aboutsummaryrefslogtreecommitdiff
path: root/guix/docker.scm
blob: 7fe83d9797e3930c64afd4ef6758caa4edc7ac52 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2017 Ricardo Wurmus <rekado@elephly.net>
;;; Copyright © 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2018 Chris Marusich <cmmarusich@gmail.com>
;;;
;;; 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 (guix docker)
  #:use-module (gcrypt hash)
  #:use-module (guix base16)
  #:use-module ((guix build utils)
                #:select (mkdir-p
                          delete-file-recursively
                          with-directory-excursion
                          invoke))
  #:use-module (gnu build install)
  #:use-module (json)                             ;guile-json
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module ((texinfo string-utils)
                #:select (escape-special-chars))
  #:use-module (rnrs bytevectors)
  #:use-module (ice-9 match)
  #:export (build-docker-image))

;; Generate a 256-bit identifier in hexadecimal encoding for the Docker image.
(define docker-id
  (compose bytevector->base16-string sha256 string->utf8))

(define (layer-diff-id layer)
  "Generate a layer DiffID for the given LAYER archive."
  (string-append "sha256:" (bytevector->base16-string (file-sha256 layer))))

;; This is the semantic version of the JSON metadata schema according to
;; https://github.com/docker/docker/blob/master/image/spec/v1.2.md
;; It is NOT the version of the image specification.
(define schema-version "1.0")

(define (image-description id time)
  "Generate a simple image description."
  `((id . ,id)
    (created . ,time)
    (container_config . #nil)))

(define (generate-tag path)
  "Generate an image tag for the given PATH."
  (match (string-split (basename path) #\-)
    ((hash name . rest) (string-append name ":" hash))))

(define (manifest path id)
  "Generate a simple image manifest."
  `(((Config . "config.json")
     (RepoTags . (,(generate-tag path)))
     (Layers . (,(string-append id "/layer.tar"))))))

;; According to the specifications this is required for backwards
;; compatibility.  It duplicates information provided by the manifest.
(define (repositories path id)
  "Generate a repositories file referencing PATH and the image ID."
  `((,(generate-tag path) . ((latest . ,id)))))

;; See https://github.com/opencontainers/image-spec/blob/master/config.md
(define* (config layer time arch #:key entry-point)
  "Generate a minimal image configuration for the given LAYER file."
  ;; "architecture" must be values matching "platform.arch" in the
  ;; runtime-spec at
  ;; https://github.com/opencontainers/runtime-spec/blob/v1.0.0-rc2/config.md#platform
  `((architecture . ,arch)
    (comment . "Generated by GNU Guix")
    (created . ,time)
    (config . ,(if entry-point
                   `((entrypoint . ,entry-point))
                   #nil))
    (container_config . #nil)
    (os . "linux")
    (rootfs . ((type . "layers")
               (diff_ids . (,(layer-diff-id layer)))))))

(define %tar-determinism-options
  ;; GNU tar options to produce archives deterministically.
  '("--sort=name" "--mtime=@1"
    "--owner=root:0" "--group=root:0"))

(define symlink-source
  (match-lambda
    ((source '-> target)
     (string-trim source #\/))))

(define (topmost-component file)
  "Return the topmost component of FILE.  For instance, if FILE is \"/a/b/c\",
return \"a\"."
  (match (string-tokenize file (char-set-complement (char-set #\/)))
    ((first rest ...)
     first)))

(define* (build-docker-image image paths prefix
                             #:key
                             (symlinks '())
                             (transformations '())
                             (system (utsname:machine (uname)))
                             database
                             entry-point
                             compressor
                             (creation-time (current-time time-utc)))
  "Write to IMAGE a Docker image archive containing the given PATHS.  PREFIX
must be a store path that is a prefix of any store paths in PATHS.

When DATABASE is true, copy it to /var/guix/db in the image and create
/var/guix/gcroots and friends.

When ENTRY-POINT is true, it must be a list of strings; it is stored as the
entry point in the Docker image JSON structure.

SYMLINKS must be a list of (SOURCE -> TARGET) tuples describing symlinks to be
created in the image, where each TARGET is relative to PREFIX.
TRANSFORMATIONS must be a list of (OLD -> NEW) tuples describing how to
transform the PATHS.  Any path in PATHS that begins with OLD will be rewritten
in the Docker image so that it begins with NEW instead.  If a path is a
non-empty directory, then its contents will be recursively added, as well.

