Remove iso8601 dependency

Our 'expires' strings are constrained by the ISO8601_DATETIME_SCHEMA
which matches regex '\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z'. This can be
parsed with just a datetime.strptime(): iso8601 module is not needed.

* Add formats.expiry_string_to_datetime() helper function
* Modify the 3 locations that used iso8601 and the api/metadata.py usage
  of datetime.strptime()
* Remove related unnecessary logger setup
* Add the missing exception documentation to relevant functions (in many
  cases the exception is rather unlikely as the schema has been verified
  many times before this though...)

Fixes #1065

Signed-off-by: Jussi Kukkonen <jkukkonen@vmware.com>

requirements-pinned.txt

@@ -6,7 +6,6 @@ cryptography==3.1.1         # via securesystemslib
 enum34==1.1.6             ; python_version < '3' # via cryptography
 idna==2.10                 # via requests
 ipaddress==1.0.23         ; python_version < '3' # via cryptography
-iso8601==0.1.13
 pycparser==2.20           # via cffi
 pynacl==1.4.0             # via securesystemslib
 python-dateutil==2.8.1    # via securesystemslib

requirements.txt

@@ -44,4 +44,3 @@
 securesystemslib[colors, crypto, pynacl]
 requests
 six
-iso8601

setup.py

@@ -114,7 +114,6 @@
   },
   python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <4",
   install_requires = [
-    'iso8601>=0.1.12',
     'requests>=2.19.1',
     'six>=1.11.0',
     'securesystemslib>=0.16.0'

tests/test_formats.py

@@ -723,6 +723,23 @@ def test_build_dict_conforming_to_schema(self):
 
 
 
+  def test_expiry_string_to_datetime(self):
+    dt = tuf.formats.expiry_string_to_datetime('1985-10-21T13:20:00Z')
+    self.assertEqual(dt, datetime.datetime(1985, 10, 21, 13, 20, 0))
+    dt = tuf.formats.expiry_string_to_datetime('2038-01-19T03:14:08Z')
+    self.assertEqual(dt, datetime.datetime(2038, 1, 19, 3, 14, 8))
+
+    # First 3 fail via securesystemslib schema, last one because of strptime()
+    invalid_inputs = [
+      '2038-1-19T03:14:08Z', # leading zeros not optional
+      '2038-01-19T031408Z', # strict time parsing
+      '2038-01-19T03:14:08Z-06:00', # timezone not allowed
+      '2038-13-19T03:14:08Z', # too many months
+    ]
+    for invalid_input in invalid_inputs:
+      with self.assertRaises(securesystemslib.exceptions.FormatError):
+        tuf.formats.expiry_string_to_datetime(invalid_input)
+
 
 
   def test_unix_timestamp_to_datetime(self):

tuf/api/metadata.py

@@ -294,9 +294,8 @@ def from_dict(cls, signed_dict: JsonDict) -> 'Signed':
         # Convert 'expires' TUF metadata string to a datetime object, which is
         # what the constructor expects and what we store. The inverse operation
         # is implemented in 'to_dict'.
-        signed_dict['expires'] = datetime.strptime(
-                signed_dict['expires'],
-                "%Y-%m-%dT%H:%M:%SZ").replace(tzinfo=None)
+        signed_dict['expires'] = tuf.formats.expiry_string_to_datetime(
+                signed_dict['expires'])
         # NOTE: We write the converted 'expires' back into 'signed_dict' above
         # so that we can pass it to the constructor as  '**signed_dict' below,
         # along with other fields that belong to Signed subclasses.

tuf/client/updater.py

@@ -145,7 +145,6 @@
 import securesystemslib.keys
 import securesystemslib.util
 import six
-import iso8601
 import requests.exceptions
 
 # The Timestamp role does not have signed metadata about it; otherwise we
@@ -163,11 +162,6 @@
 # See 'log.py' to learn how logging is handled in TUF.
 logger = logging.getLogger(__name__)
 
-# Disable 'iso8601' logger messages to prevent 'iso8601' from clogging the
-# log file.
-iso8601_logger = logging.getLogger('iso8601')
-iso8601_logger.disabled = True
-
 
 class MultiRepoUpdater(object):
   """
@@ -2377,7 +2371,8 @@ def _ensure_not_expired(self, metadata_object, metadata_rolename):
     <Exceptions>
       tuf.exceptions.ExpiredMetadataError:
         If 'metadata_rolename' has expired.
-
+      securesystemslib.exceptions.FormatError:
+        If the expiration cannot be parsed correctly
     <Side Effects>
       None.
 
