docker_pull.py

import gzip
import hashlib
import json
import os
import shutil
import sys
import tarfile
from io import BytesIO

import requests
import urllib3

urllib3.disable_warnings()

if len(sys.argv) != 2:
    print('Usage:\n\tdocker_pull.py [repository/]image[:tag]\n')
    exit(1)

# Look for the Docker image to download
repo = 'library'
tag = 'latest'
try:
    repo, imgtag = sys.argv[1].split('/')
except ValueError:
    imgtag = sys.argv[1]
try:
    img, tag = imgtag.split(':')
except ValueError:
    img = imgtag
repository = '{}/{}'.format(repo, img)

# Get Docker token and fetch manifest v2
resp = requests.get('https://auth.docker.io/token?service=registry.docker.io&scope=repository:' + repository + ':pull',
                    verify=False)
access_token = resp.json()['access_token']
auth_head = {'Authorization': 'Bearer ' + access_token,
             'Accept': 'application/vnd.docker.distribution.manifest.v2+json'}

# Get image layer digests
resp = requests.get('https://registry-1.docker.io/v2/{}/manifests/{}'.format(repository, tag), headers=auth_head,
                    verify=False)
if resp.status_code != 200:
    print('Cannot fetch manifest for {} [HTTP {}]'.format(repository, resp.status_code))
    exit(1)
layers = resp.json()['layers']

# Create tmp folder that will hold the image
imgdir = 'tmp_{}_{}'.format(img, tag)
if not os.path.exists(imgdir):
    print('Creating image structure in: ' + imgdir)
    os.mkdir(imgdir)

config = resp.json()['config']['digest']
confresp = requests.get('https://registry-1.docker.io/v2/{}/blobs/{}'.format(repository, config), headers=auth_head,
                        verify=False)
file = open('{}/{}.json'.format(imgdir, config[7:]), 'wb')
file.write(confresp.content)
file.close()

content = [{
    'Config': config[7:] + '.json',
    'RepoTags': [repository + ':' + tag],
    'Layers': []
}]

empty_json = '{"created":"1970-01-01T00:00:00Z","container_config":{"Hostname":"","Domainname":"","User":"","AttachStdin":false, \
	"AttachStdout":false,"AttachStderr":false,"Tty":false,"OpenStdin":false, "StdinOnce":false,"Env":null,"Cmd":null,"Image":"", \
	"Volumes":null,"WorkingDir":"","Entrypoint":null,"OnBuild":null,"Labels":null}}'

# Build layer folders
parentid = ''
for layer in layers:
    ublob = layer['digest']
    # FIXME: Creating fake layer ID. Don't know how Docker generates it
    fake_layerid_raw = parentid + '\n' + ublob + '\n'
    fake_layerid = hashlib.sha256(fake_layerid_raw.encode('utf-8')).hexdigest()
    layerdir = imgdir + '/' + fake_layerid
    os.mkdir(layerdir)

    # Creating VERSION file
    file = open(layerdir + '/VERSION', 'w')
    file.write('1.0')
    file.close()

    # Creating layer.tar file
    print(ublob[7:19] + ': Downloading...', )
    sys.stdout.flush()
    bresp = requests.get('https://registry-1.docker.io/v2/{}/blobs/{}'.format(repository, ublob), headers=auth_head,
                         verify=False)
    print("\r{}: Pull complete [{}]".format(ublob[7:19], bresp.headers['Content-Length']))
    content[0]['Layers'].append(fake_layerid + '/layer.tar')
    file = open(layerdir + '/layer.tar', "wb")
    mybuff = BytesIO(bresp.content)
    unzLayer = gzip.GzipFile(fileobj=mybuff)
    file.write(unzLayer.read())
    unzLayer.close()
    file.close()

    # Creating json file
    file = open(layerdir + '/json', 'w')
    # last layer = config manifest - history - rootfs
    if layers[-1]['digest'] == layer['digest']:
        # FIXME: json.loads() automatically converts to unicode, thus decoding values whereas Docker doesn't
        json_obj = json.loads(confresp.content)
        del json_obj['history']
        del json_obj['rootfs']
    else:  # other layers json are empty
        json_obj = json.loads(empty_json)
    json_obj['id'] = fake_layerid
    if parentid:
        json_obj['parent'] = parentid
    parentid = json_obj['id']
    file.write(json.dumps(json_obj))
    file.close()

file = open(imgdir + '/manifest.json', 'w')
file.write(json.dumps(content))
file.close()

content = {repository: {tag: fake_layerid}}
file = open(imgdir + '/repositories', 'w')
file.write(json.dumps(content))
file.close()

# Create image tar and clean tmp folder
docker_tar = repo + '_' + img + '.tar'
tar = tarfile.open(docker_tar, "w")
tar.add(imgdir, arcname=os.path.sep)
tar.close()
shutil.rmtree(imgdir)
print('Docker image pulled: ' + docker_tar)