Telegram Bot API 400 Error: Dynamic Image Extension Issue

Other Questions Telegram bot
1

Problem

Generating a dynamic PNG with a PHP script via sendPhoto triggers a 400 error due to its file extension. Can this check be bypassed? Example:

<?php
header('Content-Type: image/png');
header('Content-Disposition: inline; filename="dynamic.png"');
$imgCanvas = imagecreatetruecolor(120, 120);
imagesavealpha($imgCanvas, true);
$alphaColor = imagecolorallocatealpha($imgCanvas, 0, 0, 0, 127);
imagefill($imgCanvas, 0, 0, $alphaColor);
ob_start();
imagepng($imgCanvas);
ob_end_flush();
imagedestroy($imgCanvas);
?>
2

hey, i solved it by using php://temp to store the image then wrapping it as a curlfile. this avoids writing a physical file, and it bypassed the extention check. might work for u too

3

In my experience, sending a dynamically generated image to Telegram requires careful handling of the file’s properties. I encountered a similar issue where the API refused to accept the image because it didn’t detect a proper file extension. To resolve it, I started by creating the image in memory but then saved it as a temporary file with the correct .png extension before invoking sendPhoto. This workaround ensures that the API recognizes the file format, and it worked reliably in my projects without further issues.

4

After encountering a similar issue, I opted for an approach where the image data is captured using output buffering and then written to a temporary file with the correct .png extension. In this arrangement, the file is later passed to the sendPhoto method. This process bypassed the extension problem because it assures that Telegram’s API receives a file with a fully recognized format. Adjusting the workflow in this manner proved to be an effective solution, and I found it reliable in ensuring the correct interpretation of image files by the API.

5

I found an alternative that didn’t require saving the image to a disk. Instead, I generated the PNG as usual into a memory stream using fopen(‘php://memory’, ‘r+’) and wrote the image data into it. Then I wrapped this stream in a custom CURLFile instance, manually specifying a filename with the correct .png extension. This approach worked for me because it kept everything in memory while still satisfying Telegram’s API requirements regarding file extensions. It allowed me to avoid file clutter and any temporary file system permissions issues.

6

The issue I encountered led me to experiment with directly manipulating the stream output. In my implementation, I captured the image data into a variable using output buffering and then created an in-memory stream. I proceeded to wrap this stream in a CURLFile while explicitly assigning it a valid filename containing the .png extension. This guaranteed that Telegram’s API interpreted the file correctly, despite not being physically stored on disk. It is a technique that maintains efficiency and minimizes I/O overhead in dynamic image processing scenarios.