feat(dispatcher): write payload to file to reduce memory usage

dumping large json payloads was consuming up to 1GB in some cases. write
the payload to file before send it to lower memory consumption. in the
future we might need to change the API about reporting submission
result.

Author: Bogay

dispatcher/dispatcher.py

@@ -6,6 +6,7 @@
 import pathlib
 import queue
 import shutil
+import tempfile
 from datetime import datetime
 
 from runner.submission import SubmissionRunner
@@ -372,16 +373,26 @@ def on_submission_complete(self, submission_id: str):
         assert [*submission_result.keys()] == [*range(len(submission_result))]
         submission_result = [*submission_result.values()]
         # post data
-        submission_data = {
-            'tasks': submission_result,
-            'token': config.SANDBOX_TOKEN
-        }
-        self.release(submission_id)
-        logger().info(f'send to BE [submission_id={submission_id}]')
-        resp = requests.put(
-            f'{config.BACKEND_API}/submission/{submission_id}/complete',
-            json=submission_data,
-        )
+        with tempfile.NamedTemporaryFile("w") as tmpf:
+            submission_data = {
+                'tasks': submission_result,
+                'token': config.SANDBOX_TOKEN
+            }
+            # write payload to file
+            json.dump(submission_data, tmpf)
+            tmpf.flush()
+            # release resources
+            del submission_data
+            self.release(submission_id)
+
+            logger().info(f'send to BE [submission_id={submission_id}]')
+            # open in binary mode as requests needs a binary stream
+            with open(tmpf.name, "rb") as payload:
+                resp = requests.put(
+                    f'{config.BACKEND_API}/submission/{submission_id}/complete',
+                    data=payload,
+                    headers={'Content-Type': 'application/json'},
+                )
         logger().debug(f'get BE response: [{resp.status_code}] {resp.text}', )
         # clear
         if resp.ok: