fix FFI-behaviour: return default empty messages when asked for special ones

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog 
 
+## 1.0.0-beta5
+
+- fix dc_get_msg() to return empty messages when asked for special ones 
+
 ## 1.0.0-beta4
 
 - fix more than one sending of autocrypt setup message

deltachat-ffi/src/lib.rs

@@ -1382,8 +1382,21 @@ pub unsafe extern "C" fn dc_get_msg(context: *mut dc_context_t, msg_id: u32) ->
             let message = match message::Message::load_from_db(ctx, MsgId::new(msg_id)) {
                 Ok(msg) => msg,
                 Err(e) => {
-                    warn!(ctx, "Error getting msg #{}: {}", msg_id, e);
+                    if msg_id <= constants::DC_MSG_ID_LAST_SPECIAL {
-                    return ptr::null_mut();
+                        // C-core API returns empty messages, do the same
+                        warn!(
+                            ctx,
+                            "dc_get_msg called with special msg_id={}, returning empty msg",
+                            msg_id
+                        );
+                        message::Message::default()
+                    } else {
+                        error!(
+                            ctx,
+                            "dc_get_msg could not retrieve msg_id {}: {}", msg_id, e
+                        );
+                        return ptr::null_mut();
+                    }
                 }
             };
             let ffi_msg = MessageWrapper { context, message };

python/tests/test_lowlevel.py

@@ -95,6 +95,13 @@ def test_markseen_invalid_message_ids(acfactory):
     ac1._evlogger.ensure_event_not_queued("DC_EVENT_WARNING|DC_EVENT_ERROR")
 
 
+def test_get_special_message_id_returns_empty_message(acfactory):
+    ac1 = acfactory.get_configured_offline_account()
+    for i in range(1, 10):
+        msg = ac1.get_message_by_id(i)
+        assert msg.id == 0
+
+
 def test_provider_info():
     provider = lib.dc_provider_new_from_email(cutil.as_dc_charpointer("ex@example.com"))
     assert cutil.from_dc_charpointer(

src/mimefactory.rs

@@ -655,8 +655,6 @@ impl<'a> MimeFactory<'a> {
     }
 
     pub fn load_msg(context: &Context, msg_id: MsgId) -> Result<MimeFactory, Error> {
-        ensure!(!msg_id.is_special(), "Invalid chat id");
-
         let msg = Message::load_from_db(context, msg_id)?;
         let chat = Chat::load_from_db(context, msg.chat_id)?;
         let mut factory = MimeFactory::new(context, msg);