wp_crop_image() does not work when fopen() is disabled

[jadonn]

While running the WordPress PHP Unit testing framework, a single test for wp_crop_image() failed consistently. After @danielbachhuber debugged the test, he found that wp_crop_image() was failing because it depended on _load_image_to_edit_path, which he said is dependent on fopen(). WordPress is supposed to function when fopen() is disabled. wp_crop_image's dependency on fopen is incorrect.

To reproduce the issue:
Disable allow_url_fopen in PHP
Setup the PHPUnit Test Runner (​https://github.com/WordPress/phpunit-test-runner)
Run the PHPUnit Test Runner.

The test runner should report the following failed test:
Tests_Image_Functions::test_wp_crop_image_url Failed asserting that WP_Error Object (...) is not an instance of class "WP_Error". /../../../phpunit-test-runner/wp-test-runner/tests/phpunit/tests/image/functions.php:317

The WP_Error object reports the following:
Fobject(WP_Error)#9993 (2) {

errors?=>
array(1) {

invalid_image?=>
array(1) {

[0]=>
string(21) "File is not an image."

}

}
error_data?=>
array(1) {

invalid_image?=>
string(60) "​https://asdftestblog1.files.wordpress.com/2008/04/canola.jpg"

}

}

The image is a valid image otherwise, such as when viewed through the browser. The test fails on PHP 5.6, PHP 7.0, and PHP 7.1 when fopen is disabled.

[danielbachhuber]

Related: https://core.trac.wordpress.org/ticket/37681#comment:1

It appears to be hit if you're editing an image which was uploaded pre-2.7 and/or if the file metadata has gone missing. In that case, the image editors will treat the image URL as the source image through the filesystem wrappers, bypassing wp_remote_get(), which is why the fopen and allow_url_fopen are there.

Originally committed in r20384

I see a couple of options:

1. Use download_url() to download a copy of the image to /tmp, and permit image modifications from that.
   • Advantage: Greater cross-platform compatibility for this feature.
   • Disadvantage: Web server has a potentially duplicate copy of the image on the filesystem (which is likely inconsequential).
2. Mark Tests_Image_Functions::test_wp_crop_image_url as skipped when fopen isn't available or allow_url_fopen is false.
   • Advantage: Least risky approach.
   • Disadvantage: Adds yet another skipped test to the test suite.