Ensure pdf letter filename is ascii encoded and decoded

S3 can only handle ascii characters, therefore for filename which could
include non ascii characters, for example a filename with the character
'£' in it, we must encode these using urllib before saving it as s3
metadata. We then also make sure that it comes back decoded when
presenting it to the user.

app/s3_client/s3_letter_upload_client.py

@@ -21,10 +21,12 @@ def upload_letter_to_s3(
     invalid_pages=None,
     recipient=None
 ):
+    # Use of urllib.parse.quote encodes metadata into ascii, which is required by s3.
+    # Making sure data for displaying to users is decoded is taken care of by LetterMetadata
     metadata = {
         'status': status,
         'page_count': str(page_count),
-        'filename': filename,
+        'filename': urllib.parse.quote(filename),
     }
     if message:
         metadata['message'] = message
@@ -42,18 +44,8 @@ def upload_letter_to_s3(
     )
 
 
-def get_letter_pdf_and_metadata(service_id, file_id):
-    file_location = get_transient_letter_file_location(service_id, file_id)
-    s3 = resource('s3')
-    s3_object = s3.Object(current_app.config['TRANSIENT_UPLOADED_LETTERS'], file_location).get()
-
-    pdf = s3_object['Body'].read()
-
-    return pdf, LetterMetadata(s3_object['Metadata'])
-
-
 class LetterMetadata:
-    KEYS_TO_DECODE = []
+    KEYS_TO_DECODE = ["filename"]
 
     def __init__(self, metadata):
         self._metadata = metadata
@@ -64,6 +56,16 @@ class LetterMetadata:
         return self._metadata.get(key, default)
 
 
+def get_letter_pdf_and_metadata(service_id, file_id):
+    file_location = get_transient_letter_file_location(service_id, file_id)
+    s3 = resource('s3')
+    s3_object = s3.Object(current_app.config['TRANSIENT_UPLOADED_LETTERS'], file_location).get()
+
+    pdf = s3_object['Body'].read()
+
+    return pdf, LetterMetadata(s3_object['Metadata'])
+
+
 def get_letter_metadata(service_id, file_id):
     file_location = get_transient_letter_file_location(service_id, file_id)
     s3 = resource('s3')

tests/app/main/views/test_uploads.py

@@ -457,9 +457,11 @@ def test_uploaded_letter_preview(
     mocker.patch('app.main.views.uploads.service_api_client')
     recipient = 'Bugs Bunny\n123 Big Hole\rLooney Town'
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value=LetterMetadata({
-        'filename': 'my_letter.pdf', 'page_count': '1', 'status': 'valid',
+        'filename': 'my_encoded_filename%C2%A3.pdf',
+        'page_count': '1',
+        'status': 'valid',
         'recipient': urllib.parse.quote(recipient)
-        }))
+    }))
 
     service_one['restricted'] = False
     client_request.login(active_user_with_permissions, service=service_one)
@@ -470,7 +472,7 @@ def test_uploaded_letter_preview(
         file_id=fake_uuid,
     )
 
-    assert page.find('h1').text == 'my_letter.pdf'
+    assert page.find('h1').text == 'my_encoded_filename£.pdf'
     assert page.find('div', class_='letter-sent')
     assert not page.find("label", {"class": "file-upload-button"})
     assert page.find('button', {'class': 'page-footer__button', 'type': 'submit'})