How to use the securesystemslib.util.get_file_details function in securesystemslib

url_prefix = self.repository_mirrors['mirror1']['url_prefix']
    url_file = os.path.join(url_prefix, 'targets', 'file1.txt')

    # On Windows, the URL portion should not contain back slashes.
    six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_target_path)

    self.assertTrue(os.path.exists(client_target_path))
    length, hashes = securesystemslib.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)
    self.assertEqual(fileinfo, download_fileinfo)

    # Test: Download a target file that has been modified by an attacker.
    with open(target_path, 'wt') as file_object:
      file_object.write('add malicious content.')
    length, hashes = securesystemslib.util.get_file_details(target_path)
    malicious_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # On Windows, the URL portion should not contain back slashes.
    six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_target_path)

    length, hashes = securesystemslib.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # Verify 'download_fileinfo' is unequal to the original trusted version.
    self.assertNotEqual(download_fileinfo, fileinfo)

    # Verify 'download_fileinfo' is equal to the malicious version.
    self.assertEqual(download_fileinfo, malicious_fileinfo)

six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_timestamp_path)

    length, hashes = securesystemslib.util.get_file_details(client_timestamp_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # Verify 'download_fileinfo' is equal to the new version.
    self.assertEqual(download_fileinfo, new_fileinfo)

    # Restore the previous version of 'timestamp.json' on the remote repository
    # and verify that the non-TUF client downloads it (expected, but not ideal).
    shutil.move(backup_timestamp, timestamp_path)

    # On Windows, the URL portion should not contain back slashes.
    six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_timestamp_path)

    length, hashes = securesystemslib.util.get_file_details(client_timestamp_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # Verify 'download_fileinfo' is equal to the previous version.
    self.assertEqual(download_fileinfo, previous_fileinfo)
    self.assertNotEqual(download_fileinfo, new_fileinfo)

def test_13__get_file(self):
    # Test for an "unsafe" download, where the file is downloaded up to
    # a required length (and no more).  The "safe" download approach
    # downloads an exact required length.
    targets_path = os.path.join(self.repository_directory, 'metadata', 'targets.json')

    file_size, file_hashes = securesystemslib.util.get_file_details(targets_path)
    file_type = 'meta'

    def verify_target_file(targets_path):
      # Every target file must have its length and hashes inspected.
      self.repository_updater._hard_check_file_length(targets_path, file_size)
      self.repository_updater._check_hashes(targets_path, file_hashes)

    self.repository_updater._get_file('targets.json', verify_target_file,
        file_type, file_size, download_safely=True)

    self.repository_updater._get_file('targets.json', verify_target_file,
        file_type, file_size, download_safely=False)

# Test: Expected input.
    self.assertEqual(securesystemslib.util.get_file_details(filepath),
        (file_length, file_hash))

    # Test: Incorrect input.
    bogus_inputs = [self.random_string(), 1234, [self.random_string()],
        {'a': 'b'}, None]

    for bogus_input in bogus_inputs:
      if isinstance(bogus_input, six.string_types):
        self.assertRaises(securesystemslib.exceptions.Error,
            securesystemslib.util.get_file_details, bogus_input)
      else:
        self.assertRaises(securesystemslib.exceptions.FormatError,
            securesystemslib.util.get_file_details, bogus_input)

def test_with_tuf(self):
    # An attacker tries to trick a client into installing an extraneous target
    # file (a valid file on the repository, in this case) by listing it in the
    # project's metadata file.  For the purposes of test_with_tuf(),
    # 'role1.json' is treated as the metadata file that indicates all
    # the files needed to install/update the 'role1' project.  The attacker
    # simply adds the extraneous target file to 'role1.json', which the TUF
    # client should reject as improperly signed.
    role1_filepath = os.path.join(self.repository_directory, 'metadata',
                                  'role1.json')
    file1_filepath = os.path.join(self.repository_directory, 'targets',
                                  'file1.txt')
    length, hashes = securesystemslib.util.get_file_details(file1_filepath)

    role1_metadata = securesystemslib.util.load_json_file(role1_filepath)
    role1_metadata['signed']['targets']['/file2.txt'] = {}
    role1_metadata['signed']['targets']['/file2.txt']['hashes'] = hashes
    role1_metadata['signed']['targets']['/file2.txt']['length'] = length

    tuf.formats.check_signable_object_format(role1_metadata)

    with open(role1_filepath, 'wt') as file_object:
      json.dump(role1_metadata, file_object, indent=1, sort_keys=True)

    # Un-install the metadata of the top-level roles so that the client can
    # download and detect the invalid 'role1.json'.
    os.remove(os.path.join(self.client_directory, self.repository_name,
        'metadata', 'current', 'snapshot.json'))
    os.remove(os.path.join(self.client_directory, self.repository_name,

self.assertTrue(os.path.exists(client_target_path))
    length, hashes = securesystemslib.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)
    self.assertEqual(fileinfo, download_fileinfo)

