api: get_existing_msg_ids()

This API allows to check if the message with
given ID exists and distinguish between
message not existing and database error.
It might also be faster than
checking messages one by one
if multiple messages need to be checked
because of using a single SQL transaction.

src/message/message_tests.rs

@@ -764,3 +764,27 @@ async fn test_load_unknown_viewtype() -> Result<()> {
     assert_eq!(bob_msg.get_viewtype(), Viewtype::Unknown);
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_get_existing_msg_ids() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    let msg1_id = tcm.send_recv(alice, bob, "Hello 1!").await.id;
+    let msg2_id = tcm.send_recv(alice, bob, "Hello 2!").await.id;
+    let msg3_id = tcm.send_recv(alice, bob, "Hello 3!").await.id;
+    let msg4_id = tcm.send_recv(alice, bob, "Hello 4!").await.id;
+
+    assert_eq!(
+        get_existing_msg_ids(bob, &[msg1_id, msg2_id, msg3_id, msg4_id]).await?,
+        vec![msg1_id, msg2_id, msg3_id, msg4_id]
+    );
+    delete_msgs(bob, &[msg1_id, msg3_id]).await?;
+    assert_eq!(
+        get_existing_msg_ids(bob, &[msg1_id, msg2_id, msg3_id, msg4_id]).await?,
+        vec![msg2_id, msg4_id]
+    );
+
+    Ok(())
+}