Change how we validate the length of templates.

We want to add validation for an email that's too long, that way the user knows why the message is failing. At the moment if an email is too long it will get a technical failure, after the retries fail. This way the email post will get a validation error.

Once this: https://github.com/alphagov/notifications-utils/pull/804 is reverted, we can update the utils version.

app/notifications/validators.py

@@ -27,7 +27,6 @@ from app.serialised_models import SerialisedTemplate
 
 from gds_metrics.metrics import Histogram
 
-
 REDIS_EXCEEDED_RATE_LIMIT_DURATION_SECONDS = Histogram(
     'redis_exceeded_rate_limit_duration_seconds',
     'Time taken to check rate limit',
@@ -157,8 +156,7 @@ def check_notification_content_is_not_empty(template_with_content):
         raise BadRequestError(message=message)
 
 
-def validate_template(template_id, personalisation, service, notification_type):
+def validate_template(template_id, personalisation, service, notification_type, check_char_count=True):
-
     try:
         template = SerialisedTemplate.from_id_and_service_id(template_id, service.id)
     except NoResultFound:
@@ -173,6 +171,10 @@ def validate_template(template_id, personalisation, service, notification_type):
 
     check_notification_content_is_not_empty(template_with_content)
 
+    # validating the template in post_notifications happens before the file is uploaded for doc download,
+    # which means the length of the message can be exceeded because it's including the file.
+    # The document download feature is only available through the api.
+    if check_char_count:
         check_content_char_count(template_with_content)
 
     return template, template_with_content

app/v2/notifications/post_notifications.py

@@ -52,7 +52,7 @@ from app.notifications.validators import (
     validate_address,
     validate_and_format_recipient,
     validate_template,
-)
+    check_content_char_count)
 from app.schema_validation import validate
 from app.v2.errors import BadRequestError
 from app.v2.notifications.create_response import (
@@ -132,6 +132,7 @@ def post_notification(notification_type):
         form.get('personalisation', {}),
         authenticated_service,
         notification_type,
+        check_char_count=False
     )
 
     reply_to = get_reply_to_text(notification_type, form, template)
@@ -189,6 +190,9 @@ def process_sms_or_email_notification(
         # We changed personalisation which means we need to update the content
         template_with_content.values = personalisation
 
+    # validate content length after url is replaced in personalisation.
+    check_content_char_count(template_with_content)
+
     resp = create_response_for_post_notification(
         notification_id=notification_id,
         client_reference=form.get('reference', None),

tests/app/notifications/test_validators.py

@@ -404,6 +404,25 @@ def test_validate_template_calls_all_validators(mocker, fake_uuid, sample_servic
     mock_check_message_is_too_long.assert_called_once_with("content")
 
 
+def test_validate_template_calls_all_validators_exception_message_too_long(mocker, fake_uuid, sample_service):
+    template = create_template(sample_service, template_type="email")
+    mock_check_type = mocker.patch('app.notifications.validators.check_template_is_for_notification_type')
+    mock_check_if_active = mocker.patch('app.notifications.validators.check_template_is_active')
+    mock_create_conent = mocker.patch(
+        'app.notifications.validators.create_content_for_notification', return_value="content"
+    )
+    mock_check_not_empty = mocker.patch('app.notifications.validators.check_notification_content_is_not_empty')
+    mock_check_message_is_too_long = mocker.patch('app.notifications.validators.check_content_char_count')
+    template, template_with_content = validate_template(template.id, {}, sample_service, "email",
+                                                        check_char_count=False)
+
+    mock_check_type.assert_called_once_with("email", "email")
+    mock_check_if_active.assert_called_once_with(template)
+    mock_create_conent.assert_called_once_with(template, {})
+    mock_check_not_empty.assert_called_once_with("content")
+    assert not mock_check_message_is_too_long.called
+
+
 @pytest.mark.parametrize('key_type', ['team', 'live', 'test'])
 def test_that_when_exceed_rate_limit_request_fails(
         key_type,