dpi-tunnel: add an Xray Reality PQ full-tunnel client

DPI on some uplinks throttles WireGuard. Tunnel everything through Xray
VLESS + REALITY with post-quantum VLESS Encryption on tun1. Routes in
the main table that are more specific than the default (LAN, wg*
prefixes) keep priority; prefixes listed in the routes secret are
forced through the tunnel. The client's own uplink is fwmarked so it
never loops back into tun1.

UDP sessions on the tun device stay pinned to a dead mux link after
suspend or Wi-Fi loss, so restart the client on resume and whenever
NetworkManager brings up a new uplink. Stopping the unit removes all
the rules and routes.

Secrets come from secrets/dpi-tunnel.yaml through sops. Only the
.example skeleton is tracked.

Assisted-by: Claude:opus-5-5

configuration.nix

@@ -18,6 +18,7 @@
     ./modules/sops.nix
     ./modules/power.nix
     ./modules/xray.nix
+    ./modules/dpi-tunnel.nix
     ./modules/ollama.nix
     ./modules/lemonade.nix
     ./modules/gaming.nix

modules/dpi-tunnel.nix

@@ -0,0 +1,145 @@
+# Xray VLESS + REALITY + post-quantum VLESS Encryption tunnel around DPI that
+# throttles WireGuard. Server side (terraform/ansible) lives in the
+# dpi-tunnel repo; keys and server in secrets/dpi-tunnel.yaml.
+#
+# Full tunnel: everything goes via tun1 except what the main table routes
+# more specifically than a default (LAN, wg0/wg2 prefixes — their WireGuard
+# endpoints then go through the tunnel). Policy rules:
+#   999  fwmark -> main         xray's own uplink to the server
+#   1000 to <routes> -> 1011    forced prefixes (beat even specific wg* routes)
+#   1001 main, suppress /0      specific routes stay where they are
+#   1002 -> 1011                everything else
+# `systemctl stop dpi-tunnel` removes all of it (back to plain uplink).
+{ config, lib, pkgs, utils, ... }:
+
+let
+  dev = "tun1";
+  table = "1011";
+  mark = 4113; # 0x1011
+  socksPort = 11081;
+  sopsFile = "/etc/nixos/secrets/dpi-tunnel.yaml";
+  keys = [ "server" "server_name" "uuid" "short_id" "reality_password" "vless_encryption" "routes" ];
+  secret = key: config.sops.secrets."dpi-tunnel/${key}".path;
+  ip = "${pkgs.iproute2}/bin/ip";
+  jq = lib.getExe pkgs.jq;
+
+  settings = {
+    log = { loglevel = "warning"; access = "none"; }; # no per-site journal trail
+    inbounds = [
+      {
+        tag = "tun-in";
+        protocol = "tun";
+        settings = { name = dev; MTU = 1500; };
+      }
+      {
+        tag = "socks-in";
+        listen = "127.0.0.1";
+        port = socksPort;
+        protocol = "socks";
+        settings.udp = true;
+      }
+    ];
+    outbounds = [{
+      tag = "proxy";
+      protocol = "vless";
+      # UDP via XUDP; allow UDP/443 (QUIC, and WireGuard endpoints on 443),
+      # which vision rejects by default. TCP stays unmuxed.
+      mux = {
+        enabled = true;
+        concurrency = -1;
+        xudpConcurrency = 8;
+        xudpProxyUDP443 = "allow";
+      };
+      settings.vnext = [{
+        address = { _secret = secret "server"; };
+        port = 443;
+        users = [{
+          id = { _secret = secret "uuid"; };
+          flow = "xtls-rprx-vision";
+          encryption = { _secret = secret "vless_encryption"; };
+        }];
+      }];
+      streamSettings = {
+        network = "raw";
+        security = "reality";
+        realitySettings = {
+          serverName = { _secret = secret "server_name"; };
+          fingerprint = "chrome";