@@ -2385,22 +2380,15 @@ def _ensure_not_expired(self, metadata_object, metadata_rolename):
       None.
     """
 
-    # Extract the expiration time.
-    expires = metadata_object['expires']
-
-    # If the current time has surpassed the expiration date, raise an
-    # exception.  'expires' is in
-    # 'securesystemslib.formats.ISO8601_DATETIME_SCHEMA' format (e.g.,
-    # '1985-10-21T01:22:00Z'.)  Convert it to a unix timestamp and compare it
+    # Extract the expiration time. Convert it to a unix timestamp and compare it
     # against the current time.time() (also in Unix/POSIX time format, although
     # with microseconds attached.)
-    current_time = int(time.time())
-
-    # Generate a user-friendly error message if 'expires' is less than the
-    # current time (i.e., a local time.)
-    expires_datetime = iso8601.parse_date(expires)
+    expires_datetime = tuf.formats.expiry_string_to_datetime(
+        metadata_object['expires'])
     expires_timestamp = tuf.formats.datetime_to_unix_timestamp(expires_datetime)
 
+    current_time = int(time.time())
+
     if expires_timestamp < current_time:
       message = 'Metadata '+repr(metadata_rolename)+' expired on ' + \
         expires_datetime.ctime() + ' (UTC).'

tuf/formats.py

@@ -612,6 +612,37 @@ def build_dict_conforming_to_schema(schema, **kwargs):
 
 
 
+
+def expiry_string_to_datetime(expires):
+  """
+  <Purpose>
+    Convert an expiry string to a datetime object.
+  <Arguments>
+    expires:
+      The expiry date-time string in the ISO8601 format that is defined
+      in securesystemslib.ISO8601_DATETIME_SCHEMA. E.g. '2038-01-19T03:14:08Z'
+  <Exceptions>
+    securesystemslib.exceptions.FormatError, if 'expires' cannot be
+    parsed correctly.
+  <Side Effects>
+    None.
+  <Returns>
+    A datetime object representing the expiry time.
+  """
+
+  # Raise 'securesystemslib.exceptions.FormatError' if there is a mismatch.
+  securesystemslib.formats.ISO8601_DATETIME_SCHEMA.check_match(expires)
+
+  try:
+    return datetime.datetime.strptime(expires, "%Y-%m-%dT%H:%M:%SZ")
+  except ValueError as error:
+    six.raise_from(securesystemslib.exceptions.FormatError(
+        'Failed to parse ' + repr(expires) + ' as an expiry time'),
+        error)
+
+
+
+
 def datetime_to_unix_timestamp(datetime_object):
   """
   <Purpose>

tuf/repository_lib.py

@@ -52,7 +52,6 @@
 import securesystemslib.hash
 import securesystemslib.interface
 import securesystemslib.util
-import iso8601
 import six
 
 import securesystemslib.storage
@@ -61,11 +60,6 @@
 # See 'log.py' to learn how logging is handled in TUF.
 logger = logging.getLogger(__name__)
 
-# Disable 'iso8601' logger messages to prevent 'iso8601' from clogging the
-# log file.
-iso8601_logger = logging.getLogger('iso8601')
-iso8601_logger.disabled = True
-
 # The extension of TUF metadata.
 METADATA_EXTENSION = '.json'
 
@@ -704,7 +698,8 @@ def _log_warning_if_expires_soon(rolename, expires_iso8601_timestamp,
   # unix timestamp, subtract from current time.time() (also in POSIX time)
   # and compare against 'seconds_remaining_to_warn'.  Log a warning message
   # to console if 'rolename' expires soon.
-  datetime_object = iso8601.parse_date(expires_iso8601_timestamp)
+  datetime_object = tuf.formats.expiry_string_to_datetime(
+      expires_iso8601_timestamp)
   expires_unix_timestamp = \
     tuf.formats.datetime_to_unix_timestamp(datetime_object)
   seconds_until_expires = expires_unix_timestamp - int(time.time())

tuf/repository_tool.py

@@ -53,7 +53,6 @@
 import securesystemslib.keys
 import securesystemslib.formats
 import securesystemslib.util
-import iso8601
 import six
 
 import securesystemslib.storage
@@ -1317,15 +1316,12 @@ def expiration(self):
     <Purpose>
       A getter method that returns the role's expiration datetime.
 
-      >>>
-      >>>
-      >>>
-
     <Arguments>
       None.
 
     <Exceptions>
-      None.
+      securesystemslib.exceptions.FormatError, if the expiration cannot be
+      parsed correctly
 
     <Side Effects>
       None.
@@ -1337,9 +1333,7 @@ def expiration(self):
     roleinfo = tuf.roledb.get_roleinfo(self.rolename, self._repository_name)
     expires = roleinfo['expires']
 
-    expires_datetime_object = iso8601.parse_date(expires)
-
-    return expires_datetime_object
+    return tuf.formats.expiry_string_to_datetime(expires)