Programmatically using file hash to compare an external (temp) file (documentation)

something like this should work?

$file = \Drupal\file\Entity\File::create(['uri' => 'temporary://my-image.png']);
$violations = \Drupal::service('file.validator')->validate($file, ['FileHashDedupe' => []]);

Great. Thanks @mbf I'll give that a go and report back.

OK well that worked great to know it's a duplicated file.. I need to get the file id of the 'already uploaded' file... is there currently a way to just get a list id's of the duplicate existing files?

Or would the only way be to parse the -messageTemplate field?

Symfony\Component\Validator\ConstraintViolationList {#1284 ▼
  -violations: array:1 [▼
    0 => 
Symfony\Component\Validator
\
ConstraintViolation {#1596 ▼
      -message: 
Drupal\Core\StringTranslation
\
TranslatableMarkup {#1594 ▶}
      -messageTemplate: "This file has already been uploaded as <em class="placeholder"><a href="/admin/content/files/usage/171" target="_blank">17238.jpg</a></em>."
      -parameters: []
      -plural: null
      -root: 
Drupal\Core\Entity\Plugin\DataType
\
EntityAdapter {#671 ▶}
      -propertyPath: ""
      -invalidValue: 
Drupal\file\Entity
\
File {#1033 ▶}
      -constraint: 
Drupal\filehash\Plugin\Validation\Constraint
\
FileHashDedupe {#1494 ▶}
      -code: null
      -cause: null
    }
  ]
}

Howabout calling the File Hash duplicateLookup() method directly?

$fid = \Drupal::service('filehash')->duplicateLookup('sha256', $file);

You'll need to replace 'sha256' with whatever hash algorithm you've enabled.

Works perfectly. Thanks so much.

Automatically closed - issue fixed for 2 weeks with no activity.