Trigger checksum generator in Nextcloud, remotely

checksum-trigger.php

<?php

/**
 * This script uses "sabre/dav" Client to make webdav requests to a Nextcloud instance.
 * The "nextcloud-checksum-update" option is a, somewhat, hidden feature in the Sabre Connector (Checksum Update Plugin)
 * https://github.com/nextcloud/server/blob/master/apps/dav/lib/Connector/Sabre/ChecksumUpdatePlugin.php
 * 
 * The basic flow is:
 * - PROPFIND on /remote.php/dav/Photos (explicitly asking for '{http://owncloud.org/ns}checksums' property)
 * - use the proper hash from the response
 * - OR do a PATCH request, with the X-Recalculate-Hash header, to trigger the recalculation
 * - FOLLOWED BY a HEAD, with the X-Hash header, request on $file_path
 * - use the hash from that response (in the oc-checksum response-header)
 **/

define('USED_ALGORITHM', 'md5');
define('WORKING_PATH', '/Photos');

$client = new Sabre\DAV\Client([
    'baseUri' => 'https://nextcloud.example.org/remote.php/dav',
    'userName' => 'john',
    'password' => 's3cr3t'
]);


$options = $client->options();
if (in_array("nextcloud-checksum-update", $options) === false) {
    exit('Cannot update checksum, so media comparison is impossible');
}

$available_media_files = $client->propFind(WORKING_PATH, ['{http://owncloud.org/ns}checksums'], 1);
foreach ($available_media_files as $file_path => $available_media_file) {
    $hash = null;
    if (array_key_exists('{http://owncloud.org/ns}checksums', $available_media_file)) {
        foreach ($available_media_file['{http://owncloud.org/ns}checksums'] as $checksum) {
            list($algo, $possible_hash) = explode(':', $checksum['value'], 2);
            if (strcasecmp($algo, USED_ALGORITHM) === 0) {
                $hash = $possible_hash;
                break;
            }
        }
    }

    if (isset($hash) === false) {
        $client->request('PATCH', $file_path, headers: [
            'X-Recalculate-Hash' => USED_ALGORITHM
        ]);
        $file = $attempt('request', 'HEAD', $file_path, headers: [
            'X-Hash' => USED_ALGORITHM
        ]);
        foreach ($file['headers']['oc-checksum'] as $checksum) {
            list($algo, $hash) = explode(':', $checksum, 2);
            if (strcasecmp($algo, USED_ALGORITHM) === 0) {
                break;
            }
        }
    }

  
  print 'Found '.USED_ALGORITHM.' hash ' . $hash . ' for file ' . $file_id;
}