bunshin/flake.nix

{
  description = "bunshin - Smol Mail server (Rust)";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };

        bunshin = pkgs.rustPlatform.buildRustPackage {
          pname = "bunshin";
          version = "0.1.0";
          src = ./.;
          cargoLock.lockFile = ./Cargo.lock;
          nativeBuildInputs = [ pkgs.pkg-config ];
          buildInputs = [ pkgs.sqlite ];
        };
      in
      {
        packages.default = bunshin;

        apps.default = flake-utils.lib.mkApp {
          drv = bunshin;
          name = "bunshin";
        };

        devShells.default = pkgs.mkShell {
          packages = [ pkgs.cargo pkgs.rustc pkgs.rustfmt pkgs.clippy pkgs.pkg-config pkgs.gcc pkgs.sqlite ];
        };
      }) // {
        nixosModules.default = { config, lib, pkgs, ... }:
          let
            cfg = config.services.bunshin;
            inherit (lib) mkEnableOption mkOption mkIf types;
          in
          {
            options.services.bunshin = {
              enable = mkEnableOption "the bunshin Smol Mail server";

              package = mkOption {
                type = types.package;
                default = self.packages.${pkgs.system}.default;
                description = "bunshin package to run.";
              };

              host = mkOption {
                type = types.str;
                default = "0.0.0.0";
                description = "Address to listen on.";
              };

              port = mkOption {
                type = types.port;
                default = 1961;
                description = "TCP port to listen on.";
              };

              keyFile = mkOption {
                type = types.path;
                description = ''
                  Path to the server's static Noise X25519 private key
                  (32 raw bytes, generated with `bunshin keygen`). Provisioned
                  out of band; this module does not generate it.
                '';
              };

              dataDir = mkOption {
                type = types.path;
                default = "/var/lib/bunshin";
                description = "Directory holding mail.db.";
              };

              maxEnvelope = mkOption {
                type = types.ints.positive;
                default = 1048576;
                description = "Maximum accepted envelope size, in bytes.";
              };

              quota = mkOption {
                type = types.ints.positive;
                default = 67108864;
                description = "Per-mailbox storage quota, in bytes.";
              };

              retentionDays = mkOption {
                type = types.ints.positive;
                default = 30;
                description = "Days a message is retained before being purged.";
              };

              rateConnections = mkOption {
                type = types.ints.positive;
                default = 120;
                description = "Max accepted connections per minute, per source IP.";
              };

              rateSends = mkOption {
                type = types.ints.positive;
                default = 60;
                description = "Max SEND operations per minute, per source IP.";
              };

              inviteToken = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = ''
                  Registration invite token. Null means open registration.
                  Prefer `inviteTokenFile` to avoid storing the token in the
                  world-readable Nix store.
                '';
              };

              inviteTokenFile = mkOption {
                type = types.nullOr types.path;
                default = null;
                description = ''
                  Path to a file (readable by the service via LoadCredential)
                  containing the registration invite token.
                '';
              };

              openFirewall = mkOption {
                type = types.bool;
                default = false;
                description = "Open the configured TCP port in the firewall.";
              };
            };

            config = mkIf cfg.enable {
              assertions = [
                {
                  assertion = !(cfg.inviteToken != null && cfg.inviteTokenFile != null);
                  message = "services.bunshin: set only one of inviteToken or inviteTokenFile.";
                }
              ];

              systemd.services.bunshin = {
                description = "bunshin Smol Mail server";
                wantedBy = [ "multi-user.target" ];
                after = [ "network.target" ];

                serviceConfig = {
                  ExecStart = pkgs.writeShellScript "bunshin-serve" ''
                    set -euo pipefail
                    args=(
                      serve
                      --key ${cfg.keyFile}
                      --db ${cfg.dataDir}/mail.db
                      --host ${cfg.host}
                      --port ${toString cfg.port}
                      --max-envelope ${toString cfg.maxEnvelope}
                      --quota ${toString cfg.quota}
                      --retention-days ${toString cfg.retentionDays}
                      --rate-connections ${toString cfg.rateConnections}
                      --rate-sends ${toString cfg.rateSends}
                    )
                    ${lib.optionalString (cfg.inviteToken != null)
                      ''args+=(--invite-token ${lib.escapeShellArg cfg.inviteToken})''}
                    ${lib.optionalString (cfg.inviteTokenFile != null)
                      ''args+=(--invite-token "$(cat "$CREDENTIALS_DIRECTORY/invite-token")")''}
                    exec ${cfg.package}/bin/bunshin "''${args[@]}"
                  '';
                  DynamicUser = true;
                  StateDirectory = "bunshin";
                  StateDirectoryMode = "0700";
                  Restart = "on-failure";
                } // lib.optionalAttrs (cfg.inviteTokenFile != null) {
                  LoadCredential = "invite-token:${cfg.inviteTokenFile}";
                };
              };

              networking.firewall.allowedTCPPorts = mkIf cfg.openFirewall [ cfg.port ];
            };
          };
      };
}