dotfiles/modules/nixos/services/transmission.nix

# Transmission is a bittorrent client, which can run in the background for
# automated downloads with a web GUI.

{ config, pkgs, lib, ... }: {

  config = let
    namespace = config.networking.wireguard.interfaces.wg0.interfaceNamespace;
    vpnIp = lib.strings.removeSuffix "/32"
      (builtins.head config.networking.wireguard.interfaces.wg0.ips);
  in lib.mkIf config.services.transmission.enable {

    # Setup transmission
    services.transmission = {
      settings = {
        port-forwarding-enabled = false;
        rpc-authentication-required = true;
        rpc-port = 9091;
        rpc-bind-address = "0.0.0.0";
        rpc-username = config.user;
        # This is a salted hash of the real password
        # https://github.com/tomwijnroks/transmission-pwgen
        rpc-password = "{c4c5145f6e18bcd3c7429214a832440a45285ce26jDOBGVW";
        rpc-host-whitelist = config.hostnames.transmission;
        rpc-host-whitelist-enabled = true;
        rpc-whitelist = lib.mkDefault "127.0.0.1"; # Overwritten by Cloudflare
        rpc-whitelist-enabled = true;
      };
    };

    # Configure Cloudflare DNS to point to this machine
    services.cloudflare-dyndns.domains = [ config.hostnames.transmission ];

    # Bind transmission to wireguard namespace
    systemd.services.transmission = lib.mkIf config.wireguard.enable {
      bindsTo = [ "netns@${namespace}.service" ];
      requires = [ "network-online.target" "transmission-secret.service" ];
      after = [ "wireguard-wg0.service" "transmission-secret.service" ];
      unitConfig.JoinsNamespaceOf = "netns@${namespace}.service";
      serviceConfig.NetworkNamespacePath = "/var/run/netns/${namespace}";
    };

    # Create reverse proxy for web UI
    caddy.routes = let
      # Set if the download domain is the same as the Transmission domain
      useDownloadDomain = config.hostnames.download
        == config.hostnames.transmission;
    in lib.mkAfter [{
      group = if useDownloadDomain then "download" else "transmission";
      match = [{
        host = [ config.hostnames.transmission ];
        path = if useDownloadDomain then [ "/transmission*" ] else null;
      }];
      handle = [{
        handler = "reverse_proxy";
        upstreams = [{
          dial = "localhost:${
              builtins.toString config.services.transmission.settings.rpc-port
            }";
        }];
      }];
    }];

    # Caddy and Transmission both try to set rmem_max for larger UDP packets.
    # We will choose Transmission's recommendation (4 MB).
    boot.kernel.sysctl."net.core.rmem_max" = 4194304;

    # Allow inbound connections to reach namespace
    systemd.services.transmission-web-netns = lib.mkIf config.wireguard.enable {
      description = "Forward to transmission in wireguard namespace";
      requires = [ "transmission.service" ];
      after = [ "transmission.service" ];
      serviceConfig = {
        Restart = "on-failure";
        TimeoutStopSec = 300;
      };
      wantedBy = [ "multi-user.target" ];
      script = ''
        ${pkgs.iproute2}/bin/ip netns exec ${namespace} ${pkgs.iproute2}/bin/ip link set dev lo up
        ${pkgs.socat}/bin/socat tcp-listen:9091,fork,reuseaddr exec:'${pkgs.iproute2}/bin/ip netns exec ${namespace} ${pkgs.socat}/bin/socat STDIO "tcp-connect:${vpnIp}:9091"',nofork
      '';
    };

  };

}