infra/services/gerrit/default.nix

# Gerrit configuration for the Nixpkgs monorepo
# Inspired from TVL configuration.
{ pkgs, config, lib, ... }:

let
  inherit (lib) mkEnableOption mkIf mkOption types head;
  cfgGerrit = config.services.gerrit;
  cfg = config.bagel.services.gerrit;

  jdk = pkgs.openjdk21_headless;
in
{
  options.bagel.services.gerrit = {
    enable = mkEnableOption "Gerrit";
    domains = mkOption {
      type = types.listOf types.str;
      description = "List of domains that Gerrit will answer to";
    };
    canonicalDomain = mkOption {
      type = types.str;
      description = "Canonical domain for this Gerrit instance";
      default = head cfg.domains;
    };
    data = mkOption {
      type = types.path;
      default = "/var/lib/gerrit";
      description = "Root of data directory for the Gerrit";
    };
    port = mkOption {
      type = types.port;
      default = 29418;
      readOnly = true;
      description = "Port for the Gerrit SSH server";
    };
  };

  imports = [
    ./www.nix
  ];

  config = mkIf cfg.enable {
    networking.firewall.allowedTCPPorts = [ cfg.port ];

    environment.systemPackages = [ jdk ];

    fileSystems."/var/lib/gerrit" = mkIf (cfg.data != "/var/lib/gerrit") {
      device = cfg.data;
      options = [ "bind" ];
    };

    users.users.git = {
      isSystemUser = true;
      group = "git";
    };
    users.groups.git = {};

    services.gerrit = {
      enable = true;
      listenAddress = "[::]:4778"; # 4778 - grrt
      serverId = "9e5216ad-038d-4d74-a4e8-716515834a94";

      builtinPlugins = [
        "gitiles"
        "codemirror-editor"
        "reviewnotes"
        "download-commands"
        "hooks"
        "replication"
        "webhooks"
      ];

      plugins = with pkgs.gerritPlugins; [
        oauth
        metrics-reporter-prometheus
      ];

      package = pkgs.gerrit;

      jvmHeapLimit = "32g";

      jvmPackage = jdk;

      settings = {
        # Performance settings
        sshd.threads = 64;
        sshd.batchThreads = 8;

        gc.aggressive = true;
        gc.interval = "1 day";

        database.poolLimit = 250;
        database.poolMaxIdle = 16;

        httpd.maxThreads = 100;

        receive.timeout = "4min";
        # Default is 0, infinite.
        transfer.timeout = "30min";

        # We may overshoot but it's OK.
        core.packedGitWindowSize = "256k";
        # Sum of all current packfiles is ~1.2G
        # Largest packfile is 906MB.
        # Average packfile is ~5-10MB.
        core.packedGitLimit = "1g";
        # We have plenty of memory, let's avoid file system cache → Gerrit needless copies.
        core.packedGitUseStrongRefs = true;
        core.packedGitOpenFiles = 4096;
        # Big files in nixpkgs are usually lockfiles or machine-generated expressions
        # containing a lot of hashes, they would weigh at most ~15MB.
        core.streamFileThreshold = "20m";
        # `mmap()` rather than `mmap()+read()` at the risk of running out of virtual address space.
        core.packedGitMmap = true;

        ## Takes more CPU but the transfer is smaller.
        pack.deltacompression = true;
        pack.threads = 8;

        # FIXME(raito):
        # Are we supposed to have private / hidden references?
        # For a public server, that seems unlikely.
        # But, we should be careful with this option.
        # https://gerrit-documentation.storage.googleapis.com/Documentation/3.9.5/config-gerrit.html#receive.checkReferencedObjectsAreReachable
        receive.checkReferencedObjectsAreReachable = false;

