gnu/build/chromium-extension.scm

   1 ;;; GNU Guix --- Functional package management for GNU
   2 ;;; Copyright © 2020 Marius Bakke <marius@gnu.org>
   3 ;;;
   4 ;;; This file is part of GNU Guix.
   5 ;;;
   6 ;;; GNU Guix is free software; you can redistribute it and/or modify it
   7 ;;; under the terms of the GNU General Public License as published by
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   9 ;;; your option) any later version.
  10 ;;;
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  13 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 ;;; GNU General Public License for more details.
  15 ;;;
  16 ;;; You should have received a copy of the GNU General Public License
  17 ;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
  18
  19 (define-module (gnu build chromium-extension)
  20   #:use-module (gcrypt base16)
  21   #:use-module ((gcrypt hash) #:prefix hash:)
  22   #:use-module (ice-9 iconv)
  23   #:use-module (guix gexp)
  24   #:use-module (guix packages)
  25   #:use-module (gnu packages base)
  26   #:use-module (gnu packages check)
  27   #:use-module (gnu packages chromium)
  28   #:use-module (gnu packages gnupg)
  29   #:use-module (gnu packages tls)
  30   #:use-module (gnu packages xorg)
  31   #:use-module (guix build-system trivial)
  32   #:export (make-chromium-extension))
  33
  34 ;;; Commentary:
  35 ;;;
  36 ;;; Tools to deal with Chromium extensions.
  37 ;;;
  38 ;;; Code:
  39
  40 (define (make-signing-key seed)
  41   "Return a derivation for a deterministic PKCS #8 private key using SEED."
  42
  43   (define sha256sum
  44     (bytevector->base16-string (hash:sha256 (string->bytevector seed "UTF-8"))))
  45
  46   ;; certtool.c wants a 56 byte seed for a 2048 bit key.
  47   (define size 2048)
  48   (define normalized-seed (string-take sha256sum 56))
  49
  50   (computed-file (string-append seed "-signing-key.pem")
  51                  #~(system* #$(file-append gnutls "/bin/certtool")
  52                             "--generate-privkey"
  53                             "--key-type=rsa"
  54                             "--pkcs8"
  55                             ;; Use the provable FIPS-PUB186-4 algorithm for
  56                             ;; deterministic results.
  57                             "--provable"
  58                             "--password="
  59                             "--no-text"
  60                             (string-append "--bits=" #$(number->string size))
  61                             (string-append "--seed=" #$normalized-seed)
  62                             "--outfile" #$output)
  63                  #:local-build? #t))
  64
  65 (define* (make-crx signing-key package #:optional (package-output "out"))
  66   "Create a signed \".crx\" file from the unpacked Chromium extension residing
  67 in PACKAGE-OUTPUT of PACKAGE.  The extension will be signed with SIGNING-KEY."
  68   (define name (package-name package))
  69   (define version (package-version package))
  70
  71   (with-imported-modules '((guix build utils))
  72     (computed-file
  73      (string-append name "-" version ".crx")
  74      #~(begin
  75          ;; This is not great.  We pull Xorg and Chromium just to Zip and
  76          ;; sign an extension.  This should be implemented with something
  77          ;; lighter.  (TODO: where is the CRXv3 documentation..?)
  78          (use-modules (guix build utils))
  79          (let ((chromium #$(file-append ungoogled-chromium "/bin/chromium"))
  80                (xvfb #$(file-append xorg-server "/bin/Xvfb"))
  81                (packdir "/tmp/extension"))
  82            (mkdir-p (dirname packdir))
  83            (copy-recursively (ungexp package package-output) packdir)
  84            (system (string-append xvfb " :1 &"))
  85            (setenv "DISPLAY" ":1")
  86            (sleep 2)                    ;give Xorg some time to initialize...
  87            ;; Chromium stores the current time in the .crx Zip archive.
  88            ;; Use a fixed timestamp for deterministic behavior.
  89            ;; FIXME (core-updates): faketime is missing an absolute reference
  90            ;; to 'date', hence the need to set PATH.
