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- ;;; GNU Guix --- Functional package management for GNU
- ;;; Copyright © 2017 Ricardo Wurmus <rekado@elephly.net>
- ;;; Copyright © 2017, 2018 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 (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)
- "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 . #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)))
- 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.
-
- 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)
-
- (apply invoke "tar" "-cf" "layer.tar"
- `(,@transformation-options
- ,@%tar-determinism-options
- ,@paths
- ,@(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.
- (system* "tar" "--delete" "/" "-f" "layer.tar")
- (for-each delete-file-recursively
- (map (compose topmost-component symlink-source)
- symlinks)))
-
- (with-output-to-file "config.json"
- (lambda ()
- (scm->json (config (string-append id "/layer.tar")
- time arch))))
- (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)))
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