Backup original precompiled uploads to S3

This continues the work from Template Preview [1], so that we have
a complete store of original PDFs to use for testing changes to it.

Previously we did store some originals, but these were only invalid
PDFs that had failed sanitisation; for valid PDFs, the "transient"
bucket only contains the sanitised versions, which the API deletes
/ moves when the notification is sent [2].

Since the notification is only created at a later stage [3], there's
no easy way to get the final name of the PDF we send to DVLA. Instead,
we use the "upload_id", which eventually becomes the notification ID
[4]. This should be enough to trace the file for specific debugging.

Note that we only want to store original PDFs if they're valid (and
virus free!), since there's no point testing changes with bad data.

[1]: https://github.com/alphagov/notifications-template-preview/pull/545
[2]: c44ec57c17/app/service/send_notification.py (L212)
[3]: 7930a53a58/app/main/views/uploads.py (L362)
[4]: 7930a53a58/app/main/views/uploads.py (L373)

tests/app/main/views/uploads/test_upload_letter.py

@@ -42,7 +42,8 @@ def test_post_upload_letter_redirects_for_valid_file(
             json=lambda: {'file': 'VGhlIHNhbml0aXNlZCBjb250ZW50', 'recipient_address': 'The Queen'}
         )
     )
-    mock_s3 = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mock_s3_upload = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mock_s3_backup = mocker.patch('app.main.views.uploads.backup_original_letter_to_s3')
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value=LetterMetadata({
         'filename': 'tests/test_pdf_files/one_page_pdf.pdf',
         'page_count': '1',
@@ -64,7 +65,7 @@ def test_post_upload_letter_redirects_for_valid_file(
         )
     assert antivirus_mock.called
 
-    mock_s3.assert_called_once_with(
+    mock_s3_upload.assert_called_once_with(
         b'The sanitised content',
         file_location='service-{}/{}.pdf'.format(SERVICE_ONE_ID, fake_uuid),
         status='valid',
@@ -72,6 +73,13 @@ def test_post_upload_letter_redirects_for_valid_file(
         filename='tests/test_pdf_files/one_page_pdf.pdf',
         recipient='The Queen',
     )
+
+    with open('tests/test_pdf_files/one_page_pdf.pdf', 'rb') as file:
+        mock_s3_backup.assert_called_once_with(
+            file.read(),
+            upload_id=ANY,
+        )
+
     mock_sanitise.assert_called_once_with(
         ANY,
         allow_international_letters=expected_allow_international,
@@ -108,6 +116,7 @@ def test_post_upload_letter_shows_letter_preview_for_valid_file(
         )
     )
     mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mocker.patch('app.main.views.uploads.backup_original_letter_to_s3')
     mocker.patch('app.main.views.uploads.pdf_page_count', return_value=3)
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value=LetterMetadata({
         'filename': 'tests/test_pdf_files/one_page_pdf.pdf',
@@ -167,6 +176,7 @@ def test_upload_international_letter_shows_preview_with_no_choice_of_postage(
         json=lambda: {'file': 'VGhlIHNhbml0aXNlZCBjb250ZW50', 'recipient_address': 'The Queen'}
     ))
     mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mocker.patch('app.main.views.uploads.backup_original_letter_to_s3')
     mocker.patch('app.main.views.uploads.pdf_page_count', return_value=3)
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value=LetterMetadata({
         'filename': 'tests/test_pdf_files/one_page_pdf.pdf',
@@ -230,6 +240,7 @@ def test_post_upload_letter_shows_error_when_no_file_uploaded(client_request):
 
 def test_post_upload_letter_shows_error_when_file_contains_virus(mocker, client_request):
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=False)
+    mock_s3_backup = mocker.patch('app.main.views.uploads.backup_original_letter_to_s3')
 
     with open('tests/test_pdf_files/one_page_pdf.pdf', 'rb') as file:
         page = client_request.post(
@@ -240,6 +251,7 @@ def test_post_upload_letter_shows_error_when_file_contains_virus(mocker, client_
         )
     assert page.find('div', class_='banner-dangerous').find('h1').text == 'Your file contains a virus'
     assert normalize_spaces(page.find('label', class_='file-upload-button').text) == 'Upload your file again'
+    mock_s3_backup.assert_not_called()
 
 
 def test_post_choose_upload_file_when_file_is_too_big(mocker, client_request):
@@ -277,7 +289,8 @@ def test_post_choose_upload_file_when_file_is_malformed(mocker, client_request):
 def test_post_upload_letter_with_invalid_file(mocker, client_request, fake_uuid):
     mocker.patch('uuid.uuid4', return_value=fake_uuid)
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
-    mock_s3 = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mock_s3_upload = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
+    mock_s3_backup = mocker.patch('app.main.views.uploads.backup_original_letter_to_s3')
 
     mock_sanitise_response = Mock()
     mock_sanitise_response.raise_for_status.side_effect = RequestException(response=Mock(status_code=400))
@@ -302,7 +315,7 @@ def test_post_upload_letter_with_invalid_file(mocker, client_request, fake_uuid)
             _follow_redirects=True
         )
 
-        mock_s3.assert_called_once_with(
+        mock_s3_upload.assert_called_once_with(
             file_contents,
             file_location='service-{}/{}.pdf'.format(SERVICE_ONE_ID, fake_uuid),
             status='invalid',
@@ -312,6 +325,7 @@ def test_post_upload_letter_with_invalid_file(mocker, client_request, fake_uuid)
             message='content-outside-printable-area'
         )
 
+    mock_s3_backup.assert_not_called()
     assert page.find('div', class_='banner-dangerous').find('h1', {"data-error-type": 'content-outside-printable-area'})
     assert not page.find('button', {'class': 'page-footer__button', 'type': 'submit'})
 

tests/app/s3_client/test_s3_letter_upload_client.py

@@ -1,13 +1,32 @@
 import urllib
+import uuid
 
 from flask import current_app
 
 from app.s3_client.s3_letter_upload_client import (
     LetterMetadata,
+    backup_original_letter_to_s3,
     upload_letter_to_s3,
 )
 
 
+def test_backup_original_letter_to_s3(mocker, notify_admin):
+    s3_mock = mocker.patch('app.s3_client.s3_letter_upload_client.utils_s3upload')
+    upload_id = uuid.uuid4()
+
+    backup_original_letter_to_s3(
+        'pdf_data',
+        upload_id=upload_id,
+    )
+
+    s3_mock.assert_called_once_with(
+        bucket_name=current_app.config['PRECOMPILED_ORIGINALS_BACKUP_LETTERS'],
+        file_location=f'{str(upload_id)}.pdf',
+        filedata='pdf_data',
+        region=current_app.config['AWS_REGION']
+    )
+
+
 def test_upload_letter_to_s3(mocker):
     s3_mock = mocker.patch('app.s3_client.s3_letter_upload_client.utils_s3upload')