[Core] Make create_torrent return a deferred

This allows to create a torrent file on the remote server
and get its content in one call.

deluge/core/core.py

@@ -12,7 +12,6 @@ import logging
 import os
 import shutil
 import tempfile
-import threading
 from base64 import b64decode, b64encode
 from typing import Any, Dict, List, Optional, Tuple, Union
 from urllib.request import URLError, urlopen
@@ -1001,21 +1000,19 @@ class Core(component.Component):
         add_to_session=False,
     ):
         log.debug('creating torrent..')
-        threading.Thread(
-            target=self._create_torrent_thread,
-            args=(
+        return threads.deferToThread(
+            self._create_torrent_thread,
             path,
             tracker,
             piece_length,
-                comment,
-                target,
-                webseeds,
-                private,
-                created_by,
-                trackers,
-                add_to_session,
-            ),
-        ).start()
+            comment=comment,
+            target=target,
+            webseeds=webseeds,
+            private=private,
+            created_by=created_by,
+            trackers=trackers,
+            add_to_session=add_to_session,
+        )
 
     def _create_torrent_thread(
         self,
@@ -1055,12 +1052,13 @@ class Core(component.Component):
             with open(target, 'wb') as _file:
                 _file.write(filecontent)
 
+        filedump = b64encode(filecontent)
         log.debug('torrent created!')
         if add_to_session:
             options = {}
             options['download_location'] = os.path.split(path)[0]
-            filedump = b64encode(filecontent)
             self.add_torrent_file(filename, filedump, options)
+        return filename, filedump
 
     @export
     def upload_plugin(self, filename: str, filedump: Union[str, bytes]) -> None:

deluge/tests/test_core.py

@@ -3,7 +3,7 @@
 # the additional special exception to link portions of this program with the OpenSSL library.
 # See LICENSE for more details.
 #
-
+import base64
 import os
 from base64 import b64encode
 from hashlib import sha1 as sha
@@ -483,3 +483,29 @@ class TestCore(BaseTestCase):
         assert self.core._create_peer_id('2.0.1rc1') == '-DE201r-'
         assert self.core._create_peer_id('2.11.0b2') == '-DE2B0b-'
         assert self.core._create_peer_id('2.4.12b2.dev3') == '-DE24CD-'
+
+    @pytest.mark.parametrize(
+        'path',
+        [
+            common.get_test_data_file('deluge.png'),
+            os.path.dirname(common.get_test_data_file('deluge.png')),
+        ],
+    )
+    @pytest.mark.parametrize('piece_length', [2**14, 2**16])
+    @pytest_twisted.inlineCallbacks
+    def test_create_torrent(self, path, tmp_path, piece_length):
+        target = tmp_path / 'test.torrent'
+
+        filename, filedump = yield self.core.create_torrent(
+            path=path,
+            tracker=None,
+            piece_length=piece_length,
+            target=target,
+            add_to_session=False,
+        )
+        filecontent = base64.b64decode(filedump)
+
+        with open(target, 'rb') as f:
+            assert f.read() == filecontent
+
+        lt.torrent_info(filecontent)