path: root/modules-available/dozmod/api.inc.php

<?php
/* small API server that acts as a proxy to the dozmod server.
* To reduce the number of requests and connections to dozmod-server, results
* gets cached into a file cache.
*
* Required Configuration:
* CONFIG_DOZMOD_EXPIRE: Expiration time in seconds for the cache
* CONFIG_DOZMOD_URL: URL to the dozmod server
*
**/


if (!Module::isAvailable('locations')) {
    die('require locations module');
}


define('LIST_URL', CONFIG_DOZMOD_URL . '/vmchooser/list');
define('VMX_URL', CONFIG_DOZMOD_URL . '/vmchooser/lecture');
$availableRessources = ['list', 'vmx', 'test', 'netrules'];

/* BEGIN: A simple caching mechanism ---------------------------- */

function cache_hash($obj)
{
    return md5(serialize($obj));
}

function cache_key_to_filename($key)
{
    return "/tmp/bwlp-slxadmin-cache-$key"; // TODO: hash
}

function cache_put($key, $value)
{
    $filename = cache_key_to_filename($key);
    file_put_contents($filename, $value);
}

function cache_has($key)
{
    $filename = cache_key_to_filename($key);
    $mtime = @filemtime($filename);

    if ($mtime === false) {
        return false; // cache miss
    }
    if (time() - $mtime > CONFIG_DOZMOD_EXPIRE) {
        return false;
    } else {
        return true;
    }
}


function cache_get($key)
{
    $filename = cache_key_to_filename($key);
    return file_get_contents($filename);
}

/* good for large binary files */
function cache_get_passthru($key)
{
    $filename = cache_key_to_filename($key);
    $fp = fopen($filename, "r");
    if ($fp) {
        fpassthru($fp);
        exit;
    }
    error_log('Cannot passthrough cache file ' . $filename);
}

/* END: Cache ---------------------------------------------------- */


/* this script requires 2 (3 with implicit client ip) parameters
*
* resource     = vmx,...
* lecture_uuid = client can choose
**/


/**
 * Get list of active lectures for given locations.
 *
 * @return string the raw xml data.
 */
function _getLecturesForLocations($locationIds, $examMode)
{
    $ids = implode('%20', $locationIds);
    $url = LIST_URL . "?locations=$ids" . ($examMode ? '&exams' : '');
    return Download::asString($url, 60, $code);
}

/**
 * Takes raw lecture list xml, returns array of uuids.
 *
 * @param string $responseXML XML from dozmod server
 * @return array list of UUIDs, false on error
 */
function xmlToLectureIds($responseXML)
{
    $xml = new SimpleXMLElement($responseXML);
    if (!isset($xml->eintrag))
        return [];

    $uuids = [];
    foreach ($xml->eintrag as $e) {
        $uuids[] = strval($e->uuid['param'][0]);
    }
    return $uuids;
}

/** Caching wrapper around _getLecturesForLocations() */
function getListForLocations($locationIds, $raw)
{
    /* if in any of the locations there is an exam active, consider the client
        to be in "exam-mode" and only offer him exams (no lectures) */
    $key = 'lectures_' . cache_hash($locationIds);
    $examMode = false;
    if (Module::isAvailable('exams')) {
        $examMode = Exams::isInExamMode($locationIds);
        if ($examMode) {
            $key .= '_exams';
        }
    }
    $rawKey = $key . '_raw';
    if ($raw) {
        Header('Content-Type: text/xml; charset=utf-8');
        if (cache_has($rawKey)) {
            cache_get_passthru($rawKey);
        }
    } elseif (cache_has($key)) {
        return unserialize(cache_get($key));
    }
    // Not in cache
    $value = _getLecturesForLocations($locationIds, $examMode);
    if ($value === false)
        return false;
    cache_put($rawKey, $value);
    $list = xmlToLectureIds($value);
    cache_put($key, serialize($list));
    if ($raw) {
        die($value);
    }
    return $list;
}

function getLectureUuidsForLocations($locationIds)
{
    return getListForLocations($locationIds, false);
}

function outputLectureXmlForLocation($locationIds)
{
    return getListForLocations($locationIds, true);
}

function _getVMX($lecture_uuid)
{
    $url = VMX_URL . '/' . $lecture_uuid;
    $response = Download::asString($url, 60, $code);
    return $response;
}

/** Caching wrapper around _getVMX() **/
function outputVMX($lecture_uuid)
{
    $key = 'vmx_' . $lecture_uuid;
    if (cache_has($key)) {
        cache_get_passthru($key);
    } else {
        $value = _getVMX($lecture_uuid);
        if ($value === false)
            return false;
        cache_put($key, $value);
        die($value);
    }
}

function fatalDozmodUnreachable()
{
    Header('HTTP/1.1 504 Gateway Timeout');
    die('Resource not available');
}

function readLectureParam()
{
    global  $location_ids;
    $lecture  = Request::get('lecture', false, 'string');
    if ($lecture === false) {
        Header('HTTP/1.1 400 Bad Request');
        die('Missing lecture UUID');
    }
    $lectures = getLectureUuidsForLocations($location_ids);
    if ($lectures === false) {
        fatalDozmodUnreachable();
    }
    /* check that the user requests a lecture that he is allowed to have */
    if (!in_array($lecture, $lectures)) {
        Header('HTTP/1.1 403 Forbidden');
        die("You don't have permission to access this lecture");
    }
    return $lecture;
}


// -----------------------------------------------------------------------------//
/* request data, don't trust */
$resource   = Request::get('resource', false, 'string');

if ($resource === false) {
    Util::traceError("you have to specify the 'resource' parameter");
}

if (!in_array($resource, $availableRessources)) {
    Util::traceError("unknown resource: $resource");
}

$ip = $_SERVER['REMOTE_ADDR'];
if (substr($ip, 0, 7) === '::ffff:') {
    $ip = substr($ip, 7);
}


/* lookup location id(s) */
$location_ids = Location::getFromIp($ip);
$location_ids = Location::getLocationRootChain($location_ids);

if ($resource === 'vmx') {
    $lecture = readLectureParam();
    outputVMX($lecture);
    // outputVMX does not return on success
    fatalDozmodUnreachable();
}

if ($resource === 'list') {
    outputLectureXmlForLocation($location_ids);
    // Won't return on success...
    fatalDozmodUnreachable();
}

Header('HTTP/1.1 400 Bad Request');
die("I don't know how to give you that resource");