tor: initial updateScript

Tested briefly, seems to work okay. The gpg stuff could be better,
however.

pkgs/tools/security/tor/default.nix

@@ -1,5 +1,17 @@
 { stdenv, fetchurl, pkgconfig, libevent, openssl, zlib, torsocks
 , libseccomp, systemd, libcap
+
+# for update.nix
+, writeScript
+, runCommand
+, common-updater-scripts
+, bash
+, coreutils
+, curl
+, gnugrep
+, gnupg
+, gnused
+, nix
 }:
 
 stdenv.mkDerivation rec {
@@ -34,6 +46,22 @@ stdenv.mkDerivation rec {
 
   doCheck = true;
 
+  passthru.updateScript = import ./update.nix {
+    inherit (stdenv) lib;
+    inherit
+      writeScript
+      runCommand
+      common-updater-scripts
+      bash
+      coreutils
+      curl
+      gnupg
+      gnugrep
+      gnused
+      nix
+    ;
+  };
+
   meta = with stdenv.lib; {
     homepage = https://www.torproject.org/;
     repositories.git = https://git.torproject.org/git/tor;

pkgs/tools/security/tor/update.nix

@@ -0,0 +1,72 @@
+{ lib
+, writeScript
+, runCommand
+, common-updater-scripts
+, bash
+, coreutils
+, curl
+, gnugrep
+, gnupg
+, gnused
+, nix
+}:
+
+with lib;
+
+let
+  downloadPageUrl = "https://dist.torproject.org";
+
+  # See https://www.torproject.org/docs/signing-keys.html
+  signingKeys = [
+    # Roger Dingledine
+    "B117 2656 DFF9 83C3 042B C699 EB5A 896A 2898 8BF5"
+    "F65C E37F 04BA 5B36 0AE6 EE17 C218 5258 19F7 8451"
+    # Nick Mathewson
+    "2133 BC60 0AB1 33E1 D826 D173 FE43 009C 4607 B1FB"
+    "B117 2656 DFF9 83C3 042B C699 EB5A 896A 2898 8BF5"
+  ];
+in
+
+writeScript "update-tor" ''
+#! ${bash}/bin/bash
+
+set -eu -o pipefail
+
+export PATH=${makeBinPath [
+  common-updater-scripts
+  coreutils
+  curl
+  gnugrep
+  gnupg
+  gnused
+  nix
+]}
+
+srcBase=$(curl -L --list-only -- "${downloadPageUrl}" \
+  | grep -Eo 'tor-([[:digit:]]+\.?)+\.tar\.gz' \
+  | sort -Vu \
+  | tail -n1)
+srcFile=$srcBase
+srcUrl=${downloadPageUrl}/$srcBase
+
+srcName=''${srcBase/.tar.gz/}
+srcVers=(''${srcName//-/ })
+version=''${srcVers[1]}
+
+sigUrl=$srcUrl.asc
+sigFile=''${sigUrl##*/}
+
+# upstream does not support byte ranges ...
+[[ -e "$srcFile" ]] || curl -L -o "$srcFile" -- "$srcUrl"
+[[ -e "$sigFile" ]] || curl -L -o "$sigFile" -- "$sigUrl"
+
+export GNUPGHOME=$PWD/gnupg
+mkdir -m 700 -p "$GNUPGHOME"
+
+gpg --batch --recv-keys ${concatStringsSep " " (map (x: "'${x}'") signingKeys)}
+gpg --batch --verify "$sigFile" "$srcFile"
+
+sha256=$(nix-hash --type sha256 --flat --base32 "$srcFile")
+
+update-source-version tor "$version" "$sha256"
+''