        # Other settings
        log.jsonLogging = true;
        log.textLogging = false;
        sshd.advertisedAddress = "${cfg.canonicalDomain}:${cfg.port}";
        cache.web_sessions.maxAge = "3 months";
        plugins.allowRemoteAdmin = false;
        change.enableAttentionSet = true;
        change.enableAssignee = false;

        user = {
          name = "ForkOS Gerrit";
          email = "gerrit@forkos.org";
          anonymousCoward = "ForkOS contributor";
        };

        # Configures gerrit for being reverse-proxied by nginx as per
        # https://gerrit-review.googlesource.com/Documentation/config-reverseproxy.html
        gerrit = {
          canonicalWebUrl = "https://${cfg.canonicalDomain}";
          docUrl = "/Documentation";
          defaultBranch = "refs/heads/main";
        };

        httpd.listenUrl = "proxy-https://${cfgGerrit.listenAddress}";

        download.command = [
          "checkout"
          "cherry_pick"
          "format_patch"
          "pull"
        ];

        # Auto-link other CLs
        commentlink.gerrit = {
          match = "cl/(\\d+)";
          link = "https://${cfg.canonicalDomain}/$1";
        };

        # Configures integration with Keycloak, which then integrates with a
        # variety of backends.
        auth.type = "OAUTH";
        plugin.gerrit-oauth-provider-keycloak-oauth = {
          root-url = "https://identity.lix.systems";
          realm = "lix-project";
          client-id = "raito-gerrit-testing";
          # client-secret is set in /var/lib/gerrit/etc/secure.config.
        };

        plugin.code-owners = {
          # A Code-Review +2 vote is required from a code owner.
          requiredApproval = "Code-Review+2";
          # The OWNERS check can be overriden using an Owners-Override vote.
          overrideApproval = "Owners-Override+1";
          # People implicitly approve their own changes automatically.
          enableImplicitApprovals = "TRUE";
        };

        # Allow users to add additional email addresses to their accounts.
        oauth.allowRegisterNewEmail = true;

        # Use Gerrit's built-in HTTP passwords, rather than trying to use the
        # password against the backing OAuth provider.
        auth.gitBasicAuthPolicy = "HTTP";

        # Email sending (emails are relayed via the tazj.in domain's
        # GSuite currently).
        #
        # Note that sendemail.smtpPass is stored in
        # $site_path/etc/secure.config and is *not* controlled by Nix.
        #
        # Receiving email is not currently supported.
        sendemail.enable = false;
        #sendemail = {
        #  enable = false;
        #  html = false;
        #  connectTimeout = "10sec";
        #  from = "TVL Code Review <tvlbot@tazj.in>";
        #  includeDiff = true;
        #  smtpEncryption = "none";
        #  smtpServer = "localhost";
        #  smtpServerPort = 2525;
        #};
      };

      # Replication of the depot repository to secondary machines, for
      # serving cgit/josh.
      #replicationSettings = {
      #  gerrit.replicateOnStartup = true;

      #  remote.sanduny = {
      #    url = "depot@sanduny.tvl.su:/var/lib/depot";
      #    projects = "depot";
      #  };
      #};
    };

    systemd.services.gerrit = {
      serviceConfig = {
        # There seems to be no easy way to get `DynamicUser` to play
        # well with other services (e.g. by using SupplementaryGroups,
        # which seem to have no effect) so we force the DynamicUser
        # setting for the Gerrit service to be disabled and reuse the
        # existing 'git' user.
        DynamicUser = lib.mkForce false;
        User = "git";
        Group = "git";
      };
      environment.REVWALK_USE_PRIORITY_QUEUE = "true";
    };

    age.secrets.gerrit-prometheus-bearer-token.file = ../../secrets/gerrit-prometheus-bearer-token.age;
    bagel.monitoring.grafana-agent.exporters.gerrit = {
      port = 4778;  # grrt
      bearerTokenFile = config.age.secrets.gerrit-prometheus-bearer-token.path;
      scrapeConfig.metrics_path = "/plugins/metrics-reporter-prometheus/metrics";
    };
  };
}