depot/pkgs/build-support/build-fhsenv-bubblewrap/default.nix

{ lib
, stdenv
, callPackage
, runCommandLocal
, writeShellScript
, glibc
, pkgsHostTarget
, runCommandCC
, coreutils
, bubblewrap
}:

{ runScript ? "bash"
, nativeBuildInputs ? []
, extraInstallCommands ? ""
, meta ? {}
, passthru ? {}
, extraPreBwrapCmds ? ""
, extraBwrapArgs ? []
, unshareUser ? false
, unshareIpc ? false
, unsharePid ? false
, unshareNet ? false
, unshareUts ? false
, unshareCgroup ? false
, privateTmp ? false
, dieWithParent ? true
, ...
} @ args:

assert (!args ? pname || !args ? version) -> (args ? name); # You must provide name if pname or version (preferred) is missing.

let
  inherit (lib)
    concatLines
    concatStringsSep
    escapeShellArgs
    filter
    optionalString
    splitString
    ;

  inherit (lib.attrsets) removeAttrs;

  # The splicing code does not handle `pkgsi686Linux` well, so we have to be
  # explicit about which package set it's coming from.
  inherit (pkgsHostTarget) pkgsi686Linux;

  name = args.name or "${args.pname}-${args.version}";
  executableName = args.pname or args.name;
  # we don't know which have been supplied, and want to avoid defaulting missing attrs to null. Passed into runCommandLocal
  nameAttrs = lib.filterAttrs (key: value: builtins.elem key [ "name" "pname" "version" ]) args;

  buildFHSEnv = callPackage ./buildFHSEnv.nix { };

  fhsenv = buildFHSEnv (removeAttrs args [
    "runScript" "extraInstallCommands" "meta" "passthru" "extraPreBwrapCmds" "extraBwrapArgs" "dieWithParent"
    "unshareUser" "unshareCgroup" "unshareUts" "unshareNet" "unsharePid" "unshareIpc" "privateTmp"
  ]);

  etcBindEntries = let
    files = [
      # NixOS Compatibility
      "static"
      "nix" # mainly for nixUnstable users, but also for access to nix/netrc
      # Shells
      "shells"
      "bashrc"
      "zshenv"
      "zshrc"
      "zinputrc"
      "zprofile"
      # Users, Groups, NSS
      "passwd"
      "group"
      "shadow"
      "hosts"
      "resolv.conf"
      "nsswitch.conf"
      # User profiles
      "profiles"
      # Sudo & Su
      "login.defs"
      "sudoers"
      "sudoers.d"
      # Time
      "localtime"
      "zoneinfo"
      # Other Core Stuff
      "machine-id"
      "os-release"
      # PAM
      "pam.d"
      # Fonts
      "fonts"
      # ALSA
      "alsa"
      "asound.conf"
      # SSL
      "ssl/certs"
      "ca-certificates"
      "pki"
    ];
  in map (path: "/etc/${path}") files;

  # Here's the problem case:
  # - we need to run bash to run the init script
  # - LD_PRELOAD may be set to another dynamic library, requiring us to discover its dependencies
  # - oops! ldconfig is part of the init script, and it hasn't run yet
  # - everything explodes
  #
  # In particular, this happens with fhsenvs in fhsenvs, e.g. when running
  # a wrapped game from Steam.
  #
  # So, instead of doing that, we build a tiny static (important!) shim
  # that executes ldconfig in a completely clean environment to generate
  # the initial cache, and then execs into the "real" init, which is the
  # first time we see anything dynamically linked at all.
  #
  # Also, the real init is placed strategically at /init, so we don't
  # have to recompile this every time.
  containerInit = runCommandCC "container-init" {
    buildInputs = [ stdenv.cc.libc.static or null ];
  } ''
    $CXX -static -s -o $out ${./container-init.cc}
  '';

  realInit = run: writeShellScript "${name}-init" ''
    source /etc/profile
    exec ${run} "$@"
  '';

  indentLines = str: concatLines (map (s: "  " + s) (filter (s: s != "") (splitString "\n" str)));
  bwrapCmd = { initArgs ? "" }: ''
    ignored=(/nix /dev /proc /etc ${optionalString privateTmp "/tmp"})
    ro_mounts=()
    symlinks=()
    etc_ignored=()

    ${extraPreBwrapCmds}

    # loop through all entries of root in the fhs environment, except its /etc.
    for i in ${fhsenv}/*; do
      path="/''${i##*/}"
      if [[ $path == '/etc' ]]; then
        :
      elif [[ -L $i ]]; then
        symlinks+=(--symlink "$(${coreutils}/bin/readlink "$i")" "$path")
        ignored+=("$path")
      else
        ro_mounts+=(--ro-bind "$i" "$path")
        ignored+=("$path")
      fi
    done

    # loop through the entries of /etc in the fhs environment.
    if [[ -d ${fhsenv}/etc ]]; then
      for i in ${fhsenv}/etc/*; do
        path="/''${i##*/}"
        # NOTE: we're binding /etc/fonts and /etc/ssl/certs from the host so we
        # don't want to override it with a path from the FHS environment.
        if [[ $path == '/fonts' || $path == '/ssl' ]]; then
          continue
        fi
        if [[ -L $i ]]; then
          symlinks+=(--symlink "$i" "/etc$path")
        else
          ro_mounts+=(--ro-bind "$i" "/etc$path")
        fi
        etc_ignored+=("/etc$path")
      done
    fi

    # propagate /etc from the actual host if nested
    if [[ -e /.host-etc ]]; then
      ro_mounts+=(--ro-bind /.host-etc /.host-etc)
    else
      ro_mounts+=(--ro-bind /etc /.host-etc)
    fi

