通过php在本地保存dataURL图像

Question

I'm making a PNG image file from a dataURL string (thanks to the example from The PHP manual). I'd like this code to open the "Download file" dialog in the browser, so users can save this image locally, but calling the function imagepng() saves the image to my server instead. Am I using the wrong function when calling imagepng()? I'm trying to trigger a download by changing the headers, but it's still saving to the server.

<?php
$data = 'iVBORw0KGgoAAAANSUhEUgAAABwAAAASCAMAAAB/2U7WAAAABl'
    . 'BMVEUAAAD///+l2Z/dAAAASUlEQVR4XqWQUQoAIAxC2/0vXZDr'
    . 'EX4IJTRkb7lobNUStXsB0jIXIAMSsQnWlsV+wULF4Avk9fLq2r'
    . '8a5HSE35Q3eO2XP1A1wQkZSgETvDtKdQAAAABJRU5ErkJggg==';

$data = base64_decode($data);

$im = imagecreatefromstring($data);

// set the headers, to trigger a download
header('Content-Disposition: attachment; filename="image.png"');
header('Content-Type: image/png');
imagepng($im, 'test_2.png');
imagedestroy($im);
?>

Also, I'm calling the PHP via the following JavaScript, (not sure if this is relevant to the results I'm getting)

$.ajax({ 
    type: "POST", 
    url: "php/downloadimg.php",
    dataType: 'text',
    data: {
        data : finishedImage.src
    }
})

Answer 1

just call the imagepng function without the second parameter. if you follow the imagepng documentation you read that filling in the second parameter the image is saved to this filename.

pass only the image resource to the function and the raw image are send to the client.

http://php.net/manual/de/function.imagepng.php

header('Content-Disposition: attachment; filename="image.png"');
header('Content-Type: image/png');
imagepng($im);
imagedestroy($im);

if you use php only files don't use the php close tag ?> to avoid leaked whitespaces and messed up your output stream.