Remove TUF-specific util.get_target_hash function

Also remove now obsolete util.HASH_FUNCTION and corresponding
tests.

The function is added back to tuf in theupdateframework/python-tuf#909.

securesystemslib/util.py

@@ -39,11 +39,6 @@
 
 import six
 
-# The algorithm used by the repository to generate the digests of the
-# target filepaths, which are included in metadata files and may be prepended
-# to the filenames of consistent snapshots.
-HASH_FUNCTION = 'sha256'
-
 logger = logging.getLogger('securesystemslib_util')
 
 
@@ -486,48 +481,7 @@ def file_in_confined_directories(filepath, confined_directories):
   return False
 
 
-# TODO: Move get_target_hash back to TUF; it's TUF-specific.
-def get_target_hash(target_filepath):
-  """
-  <Purpose>
-    Compute the hash of 'target_filepath'. This is useful in conjunction with
-    the "path_hash_prefixes" attribute in a delegated targets role, which tells
-    us which paths it is implicitly responsible for.
-
-    The repository may optionally organize targets into hashed bins to ease
-    target delegations and role metadata management.  The use of consistent
-    hashing allows for a uniform distribution of targets into bins.
-
-  <Arguments>
-    target_filepath:
-      The path to the target file on the repository. This will be relative to
-      the 'targets' (or equivalent) directory on a given mirror.
-
-  <Exceptions>
-    None.
-
-  <Side Effects>
-    None.
-
-  <Returns>
-    The hash of 'target_filepath'.
-  """
-
-  # Does 'target_filepath' have the correct format?
-  # Ensure the arguments have the appropriate number of objects and object
-  # types, and that all dict keys are properly named.
-  # Raise 'securesystemslib.exceptions.FormatError' if there is a mismatch.
-  securesystemslib.formats.PATH_SCHEMA.check_match(target_filepath)
-
-  # Calculate the hash of the filepath to determine which bin to find the
-  # target.  The client currently assumes the repository uses
-  # 'HASH_FUNCTION' to generate hashes and 'utf-8'.
-  digest_object = securesystemslib.hash.digest(HASH_FUNCTION)
-  encoded_target_filepath = target_filepath.encode('utf-8')
-  digest_object.update(encoded_target_filepath)
-  target_filepath_hash = digest_object.hexdigest()
 
-  return target_filepath_hash
 
 
 _json_module = None

tests/test_util.py

@@ -385,24 +385,6 @@ def  test_B6_load_json_file(self):
 
 
 
-  def test_C1_get_target_hash(self):
-    # Test normal case.
-    expected_target_hashes = {
-      '/file1.txt': 'e3a3d89eb3b70ce3fbce6017d7b8c12d4abd5635427a0e8a238f53157df85b3d',
-      '/README.txt': '8faee106f1bb69f34aaf1df1e3c2e87d763c4d878cb96b91db13495e32ceb0b0',
-      '/warehouse/file2.txt': 'd543a573a2cec67026eff06e75702303559e64e705eba06f65799baaf0424417'
-    }
-    for filepath, target_hash in six.iteritems(expected_target_hashes):
-      self.assertTrue(securesystemslib.formats.PATH_SCHEMA.matches(filepath))
-      self.assertTrue(securesystemslib.formats.HASH_SCHEMA.matches(target_hash))
-      self.assertEqual(securesystemslib.util.get_target_hash(filepath), target_hash)
-
-    # Test for improperly formatted argument.
-    self.assertRaises(securesystemslib.exceptions.FormatError,
-        securesystemslib.util.get_target_hash, 8)
-
-
-
   def test_C5_unittest_toolbox_make_temp_directory(self):
     # Verify that the tearDown function does not fail when
     # unittest_toolbox.make_temp_directory deletes the generated temp directory