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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2020 Marius Bakke <marius@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (gnu build chromium-extension)
#:use-module (gcrypt base16)
#:use-module ((gcrypt hash) #:prefix hash:)
#:use-module (ice-9 iconv)
#:use-module (guix gexp)
#:use-module (guix packages)
#:use-module (gnu packages base)
#:use-module (gnu packages check)
#:use-module (gnu packages chromium)
#:use-module (gnu packages gnupg)
#:use-module (gnu packages tls)
#:use-module (gnu packages xorg)
#:use-module (guix build-system trivial)
#:export (make-chromium-extension))
;;; Commentary:
;;;
;;; Tools to deal with Chromium extensions.
;;;
;;; Code:
(define (make-signing-key seed)
"Return a derivation for a deterministic PKCS #8 private key using SEED."
(define sha256sum
(bytevector->base16-string (hash:sha256 (string->bytevector seed "UTF-8"))))
;; certtool.c wants a 56 byte seed for a 2048 bit key.
(define size 2048)
(define normalized-seed (string-take sha256sum 56))
(computed-file (string-append seed "-signing-key.pem")
#~(system* #$(file-append gnutls "/bin/certtool")
"--generate-privkey"
"--key-type=rsa"
"--pkcs8"
;; Use the provable FIPS-PUB186-4 algorithm for
;; deterministic results.
"--provable"
"--password="
"--no-text"
(string-append "--bits=" #$(number->string size))
(string-append "--seed=" #$normalized-seed)
"--outfile" #$output)
#:local-build? #t))
(define* (make-crx signing-key package #:optional (package-output "out"))
"Create a signed \".crx\" file from the unpacked Chromium extension residing
in PACKAGE-OUTPUT of PACKAGE. The extension will be signed with SIGNING-KEY."
(define name (package-name package))
(define version (package-version package))
(with-imported-modules '((guix build utils))
(computed-file
(string-append name "-" version ".crx")
#~(begin
;; This is not great. We pull Xorg and Chromium just to Zip and
;; sign an extension. This should be implemented with something
;; lighter. (TODO: where is the CRXv3 documentation..?)
(use-modules (guix build utils))
(let ((chromium #$(file-append ungoogled-chromium "/bin/chromium"))
(xvfb #$(file-append xorg-server "/bin/Xvfb"))
(packdir "/tmp/extension"))
(mkdir-p (dirname packdir))
(copy-recursively (ungexp package package-output) packdir)
(system (string-append xvfb " :1 &"))
(setenv "DISPLAY" ":1")
(sleep 2) ;give Xorg some time to initialize...
;; Chromium stores the current time in the .crx Zip archive.
;; Use a fixed timestamp for deterministic behavior.
;; FIXME (core-updates): faketime is missing an absolute reference
;; to 'date', hence the need to set PATH.
(setenv "PATH" #$(file-append coreutils "/bin"))
(invoke #$(file-append libfaketime "/bin/faketime")
"2000-01-01 00:00:00"
chromium
"--user-data-dir=/tmp/signing-profile"
(string-append "--pack-extension=" packdir)
(string-append "--pack-extension-key=" #$signing-key))
(copy-file (string-append packdir ".crx") #$output)))
#:local-build? #t)))
(define* (crx->chromium-json crx version)
"Return a derivation that creates a Chromium JSON settings file for the
extension given as CRX. VERSION is used to signify the CRX version, and
must match the version listed in the extension manifest.json."
;; See chrome/browser/extensions/external_provider_impl.cc and
;; extensions/common/extension.h for documentation on the JSON format.
(computed-file "extension.json"
#~(call-with-output-file #$output
(lambda (port)
(format port "{
\"external_crx\": \"~a\",
\"external_version\": \"~a\"
}
"
#$crx #$version)))
#:local-build? #t))
(define (signing-key->public-der key)
"Return a derivation for a file containing the public key of KEY in DER
format."
(computed-file "der"
#~(system* #$(file-append gnutls "/bin/certtool")
"--load-privkey" #$key
"--pubkey-info"
"--outfile" #$output
"--outder")
#:local-build? #t))
(define (chromium-json->profile-object json signing-key)
"Return a derivation that installs JSON to the directory searched by
Chromium, using a file name (aka extension ID) derived from SIGNING-KEY."
(define der (signing-key->public-der signing-key))
(with-extensions (list guile-gcrypt)
(with-imported-modules '((guix build utils))
(computed-file
"chromium-extension"
#~(begin
(use-modules (guix build utils)
(gcrypt base16)
(gcrypt hash))
(define (base16-string->chromium-base16 str)
;; Translate STR, a hexadecimal string, to a Chromium-style
;; representation using the letters a-p (where a=0, p=15).
(define s1 "0123456789abcdef")
(define s2 "abcdefghijklmnop")
(let loop ((chars (string->list str))
(converted '()))
(if (null? chars)
(list->string (reverse converted))
(loop (cdr chars)
(cons (string-ref s2 (string-index s1 (car chars)))
converted)))))
(let* ((checksum (bytevector->base16-string (file-sha256 #$der)))
(file-name (base16-string->chromium-base16
(string-take checksum 32)))
(extension-directory (string-append #$output
"/share/chromium/extensions")))
(mkdir-p extension-directory)
(symlink #$json (string-append extension-directory "/"
file-name ".json"))))
#:local-build? #t))))
(define* (make-chromium-extension p #:optional (output "out"))
"Create a Chromium extension from package P and return a package that,
when installed, will make the extension contained in P available as a
Chromium browser extension. OUTPUT specifies which output of P to use."
(let* ((pname (package-name p))
(version (package-version p))
(signing-key (make-signing-key pname)))
(package
(inherit p)
(name (string-append pname "-chromium"))
(source #f)
(build-system trivial-build-system)
(native-inputs '())
(inputs
`(("extension" ,(chromium-json->profile-object
(crx->chromium-json (make-crx signing-key p output)
version)
signing-key))))
(propagated-inputs '())
(outputs '("out"))
(arguments
'(#:modules ((guix build utils))
#:builder
(begin
(use-modules (guix build utils))
(copy-recursively (assoc-ref %build-inputs "extension")
(assoc-ref %outputs "out"))))))))
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