Make image archive/save idempotent, using image id and repo tags as keys (#500)

plugins/module_utils/image_archive.py

@@ -0,0 +1,157 @@
+# Copyright 2022 Red Hat | Ansible
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import json
+import os
+import tarfile
+
+from ansible.module_utils.common.text.converters import to_native
+
+
+class ImageArchiveManifestSummary(object):
+    '''
+    Represents data extracted from a manifest.json found in the tar archive output of the
+    "docker image save some:tag > some.tar" command.
+    '''
+
+    def __init__(self, image_id, repo_tags):
+        '''
+        :param image_id:  File name portion of Config entry, e.g. abcde12345 from abcde12345.json
+        :type image_id: str
+        :param repo_tags  Docker image names, e.g. ["hello-world:latest"]
+        :type repo_tags: list
+        '''
+
+        self.image_id = image_id
+        self.repo_tags = repo_tags
+
+
+class ImageArchiveInvalidException(Exception):
+    def __init__(self, message, cause):
+        '''
+        :param message: Exception message
+        :type message: str
+        :param cause: Inner exception that this exception wraps
+        :type cause: Exception | None
+        '''
+
+        super(ImageArchiveInvalidException, self).__init__(message)
+
+        # Python 2 doesn't support causes
+        self.cause = cause
+
+
+def api_image_id(archive_image_id):
+    '''
+    Accepts an image hash in the format stored in manifest.json, and returns an equivalent identifier
+    that represents the same image hash, but in the format presented by the Docker Engine API.
+
+    :param archive_image_id: plain image hash
+    :type archive_image_id: str
+
+    :returns: Prefixed hash used by REST api
+    :rtype: str
+    '''
+
+    return 'sha256:%s' % archive_image_id
+
+
+def archived_image_manifest(archive_path):
+    '''
+    Attempts to get Image.Id and image name from metadata stored in the image
+    archive tar file.
+
+    The tar should contain a file "manifest.json" with an array with a single entry,
+    and the entry should have a Config field with the image ID in its file name, as
+    well as a RepoTags list, which typically has only one entry.
+
+    :raises:
+        ImageArchiveInvalidException: A file already exists at archive_path, but could not extract an image ID from it.
+
+    :param archive_path: Tar file to read
+    :type archive_path: str
+
+    :return: None, if no file at archive_path, or the extracted image ID, which will not have a sha256: prefix.
+    :rtype: ImageArchiveManifestSummary
+    '''
+
+    try:
+        # FileNotFoundError does not exist in Python 2
+        if not os.path.isfile(archive_path):
+            return None
+
+        tf = tarfile.open(archive_path, 'r')
+        try:
+            try:
+                ef = tf.extractfile('manifest.json')
+                try:
+                    text = ef.read().decode('utf-8')
+                    manifest = json.loads(text)
+                except Exception as exc:
+                    raise ImageArchiveInvalidException(
+                        "Failed to decode and deserialize manifest.json: %s" % to_native(exc),
+                        exc
+                    )
+                finally:
+                    # In Python 2.6, this does not have __exit__
+                    ef.close()
+
+                if len(manifest) != 1:
+                    raise ImageArchiveInvalidException(
+                        "Expected to have one entry in manifest.json but found %s" % len(manifest),
+                        None
+                    )
+
+                m0 = manifest[0]
+
+                try:
+                    config_file = m0['Config']
+                except KeyError as exc:
+                    raise ImageArchiveInvalidException(
+                        "Failed to get Config entry from manifest.json: %s" % to_native(exc),
+                        exc
+                    )
+
+                # Extracts hash without 'sha256:' prefix
+                try:
+                    # Strip off .json filename extension, leaving just the hash.
+                    image_id = os.path.splitext(config_file)[0]
+                except Exception as exc:
+                    raise ImageArchiveInvalidException(
+                        "Failed to extract image id from config file name %s: %s" % (config_file, to_native(exc)),
+                        exc
+                    )
+
+                try:
+                    repo_tags = m0['RepoTags']
+                except KeyError as exc:
+                    raise ImageArchiveInvalidException(
+                        "Failed to get RepoTags entry from manifest.json: %s" % to_native(exc),
+                        exc
+                    )
+
+                return ImageArchiveManifestSummary(
+                    image_id=image_id,
+                    repo_tags=repo_tags
+                )
+
+            except ImageArchiveInvalidException:
+                raise
+            except Exception as exc:
+                raise ImageArchiveInvalidException(
+                    "Failed to extract manifest.json from tar file %s: %s" % (archive_path, to_native(exc)),
+                    exc
+                )
+
+        finally:
+            # In Python 2.6, TarFile does not have __exit__
+            tf.close()
+
+    except ImageArchiveInvalidException:
+        raise
+    except Exception as exc:
+        raise ImageArchiveInvalidException("Failed to open tar file %s: %s" % (archive_path, to_native(exc)), exc)