nix-config/modules/nixos/services/coturn.nix

{ config, lib, self, ... }:

let
  cfg = config.modules.services.coturn;
in {
  options.modules.services.coturn = {
    enable = lib.mkOption {
      default = false;
      example = true;
    };
    realm = lib.mkOption {
      type = lib.types.str;
      description = "The realm to be used by the TURN server.";
      example = "turn.vimium.com";
    };
    matrixIntegration = lib.mkOption {
      default = false;
      description = "Configure the matrix-synapse module to use this TURN server.";
      example = true;
    };
  };

  config = lib.mkIf cfg.enable {
    networking.firewall = let
      range = with config.services.coturn; lib.singleton {
        from = min-port;
        to = max-port;
      };
    in {
      allowedTCPPorts = [
        3478  # TURN listener
        5349  # STUN TLS
        5350  # STUN TLS alt
      ];
      allowedUDPPorts = [
        3478  # TURN listener
        5349  # TLS
        5350  # TLS alt
      ];
      allowedUDPPortRanges = range; # TURN peer relays
    };

    security.acme.certs = {
      "${config.services.coturn.realm}" = {
        group = "turnserver";
        reloadServices = [ "coturn" ];
      };
    };

    age.secrets = {
      "passwords/services/coturn/static-auth-secret" = {
        file = "${self.inputs.secrets}/passwords/services/coturn/static-auth-secret.age";
        owner = "turnserver";
        group = "turnserver";
      };
    } // (if cfg.matrixIntegration then {
      "passwords/services/coturn/matrix-turn-config.yml" = {
        file = "${self.inputs.secrets}/passwords/services/coturn/matrix-turn-config.yml.age";
        owner = "matrix-synapse";
        group = "matrix-synapse";
      };
    } else {});

    services.coturn = rec {
      enable = true;
      realm = cfg.realm;
      use-auth-secret = true;
      static-auth-secret-file = config.age.secrets."passwords/services/coturn/static-auth-secret".path;
      cert = "${config.security.acme.certs.${realm}.directory}/full.pem";
      pkey = "${config.security.acme.certs.${realm}.directory}/key.pem";
      min-port = 49000;
      max-port = 50000;
      no-cli = true;
      no-tcp-relay = true;
      extraConfig = ''
        cipher-list="HIGH"
        no-multicast-peers

        # Ban private CIDR blocks
        denied-peer-ip=0.0.0.0-0.255.255.255
        denied-peer-ip=10.0.0.0-10.255.255.255
        denied-peer-ip=100.64.0.0-100.127.255.255
        denied-peer-ip=127.0.0.0-127.255.255.255
        denied-peer-ip=169.254.0.0-169.254.255.255
        denied-peer-ip=172.16.0.0-172.31.255.255
        denied-peer-ip=192.0.0.0-192.0.0.255
        denied-peer-ip=192.0.2.0-192.0.2.255
        denied-peer-ip=192.88.99.0-192.88.99.255
        denied-peer-ip=192.168.0.0-192.168.255.255
        denied-peer-ip=198.18.0.0-198.19.255.255
        denied-peer-ip=198.51.100.0-198.51.100.255
        denied-peer-ip=203.0.113.0-203.0.113.255
        denied-peer-ip=240.0.0.0-255.255.255.255
        denied-peer-ip=::1
        denied-peer-ip=64:ff9b::-64:ff9b::ffff:ffff
        denied-peer-ip=::ffff:0.0.0.0-::ffff:255.255.255.255
        denied-peer-ip=100::-100::ffff:ffff:ffff:ffff
        denied-peer-ip=2001::-2001:1ff:ffff:ffff:ffff:ffff:ffff:ffff
        denied-peer-ip=2002::-2002:ffff:ffff:ffff:ffff:ffff:ffff:ffff
        denied-peer-ip=fc00::-fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
        denied-peer-ip=fe80::-febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff
      '';
    };

    services.matrix-synapse = lib.mkIf cfg.matrixIntegration {
      settings = with config.services.coturn; {
        turn_uris = [
          "turn:${realm}:3478?transport=udp"
          "turn:${realm}:3478?transport=tcp"
        ];
        turn_user_lifetime = "1h";
      };
      extraConfigFiles = [
        config.age.secrets."passwords/services/coturn/matrix-turn-config.yml".path
      ];
    };
  };
}