cnx-network-clan/modules/clan/router/wifi.nix

# Wireless access point on the router itself (hostapd). Every SSID is a BSS
# interface that joins the VLAN bridge as an untagged access port of its VLAN,
# so wireless clients get exactly the same DHCP/DNS/firewall treatment as a
# wired port in that VLAN. Passphrases are vars prompts, never in the store.
#
# hostapd names BSS interfaces <radio>, <radio>-1, <radio>-2 ... and wants a
# fixed BSSID for every extra one; they are derived from the radio's hardware
# address by setting the locally-administered bit and flipping bits 2-3 of
# the first octet per index (02 -> 06, 0a, 0e), which never collides with the
# radio's own address.
{ settings }:
{
  config,
  lib,
  pkgs,
  ...
}:
let
  cfg = settings;
  wifi = cfg.wifi;

  bssIf = radio: i: if i == 0 then radio else "${radio}-${toString i}";

  hexDigit =
    c:
    {
      "0" = 0;
      "1" = 1;
      "2" = 2;
      "3" = 3;
      "4" = 4;
      "5" = 5;
      "6" = 6;
      "7" = 7;
      "8" = 8;
      "9" = 9;
      a = 10;
      b = 11;
      c = 12;
      d = 13;
      e = 14;
      f = 15;
    }
    .${lib.toLower c};
  octetToInt = s: 16 * hexDigit (builtins.substring 0 1 s) + hexDigit (builtins.substring 1 1 s);
  intToOctet = n: lib.toLower (lib.fixedWidthString 2 "0" (lib.toHexString n));
  deriveBssid =
    mac: i:
    let
      octets = lib.splitString ":" mac;
      first = builtins.bitXor (builtins.bitOr (octetToInt (builtins.head octets)) 2) (i * 4);
    in
    lib.concatStringsSep ":" ([ (intToOctet first) ] ++ builtins.tail octets);

  # Every BSS of every radio, flattened.
  bsses = lib.concatLists (
    lib.mapAttrsToList (
      radio: r:
      lib.imap0 (i: name: {
        inherit radio name;
        index = i;
        iface = bssIf radio i;
        net = wifi.networks.${name} or null;
      }) r.networks
    ) wifi.radios
  );

  referenced = lib.unique (map (b: b.name) bsses);
  secured = lib.filter (name: wifi.networks.${name}.security != "open") (
    lib.filter (name: wifi.networks ? ${name}) referenced
  );
  passphraseFile =
    name: config.clan.core.vars.generators."wifi-${name}-passphrase".files.passphrase.path;

  authentication =
    name: net:
    {
      wpa3 = {
        mode = "wpa3-sae";
        saePasswordsFile = passphraseFile name;
      };
      wpa3-transition = {
        mode = "wpa3-sae-transition";
        saePasswordsFile = passphraseFile name;
        wpaPasswordFile = passphraseFile name;
      };
      wpa2 = {
        mode = "wpa2-sha1";
        wpaPasswordFile = passphraseFile name;
      };
      open.mode = "none";
    }
    .${net.security};
in
{
  config = lib.mkIf wifi.enable {
    assertions = [
      {
        assertion = wifi.radios != { };
        message = "router: wifi.enable needs at least one radio in wifi.radios.";
      }
      {
        assertion = wifi.countryCode != null;
        message = "router: wifi.countryCode is required when wifi.enable is set (regulatory domain).";
      }
      {
        assertion = lib.all (b: b.net != null) bsses;
        message = "router: every wifi.radios.<radio>.networks entry must name a network in wifi.networks.";
      }
      {
        assertion = lib.all (b: b.net == null || cfg.vlans ? ${b.net.vlan}) bsses;
        message = "router: every wifi.networks.<name>.vlan must name a VLAN in vlans.";
      }
      {
        assertion = lib.all (r: lib.length r.networks <= 4) (lib.attrValues wifi.radios);
        message = "router: a radio can broadcast at most four networks.";
      }
      {
        assertion = lib.all (r: lib.length r.networks <= 1 || r.macAddress != null) (
          lib.attrValues wifi.radios
        );
        message = "router: wifi.radios.<radio>.macAddress is required for radios broadcasting more than one network.";
      }
    ];

    # Regulatory database for the kernel, so countryCode actually applies.
    hardware.wirelessRegulatoryDatabase = true;

    # The kernel refuses to bridge a wireless interface in station mode, and
    # networkd stops retrying before hostapd switches the radio to AP mode;
    # so put it in AP mode the moment it appears (kernel name or the renamed
    # one, whichever the user configured). hostapd finds it already there.
    services.udev.extraRules = lib.concatMapStrings (
      radio:
      let
        run = ''RUN+="${pkgs.iw}/bin/iw dev ${radio} set type __ap"'';
      in
      ''
        ACTION=="add", SUBSYSTEM=="net", KERNEL=="${radio}", ${run}
        ACTION=="add", SUBSYSTEM=="net", NAME=="${radio}", ${run}
      ''
    ) (lib.attrNames wifi.radios);

    clan.core.vars.generators = lib.genAttrs (map (name: "wifi-${name}-passphrase") secured) (
      gen:
      let
        name = lib.removeSuffix "-passphrase" (lib.removePrefix "wifi-" gen);
      in
      {
        prompts.passphrase = {
          description = "Wi-Fi passphrase for SSID \"${wifi.networks.${name}.ssid}\" (8-63 ASCII characters)";
          type = "hidden";
        };
        files.passphrase.secret = true;
        # No trailing newline: hostapd turns every line of the file into a
        # sae_password entry, and an empty one wipes the list.
        script = ''printf '%s' "$(cat "$prompts"/passphrase)" > "$out"/passphrase'';
      }
    );

    services.hostapd = {
      enable = true;
      radios = lib.mapAttrs (radio: r: {
        inherit (r) band channel;
        inherit (wifi) countryCode;
        wifi6.enable = r.wifi6;
        networks = lib.listToAttrs (
          map (
            b:
            lib.nameValuePair b.iface (
              {
                inherit (b.net) ssid;
                ignoreBroadcastSsid = if b.net.hidden then "empty" else "disabled";
                apIsolate = b.net.isolateClients;
                authentication = authentication b.name b.net;
              }
              // lib.optionalAttrs (lib.length r.networks > 1) {
                bssid = if b.index == 0 then r.macAddress else deriveBssid r.macAddress b.index;
              }
            )
          ) (lib.filter (b: b.radio == radio) bsses)
        );
      }) wifi.radios;
    };

    # Each BSS is an untagged access port of its VLAN on br0 (cf. accessPorts
    # in network.nix); networkd enslaves the interface once hostapd creates it.
    systemd.network.networks = lib.listToAttrs (
      map (
        b:
        lib.nameValuePair "27-wifi-${b.iface}" {
          matchConfig.Name = b.iface;
          networkConfig.Bridge = "br0";
          bridgeVLANs = [
            {
              VLAN = cfg.vlans.${b.net.vlan}.id;
              PVID = cfg.vlans.${b.net.vlan}.id;
              EgressUntagged = cfg.vlans.${b.net.vlan}.id;
            }
          ];
          linkConfig.RequiredForOnline = "no";
        }
      ) bsses
    );
  };
}