Merge pull request #3474 from alphagov/fix-returned-letters

split returned letters tasks into a max count of returned letters

app/letters/rest.py

@@ -9,11 +9,19 @@ from app.v2.errors import register_errors
 letter_job = Blueprint("letter-job", __name__)
 register_errors(letter_job)
 
+# too many references will make SQS error (as the task can only be 256kb)
+MAX_REFERENCES_PER_TASK = 5000
+
 
 @letter_job.route('/letters/returned', methods=['POST'])
 def create_process_returned_letters_job():
-    references = validate(request.get_json(), letter_references)
+    references = validate(request.get_json(), letter_references)['references']
 
-    process_returned_letters_list.apply_async([references['references']], queue=QueueNames.DATABASE)
+    for start_index in range(0, len(references), MAX_REFERENCES_PER_TASK):
+        process_returned_letters_list.apply_async(
+            args=(references[start_index:start_index + MAX_REFERENCES_PER_TASK], ),
+            queue=QueueNames.DATABASE,
+            compression='zlib'
+        )
 
-    return jsonify(references=references['references']), 200
+    return jsonify(references=references), 200

tests/app/letters/test_returned_letters.py

@@ -20,4 +20,23 @@ def test_process_returned_letters(status, references, admin_request, mocker):
     if status != 200:
         assert '{} does not match'.format(references[0]) in response['errors'][0]['message']
     else:
-        mock_celery.assert_called_once_with([references], queue='database-tasks')
+        mock_celery.assert_called_once_with(args=(references,), queue='database-tasks', compression='zlib')
+
+
+def test_process_returned_letters_splits_tasks_up(admin_request, mocker):
+    mock_celery = mocker.patch("app.letters.rest.process_returned_letters_list.apply_async")
+    mocker.patch("app.letters.rest.MAX_REFERENCES_PER_TASK", 3)
+
+    references = [f'{x:016}' for x in range(10)]
+
+    admin_request.post(
+        'letter-job.create_process_returned_letters_job',
+        _data={"references": references},
+    )
+
+    assert mock_celery.call_count == 4
+
+    assert mock_celery.call_args_list[0][1]['args'][0] == ['0000000000000000', '0000000000000001', '0000000000000002']
+    assert mock_celery.call_args_list[1][1]['args'][0] == ['0000000000000003', '0000000000000004', '0000000000000005']
+    assert mock_celery.call_args_list[2][1]['args'][0] == ['0000000000000006', '0000000000000007', '0000000000000008']
+    assert mock_celery.call_args_list[3][1]['args'][0] == ['0000000000000009']