stockholm/krebs/3modules/git.nix

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

# TODO unify logging of shell scripts to user and journal
# TODO move all scripts to ${etcDir}, so ControlMaster connections
#       immediately pick up new authenticators
# TODO when authorized_keys changes, then restart ssh
#       (or kill already connected users somehow)

with import <stockholm/lib>;
let
  cfg = config.krebs.git;

  out = {
    options.krebs.git = api;
    config = with lib; mkIf cfg.enable (mkMerge [
      (mkIf cfg.cgit.enable cgit-imp)
      git-imp
    ]);
  };

  api = {
    enable = mkEnableOption "krebs.git";

    cgit = mkOption {
      type = types.submodule {
        options = {
          enable = mkEnableOption "krebs.git.cgit" // { default = true; };
          fcgiwrap = {
            group = mkOption {
              type = types.group;
              default = {
                name = "fcgiwrap";
              };
            };
            user = mkOption {
              type = types.user;
              default = {
                name = "fcgiwrap";
                home = toString pkgs.empty;
              };
            };
          };
          settings = mkOption {
            apply = flip removeAttrs ["_module"];
            default = {};
            type = subtypes.cgit-settings;
          };
        };
      };
      default = {};
      description = ''
          Cgit is an attempt to create a fast web interface for the git version
          control system, using a built in cache to decrease pressure on the
          git server.
          cgit in this module is being served via fastcgi nginx.This module
          deploys a http://cgit.<hostname> nginx configuration and enables nginx
          if not yet enabled.
          '';
    };
    dataDir = mkOption {
      type = types.str;
      default = "/var/lib/git";
      description = "Directory used to store repositories.";
    };
    etcDir = mkOption {
      type = mkOptionType {
        name = "${types.absolute-pathname.name} starting with `/etc/'";
        check = x: types.absolute-pathname.check x && hasPrefix "/etc/" x;
        merge = mergeOneOption;
      };
      default = "/etc/git";
    };
    repos = mkOption {
      type = types.attrsOf subtypes.repo;
      default = {};
      example = literalExample ''
        {
          testing = {
            name = "testing";
            hooks.post-update = '''
              #! /bin/sh
              set -euf
              echo post-update hook: $* >&2
            ''';
          };
          testing2 = { name = "testing2"; };
        }
      '';
      description = ''
        Repositories.
      '';
    };
    rules = mkOption {
      type = types.listOf subtypes.rule;
      default = [];
      example = literalExample ''
        singleton {
          user = [ config.krebs.users.tv ];
          repo = [ testing ]; # see literal example of repos
          perm = push "refs/*" (with git; [
            non-fast-forward create delete merge
          ]);
        }
      '';
      description = ''
        access and permission rules for git repositories.
      '';
    };

    user = mkOption {
      type = types.user;
      default = {
        name = "git";
        home = toString pkgs.empty;
      };
    };
  };

  # TODO put into krebs/4lib/types.nix?
  subtypes = {
    cgit-settings = types.submodule {
      # A setting's value of `null` means cgit's default should be used.
      options = {
        cache-root = mkOption {
          type = types.absolute-pathname;
          default = "/tmp/cgit";
        };
        cache-size = mkOption {
          type = types.uint;
          default = 1000;
        };
        css = mkOption {
          type = types.absolute-pathname;
          default = "/static/cgit.css";
        };
        enable-commit-graph = mkOption {
          type = types.bool;
          default = true;
        };
        enable-index-links = mkOption {
          type = types.bool;
          default = true;
        };
        enable-index-owner = mkOption {
          type = types.bool;
          default = false;
        };
        enable-log-filecount = mkOption {
          type = types.bool;
          default = true;
        };
        enable-log-linecount = mkOption {
          type = types.bool;
          default = true;
        };
        enable-remote-branches = mkOption {
          type = types.bool;
          default = true;
        };
        logo = mkOption {
          type = types.absolute-pathname;
          default = "/static/cgit.png";
        };
        max-stats = mkOption {
          type =
            types.nullOr (types.enum ["week" "month" "quarter" "year"]);
          default = "year";
        };
        robots = mkOption {
          type = types.nullOr (types.listOf types.str);
          default = ["nofollow" "noindex"];
        };
        root-desc = mkOption {
          type = types.nullOr types.str;
          default = null;
        };
        root-title = mkOption {
          type = types.nullOr types.str;
          default = null;
        };
        virtual-root = mkOption {
          type = types.nullOr types.absolute-pathname;
          default = "/";
        };
      };
    };
    repo = types.submodule ({ config, ... }: {
      options = {
        cgit = {
          desc = mkOption {
            type = types.nullOr types.str;
            default = null;
            description = ''
              Repository description.
            '';
          };
          path = mkOption {
            type = types.str;
            default = "${cfg.dataDir}/${config.name}";
            description = ''
              An absolute path to the repository directory. For non-bare
              repositories this is the .git-directory.
            '';
          };
          section = mkOption {
            type = types.nullOr types.str;
            default = null;
            description = ''
              Repository section.
            '';
          };
          url = mkOption {
            type = types.str;
            default = config.name;
            description = ''
              The relative url used to access the repository.
            '';
          };
        };
        collaborators = mkOption {
          type = types.listOf types.user;
          default = [];
          description = ''
            List of users that should be able to fetch from this repo.

