Check that the request payload data is valid json.

By adding `force=True` to request.get_json() the mime type is ignore. If the data is not valid json the method will return a `BadRequestError` we catch that and throw our own error with a clear error message "Invalid JSON supplied in POST data".
If the json is valid return the json data or an empty dict if None is passed in.

This PR improves the error messages if the json is invalid, previously, the error message was "None object type" message which is not very helpful.

app/schema_validation/__init__.py

@@ -7,8 +7,6 @@ from jsonschema import (Draft7Validator, ValidationError, FormatChecker)
 from notifications_utils.recipients import (validate_phone_number, validate_email_address, InvalidPhoneError,
                                             InvalidEmailError)
 
-from app.v2.errors import BadRequestError
-
 format_checker = FormatChecker()
 
 
@@ -57,9 +55,6 @@ def validate_schema_date_with_hour(instance):
 
 
 def validate(json_to_validate, schema):
-    if json_to_validate is None:
-        raise BadRequestError(message="Request body is empty.",
-                              status_code=400)
     validator = Draft7Validator(schema, format_checker=format_checker)
     errors = list(validator.iter_errors(json_to_validate))
     if errors.__len__() > 0:

app/v2/notifications/post_notifications.py

@@ -3,7 +3,6 @@ import functools
 
 from flask import request, jsonify, current_app, abort
 from notifications_utils.recipients import try_validate_and_format_phone_number
-from werkzeug.exceptions import BadRequest
 
 from app import api_user, authenticated_service, notify_celery, document_download_client
 from app.celery.letters_pdf_tasks import create_letters_pdf, process_virus_scan_passed
@@ -58,6 +57,7 @@ from app.v2.notifications.notification_schemas import (
     post_letter_request,
     post_precompiled_letter_request
 )
+from app.v2.utils import get_valid_json
 
 
 @v2_notification_blueprint.route('/{}'.format(LETTER_TYPE), methods=['POST'])
@@ -173,15 +173,6 @@ def post_notification(notification_type):
     return jsonify(resp), 201
 
 
-def get_valid_json():
-    try:
-        request_json = request.get_json(force=True)
-    except BadRequest:
-        raise BadRequestError(message="Invalid JSON supplied in POST data",
-                              status_code=400)
-    return request_json
-
-
 def process_sms_or_email_notification(*, form, notification_type, api_key, template, service, reply_to_text=None):
     form_send_to = form['email_address'] if notification_type == EMAIL_TYPE else form['phone_number']
 

app/v2/template/post_template.py

@@ -6,17 +6,21 @@ from app.schema_validation import validate
 from app.utils import get_template_instance
 from app.v2.errors import BadRequestError
 from app.v2.template import v2_template_blueprint
-from app.v2.template.template_schemas import post_template_preview_request, create_post_template_preview_response
+from app.v2.template.template_schemas import (
+    post_template_preview_request,
+    create_post_template_preview_response
+)
+from app.v2.utils import get_valid_json
 
 
 @v2_template_blueprint.route("/<template_id>/preview", methods=['POST'])
 def post_template_preview(template_id):
-    if not request.content_type or request.content_type != 'application/json':
+    # If the payload is is empty if there is no personalisation in the template.
-        raise BadRequestError(message="Content-Type header is not set to application/json.",
+    _data = request.get_data(as_text=True)
-                              status_code=400)
+    if not _data:
-    _data = request.get_json()
-    if _data is None:
         _data = {}
+    else:
+        _data = get_valid_json()
 
     _data['id'] = template_id
 

app/v2/utils.py

@@ -0,0 +1,13 @@
+from flask import request
+
+from app.v2.errors import BadRequestError
+from werkzeug.exceptions import BadRequest
+
+
+def get_valid_json():
+    try:
+        request_json = request.get_json(force=True)
+    except BadRequest:
+        raise BadRequestError(message="Invalid JSON supplied in POST data",
+                              status_code=400)
+    return request_json or {}

tests/app/v2/notifications/test_post_notifications.py

@@ -931,4 +931,7 @@ def test_post_email_notification_when_data_is_empty_returns_400(
     )
     error_msg = json.loads(response.get_data(as_text=True))["errors"][0]["message"]
     assert response.status_code == 400
-    assert error_msg == 'Request body is empty.'
+    if notification_type == 'sms':
+        assert error_msg == 'phone_number is a required property'
+    else:
+        assert error_msg == 'email_address is a required property'

tests/app/v2/template/test_post_template.py

@@ -154,13 +154,40 @@ def test_post_template_with_non_existent_template_id_returns_404(client, fake_uu
     }
 
 
-def test_post_template_without_content_header(client, sample_template):
+def test_post_template_returns_200_without_personalisation(client, sample_template):
+    response = client.post(
+        path='/v2/template/{}/preview'.format(sample_template.id),
+        data=None,
+        headers=[('Content-Type', 'application/json'),
+                 create_authorization_header(service_id=sample_template.service_id)]
+    )
+    assert response.status_code == 200
+
+
+def test_post_template_returns_200_without_personalisation_and_missing_content_header(client, sample_template):
+    response = client.post(
+        path='/v2/template/{}/preview'.format(sample_template.id),
+        data=None,
+        headers=[create_authorization_header(service_id=sample_template.service_id)]
+    )
+    assert response.status_code == 200
+
+
+def test_post_template_returns_200_without_personalisation_as_valid_json_and_missing_content_header(
+        client, sample_template
+):
+    response = client.post(
+        path='/v2/template/{}/preview'.format(sample_template.id),
+        data=json.dumps(None),
+        headers=[create_authorization_header(service_id=sample_template.service_id)]
+    )
+    assert response.status_code == 200
+
+
+def test_post_template_returns_200_with_valid_json_and_missing_content_header(client, sample_template):
     response = client.post(
         path='/v2/template/{}/preview'.format(sample_template.id),
         data=json.dumps(valid_personalisation),
         headers=[create_authorization_header(service_id=sample_template.service_id)]
     )
-
+    assert response.status_code == 200
-    assert response.status_code == 400
-    json_response = json.loads(response.get_data(as_text=True))
-    assert json_response['errors'][0]['message'] == 'Content-Type header is not set to application/json.'