+          password = { _secret = secret "reality_password"; };
+          shortId = { _secret = secret "short_id"; };
+        };
+        # Marked so rule 999 keeps the uplink off tun1 (no loop).
+        sockopt.mark = mark;
+      };
+    }];
+  };
+in
+{
+  sops.secrets = lib.genAttrs (map (k: "dpi-tunnel/${k}") keys) (name: {
+    inherit sopsFile;
+    key = lib.removePrefix "dpi-tunnel/" name;
+    restartUnits = [ "dpi-tunnel.service" ];
+  });
+
+  systemd.services.dpi-tunnel = {
+    description = "Xray VLESS Reality PQ client";
+    after = [ "network-online.target" ];
+    wants = [ "network-online.target" ];
+    wantedBy = [ "multi-user.target" ];
+    preStart = utils.genJqSecretsReplacementSnippet settings "/run/dpi-tunnel/config.json";
+    postStart = ''
+      for _ in $(seq 50); do [ -e /sys/class/net/${dev} ] && break; sleep 0.1; done
+      ${ip} link set ${dev} up
+      for v in -4 -6; do
+        ${ip} $v route replace default dev ${dev} table ${table}
+        ${ip} $v rule add fwmark ${toString mark} lookup main priority 999
+        ${ip} $v rule add lookup main suppress_prefixlength 0 priority 1001
+        ${ip} $v rule add lookup ${table} priority 1002
+      done
+      for cidr in $(${jq} -r '.[]' ${secret "routes"}); do
+        ${ip} route replace "$cidr" dev ${dev} table ${table}
+        ${ip} rule add to "$cidr" lookup ${table} priority 1000
+      done
+    '';
+    postStop = ''
+      for v in -4 -6; do
+        for p in 999 1000 1001 1002; do
+          while ${ip} $v rule del priority $p 2>/dev/null; do :; done
+        done
+        ${ip} $v route flush table ${table} 2>/dev/null || true
+      done
+    '';
+    serviceConfig = {
+      ExecStart = "${lib.getExe pkgs.xray} run -c /run/dpi-tunnel/config.json";
+      RuntimeDirectory = "dpi-tunnel";
+      RuntimeDirectoryMode = "0700";
+      AmbientCapabilities = [ "CAP_NET_ADMIN" ];
+      CapabilityBoundingSet = [ "CAP_NET_ADMIN" ];
+      NoNewPrivileges = true;
+      ProtectSystem = "strict";
+      ProtectHome = true;
+      Restart = "on-failure";
+      RestartSec = 5;
+    };
+  };
+
+  # Xray keeps tun UDP sessions alive while packets arrive, so a WireGuard
+  # keepalive pins a session whose mux link died (suspend, Wi-Fi loss)
+  # forever. Start clean after resume and on every new uplink.
+  systemd.services.dpi-tunnel-resume = rec {
+    description = "Restart dpi-tunnel after resume";
+    after = [ "suspend.target" "hibernate.target" "hybrid-sleep.target" "suspend-then-hibernate.target" ];
+    wantedBy = after;
+    serviceConfig.Type = "oneshot";
+    script = "systemctl try-restart dpi-tunnel.service";
+  };
+
+  networking.networkmanager.dispatcherScripts = [{
+    type = "basic";
+    source = pkgs.writeShellScript "dpi-tunnel-uplink" ''
+      case "$1" in lo|wg*|tun*|docker*|br-*|veth*|virbr*) exit 0 ;; esac
+      [ "$2" = up ] && systemctl try-restart dpi-tunnel.service
+      exit 0
+    '';
+  }];
+}

secrets/dpi-tunnel.yaml.example

@@ -0,0 +1,10 @@
+# sops-encrypted; generate with scripts/gen-secrets.sh in the dpi-tunnel repo
+server: 203.0.113.10
+server_name: www.microsoft.com
+uuid: 00000000-0000-0000-0000-000000000000
+short_id: 0123456789abcdef
+reality_private_key: <server only>
+reality_password: <x25519 public key>
+vless_decryption: <server only>
+vless_encryption: mlkem768x25519plus.native.0rtt.<...>
+routes: '["198.51.100.1/32"]'  # forced via tun1 even over specific wg* routes