Use json schema to validate post request to send PDF letter

This approach was suggested as the way to do validation things on
Notify.

app/service/rest.py

@@ -93,6 +93,7 @@ from app.models import (
 from app.notifications.process_notifications import persist_notification, send_notification_to_queue
 from app.schema_validation import validate
 from app.service import statistics
+from app.service.send_pdf_letter_schema import send_pdf_letter_request
 from app.service.service_data_retention_schema import (
     add_service_data_retention_request,
     update_service_data_retention_request
@@ -650,7 +651,8 @@ def create_one_off_notification(service_id):
 
 @service_blueprint.route('/<uuid:service_id>/send-pdf-letter', methods=['POST'])
 def create_pdf_letter(service_id):
-    resp = send_pdf_letter_notification(service_id, request.get_json())
+    data = validate(request.get_json(), send_pdf_letter_request)
+    resp = send_pdf_letter_notification(service_id, data)
     return jsonify(resp), 201
 
 

app/service/send_notification.py

@@ -23,7 +23,6 @@ from app.models import (
     SMS_TYPE,
     EMAIL_TYPE,
     LETTER_TYPE,
-    POSTAGE_TYPES,
     NOTIFICATION_DELIVERED,
     UPLOAD_LETTERS,
 )
@@ -149,11 +148,6 @@ def send_pdf_letter_notification(service_id, post_data):
         allow_whitelisted_recipients=False,
     )
 
-    postage = post_data.get('postage')
-    if postage not in POSTAGE_TYPES:
-        message = "postage must be set as 'first' or 'second'"
-        raise BadRequestError(message=message)
-
     template = get_precompiled_letter_template(service.id)
     file_location = 'service-{}/{}.pdf'.format(service.id, post_data['file_id'])
 
@@ -188,7 +182,7 @@ def send_pdf_letter_notification(service_id, post_data):
         client_reference=post_data['filename'],
         created_by_id=post_data['created_by'],
         billable_units=billable_units,
-        postage=postage,
+        postage=post_data['postage'],
     )
 
     upload_filename = get_letter_pdf_filename(

app/service/send_pdf_letter_schema.py

@@ -0,0 +1,14 @@
+send_pdf_letter_request = {
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "description": "POST send uploaded pdf letter",
+    "type": "object",
+    "title": "Send an uploaded pdf letter",
+    "properties": {
+        "postage": {"enum": ["first", "second"]},
+        "filename": {"type": "string"},
+        "created_by": {"type": "string"},
+        "file_id": {"type": "string"},
+    },
+
+    "required": ["postage", "filename", "created_by", "file_id"]
+}