Support Register Unsafely in Update (#8212)

* Allow user to remove email using update command

Fixes #3162. Slight change to control flow to replace current email
addresses with an empty list. Also add appropriate result message when
an email is removed.

* Update ACME to allow update to remove fields

- New field type "UnFalseyField" that treats all non-None fields as
  non-empty
- Contact changed to new field type to allow sending of empty contact
  field
- Certbot update adjusted to use tuple instead of None when empty
- Test updated to check more logic
- Unrelated type hint added to keep pycharm gods happy

* Moved some mocks into decorators

* Restore default to `contact` but do not serialize

- Add `to_partial_json` and `fields_to_partial_json` to Registration
- Store private variable noting if the value of the `contact` field was
  provided by the user.
- Change message when updating without email to reflect removal of
  all contact info.
- Add note in changelog that `update_account` with the
  `--register-unsafely-without-email` flag will remove contact
  from an account.

* Reverse logic for field handling on serialization

Now forcably add contact when serilizing, but go back to base `jose`
field type.

* Responding to Review

- change out of date name
- update several comments
- update `from_data` function of `Registration`
- Update test to remove superfluous mock

* Responding to review

- Change comments to make from_data more clear
- Remove code worried about None (omitempty has got my back)
- Update test to be more reliable
- Add typing import with comment to avoid pylint bug

2 files changed, 67 insertions, 2 deletions

diff --git a/acme/acme/messages.py b/acme/acme/messages.py
index 030e62d6c..8c9bf9701 100644
--- a/acme/acme/messages.py
+++ b/acme/acme/messages.py
@@ -315,6 +315,9 @@ class Registration(ResourceBody):
     # on new-reg key server ignores 'key' and populates it based on
     # JWS.signature.combined.jwk
     key = jose.Field('key', omitempty=True, decoder=jose.JWK.from_json)
+    # Contact field implements special behavior to allow messages that clear existing
+    # contacts while not expecting the `contact` field when loading from json.
+    # This is implemented in the constructor and *_json methods.
     contact = jose.Field('contact', omitempty=True, default=())
     agreement = jose.Field('agreement', omitempty=True)
     status = jose.Field('status', omitempty=True)
@@ -327,24 +330,73 @@ class Registration(ResourceBody):
 
     @classmethod
     def from_data(cls, phone=None, email=None, external_account_binding=None, **kwargs):
-        """Create registration resource from contact details."""
+        """
+        Create registration resource from contact details.
+
+        The `contact` keyword being passed to a Registration object is meaningful, so
+        this function represents empty iterables in its kwargs by passing on an empty
+        `tuple`.
+        """
+
+        # Note if `contact` was in kwargs.
+        contact_provided = 'contact' in kwargs
+
+        # Pop `contact` from kwargs and add formatted email or phone numbers
         details = list(kwargs.pop('contact', ()))
         if phone is not None:
             details.append(cls.phone_prefix + phone)
         if email is not None:
             details.extend([cls.email_prefix + mail for mail in email.split(',')])
-        kwargs['contact'] = tuple(details)
+
+        # Insert formatted contact information back into kwargs
+        # or insert an empty tuple if `contact` provided.
+        if details or contact_provided:
+            kwargs['contact'] = tuple(details)
 
         if external_account_binding:
             kwargs['external_account_binding'] = external_account_binding
 
         return cls(**kwargs)
 
+    def __init__(self, **kwargs):
+        """Note if the user provides a value for the `contact` member."""
+        if 'contact' in kwargs:
+            # Avoid the __setattr__ used by jose.TypedJSONObjectWithFields
+            object.__setattr__(self, '_add_contact', True)
+        super(Registration, self).__init__(**kwargs)
+
     def _filter_contact(self, prefix):
         return tuple(
             detail[len(prefix):] for detail in self.contact  # pylint: disable=not-an-iterable
             if detail.startswith(prefix))
 
+    def _add_contact_if_appropriate(self, jobj):
+        """
+        The `contact` member of Registration objects should not be required when
+        de-serializing (as it would be if the Fields' `omitempty` flag were `False`), but
+        it should be included in serializations if it was provided.
+
+        :param jobj: Dictionary containing this Registrations' data
+        :type jobj: dict
+
+        :returns: Dictionary containing Registrations data to transmit to the server
+        :rtype: dict
+        """
+        if getattr(self, '_add_contact', False):
+            jobj['contact'] = self.encode('contact')
+
+        return jobj
+
+    def to_partial_json(self):
+        """Modify josepy.JSONDeserializable.to_partial_json()"""
+        jobj = super(Registration, self).to_partial_json()
+        return self._add_contact_if_appropriate(jobj)
+
+    def fields_to_partial_json(self):
+        """Modify josepy.JSONObjectWithFields.fields_to_partial_json()"""
+        jobj = super(Registration, self).fields_to_partial_json()
+        return self._add_contact_if_appropriate(jobj)
+
     @property
     def phones(self):
         """All phones found in the ``contact`` field."""
diff --git a/acme/tests/messages_test.py b/acme/tests/messages_test.py
index 890a5f413..3458105b2 100644
--- a/acme/tests/messages_test.py
+++ b/acme/tests/messages_test.py
@@ -254,6 +254,19 @@ class RegistrationTest(unittest.TestCase):
         from acme.messages import Registration
         hash(Registration.from_json(self.jobj_from))
 
+    def test_default_not_transmitted(self):
+        from acme.messages import NewRegistration
+        empty_new_reg = NewRegistration()
+        new_reg_with_contact = NewRegistration(contact=())
+
+        self.assertEqual(empty_new_reg.contact, ())
+        self.assertEqual(new_reg_with_contact.contact, ())
+
+        self.assertTrue('contact' not in empty_new_reg.to_partial_json())
+        self.assertTrue('contact' not in empty_new_reg.fields_to_partial_json())
+        self.assertTrue('contact' in new_reg_with_contact.to_partial_json())
+        self.assertTrue('contact' in new_reg_with_contact.fields_to_partial_json())
+
 
 class UpdateRegistrationTest(unittest.TestCase):
     """Tests for acme.messages.UpdateRegistration."""