Subsequent calls to Output() of pdf with images are missing images in 2++ data

[manitu-opensource]

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Description of the bug

When calling Output() on a mpdf which has images for 2 or more times the subsequent calls to Output() are missing the images.

Background: Maybe you want to show a Mpdf in browser and save it in filesystem, so one would call $mpdf->Output() and $mpdf->Output('some_filename', 'F');

The second, third, ... calls to Output() are generating pdf data / files which have images missing.

The reason is in mpdf/mpdf/src/Writer/ImageWriter.php line 96:

unset($this->mpdf->images[$file]['data']);

The image file data are cleaned after the first Output()call.

Even clone of the $mpdf object will not help since the ImageWriter class has its own reference to the original mpdf object.

mPDF version

8.2.3 / current

PHP Version and environment (server type, cli provider etc., enclosing libraries and their respective versions)

PHP 8.1 / 8.2 / 8.3

Reproducible PHP+CSS+HTML snippet suffering by the error

1. Generate new mpdf
2. Add images
3. Call $mpdf->Output() for the first time
4. Call $mpdf->Output() for the second time

The problem is also seen in php error / warning log
strlen(): Passing null to parameter #1 ($string) of type string is deprecated

which occurs in the second call.

[finwe]

mPDF does not work well with consecutive Output calls. Create a separate instance for each desired Output.

The second Output call could throw an Exception, maybe in future versions.