Fix: PDF thumbnails to WEBP/AVIF

[AhmarZaidi]

Summary

This PR adds support for generating Modern Format (webp/aif) image thumbnails from PDF files.

Fixes #1766

Relevant technical choices

• Added application/pdf mimetype to the default transforms list and use get_attached_file() function for getting the original pdf file path if mime type is application/pdf to bypass $image_path = wp_get_original_image_path( $attachment_id );
• Add unit tests for web uploads helper functions to check if 'application/pdf' is included in the MIME transforms array.

Screen records

Screen.Recording.2025-02-12.at.8.48.56.AM.mov

[AhmarZaidi]

As mentioned in the issue comment, the solution doesn't seem work when we test it on the dev environment run using npm run wp-env start and shows security policy error:

WP_Error Object
(
    [errors] => Array
    (
        [invalid_image] => Array
        (
            [0] => attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/426
        )
    )

    [error_data] => Array
    (
        [invalid_image] => /var/www/html/wp-content/uploads/2025/02/test.pdf
    )

    [additional_data:protected] => Array ()
)

This appears to be an issue with ImageMagick policy used in the docker WordPress environment. Solutions suggest changing the ImageMagick policy

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.65%. Comparing base (6274111) to head (2306f64).

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #1868      +/-   ##
==========================================
+ Coverage   68.64%   68.65%   +0.01%     
==========================================
  Files          90       90              
  Lines        7969     7972       +3     
==========================================
+ Hits         5470     5473       +3     
  Misses       2499     2499              

Flag	Coverage Δ
multisite	68.65% <100.00%> (+0.01%)	⬆️
single	35.36% <100.00%> (+0.02%)	⬆️

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[westonruter]

Minor point: This is easier to read and it would facilitate ensuring test coverage is present for both code paths. Also, in the future maybe there will be more such special cases.

Suggested change

	$image_path = 'application/pdf' !== get_post_mime_type( $attachment_id ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );
	if ( 'application/pdf' === get_post_mime_type( $attachment_id ) {
	$image_path = get_attached_file( $attachment_id );
	} else {
	$image_path = wp_get_original_image_path( $attachment_id ); }

[AhmarZaidi]

I was thinking something like this:

$image_path = wp_attachment_is_image( $attachment_id ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );

This way we can use wp_get_original_image_path() only when attatchment is an image and in all other cases we can use get_attached_file ()

This is also more in accordance with latest suggestions made on the issue thread: #1766 (comment)

[westonruter]

@AhmarZaidi Hey! Are you planning to pick this up?

[github-actions]

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Co-authored-by: AhmarZaidi <[email protected]>
Co-authored-by: westonruter <[email protected]>
Co-authored-by: phanduynam <[email protected]>
Co-authored-by: adamsilverstein <[email protected]>
Co-authored-by: 1ucay <[email protected]>

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[AhmarZaidi]

Hey @westonruter

I've updates the branch and marked it as ready for review, let me know if any changes are required.

[adamsilverstein]

@AhmarZaidi thanks for this PR, great idea! I'm curious if you have tested on a system that uses GD instead of Imagick. Since GD doesn't support extracting PDF thumbnails, I want to make sure adding the mapping doesn't have any unintended consequences.