SYSTEM is a GNU triplet (or prefix thereof) of the system the binaries in
PATHS are for; it is used to produce metadata in the image.  Use COMPRESSOR, a
command such as '(\"gzip\" \"-9n\"), to compress IMAGE.  Use CREATION-TIME, a
SRFI-19 time-utc object, as the creation time in metadata."
  (define (sanitize path-fragment)
    (escape-special-chars
     ;; GNU tar strips the leading slash off of absolute paths before applying
     ;; the transformations, so we need to do the same, or else our
     ;; replacements won't match any paths.
     (string-trim path-fragment #\/)
     ;; Escape the basic regexp special characters (see: "(sed) BRE syntax").
     ;; We also need to escape "/" because we use it as a delimiter.
     "/*.^$[]\\"
     #\\))
  (define transformation->replacement
    (match-lambda
      ((old '-> new)
       ;; See "(tar) transform" for details on the expression syntax.
       (string-append "s/^" (sanitize old) "/" (sanitize new) "/"))))
  (define (transformations->expression transformations)
    (let ((replacements (map transformation->replacement transformations)))
      (string-append
       ;; Avoid transforming link targets, since that would break some links
       ;; (e.g., symlinks that point to an absolute store path).
       "flags=rSH;"
       (string-join replacements ";")
       ;; Some paths might still have a leading path delimiter even after tar
       ;; transforms them (e.g., "/a/b" might be transformed into "/b"), so
       ;; strip any leading path delimiters that remain.
       ";s,^//*,,")))
  (define transformation-options
    (if (eq? '() transformations)
        '()
        `("--transform" ,(transformations->expression transformations))))
  (let* ((directory "/tmp/docker-image") ;temporary working directory
         (id (docker-id prefix))
         (time (date->string (time-utc->date creation-time) "~4"))
         (arch (let-syntax ((cond* (syntax-rules ()
                                     ((_ (pattern clause) ...)
                                      (cond ((string-prefix? pattern system)
                                             clause)
                                            ...
                                            (else
                                             (error "unsupported system"
                                                    system)))))))
                 (cond* ("x86_64" "amd64")
                        ("i686"   "386")
                        ("arm"    "arm")
                        ("mips64" "mips64le")))))
    ;; Make sure we start with a fresh, empty working directory.
    (mkdir directory)
    (with-directory-excursion directory
      (mkdir id)
      (with-directory-excursion id
        (with-output-to-file "VERSION"
          (lambda () (display schema-version)))
        (with-output-to-file "json"
          (lambda () (scm->json (image-description id time))))

        ;; Create SYMLINKS.
        (for-each (match-lambda
                    ((source '-> target)
                     (let ((source (string-trim source #\/)))
                       (mkdir-p (dirname source))
                       (symlink (string-append prefix "/" target)
                                source))))
                  symlinks)

        (when database
          ;; Initialize /var/guix, assuming PREFIX points to a profile.
          (install-database-and-gc-roots "." database prefix))

        (apply invoke "tar" "-cf" "layer.tar"
               `(,@transformation-options
                 ,@%tar-determinism-options
                 ,@paths
                 ,@(if database '("var") '())
                 ,@(map symlink-source symlinks)))
        ;; It is possible for "/" to show up in the archive, especially when
        ;; applying transformations.  For example, the transformation
        ;; "s,^/a,," will (perhaps surprisingly) cause GNU tar to transform
        ;; the path "/a" into "/".  The presence of "/" in the archive is
        ;; probably benign, but it is definitely safe to remove it, so let's
        ;; do that.  This fails when "/" is not in the archive, so use system*
        ;; instead of invoke to avoid an exception in that case, and redirect
        ;; stderr to the bit bucket to avoid "Exiting with failure status"
        ;; error messages.
        (with-error-to-port (%make-void-port "w")
          (lambda ()
            (system* "tar" "--delete" "/" "-f" "layer.tar")))

        (for-each delete-file-recursively
                  (map (compose topmost-component symlink-source)
                       symlinks))

        ;; Delete /var/guix.
        (when database
          (delete-file-recursively "var")))

      (with-output-to-file "config.json"
        (lambda ()
          (scm->json (config (string-append id "/layer.tar")
                             time arch
                             #:entry-point entry-point))))
      (with-output-to-file "manifest.json"
        (lambda ()
          (scm->json (manifest prefix id))))
      (with-output-to-file "repositories"
        (lambda ()
          (scm->json (repositories prefix id)))))

    (apply invoke "tar" "-cf" image "-C" directory
           `(,@%tar-determinism-options
             ,@(if compressor
                   (list "-I" (string-join compressor))
                   '())
             "."))
    (delete-file-recursively directory)))