From 5b0ad6042d0205c24ab211fc8fbaae0fa38426c7 Mon Sep 17 00:00:00 2001
From: iequidoo <dgreshilov@gmail.com>
Date: Sat, 31 Jan 2026 08:39:01 -0300
Subject: [PATCH] fix: Don't set download state to Failure if message is
 available on another Session's transport (#7684)

---
 .../tests/test_multitransport.py              | 28 ++++++++++++++++
 src/download.rs                               | 33 +++++++++++--------
 2 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/deltachat-rpc-client/tests/test_multitransport.py b/deltachat-rpc-client/tests/test_multitransport.py
index fda851b48f..1a2ab6daaa 100644
--- a/deltachat-rpc-client/tests/test_multitransport.py
+++ b/deltachat-rpc-client/tests/test_multitransport.py
@@ -1,6 +1,7 @@
 import pytest
 
 from deltachat_rpc_client import EventType
+from deltachat_rpc_client.const import DownloadState
 from deltachat_rpc_client.rpc import JsonRpcError
 
 
@@ -120,6 +121,33 @@ def test_change_address(acfactory) -> None:
     assert sender_addr2 == new_alice_addr
 
 
+def test_download_on_demand(acfactory) -> None:
+    alice, bob = acfactory.get_online_accounts(2)
+    alice.set_config("download_limit", "1")
+
+    alice.stop_io()
+    qr = acfactory.get_account_qr()
+    alice.add_transport_from_qr(qr)
+    alice.start_io()
+
+    alice.create_chat(bob)
+    chat_bob_alice = bob.create_chat(alice)
+    chat_bob_alice.send_message(file="../test-data/image/screenshot.jpg")
+    msg = alice.wait_for_incoming_msg()
+    snapshot = msg.get_snapshot()
+    assert snapshot.download_state == DownloadState.AVAILABLE
+    chat_id = snapshot.chat_id
+    # Actually the message isn't available yet. Wait somehow for the post-message to arrive.
+    chat_bob_alice.send_message("Now you can download my previous message")
+    alice.wait_for_incoming_msg()
+    alice._rpc.download_full_message(alice.id, msg.id)
+    for dstate in [DownloadState.IN_PROGRESS, DownloadState.DONE]:
+        event = alice.wait_for_event(EventType.MSGS_CHANGED)
+        assert event.chat_id == chat_id
+        assert event.msg_id == msg.id
+        assert msg.get_snapshot().download_state == dstate
+
+
 @pytest.mark.parametrize("is_chatmail", ["0", "1"])
 def test_mvbox_move_first_transport(acfactory, is_chatmail) -> None:
     """Test that mvbox_move is disabled by default even for non-chatmail accounts.
diff --git a/src/download.rs b/src/download.rs
index 8046540e2e..2ec995fd88 100644
--- a/src/download.rs
+++ b/src/download.rs
@@ -99,7 +99,8 @@ impl MsgId {
         Ok(())
     }
 
-    /// Updates the message download state. Returns `Ok` if the message doesn't exist anymore.
+    /// Updates the message download state. Returns `Ok` if the message doesn't exist anymore or has
+    /// the download state up to date.
     pub(crate) async fn update_download_state(
         self,
         context: &Context,
@@ -108,7 +109,7 @@ impl MsgId {
         if context
             .sql
             .execute(
-                "UPDATE msgs SET download_state=? WHERE id=?;",
+                "UPDATE msgs SET download_state=? WHERE id=? AND download_state<>?1",
                 (download_state, self),
             )
             .await?
@@ -135,42 +136,46 @@ impl Message {
     }
 }
 
-/// Actually download a message partially downloaded before.
+/// Actually downloads a message partially downloaded before if the message is available on the
+/// session transport, in which case returns `Some`. If the message is available on another
+/// transport, returns `None`.
 ///
 /// Most messages are downloaded automatically on fetch instead.
 pub(crate) async fn download_msg(
     context: &Context,
     rfc724_mid: String,
     session: &mut Session,
-) -> Result<()> {
+) -> Result<Option<()>> {
     let transport_id = session.transport_id();
     let row = context
         .sql
         .query_row_optional(
-            "SELECT uid, folder FROM imap
-             WHERE rfc724_mid=?
-             AND transport_id=?
-             AND target!=''",
+            "SELECT uid, folder, transport_id FROM imap
+             WHERE rfc724_mid=? AND target!=''
+             ORDER BY transport_id=? DESC LIMIT 1",
             (&rfc724_mid, transport_id),
             |row| {
                 let server_uid: u32 = row.get(0)?;
                 let server_folder: String = row.get(1)?;
-                Ok((server_uid, server_folder))
+                let msg_transport_id: u32 = row.get(2)?;
+                Ok((server_uid, server_folder, msg_transport_id))
             },
         )
         .await?;
 
-    let Some((server_uid, server_folder)) = row else {
+    let Some((server_uid, server_folder, msg_transport_id)) = row else {
         // No IMAP record found, we don't know the UID and folder.
         return Err(anyhow!(
             "IMAP location for {rfc724_mid:?} post-message is unknown"
         ));
     };
-
+    if msg_transport_id != transport_id {
+        return Ok(None);
+    }
     session
         .fetch_single_msg(context, &server_folder, server_uid, rfc724_mid)
         .await?;
-    Ok(())
+    Ok(Some(()))
 }
 
 impl Session {
@@ -272,7 +277,7 @@ pub(crate) async fn download_msgs(context: &Context, session: &mut Session) -> R
 
     for rfc724_mid in &rfc724_mids {
         let res = download_msg(context, rfc724_mid.clone(), session).await;
-        if res.is_ok() {
+        if let Ok(Some(())) = res {
             delete_from_downloads(context, rfc724_mid).await?;
             delete_from_available_post_msgs(context, rfc724_mid).await?;
         }
@@ -327,7 +332,7 @@ pub(crate) async fn download_known_post_messages_without_pre_message(
             // The message may be in the wrong order,
             // but at least we have it at all.
             let res = download_msg(context, rfc724_mid.clone(), session).await;
-            if res.is_ok() {
+            if let Ok(Some(())) = res {
                 delete_from_available_post_msgs(context, rfc724_mid).await?;
             }
             if let Err(err) = res {