Check the upload size of a gravity forms multi-upload

gravity-forms-check-upload-size.php

<?php 
add_filter('gform_validation', 'limit_file_upload_size');

function limit_file_upload_size( $validation_result ) {

	$form = $validation_result['form'];
	$total_file_size = 0;
	$num_files = 0;
	$max_file_size = 41943040; //40MB - https://convertlive.com/u/convert/megabytes/to/bytes
	
	foreach( $form['fields'] as &$field ){

		// Add a custom CSS class to your upload field and grab onto it here...        
		if( strpos( $field['cssClass'], 'OAG-upload' ) === false )
			continue;
		
		//find the temporary location of the uploaded file
		$input_name = 'input_' . $field['id'];
		$temp_filename = RGFormsModel::get_temp_filename($form['id'], $input_name);
		$temp_location = RGFormsModel::get_upload_path($form['id']) . '/tmp/' . $temp_filename['uploaded_filename'][0]['temp_filename'];

		
		//loop through each file in a multi-file upload	and add up the total file size
		foreach( $temp_filename['uploaded_filename'] as $f){
			$filesize = filesize( $temp_location );
			$total_file_size += $filesize;
			$num_files ++;

		}

		// return the GF error if the total size is greater than the max size
		if ( $total_file_size > $max_file_size ) {
			$validation_result['is_valid'] = false;
			$field['failed_validation'] = true;
			$field['validation_message'] = 'You attempted to upload a total of '. human_filesize($total_file_size, 0).'. The total size of all uploads cannot exceed 40 MB. Try compressing your files <a target="_blank" href="https://www.wikihow.com/Make-a-Zip-File">by zipping them </a> and attempt to re-upload.';
			unset( RGFormsModel::$uploaded_files[$form['id']][$input_name], $_FILES[$input_name] );
				continue;
		}
    }
    GFCommon::log_debug( __METHOD__ . "(): Total Upload Size was ".$total_file_size);

    $validation_result['form'] = $form;
    return $validation_result;
}



function human_filesize($bytes, $decimals = 2) {
    $factor = floor((strlen($bytes) - 1) / 3);
    if ($factor > 0) $sz = 'KMGT';
    return sprintf("%.{$decimals}f", $bytes / pow(1024, $factor)) . @$sz[$factor - 1] . 'B';
}
?>