fix: assign messages to chats based on not fully downloaded references

deltachat-rpc-client/tests/test_something.py

@@ -538,3 +538,49 @@ def test_reactions_for_a_reordering_move(acfactory):
     assert len(contacts) == 1
     assert contacts[0].get_snapshot().address == ac1.get_config("addr")
     assert list(reactions.reactions_by_contact.values())[0] == [react_str]
+
+
+@pytest.mark.parametrize("n_accounts", [3, 2])
+def test_download_limit_chat_assignment(acfactory, tmp_path, n_accounts):
+    download_limit = 300000
+
+    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!"
+
+        contact_addr = account.get_config("addr")
+        contact = alice.create_contact(contact_addr, "")
+
+        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")
+    snapshot = bob.get_message_by_id(bob.wait_for_incoming_msg_event().msg_id).get_snapshot()
+    assert snapshot.text == "hi"
+    bob_group = snapshot.chat
+
+    path = tmp_path / "large"
+    path.write_bytes(os.urandom(download_limit + 1))
+
+    for i in range(10):
+        logging.info("Sending message %s", i)
+        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
+        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/chat.rs

@@ -209,24 +209,11 @@ impl ChatId {
     }
 
     /// Returns [`ChatId`] of a chat that `msg` belongs to.
-    ///
-    /// Checks that `msg` is assigned to the right chat.
     pub(crate) fn lookup_by_message(msg: &Message) -> Option<Self> {
         if msg.chat_id == DC_CHAT_ID_TRASH {
             return None;
         }
-        if msg.download_state != DownloadState::Done
-            // TODO (2023-09-12): Added for backward compatibility with versions that did not have
-            // `DownloadState::Undecipherable`. Remove eventually with the comment in
-            // `MimeMessage::from_bytes()`.
-            || msg
-                .error
-                .as_ref()
-                .filter(|e| e.starts_with("Decrypting failed:"))
-                .is_some()
-        {
-            // If `msg` is not fully downloaded or undecipherable, it may have been assigned to the
-            // wrong chat (they often get assigned to the 1:1 chat with the sender).
+        if msg.download_state == DownloadState::Undecipherable {
             return None;
         }
         Some(msg.chat_id)

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;