Unable to persist fileId through instance recreation

[Anfet]

Hello to everyone.

I'm trying to keep a persistent chat feed and stumbled across a unknown behavior. The goal is to retrieve chat content via getChatHistory, store its content in database, then retrieve and show it. Right now I'm retrieving chat history, then serialize message content and store it in db; And sometimes later the Invalid file identifier comes into play. I'm guessing the local fileId becomes outdated for some reason while still containing file on disk.

But how do you retrieve fileId without fetching message and it's content again from telegram? I see no functions that can resolve remoteId to fileId. And downloadFile only accepts local id;

Is there a possibility? Or what would be the correct approach?

[levlam]

File identifiers aren't persistent and are valid only until TDLib instance is closed. Apps supposed to save nothing between TDLib restarts.

The correct approach is to fetch the message from TDLib using getMessage, get file identifier from the message content and download the file using the identifier. There is no way to download the file without having access to the message.

[Anfet]

Hm. Will getMessage use network request or assemble result from local copy?

Supposedly I've got chat history and stored message ids. And when user will be browsing the history I must getMessage one by one as they appear? Is this correct? Won't this be a heavy load on telegram?

[levlam]

Will getMessage use network request or assemble result from local copy?

If a request is possible to complete locally, it will be completed locally.

And when user will be browsing the history I must getMessage one by one as they appear?

In fact, ordinary apps almost never need to use getMessage. See https://core.telegram.org/tdlib/getting-started and https://core.telegram.org/tdlib/getting-started#getting-chat-messages in particular.