            This option is currently not used by krebs.git but instead can be
            used to create rules.  See e.g. <stockholm/tv/2configs/git.nix> for
            an example.
          '';
        };
        name = mkOption {
          type = types.str;
          description = ''
            Repository name.
          '';
        };
        hooks = mkOption {
          type = types.attrsOf types.str;
          default = {};
          description = ''
            Repository-specific hooks.
          '';
        };
        public = mkOption {
          type = types.bool;
          default = false;
          description = ''
            Allow everybody to read the repository via HTTP if cgit enabled.
          '';
          # TODO allow every configured user to fetch the repository via SSH.
        };
      };
    });
    rule = types.submodule ({ config, ... }: {
      options = {
        user = mkOption {
          type = types.listOf types.user;
          description = ''
            List of users this rule should apply to.
            Checked by authorize-command.
          '';
        };
        repo = mkOption {
          type = types.listOf subtypes.repo;
          description = ''
            List of repos this rule should apply to.
            Checked by authorize-command.
          '';
        };
        perm = mkOption {
          type = types.submodule {
            # TODO generate enum argument from krebs/4lib/git.nix
            options = {
              allow-commands = mkOption {
                type = types.listOf (types.enum (with git; [
                  git-receive-pack
                  git-upload-pack
                ]));
                default = [];
                description = ''
                  List of commands the rule's users are allowed to execute.
                  Checked by authorize-command.
                '';
              };
              allow-receive-ref = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = ''
                  Ref that can receive objects.
                  Checked by authorize-push.
                '';
              };
              allow-receive-modes = mkOption {
                type = types.listOf (types.enum (with git; [
                  fast-forward
                  non-fast-forward
                  create
                  delete
                  merge
                ]));
                default = [];
                description = ''
                  List of allowed receive modes.
                  Checked by pre-receive hook.
                '';
              };
            };
          };
          description = ''
            Permissions granted.
          '';
        };
      };
    });
  };

  git-imp = {
    system.activationScripts.git-init = "${init-script}";

    # TODO maybe put all scripts here and then use PATH?
    environment.etc.${removePrefix "/etc/" cfg.etcDir}.source =
      scriptFarm "git-ssh-authorizers" {
        authorize-command = makeAuthorizeScript (map (rule: [
          (map getName (toList rule.user))
          (map getName (toList rule.repo))
          (map getName rule.perm.allow-commands)
        ]) cfg.rules);

        authorize-push = makeAuthorizeScript (map (rule: [
          (map getName (toList rule.user))
          (map getName (toList rule.repo))
          (toList rule.perm.allow-receive-ref)
          (map getName rule.perm.allow-receive-modes)
        ]) (filter (rule: rule.perm.allow-receive-ref != null) cfg.rules));
      };

    users.users.${cfg.user.name} = {
      inherit (cfg.user) home name uid;
      description = "Git repository hosting user";
      shell = "/bin/sh";
      openssh.authorizedKeys.keys =
        mapAttrsToList (_: makeAuthorizedKey git-ssh-command)
                       (filterAttrs (_: user: isString user.pubkey)
                                    config.krebs.users);
    };
  };

  cgit-imp = {
    users = {
      groups.${cfg.cgit.fcgiwrap.group.name} = {
        inherit (cfg.cgit.fcgiwrap.group) name gid;
      };
      users.${cfg.cgit.fcgiwrap.user.name} = {
        inherit (cfg.cgit.fcgiwrap.user) home name uid;
        group = cfg.cgit.fcgiwrap.group.name;
      };
    };

    services.fcgiwrap = {
      enable = true;
      user = cfg.cgit.fcgiwrap.user.name;
      group = cfg.cgit.fcgiwrap.group.name;
      # socketAddress = "/run/fcgiwrap.sock" (default)
      # socketType = "unix" (default)
    };

