ChatMemberUpdated.invite_link missing when joining public groups

[Bibo-Joshi]

Hi. I did some testing and it looks like the invite_link field of the ChatMemberUpdated class is present only when joining private groups. For public groups, the field is missing even when the user does join via a link and not via the username of the group.
I expect that the added value of the invite link is smaller for public groups as they can be found by anyone, but this behavior is was unexpected as the documentation does not suggest it. If you could document this behavior or if the behavior could be updated, I'd be grateful.

[Poolitzer]

It works however when people join when pressing on a chat folder invite link.

[Bibo-Joshi]

Apparently in case of folder-join the groups primary link is used and the via_chat_folder_invite_link attribute is set to True. IMO the invite_link still being set is a bit surprising as the user didn't actively use the link. While it's understandable that the joining has to be established somehow, I would prefer for either the attribute to be or this behavior to be documented.

[Bibo-Joshi]

Another insight: Apparently the link is there for groups that are newly created today …

[levlam]

For public groups, the field is missing even when the user does join via a link and not via the username of the group.

This is not true. If the user joins the group via an invite link, the field invite_link is present. If the group is public, then users are free to join it directly, even the group was opened via an invite link. And this is exactly the behavior of most apps when user press "Join" button on the chat history screen.

[Bibo-Joshi]

Thanks for the quick reply! Your explanation about the "Join" button hiding away the invite_link does sound understandable. However, joining a newly created group via invite link + join button does give the invite_link attribute (just double checked again on TG desktop windows and webk). So it seems to me that either the behavior is different for groups greated after some date or it is just inconsistent :/

[levlam]

The behavior depends on the used app. The official Android app is known to use direct join instead of invite link for public chats.

[Poolitzer]

I do not believe it is an app issue only.

I can use Telethon to join a chat with the same invite link with different accounts, in one chat member update it has the link, one doesn't

[levlam]

I tested this again multiple times and each time the invite_link field is present if the user joins the chat using the invite link. I've never managed to reproduce the issue if the chat is joined using the method messages.importChatInvite, and apps don't use the method to join public chats and join them directly, hence absence of the field invite_link is expected.