fix: do not fail to fully download previously trashed messages

src/download.rs

@@ -283,8 +283,9 @@ mod tests {
     use super::*;
     use crate::chat::{get_chat_msgs, send_msg};
     use crate::ephemeral::Timer;
+    use crate::message::delete_msgs;
     use crate::receive_imf::receive_imf_from_inbox;
-    use crate::test_utils::{E2EE_INFO_MSGS, TestContext};
+    use crate::test_utils::{E2EE_INFO_MSGS, TestContext, TestContextManager};
 
     #[test]
     fn test_downloadstate_values() {
@@ -543,4 +544,43 @@ mod tests {
 
         Ok(())
     }
+
+    /// Tests that fully downloading the message
+    /// works even if the Message-ID already exists
+    /// in the database assigned to the trash chat.
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_partial_download_trashed() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+
+        let imf_raw = b"From: Bob <bob@example.org>\n\
+              To: Alice <alice@example.org>\n\
+              Chat-Version: 1.0\n\
+              Subject: subject\n\
+              Message-ID: <first@example.org>\n\
+              Date: Sun, 14 Nov 2021 00:10:00 +0000\
+              Content-Type: text/plain";
+
+        // Download message from Bob partially.
+        let partial_received_msg =
+            receive_imf_from_inbox(alice, "first@example.org", imf_raw, false, Some(100000))
+                .await?
+                .unwrap();
+        assert_eq!(partial_received_msg.msg_ids.len(), 1);
+
+        // Delete the received message.
+        // Not it is still in the database,
+        // but in the trash chat.
+        delete_msgs(alice, &[partial_received_msg.msg_ids[0]]).await?;
+
+        // Fully download message after deletion.
+        let full_received_msg =
+            receive_imf_from_inbox(alice, "first@example.org", imf_raw, false, None).await?;
+
+        // The message does not reappear.
+        // However, `receive_imf` should not fail.
+        assert!(full_received_msg.is_none());
+
+        Ok(())
+    }
 }

src/receive_imf.rs

@@ -557,13 +557,17 @@ pub(crate) async fn receive_imf_inner(
     // make sure, this check is done eg. before securejoin-processing.
     let (replace_msg_id, replace_chat_id);
     if let Some((old_msg_id, _)) = message::rfc724_mid_exists(context, rfc724_mid).await? {
-        let msg = Message::load_from_db(context, old_msg_id).await?;
         replace_msg_id = Some(old_msg_id);
-        replace_chat_id = if msg.download_state() != DownloadState::Done {
+        replace_chat_id = if let Some(msg) = Message::load_from_db_optional(context, old_msg_id)
+            .await?
+            .filter(|msg| msg.download_state() != DownloadState::Done)
+        {
             // the message was partially downloaded before and is fully downloaded now.
             info!(context, "Message already partly in DB, replacing.");
             Some(msg.chat_id)
         } else {
+            // The message was already fully downloaded
+            // or cannot be loaded because it is deleted.
             None
         };
     } else {