    environment.etc."cgitrc".text = let
      repo-to-cgitrc = _: repo:
        optionals (isPublicRepo repo) (concatLists [
          [""] # empty line
          [(kv-to-cgitrc "repo.url" repo.cgit.url)]
          (mapAttrsToList kv-to-cgitrc
            (mapAttrs' (k: nameValuePair "repo.${k}")
              (removeAttrs repo.cgit ["url"])))
        ]);

      kv-to-cgitrc = k: v: getAttr (typeOf v) {
        bool = kv-to-cgitrc k (if v then 1 else 0);
        null = []; # This will be removed by `flatten`.
        list = "${k}=${concatStringsSep ", " v}";
        int = "${k}=${toString v}";
        string = "${k}=${v}";
      };
    in
      concatStringsSep "\n"
        (flatten (
          mapAttrsToList kv-to-cgitrc cfg.cgit.settings
          ++
          mapAttrsToList repo-to-cgitrc cfg.repos
        ));

    environment.systemPackages = [
      (pkgs.writeDashBin "cgit-clear-cache" ''
        ${pkgs.coreutils}/bin/rm -f ${cfg.cgit.settings.cache-root}/*
      '')
    ];

    system.activationScripts.cgit = ''
      mkdir -m 0700 -p ${cfg.cgit.settings.cache-root}
      chown ${toString cfg.cgit.fcgiwrap.user.uid}:${toString cfg.cgit.fcgiwrap.group.gid} ${cfg.cgit.settings.cache-root}
    '';

    krebs.nginx = {
      enable = true;
      servers.cgit = {
        server-names = [
          "cgit.${config.networking.hostName}"
          "cgit.${config.networking.hostName}.r"
          "cgit.${config.networking.hostName}.retiolum"
        ];
        locations = [
          (nameValuePair "/" ''
            include             ${pkgs.nginx}/conf/fastcgi_params;
            fastcgi_param       SCRIPT_FILENAME ${pkgs.cgit}/cgit/cgit.cgi;
            fastcgi_param       PATH_INFO       $uri;
            fastcgi_param       QUERY_STRING    $args;
            fastcgi_param       HTTP_HOST       $server_name;
            fastcgi_pass        unix:${config.services.fcgiwrap.socketAddress};
          '')
          (nameValuePair "/static/" ''
            root ${pkgs.cgit}/cgit;
            rewrite ^/static(/.*)$ $1 break;
          '')
        ];
      };
    };
  };

  getName = x: x.name;

  isPublicRepo = getAttr "public"; # TODO this is also in ./cgit.nix

  makeAuthorizedKey = git-ssh-command: user@{ name, pubkey, ... }:
    # TODO assert name
    # TODO assert pubkey
    let
      options = concatStringsSep "," [
        ''command="exec ${git-ssh-command} ${name}"''
        "no-agent-forwarding"
        "no-port-forwarding"
        "no-pty"
        "no-X11-forwarding"
      ];
    in
    "${options} ${pubkey}";

  # [case-pattern] -> shell-script
  # Create a shell script that succeeds (exit 0) when all its arguments
  # match the case patterns (in the given order).
  makeAuthorizeScript =
    let
      # TODO escape
      to-pattern = x: concatStringsSep "|" (toList x);
      go = i: ps:
        if ps == []
          then "exit 0"
          else ''
            case ''$${toString i} in ${to-pattern (head ps)})
            ${go (i + 1) (tail ps)}
            esac'';
    in
    patterns: ''
      #! /bin/sh
      set -euf
      ${concatStringsSep "\n" (map (go 1) patterns)}
      exit -1
    '';

  reponames = rules: sort lessThan (unique (map (x: x.repo.name) rules));

  # TODO use `writeOut`
  scriptFarm =
    farm-name: scripts:
    let
      makeScript = script-name: script-string: {
        name = script-name;
        path = pkgs.writeScript "${farm-name}_${script-name}" script-string;
      };
    in
    pkgs.linkFarm farm-name (mapAttrsToList makeScript scripts);


  git-ssh-command = pkgs.writeScript "git-ssh-command" ''
    #! /bin/sh
    set -euf

    PATH=${makeBinPath (with pkgs; [
      coreutils
      git
      gnugrep
      gnused
      systemd
    ])}

    abort() {
      echo "error: $1" >&2
      systemd-cat -p err -t git echo "error: $1"
      exit -1
    }

    GIT_SSH_USER=$1

    systemd-cat -p info -t git echo \
      "authorizing $GIT_SSH_USER $SSH_CONNECTION $SSH_ORIGINAL_COMMAND"

    # References: The Base Definitions volume of
    # POSIX.1‐2013, Section 3.278, Portable Filename Character Set
    portable_filename_bre="^[A-Za-z0-9._-]\\+$"

    command=$(echo "$SSH_ORIGINAL_COMMAND" \
      | sed -n 's/^\([^ ]*\) '"'"'\(.*\)'"'"'/\1/p' \
      | grep "$portable_filename_bre" \
      || abort 'cannot read command')

