Telegram bot - receive photo URL

This is a three steps process First when the user send an image, your bot get a JSON structure like this:

Array
(
    [update_id] => 820488009
    [message] => Array
        (
            [message_id] => 11338
            [from] => Array
                (
                    [id] => xxxxxx
                    [is_bot] => 
                    [first_name] => ANSB
                    [language_code] => fr
                )

            [chat] => Array
                (
                    [id] => 333333333
                    [first_name] => ANSB
                    [type] => private
                )

            [date] => 1606316785
            [photo] => Array
                (
                    [0] => Array
                        (
                            [file_id] => AgACAgEAAxkBAAIsSl--cvE_bez8g1Kzbk6LsR4JZOJWAALxqDEbw8TxRQpbG7Np1dvbARV2ShcAAwEAAwIAA20AA6SRAAIeBA
                            [file_unique_id] => AQADARV2ShcAA6SRAAI
                            [file_size] => 34888
                            [width] => 320
                            [height] => 240
                        )

                    [1] => Array
                        (
                            [file_id] => AgACAgEAAxkBAAIsSl--cvE_bez8g1Kzbk6LsR4JZOJWAALxqDEbw8TxRQpbG7Np1dvbARV2ShcAAwEAAwIAA3gAA6WRAAIeBA
                            [file_unique_id] => AQADARV2ShcAA6WRAAI
                            [file_size] => 204583
                            [width] => 800
                            [height] => 600
                        )

                    [2] => Array
                        (
                            [file_id] => AgACAgEAAxkBAAIsSl--cvE_bez8g1Kzbk6LsR4JZOJWAALxqDEbw8TxRQpbG7Np1dvbARV2ShcAAwEAAwIAA3kAA6KRAAIeBA
                            [file_unique_id] => AQADARV2ShcAA6KRAAI
                            [file_size] => 372915
                            [width] => 1280
                            [height] => 960
                        )
                )
        )
)

As you can see, Telegram create low resolution of the image. If the original image is small, you can have only the original. If it's medium you'll get two. Here yu can see I have 3 images (the original is the big one 1280*960). So you have to check the size of the array of image wih (eg i PHP)

$nbr_image = count($jsondata['message']['photo']);

in order to read the file_id of your choice so the oe of the smallest, the biggest etc... Take care, the id is NOT the file_unique_id but the big one so the file_id.

Notice if the user send in one time more than one picture, you will get one message for each picture. So each message is about ONE picture, in multiple resolutions.

Once your bot has the file_id, you must call Telegram sending the file_id. The call is a basic one with:

https://api.telegram.org/bot<token_of_your_bot>/getFile?file_id=<file_id of the picture>

You get back a JSON with:

{"ok":true,
   "result":
   {"file_id":"AgACAgEAAxkBAAIsUV--hZoxZ5_ctnfbVa0zFWjRtMYUAALyqDEbw8TxRdkTI6iDNvHUmKQSMAAEAQADAgADeAADsx8EAAEeBA",
   "file_unique_id":"AQADmKQSMAAEsx8EAAE",
   "file_size":41597,
   "file_path":"photos/file_0.jpg"
 }

So a copy of the file_id, the weight (notice you don't get back pixel size!) and the path.

After that, just make a call using the path like this:

https://api.telegram.org/file/bot<token_of_your_bot>/<file_path from the JSON>

and you'll get the picture

One point: each time I get a JSON with the picture in more than one resolution, the big one is the last. But I've find nothing in the doc about that fact. So I'm note sure you can't have the big one in index [0]...

I know I'm too late, but I was researching for it too long. Here is the answer:

const TelegramBot =         require('node-telegram-bot-api');
let bot = new TelegramBot(token, {polling: true});

And the function to download it requires file id, which comes within the message

var file_id  = (msg.photo[msg.photo.length-1].file_id);




  var downloadDir = './images';
  let something = ''
  var https = require('https')
  bot.getFileLink(fileId).then( async (fileUri) => {
    var base64Img = require('base64-img');

      let time = process.hrtime();
      let extension = fileUri.split('.').pop();
      let newName = `${time[0]}${time[1]}.${extension}`;
      let file = fs.createWriteStream(`${downloadDir}/${newName}`);
      let request = await https.get(fileUri, (response) => {
         response.pipe(file);

        });
        file.on('finish', () =>{
          console.log('msg.text ='/images/'+newName')
         })
      //

  });
};

Main function is the bot.getFileLink(fileId). Hope it will help who will read this :)