Download

The standard file download path looks like this:

• Call getFile with file_id
• Extract file_path from response
• Construct a link of the following type https://api.telegram.org/file/bot<token>/<file_path>
• Send request and download the requested media
• ? Maybe save file in FS ?

but in our case it looks more convenient and simpler.

Via context methods

bot.on("message", async (context) => {
    if (!context.document) return;
    // download to ./file-name
    await context.download(context.document.fileName || "file-name");
    // get ArrayBuffer
    const buffer = await context.download();

    return context.send("Thank you!");
});

IMPORTANT

One message contain only one attachment. Therefore, to download an attachment, you can simply use the context.download method

Via bot instance method

const chat = await bot.api.getChat({ chat_id: "@not_found" });

if (!chat.photo?.big_file_id) return;

// download to ./not_found_chat_photo.png
await bot.downloadFile(chat.photo.big_file_id, "not_found_chat_photo.png");
// get ArrayBuffer
const buffer = await bot.downloadFile(chat.photo.big_file_id);