    GIT_SSH_REPO=$(echo "$SSH_ORIGINAL_COMMAND" \
      | sed -n 's/^\([^ ]*\) '"'"'\(.*\)'"'"'/\2/p' \
      | grep "$portable_filename_bre" \
      || abort 'cannot read reponame')

    ${cfg.etcDir}/authorize-command \
        "$GIT_SSH_USER" "$GIT_SSH_REPO" "$command" \
      || abort 'access denied'

    repodir=${escapeShellArg cfg.dataDir}/$GIT_SSH_REPO

    systemd-cat -p info -t git \
      echo "authorized exec $command $repodir"

    export GIT_SSH_USER
    export GIT_SSH_REPO
    exec "$command" "$repodir"
  '';

  init-script = pkgs.writeScript "git-init" ''
    #! /bin/sh
    set -euf

    PATH=${makeBinPath (with pkgs; [
      coreutils
      findutils
      gawk
      git
      gnugrep
      gnused
    ])}

    dataDir=${escapeShellArg cfg.dataDir}
    mkdir -p "$dataDir"

    # Notice how the presence of hooks symlinks determine whether
    # we manage a repositry or not.

    # Make sure that no existing repository has hooks.  We can delete
    # symlinks because we assume we created them.
    find "$dataDir" -mindepth 2 -maxdepth 2 -name hooks -type l -delete
    bad_hooks=$(find "$dataDir" -mindepth 2 -maxdepth 2 -name hooks)
    if echo "$bad_hooks" | grep -q .; then
      printf 'error: unknown hooks:\n%s\n' \
        "$(echo "$bad_hooks" | sed 's/^/  /')" \
        >&2
      exit -1
    fi

    # Initialize repositories.
    ${concatMapStringsSep "\n" (repo:
      let
        hooks = scriptFarm "git-hooks" (makeHooks repo);
      in
      ''
        reponame=${escapeShellArg repo.name}
        repodir=$dataDir/$reponame
        mode=${toString (if isPublicRepo repo then 0711 else 0700)}
        if ! test -d "$repodir"; then
          mkdir -m "$mode" "$repodir"
          git init --bare --template=/var/empty "$repodir"
          chown -R git:nogroup "$repodir"
        fi
        ln -s ${hooks} "$repodir/hooks"
      ''
    ) (attrValues cfg.repos)}

    # Warn about repositories that exist but aren't mentioned in the
    # current configuration (and thus didn't receive a hooks symlink).
    unknown_repos=$(find "$dataDir" -mindepth 1 -maxdepth 1 \
      -type d \! -exec test -e '{}/hooks' \; -print)
    if echo "$unknown_repos" | grep -q .; then
      printf 'warning: stale repositories:\n%s\n' \
        "$(echo "$unknown_repos" | sed 's/^/  /')" \
        >&2
    fi
  '';

  makeHooks = repo: removeAttrs repo.hooks [ "pre-receive" ] // {
    pre-receive = ''
      #! /bin/sh
      set -euf

      PATH=${makeBinPath (with pkgs; [
        coreutils # env
        git
        systemd
      ])}

      accept() {
        #systemd-cat -p info -t git echo "authorized $1"
        accept_string="''${accept_string+$accept_string
      }authorized $1"
      }
      reject() {
        #systemd-cat -p err -t git echo "denied $1"
        #echo 'access denied' >&2
        #exit_code=-1
        reject_string="''${reject_string+$reject_string
      }access denied: $1"
      }

      empty=0000000000000000000000000000000000000000

      accept_string=
      reject_string=
      while read oldrev newrev ref; do

        if [ $oldrev = $empty ]; then
          receive_mode=create
        elif [ $newrev = $empty ]; then
          receive_mode=delete
        elif [ "$(git merge-base $oldrev $newrev)" = $oldrev ]; then
          receive_mode=fast-forward
        else
          receive_mode=non-fast-forward
        fi

        if ${cfg.etcDir}/authorize-push \
            "$GIT_SSH_USER" "$GIT_SSH_REPO" "$ref" "$receive_mode"; then
          accept "$receive_mode $ref"
        else
          reject "$receive_mode $ref"
        fi
      done

      if [ -n "$reject_string" ]; then
        systemd-cat -p err -t git echo "$reject_string"
        exit -1
      fi

      systemd-cat -p info -t git echo "$accept_string"

      ${optionalString (hasAttr "post-receive" repo.hooks) ''
        # custom post-receive hook
        ${repo.hooks.post-receive}''}
    '';
  };

in
out