server/apps/files/ajax/upload.php

<?php

// Init owncloud


// Firefox and Konqueror tries to download application/json for me.  --Arthur
OCP\JSON::setContentTypeHeader('text/plain');

OCP\JSON::checkLoggedIn();
OCP\JSON::callCheck();
$l = OC_L10N::get('files');

// get array with current storage stats (e.g. max file size)
$storageStats = \OCA\files\lib\Helper::buildFileStorageStatistics($dir);

if (!isset($_FILES['files'])) {
	OCP\JSON::error(array('data' => array_merge(array('message' => $l->t('No file was uploaded. Unknown error')), $storageStats)));
	exit();
}

foreach ($_FILES['files']['error'] as $error) {
	if ($error != 0) {
		$errors = array(
			UPLOAD_ERR_OK         => $l->t('There is no error, the file uploaded with success'),
			UPLOAD_ERR_INI_SIZE   => $l->t('The uploaded file exceeds the upload_max_filesize directive in php.ini: ')
				. ini_get('upload_max_filesize'),
			UPLOAD_ERR_FORM_SIZE  => $l->t('The uploaded file exceeds the MAX_FILE_SIZE directive that was specified'
				. ' in the HTML form'),
			UPLOAD_ERR_PARTIAL    => $l->t('The uploaded file was only partially uploaded'),
			UPLOAD_ERR_NO_FILE    => $l->t('No file was uploaded'),
			UPLOAD_ERR_NO_TMP_DIR => $l->t('Missing a temporary folder'),
			UPLOAD_ERR_CANT_WRITE => $l->t('Failed to write to disk'),
		);
		OCP\JSON::error(array('data' => array_merge(array('message' => $errors[$error]), $storageStats)));
		exit();
	}
}
$files = $_FILES['files'];

$dir = $_POST['dir'];
$error = '';

$totalSize = 0;
foreach ($files['size'] as $size) {
	$totalSize += $size;
}
if($totalSize>\OC\Files\Filesystem::free_space($dir)) {
	OCP\JSON::error(array('data' => array( 'message' => $l->t( 'Not enough space available' ),
		'uploadMaxFilesize'=>$maxUploadFilesize,
		'maxHumanFilesize'=>$maxHumanFilesize)));
	exit();
}

$result = array();
if (strpos($dir, '..') === false) {
	$fileCount = count($files['name']);
	for ($i = 0; $i < $fileCount; $i++) {
		$target = OCP\Files::buildNotExistingFileName(stripslashes($dir), $files['name'][$i]);
		// $path needs to be normalized - this failed within drag'n'drop upload to a sub-folder
		$target = \OC\Files\Filesystem::normalizePath($target);
		if(is_uploaded_file($files['tmp_name'][$i]) and \OC\Files\Filesystem::fromTmpFile($files['tmp_name'][$i], $target)) {
			$meta = \OC\Files\Filesystem::getFileInfo($target);
			// updated max file size after upload
			$storageStats = \OCA\files\lib\Helper::buildFileStorageStatistics($dir);

			$result[]=array( 'status' => 'success',
				'mime'=>$meta['mimetype'],
				'size'=>$meta['size'],
				'id'=>$id,
				'name'=>basename($target),
				'uploadMaxFilesize'=>$maxUploadFilesize,
				'maxHumanFilesize'=>$maxHumanFilesize
			);
		}
	}
	OCP\JSON::encodedPrint($result);
	exit();
} else {
	$error = $l->t('Invalid directory.');
}

OCP\JSON::error(array('data' => array_merge(array('message' => $error), $storageStats)));