Gravity Forms Validate Uploaded File

gf_validate_file.php

add_filter( 'gform_validation', 'custom_validation' );
function custom_validation( $validation_result ) {
	$form = $validation_result['form'];

	foreach ( $form['fields'] as $field ) {
		if ( strpos( $field->cssClass, 'myfileclass' ) !== false ) {
			$input          = 'input_' . $field->id;
			$uploaded_files = json_decode( rgpost( "gform_uploaded_files" ) );
			$is_file_uploaded = isset( $uploaded_files->$input );
			$filename             = '';

			//file got uploaded while validating other fields
			if ( $is_file_uploaded ) {
				write_log( 'file was uploaded by gravity forms already' );
				$temp_file = GFFormsModel::get_temp_filename($form['id'], $input);

				if(isset($temp_file['temp_filename'])){
					$file = $temp_file['temp_filename'];
					$upload_path = GFFormsModel::get_upload_path( $form['id'] );
					$filename = $upload_path . '/tmp/' . $file;
				}

			} else {
       //file was not uploaded yet by gf
				if ( ! empty( $_FILES[ $input ]["name"] ) ) {
					write_log( 'file not uploaded yet. file in tmp' );
					$filename = $_FILES[ $input ]["tmp_name"];
				}
			}

     //we should have a have filename now.

			//now do something with the $filename. Check it or whatever and validate
			//$validation_result['is_valid'] = false;
		}
	}

	//Assign modified $form object back to the validation result
	$validation_result['form'] = $form;

	return $validation_result;

}