Adjust image style flush in postSave()

Problem/Motivation

For sites that serve their images from example Amazon S3 or some other cloud based file storage, the image style flush operation can get expensive, so I'm proposing a change that could reduce unnecessary image style flushes.

When creating a new File Entity with an image, it's a multi-step process:

1. Upload a new file
2. Determine destination (public, etc -- if there's a choice)
3. Add any info to the fields on the entity (if present)
4. Save

When the file is uploaded, this triggers FileEntity::postSave(). This is the initial save. When you click the "Save" button, this this triggers FileEntity::postSave() again, but in this case, it is an update.

Taking a look at this method in detail:

/**
 * Implements hook_file_insert().
 */
public function postSave(EntityStorageInterface $storage, $update = TRUE) {
  parent::postSave($storage, $update);
  // Save file metadata.
  if (!empty($this->metadata)) {
  if ($update) {
    db_delete('file_metadata')->condition('fid', $this->id())->execute();
  }
    $query = db_insert('file_metadata')->fields(array('fid', 'name', 'value'));
    foreach ($this->getAllMetadata() as $name => $value) {
      $query->values(array(
        'fid' => $this->id(),
        'name' => $name,
        'value' => serialize($value),
      ));
    }
    $query->execute();
  }

  if ($update) {
    if (\Drupal::moduleHandler()->moduleExists('image') && $this->getMimeTypeType() == 'image' && $this->getSize()) {
      // If the image dimensions have changed, update any image field references
      // to this file and flush image style derivatives.
      if ($this->original->getMetadata('width') && ($this->getMetadata('width') != $this->original->getMetadata('width') || $this->getMetadata('height') != $this->original->getMetadata('height'))) {
        $this->updateImageFieldDimensions();
      }

      // Flush image style derivatives whenever an image is updated.
      image_path_flush($this->getFileUri());
    }
  }
}

We see that whenever the File Entity is updated, the image styles are flushed. Currently, image styles would be flushed even if the only change made was an update to a field on the entity (so a change that would not affect the image style derivative).

There appears to be a few scenarios that would require flushing image styles:

• the width or height changed
• the file URI changed
• the file was replaced

Also, I did take a look at the D7 version of this module and it is the same setup as in D8: flush the image styles whenever the entity is updated.

Proposed resolution

I propose that the image_path_flush() call moves up into the width / height change check:

if ($update) {
    if (\Drupal::moduleHandler()->moduleExists('image') && $this->getMimeTypeType() == 'image' && $this->getSize()) {
      // If the image dimensions have changed, update any image field references
      // to this file and flush image style derivatives.
      if ($this->original->getMetadata('width') && ($this->getMetadata('width') != $this->original->getMetadata('width') || $this->getMetadata('height') != $this->original->getMetadata('height'))) {
        $this->updateImageFieldDimensions();
        
        // Flush image style derivatives.
        image_path_flush($this->getFileUri());
      }
    }
  }

I tried some testing to test if the image styles would flush appropriately. For this, I made sure that the default view mode for the File Entity used an image style rather than original image.

Replaced Image with new image that has different dimensions:

1. Create a new File Entity and save it will my initial image (filename = "NB1_1025_mai_smaller_delete.jpg")
2. Edited this entity and used the Replace File button and uploaded a new image with different dimensions (filename = "GE2_8890_smaller_mai_delete.jpg")
3. Saved the entity

The image style is flushed as expected and shows as the updated image. I noticed that the file uri did not change.

Replaced Image with an image that is exactly the same except for the filename:

1. Create a new File Entity and save it will my initial image (filename = "NB1_1025_mai_smaller_delete.jpg")
2. Edited this entity and used the Replace File button and uploaded a new image with different dimensions (filename = "NB1_1025_mai_smaller_delete copy.jpg")
3. Saved the entity

The image style is flushed as expected (confirmed via xdebug) and shows as the updated image (which is exactly the same). Again, I noticed that the file uri did not change. I also tried these same steps when a slightly altered version of NB1_1025_mai_smaller_delete copy.jpg (The modification = added a red rectangle to the image -- so height/width remains the same).

I must be missing the case when the image file uri changes...when the file is replaced, it looks like Drupal\file_entity\Form\FileEditForm::submitForm() takes care of deleting the old file:

Snippet from Drupal\file_entity\Form\FileEditForm::submitForm():

if (file_unmanaged_copy($entity_replacement->getFileUri(), $this->entity->getFileUri(), FILE_EXISTS_REPLACE)) {
  $entity_replacement->delete();
  \Drupal::logger('file_entity')->info('File @old was replaced by @new', $log_args);
}

It also looks like by the time we get to FileEntity::postSave(), the original file uri and the current file uri are the same.