api(deltachat-rpc-client): add Message.exists()

deltachat-rpc-client/src/deltachat_rpc_client/message.py

@@ -60,6 +60,10 @@ class Message:
         """Mark the message as seen."""
         self._rpc.markseen_msgs(self.account.id, [self.id])
 
+    def exists(self) -> bool:
+        """Return True if the message exists."""
+        return bool(self._rpc.get_existing_msg_ids(self.account.id, [self.id]))
+
     def continue_autocrypt_key_transfer(self, setup_code: str) -> None:
         """Continue the Autocrypt Setup Message key transfer.
 

deltachat-rpc-client/tests/test_something.py

@@ -993,3 +993,22 @@ def test_background_fetch(acfactory, dc):
         snapshot = messages[-1].get_snapshot()
         if snapshot.text == "Hello again!":
             break
+
+
+def test_message_exists(acfactory):
+    ac1, ac2 = acfactory.get_online_accounts(2)
+    chat = ac1.create_chat(ac2)
+    message1 = chat.send_text("Hello!")
+    message2 = chat.send_text("Hello again!")
+    assert message1.exists()
+    assert message2.exists()
+
+    ac1.delete_messages([message1])
+    assert not message1.exists()
+    assert message2.exists()
+
+    # There is no error when checking if
+    # the message exists for deleted account.
+    ac1.remove()
+    assert not message1.exists()
+    assert not message2.exists()