while iptables -t mangle -C "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1400 2>/dev/null; do
            iptables -t mangle -D "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1400 2>/dev/null || break
        done
        while iptables -t mangle -C "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1440 2>/dev/null; do
            iptables -t mangle -D "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss 1440 2>/dev/null || break
        done
    done
}

set_mss() {
    local value="$1"
    clear_mss
    if [ "$value" != "0" ]; then
        for chain in OUTPUT POSTROUTING; do
            iptables -t mangle -A "$chain" -p tcp --tcp-flags SYN,RST SYN \
                -j TCPMSS --set-mss "$value" 2>/dev/null
        done
    fi
}

measure() {
    local ok=0 bad=0 consec=0 maxconsec=0
    for i in $(seq 1 $PROBE); do
        c=$(timeout 12 curl -4 -s -o /dev/null -w '%{http_code}' \
            -H 'User-Agent: LanRemote/1.4.0' "$URL/v1/health" 2>/dev/null)
        c=${c:-000}
        if [ "$c" = "200" ]; then
            ok=$((ok+1)); consec=0
        else
            bad=$((bad+1)); consec=$((consec+1))
            [ "$consec" -gt "$maxconsec" ] && maxconsec=$consec
        fi
        sleep 2
    done
    echo "$ok|$maxconsec"
}

: > /root/mss_result.txt

for mss in 0 1300 1360 1400 1440; do
    label=$( [ "$mss" = "0" ] && echo "不夹(1500)" || echo "MSS $mss" )
    set_mss "$mss"
    # 让新参数生效：重启隧道
    systemctl restart lanremote-tunnel >/dev/null 2>&1
    sleep 30
    result=$(measure)
    ok=$(echo "$result" | cut -d'|' -f1)
    mc=$(echo "$result" | cut -d'|' -f2)
    pct=$((ok * 100 / PROBE))
    printf "  %-12s 可用 %2d/%d = %3d%%   最长连续失败 %s 次\n" \
        "$label" "$ok" "$PROBE" "$pct" "$mc"
    echo "$label|$pct|$mc" >> /root/mss_result.txt
done

echo
echo "===== 汇总（按可用率排序）====="
sort -t'|' -k2 -rn /root/mss_result.txt | while IFS='|' read -r label pct mc; do
    printf "  %-12s %3d%%  (最长连败 %s)\n" "$label" "$pct" "$mc"
done

BEST=$(sort -t'|' -k2 -rn /root/mss_result.txt | head -1)
BEST_LABEL=$(echo "$BEST" | cut -d'|' -f1)
BEST_PCT=$(echo "$BEST" | cut -d'|' -f2)
echo
echo "  最优：$BEST_LABEL（$BEST_PCT%）"

# 恢复成最优值
case "$BEST_LABEL" in
    "不夹(1500)") FINAL=0 ;;
    "MSS 1300")   FINAL=1300 ;;
    "MSS 1360")   FINAL=1360 ;;
    "MSS 1400")   FINAL=1400 ;;
    "MSS 1440")   FINAL=1440 ;;
    *)            FINAL=1360 ;;
esac
set_mss "$FINAL"
if [ "$FINAL" != "0" ]; then
    sed -i "s/^MSS_VALUE=.*/MSS_VALUE=$FINAL/" "$RELAY_DIR/net-tune.sh" 2>/dev/null
fi
systemctl restart lanremote-tunnel >/dev/null 2>&1
echo "  已把最优值写进 net-tune.sh 并重启隧道"
grep '^MSS_VALUE=' "$RELAY_DIR/net-tune.sh" 2>/dev/null | sed 's/^/    /'