Telegram bot API error 400 Photo has unsupported extension - php

Question

I am trying to send a dynamically created png image (php script that generates a png file, [code below]) through one of my telegram bots using "sendPhoto" method.
It works fine when I link a physical png file (in the multipart field parameter), but when I try and use the php file, I receive the following error from Telegram:
Photo has unsupported extension. Use one of .jpg, .jpeg, .gif, .png, .tif or .bmp
The PHP code is simple enough, works well when I open the file in my browser (i'm shown a dialog to download the png file and it opens fine on my computer):
header("Content-type: image/png");
header('Content-Disposition: attachment; filename="moo.png"');
$image = imagecreatetruecolor(50, 50);
imagesavealpha($image, true);
$transparent = imagecolorallocatealpha($image, 0, 0, 0, 127);
imagefill($image, 0, 0, $transparent);
ob_start ();
imagepng($image);
ob_end_flush();
imagedestroy($image);
Is there a way I can bypass this extension check and send my dynamic image script (file with .php extension) in my telegram request?

Answer 1

turns out bot API had nothing to do with it.
i wrongfully attached the script file when I really should have needed to attach the script output (duh!) :/
So, flushing the output buffer into a tmpfile and then sending it did the trick
function pngCraft($width = 100, $height = 100, $asBase64 = FALSE)
{
$image = imagecreatetruecolor($width, $height);
imagesavealpha($image, true);
$transparent = imagecolorallocatealpha($image, 0, 0, 0, 127);
imagefill($image, 0, 0, $transparent);
ob_start ();
imagepng($image);
$image_data = ob_get_contents();
ob_end_clean ();
$out = ($asBase64) ? base64_encode($image_data) : $image_data;
imagedestroy($image);
return $out;
}
$file = tmpfile();
fwrite($file, pngCraft());
fseek($file,0);
$a = stream_get_meta_data($file);
$uri = $a['uri'];
rename($uri, $uri.='.png');
$fields[TG_METHOD_SENDPHOTO_PHOTO] = '#'.$uri;
$fields[TG_METHOD_SENDPHOTO_CAPTION] = 'Yay!';