    # Test: Download a target file that has been modified by an attacker.
    with open(target_path, 'wt') as file_object:
      file_object.write('add malicious content.')
    length, hashes = securesystemslib.util.get_file_details(target_path)
    malicious_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # On Windows, the URL portion should not contain back slashes.
    six.moves.urllib.request.urlretrieve(url_file.replace('\\', '/'), client_target_path)

    length, hashes = securesystemslib.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)

    # Verify 'download_fileinfo' is unequal to the original trusted version.
    self.assertNotEqual(download_fileinfo, fileinfo)

    # Verify 'download_fileinfo' is equal to the malicious version.
    self.assertEqual(download_fileinfo, malicious_fileinfo)

def test_2__fileinfo_has_changed(self):
      #  Verify that the method returns 'False' if file info was not changed.
      root_filepath = os.path.join(self.client_metadata_current, 'root.json')
      length, hashes = securesystemslib.util.get_file_details(root_filepath)
      root_fileinfo = tuf.formats.make_fileinfo(length, hashes)
      self.assertFalse(self.repository_updater._fileinfo_has_changed('root.json',
                                                             root_fileinfo))

      # Verify that the method returns 'True' if length or hashes were changed.
      new_length = 8
      new_root_fileinfo = tuf.formats.make_fileinfo(new_length, hashes)
      self.assertTrue(self.repository_updater._fileinfo_has_changed('root.json',
                                                             new_root_fileinfo))
      # Hashes were changed.
      new_hashes = {'sha256': self.random_string()}
      new_root_fileinfo = tuf.formats.make_fileinfo(length, new_hashes)
      self.assertTrue(self.repository_updater._fileinfo_has_changed('root.json',
                                                             new_root_fileinfo))

      # Verify that _fileinfo_has_changed() returns True if no fileinfo (or set

# Try to add more consistent metadata files.
    version_number += 1
    root_signable['signed']['version'] = version_number
    repo_lib.write_metadata_file(root_signable, output_filename,
        version_number, consistent_snapshot=True)

    # Test if the latest root.json points to the expected consistent file
    # and consistent metadata do not all point to the same root.json
    version_and_filename = str(version_number) + '.' + 'root.json'
    second_version_output_file = os.path.join(temporary_directory, version_and_filename)
    self.assertTrue(os.path.exists(second_version_output_file))

    # Verify that the second version is equal to the second output file, and
    # that the second output filename differs from the first.
    self.assertEqual(securesystemslib.util.get_file_details(output_filename),
        securesystemslib.util.get_file_details(second_version_output_file))
    self.assertNotEqual(securesystemslib.util.get_file_details(output_filename),
        securesystemslib.util.get_file_details(first_version_output_file))

    # Test for an improper settings.CONSISTENT_METHOD string value.
    tuf.settings.CONSISTENT_METHOD = 'somebadidea'

    # Test for invalid consistent methods on systems other than Windows,
    # which always uses the copy method.
    if platform.system() == 'Windows':
      pass

    else:
      self.assertRaises(securesystemslib.exceptions.InvalidConfigurationError,
          repo_lib.write_metadata_file, root_signable, output_filename,
          version_number, consistent_snapshot=True)

version_number += 1
    root_signable['signed']['version'] = version_number
    repo_lib.write_metadata_file(root_signable, output_filename,
        version_number, consistent_snapshot=True)

    # Test if the latest root.json points to the expected consistent file
    # and consistent metadata do not all point to the same root.json
    version_and_filename = str(version_number) + '.' + 'root.json'
    second_version_output_file = os.path.join(temporary_directory, version_and_filename)
    self.assertTrue(os.path.exists(second_version_output_file))

    # Verify that the second version is equal to the second output file, and
    # that the second output filename differs from the first.
    self.assertEqual(securesystemslib.util.get_file_details(output_filename),
        securesystemslib.util.get_file_details(second_version_output_file))
    self.assertNotEqual(securesystemslib.util.get_file_details(output_filename),
        securesystemslib.util.get_file_details(first_version_output_file))

    # Test for an improper settings.CONSISTENT_METHOD string value.
    tuf.settings.CONSISTENT_METHOD = 'somebadidea'

    # Test for invalid consistent methods on systems other than Windows,
    # which always uses the copy method.
    if platform.system() == 'Windows':
      pass

    else:
      self.assertRaises(securesystemslib.exceptions.InvalidConfigurationError,
          repo_lib.write_metadata_file, root_signable, output_filename,
          version_number, consistent_snapshot=True)

    # Try to create a link to root.json when root.json doesn't exist locally.