Retrieving MIME types for images in Telegram Bot API

Other Questions Telegram bot
1

Hey everyone! I’m working on a Telegram bot and I’m stuck. I need to figure out how to get the MIME type for pictures users send to my bot. I’m using the Telegram Bot API with Telegraf.

My bot saves file IDs for photos and videos. I want to download these files later but I’m confused about keeping the original file info. The API docs mention saving the MIME type and filename when you receive the File object, but I’m not entirely clear on when this happens.

I noticed that update types for various files usually include MIME type information, yet the photo update object doesn’t provide it. Is there another way to obtain the MIME type for photos?

Here’s an example of what I’m trying to achieve:

bot.on('photo', (ctx) => {
  const fileId = ctx.message.photo[0].file_id;
  // How can I retrieve the MIME type here?
  savePicture(fileId, mimeType);
});

Any help would be greatly appreciated! Thanks!

2

From my experience working with the Telegram Bot API, handling MIME types for photos can be challenging. The API does not supply the MIME type directly, so an effective workaround is to call the getFile method when you receive a photo. This returns a file_path from which you can extract the file extension. Using this extension, you can map to a common MIME type such as image/jpeg. While this method isn’t foolproof, it is generally reliable. It is important to implement proper error handling and to consider non-standard file extensions as edge cases.

3

hey zack, ran into this issue too. the api’s weird with photo mime types. what i did was use getFile() to grab the file_path, then guess the mime type from the extension. like .jpg = image/jpeg. not perfect but works most of the time. just watch out for weird file types, ya know?

4

I encountered a similar issue while developing my bot. The MIME type for photos isn’t directly provided in the update object, so I had to use a workaround. After receiving the photo, I invoked the getFile() method to obtain the file path. Once you have the file path, you can extract the file extension and then construct the MIME type, for example, using the format image/jpeg. Although this method relies on inferring the type from the file extension, it has worked reliably in my projects. Just be sure to include proper error handling.