fix: do not create ad-hoc groups from partial downloads

deltachat-rpc-client/tests/test_something.py

@@ -540,25 +540,26 @@ def test_reactions_for_a_reordering_move(acfactory):
     assert list(reactions.reactions_by_contact.values())[0] == [react_str]
 
 
-def test_download_limit_chat_assignment(acfactory, tmp_path):
+@pytest.mark.parametrize("n_accounts", [3, 2])
+def test_download_limit_chat_assignment(acfactory, tmp_path, n_accounts):
     download_limit = 300000
-    alice, bob, carol = acfactory.get_online_accounts(3)
 
-    for account in bob, carol:
+    alice, *others = acfactory.get_online_accounts(n_accounts)
+    bob = others[0]
+
+    alice_group = alice.create_group("test group")
+    for account in others:
         chat = account.create_chat(alice)
         chat.send_text("Hello Alice!")
         assert alice.get_message_by_id(alice.wait_for_incoming_msg_event().msg_id).get_snapshot().text == "Hello Alice!"
 
-    bob_addr = bob.get_config("addr")
-    alice_contact_bob = alice.create_contact(bob_addr, "Bob")
+        contact_addr = account.get_config("addr")
+        contact = alice.create_contact(contact_addr, "")
 
-    carol_addr = carol.get_config("addr")
-    alice_contact_carol = alice.create_contact(carol_addr, "Carol")
-
-    alice_group = alice.create_group("test group")
-    alice_group.add_contact(alice_contact_bob)
-    alice_group.add_contact(alice_contact_carol)
+        alice_group.add_contact(contact)
 
+    if n_accounts == 2:
+        bob_chat_alice = bob.create_chat(alice)
     bob.set_config("download_limit", str(download_limit))
 
     alice_group.send_text("hi")
@@ -574,4 +575,12 @@ def test_download_limit_chat_assignment(acfactory, tmp_path):
         alice_group.send_file(str(path))
         snapshot = bob.get_message_by_id(bob.wait_for_incoming_msg_event().msg_id).get_snapshot()
         assert snapshot.download_state == DownloadState.AVAILABLE
-        assert snapshot.chat == bob_group
+        if n_accounts > 2:
+            assert snapshot.chat == bob_group
+        else:
+            # Group contains only Alice and Bob,
+            # so partially downloaded messages are
+            # hard to distinguish from private replies to group messages.
+            #
+            # Message may be a private reply, so we assign it to 1:1 chat with Alice.
+            assert snapshot.chat == bob_chat_alice

src/receive_imf.rs

@@ -1749,7 +1749,19 @@ async fn create_or_lookup_group(
 ) -> Result<Option<(ChatId, Blocked)>> {
     let grpid = if let Some(grpid) = try_getting_grpid(mime_parser) {
         grpid
-    } else if allow_creation {
+    } else if !allow_creation {
+        info!(context, "Creating ad-hoc group prevented from caller.");
+        return Ok(None);
+    } else if is_partial_download {
+        // Partial download may be an encrypted message with protected Subject header.
+        //
+        // We do not want to create a group with "..." or "Encrypted message" as a subject.
+        info!(
+            context,
+            "Ad-hoc group cannot be created from partial download."
+        );
+        return Ok(None);
+    } else {
         let mut member_ids: Vec<ContactId> = to_ids.to_vec();
         if !member_ids.contains(&(from_id)) {
             member_ids.push(from_id);
@@ -1763,9 +1775,6 @@ async fn create_or_lookup_group(
             .context("could not create ad hoc group")?
             .map(|chat_id| (chat_id, create_blocked));
         return Ok(res);
-    } else {
-        info!(context, "Creating ad-hoc group prevented from caller.");
-        return Ok(None);
     };
 
     let mut chat_id;