  91            (setenv "PATH" #$(file-append coreutils "/bin"))
  92            (invoke #$(file-append libfaketime "/bin/faketime")
  93                    "2000-01-01 00:00:00"
  94                    chromium
  95                    "--user-data-dir=/tmp/signing-profile"
  96                    (string-append "--pack-extension=" packdir)
  97                    (string-append "--pack-extension-key=" #$signing-key))
  98            (copy-file (string-append packdir ".crx") #$output)))
  99      #:local-build? #t)))
 100
 101 (define* (crx->chromium-json crx version)
 102   "Return a derivation that creates a Chromium JSON settings file for the
 103 extension given as CRX.  VERSION is used to signify the CRX version, and
 104 must match the version listed in the extension manifest.json."
 105   ;; See chrome/browser/extensions/external_provider_impl.cc and
 106   ;; extensions/common/extension.h for documentation on the JSON format.
 107   (computed-file "extension.json"
 108                  #~(call-with-output-file #$output
 109                      (lambda (port)
 110                        (format port "{
 111   \"external_crx\": \"~a\",
 112   \"external_version\": \"~a\"
 113 }
 114 "
 115                                #$crx #$version)))
 116                  #:local-build? #t))
 117
 118
 119 (define (signing-key->public-der key)
 120   "Return a derivation for a file containing the public key of KEY in DER
 121 format."
 122   (computed-file "der"
 123                  #~(system* #$(file-append gnutls "/bin/certtool")
 124                             "--load-privkey" #$key
 125                             "--pubkey-info"
 126                             "--outfile" #$output
 127                             "--outder")
 128                  #:local-build? #t))
 129
 130 (define (chromium-json->profile-object json signing-key)
 131   "Return a derivation that installs JSON to the directory searched by
 132 Chromium, using a file name (aka extension ID) derived from SIGNING-KEY."
 133   (define der (signing-key->public-der signing-key))
 134
 135   (with-extensions (list guile-gcrypt)
 136     (with-imported-modules '((guix build utils))
 137       (computed-file
 138        "chromium-extension"
 139        #~(begin
 140            (use-modules (guix build utils)
 141                         (gcrypt base16)
 142                         (gcrypt hash))
 143            (define (base16-string->chromium-base16 str)
 144              ;; Translate STR, a hexadecimal string, to a Chromium-style
 145              ;; representation using the letters a-p (where a=0, p=15).
 146              (define s1 "0123456789abcdef")
 147              (define s2 "abcdefghijklmnop")
 148              (let loop ((chars (string->list str))
 149                         (converted '()))
 150                (if (null? chars)
 151                    (list->string (reverse converted))
 152                    (loop (cdr chars)
 153                          (cons (string-ref s2 (string-index s1 (car chars)))
 154                                converted)))))
 155
 156            (let* ((checksum (bytevector->base16-string (file-sha256 #$der)))
 157                   (file-name (base16-string->chromium-base16
 158                               (string-take checksum 32)))
 159                   (extension-directory (string-append #$output
 160                                                       "/share/chromium/extensions")))
 161              (mkdir-p extension-directory)
 162              (symlink #$json (string-append extension-directory "/"
 163                                             file-name ".json"))))
 164        #:local-build? #t))))
 165
 166 (define* (make-chromium-extension p #:optional (output "out"))
 167   "Create a Chromium extension from package P and return a package that,
 168 when installed, will make the extension contained in P available as a
 169 Chromium browser extension.  OUTPUT specifies which output of P to use."
 170   (let* ((pname (package-name p))
 171          (version (package-version p))
 172          (signing-key (make-signing-key pname)))
 173     (package
 174       (inherit p)
 175       (name (string-append pname "-chromium"))
 176       (source #f)
 177       (build-system trivial-build-system)
 178       (native-inputs '())
 179       (inputs
 180        `(("extension" ,(chromium-json->profile-object
 181                         (crx->chromium-json (make-crx signing-key p output)
 182                                             version)
 183                         signing-key))))
 184       (propagated-inputs '())
 185       (outputs '("out"))
 186       (arguments
 187        '(#:modules ((guix build utils))
 188          #:builder
 189          (begin
 190            (use-modules (guix build utils))
 191            (copy-recursively (assoc-ref %build-inputs "extension")
 192                              (assoc-ref %outputs "out"))))))))