fix: Fetch existing messages for bots as InFresh (#4976)

Before, if `Config::FetchExistingMsgs` is set, existing messages were received with the `InSeen`
state set, but for bots they must be `InFresh` and also `IncomingMsg` events should be emitted for
them so that they are processed by bots as it happens with new messages.

deltachat-ffi/deltachat.h

@@ -481,8 +481,9 @@ char*           dc_get_blobdir               (const dc_context_t* context);
  * - `bot`          = Set to "1" if this is a bot.
  *                    Prevents adding the "Device messages" and "Saved messages" chats,
  *                    adds Auto-Submitted header to outgoing messages,
- *                    accepts contact requests automatically (calling dc_accept_chat() is not needed for bots)
+ *                    accepts contact requests automatically (calling dc_accept_chat() is not needed),
- *                    and does not cut large incoming text messages.
+ *                    does not cut large incoming text messages,
+ *                    handles existing messages the same way as new ones if `fetch_existing_msgs=1`.
  * - `last_msg_id` = database ID of the last message processed by the bot.
  *                   This ID and IDs below it are guaranteed not to be returned
  *                   by dc_get_next_msgs() and dc_wait_next_msgs().
@@ -493,8 +494,8 @@ char*           dc_get_blobdir               (const dc_context_t* context);
  *                   For most bots calling `dc_markseen_msgs()` is the
  *                   recommended way to update this value
  *                   even for self-sent messages.
- * - `fetch_existing_msgs` = 1=fetch most recent existing messages on configure (default),
+ * - `fetch_existing_msgs` = 0=do not fetch existing messages on configure (default),
- *                    0=do not fetch existing messages on configure.
+ *                    1=fetch most recent existing messages on configure.
  *                    In both cases, existing recipients are added to the contact database.
  * - `disable_idle` = 1=disable IMAP IDLE even if the server supports it,
  *                    0=use IMAP IDLE if the server supports it.

src/receive_imf.rs

@@ -696,6 +696,9 @@ async fn add_parts(
     prevent_rename: bool,
     verified_encryption: VerifiedEncryption,
 ) -> Result<ReceivedMsg> {
+    let is_bot = context.get_config_bool(Config::Bot).await?;
+    // Bots handle existing messages the same way as new ones.
+    let fetching_existing_messages = fetching_existing_messages && !is_bot;
     let rfc724_mid_orig = &mime_parser
         .get_rfc724_mid()
         .unwrap_or(rfc724_mid.to_string());
@@ -788,9 +791,6 @@ async fn add_parts(
             info!(context, "Message is an MDN (TRASH).",);
         }
 
-        // signals whether the current user is a bot
-        let is_bot = context.get_config_bool(Config::Bot).await?;
-
         let create_blocked_default = if is_bot {
             Blocked::Not
         } else {

src/receive_imf/tests.rs

@@ -3276,6 +3276,46 @@ async fn test_send_as_bot() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_bot_recv_existing_msg() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let bob = &tcm.bob().await;
+    bob.set_config(Config::Bot, Some("1")).await.unwrap();
+    bob.set_config(Config::FetchExistingMsgs, Some("1"))
+        .await
+        .unwrap();
+    let fetching_existing_messages = true;
+    let msg = receive_imf_from_inbox(
+        bob,
+        "first@example.org",
+        b"From: Alice <alice@example.org>\n\
+          To: Bob <bob@example.net>\n\
+          Chat-Version: 1.0\n\
+          Message-ID: <first@example.org>\n\
+          Date: Sun, 14 Nov 2021 00:10:00 +0000\n\
+          Content-Type: text/plain\n\
+          \n\
+          hello\n",
+        false,
+        None,
+        fetching_existing_messages,
+    )
+    .await?
+    .unwrap();
+    let msg = Message::load_from_db(bob, msg.msg_ids[0]).await?;
+    assert_eq!(msg.state, MessageState::InFresh);
+    let event = bob
+        .evtracker
+        .get_matching(|ev| matches!(ev, EventType::IncomingMsg { .. }))
+        .await;
+    let EventType::IncomingMsg { chat_id, msg_id } = event else {
+        unreachable!();
+    };
+    assert_eq!(chat_id, msg.chat_id);
+    assert_eq!(msg_id, msg.id);
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_no_private_reply_to_blocked_account() -> Result<()> {
     let mut tcm = TestContextManager::new();