Tell template preview whether a letter can be sent internationally

If a service has permission to send international letters then the admin
app should tell template preview, so that template preview knows what
rules to apply when it’s validating the address of the letter.

We don’t need to wait for template preview to start looking at this
query string argument – it will just ignore it for now.

app/main/views/uploads.py

@@ -115,7 +115,12 @@ def upload_letter(service_id):
         file_location = get_transient_letter_file_location(service_id, upload_id)
 
         try:
-            response = sanitise_letter(BytesIO(pdf_file_bytes))
+            response = sanitise_letter(
+                BytesIO(pdf_file_bytes),
+                allow_international_letters=current_service.has_permission(
+                    'international_letters'
+                ),
+            )
             response.raise_for_status()
         except RequestException as ex:
             if ex.response is not None and ex.response.status_code == 400:

app/template_previews.py

@@ -94,9 +94,12 @@ def get_page_count_for_letter(template, values=None):
     return page_count
 
 
-def sanitise_letter(pdf_file):
+def sanitise_letter(pdf_file, *, allow_international_letters):
     return requests.post(
-        '{}/precompiled/sanitise'.format(current_app.config['TEMPLATE_PREVIEW_API_HOST']),
+        '{}/precompiled/sanitise?allow_international_letters={}'.format(
+            current_app.config['TEMPLATE_PREVIEW_API_HOST'],
+            'true' if allow_international_letters else 'false',
+        ),
         data=pdf_file,
         headers={'Authorization': 'Token {}'.format(current_app.config['TEMPLATE_PREVIEW_API_KEY'])}
     )