[Core] Don't always write create_torrent metafile to disk

If target=None and add_to_session is True, the torrent will be
directly added to the session without writing the torrent file
to disk. This will allow to programmatically control deluge via
RPC without creating .torrent files all over the place.

Also, make most create_torrent parameters optional.

deluge/core/core.py

@@ -17,7 +17,7 @@
 from typing import Any, Dict, List, Optional, Tuple, Union
 from urllib.request import URLError, urlopen
 
-from twisted.internet import defer, reactor, task
+from twisted.internet import defer, reactor, task, threads
 from twisted.web.client import Agent, readBody
 
 import deluge.common
@@ -992,13 +992,13 @@ def create_torrent(
         path,
         tracker,
         piece_length,
-        comment,
-        target,
-        webseeds,
-        private,
-        created_by,
-        trackers,
-        add_to_session,
+        comment=None,
+        target=None,
+        webseeds=None,
+        private=False,
+        created_by=None,
+        trackers=None,
+        add_to_session=False,
     ):
         log.debug('creating torrent..')
         threading.Thread(
@@ -1032,24 +1032,35 @@ def _create_torrent_thread(
     ):
         from deluge import metafile
 
-        metafile.make_meta_file(
+        filecontent = metafile.make_meta_file_content(
             path,
             tracker,
             piece_length,
             comment=comment,
-            target=target,
             webseeds=webseeds,
             private=private,
             created_by=created_by,
             trackers=trackers,
         )
+
+        write_file = False
+        if target or not add_to_session:
+            write_file = True
+
+        if not target:
+            target = metafile.default_meta_file_path(path)
+        filename = os.path.split(target)[-1]
+
+        if write_file:
+            with open(target, 'wb') as _file:
+                _file.write(filecontent)
+
         log.debug('torrent created!')
         if add_to_session:
             options = {}
             options['download_location'] = os.path.split(path)[0]
-            with open(target, 'rb') as _file:
-                filedump = b64encode(_file.read())
-                self.add_torrent_file(os.path.split(target)[1], filedump, options)
+            filedump = b64encode(filecontent)
+            self.add_torrent_file(filename, filedump, options)
 
     @export
     def upload_plugin(self, filename: str, filedump: Union[str, bytes]) -> None:

deluge/metafile.py

@@ -51,7 +51,7 @@ def __call__(self, piece_count, num_pieces):
         )
 
 
-def make_meta_file(
+def make_meta_file_content(
     path,
     url,
     piece_length,
@@ -60,7 +60,6 @@ def make_meta_file(
     comment=None,
     safe=None,
     content_type=None,
-    target=None,
     webseeds=None,
     name=None,
     private=False,
@@ -70,14 +69,6 @@ def make_meta_file(
     data = {'creation date': int(gmtime())}
     if url:
         data['announce'] = url.strip()
-    a, b = os.path.split(path)
-    if not target:
-        if b == '':
-            f = a + '.torrent'
-        else:
-            f = os.path.join(a, b + '.torrent')
-    else:
-        f = target
 
     if progress is None:
         progress = dummy
@@ -121,8 +112,55 @@ def make_meta_file(
         data['announce-list'] = trackers
 
     data['encoding'] = 'UTF-8'
-    with open(f, 'wb') as file_:
-        file_.write(bencode(utf8_encode_structure(data)))
+    return bencode(utf8_encode_structure(data))
+
+
+def default_meta_file_path(content_path):
+    a, b = os.path.split(content_path)
+    if b == '':
+        f = a + '.torrent'
+    else:
+        f = os.path.join(a, b + '.torrent')
+    return f
+
+
+def make_meta_file(
+    path,
+    url,
+    piece_length,
+    progress=None,
+    title=None,
+    comment=None,
+    safe=None,
+    content_type=None,
+    target=None,
+    webseeds=None,
+    name=None,
+    private=False,
+    created_by=None,
+    trackers=None,
+):
+    if not target:
+        target = default_meta_file_path(path)
+
+    file_content = make_meta_file_content(
+        path,
+        url,
+        piece_length,
+        progress=progress,
+        title=title,
+        comment=comment,
+        safe=safe,
+        content_type=content_type,
+        webseeds=webseeds,
+        name=name,
+        private=private,
+        created_by=created_by,
+        trackers=trackers,
+    )
+
+    with open(target, 'wb') as file_:
+        file_.write(file_content)
 
 
 def calcsize(path):