    # link selected etc entries from the actual root
    for i in ${escapeShellArgs etcBindEntries}; do
      if [[ "''${etc_ignored[@]}" =~ "$i" ]]; then
        continue
      fi
      if [[ -e $i ]]; then
        symlinks+=(--symlink "/.host-etc/''${i#/etc/}" "$i")
      fi
    done

    declare -a auto_mounts
    # loop through all directories in the root
    for dir in /*; do
      # if it is a directory and it is not ignored
      if [[ -d "$dir" ]] && [[ ! "''${ignored[@]}" =~ "$dir" ]]; then
        # add it to the mount list
        auto_mounts+=(--bind "$dir" "$dir")
      fi
    done

    declare -a x11_args
    # Always mount a tmpfs on /tmp/.X11-unix
    # Rationale: https://github.com/flatpak/flatpak/blob/be2de97e862e5ca223da40a895e54e7bf24dbfb9/common/flatpak-run.c#L277
    x11_args+=(--tmpfs /tmp/.X11-unix)

    # Try to guess X socket path. This doesn't cover _everything_, but it covers some things.
    if [[ "$DISPLAY" == *:* ]]; then
      # recover display number from $DISPLAY formatted [host]:num[.screen]
      display_nr=''${DISPLAY/#*:} # strip host
      display_nr=''${display_nr/%.*} # strip screen
      local_socket=/tmp/.X11-unix/X$display_nr
      x11_args+=(--ro-bind-try "$local_socket" "$local_socket")
    fi

    ${optionalString privateTmp ''
    # sddm places XAUTHORITY in /tmp
    if [[ "$XAUTHORITY" == /tmp/* ]]; then
      x11_args+=(--ro-bind-try "$XAUTHORITY" "$XAUTHORITY")
    fi

    # dbus-run-session puts the socket in /tmp
    IFS=";" read -ra addrs <<<"$DBUS_SESSION_BUS_ADDRESS"
    for addr in "''${addrs[@]}"; do
      [[ "$addr" == unix:* ]] || continue
      IFS="," read -ra parts <<<"''${addr#unix:}"
      for part in "''${parts[@]}"; do
        printf -v part '%s' "''${part//\\/\\\\}"
        printf -v part '%b' "''${part//%/\\x}"
        [[ "$part" == path=/tmp/* ]] || continue
        x11_args+=(--ro-bind-try "''${part#path=}" "''${part#path=}")
      done
    done
    ''}

    cmd=(
      ${bubblewrap}/bin/bwrap
      --dev-bind /dev /dev
      --proc /proc
      --chdir "$(pwd)"
      ${optionalString unshareUser "--unshare-user"}
      ${optionalString unshareIpc "--unshare-ipc"}
      ${optionalString unsharePid "--unshare-pid"}
      ${optionalString unshareNet "--unshare-net"}
      ${optionalString unshareUts "--unshare-uts"}
      ${optionalString unshareCgroup "--unshare-cgroup"}
      ${optionalString dieWithParent "--die-with-parent"}
      --ro-bind /nix /nix
      ${optionalString privateTmp "--tmpfs /tmp"}
      # Our glibc will look for the cache in its own path in `/nix/store`.
      # As such, we need a cache to exist there, because pressure-vessel
      # depends on the existence of an ld cache. However, adding one
      # globally proved to be a bad idea (see #100655), the solution we
      # settled on being mounting one via bwrap.
      # Also, the cache needs to go to both 32 and 64 bit glibcs, for games
      # of both architectures to work.
      --tmpfs ${glibc}/etc \
      --tmpfs /etc \
      --symlink /etc/ld.so.conf ${glibc}/etc/ld.so.conf \
      --symlink /etc/ld.so.cache ${glibc}/etc/ld.so.cache \
      --ro-bind ${glibc}/etc/rpc ${glibc}/etc/rpc \
      --remount-ro ${glibc}/etc \
      --symlink ${realInit runScript} /init \
  '' + optionalString fhsenv.isMultiBuild (indentLines ''
      --tmpfs ${pkgsi686Linux.glibc}/etc \
      --symlink /etc/ld.so.conf ${pkgsi686Linux.glibc}/etc/ld.so.conf \
      --symlink /etc/ld.so.cache ${pkgsi686Linux.glibc}/etc/ld.so.cache \
      --ro-bind ${pkgsi686Linux.glibc}/etc/rpc ${pkgsi686Linux.glibc}/etc/rpc \
      --remount-ro ${pkgsi686Linux.glibc}/etc \
  '') + ''
      "''${ro_mounts[@]}"
      "''${symlinks[@]}"
      "''${auto_mounts[@]}"
      "''${x11_args[@]}"
      ${concatStringsSep "\n  " extraBwrapArgs}
      ${containerInit} ${initArgs}
    )
    exec "''${cmd[@]}"
  '';

  bin = writeShellScript "${name}-bwrap" (bwrapCmd { initArgs = ''"$@"''; });
in runCommandLocal name (nameAttrs // {
  inherit nativeBuildInputs meta;

  passthru = passthru // {
    env = runCommandLocal "${name}-shell-env" {
      shellHook = bwrapCmd {};
    } ''
      echo >&2 ""
      echo >&2 "*** User chroot 'env' attributes are intended for interactive nix-shell sessions, not for building! ***"
      echo >&2 ""
      exit 1
    '';
    inherit args fhsenv;
  };
}) ''
  mkdir -p $out/bin
  ln -s ${bin} $out/bin/${executableName}

  ${extraInstallCommands}
''