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 to the dozmod server
*
**/


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


define('LIST_URL', CONFIG_DOZMOD . '/vmchooser/list');
define('VMX_URL', CONFIG_DOZMOD . '/vmchooser/lecture');
$availableRessources = ['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) {
        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);
    } else {
        Util::traceError("cannot open file");
    }
}

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


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


function println($str) { echo "$str\n"; }

/* return an array of lecutre uuids.
* Parameter: an array with location Ids
* */
function _getLecturesForLocations($locationIds)
{

    /* 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) */
    $examMode = false;

    if (Module::isAvailable('exams')) {
        $examMode = Exams::isInExamMode($locationIds);
    }
    $ids = implode('%20', $locationIds);
    $url = LIST_URL . "?locations=$ids" . ($examMode ? '&exams' : '');
    $responseXML = Download::asString($url, 60, $code);
    $xml = new SimpleXMLElement($responseXML);

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

/** Caching wrapper around _getLecturesForLocations() */
function getLecturesForLocations($locationIds)
{
    $key = 'lectures_' . cache_hash($locationIds);
    if (cache_has($key)) {
        return unserialize(cache_get($key));
    } else {
        $value = _getLecturesForLocations($locationIds);
        cache_put($key, serialize($value));
        return $value;
    }
}

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

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


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

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

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

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

/* lookup lecture uuids */
$lectures = getLecturesForLocations($location_ids);

/* validate request -------------------------------------------- */
/* check resources */
if (!in_array($resource, $availableRessources)) {
    Util::traceError("unknown resource: $resource");
}

/* check that the user requests a lecture that he is allowed to have */
if (!in_array($lecture, $lectures)) {
    Util::traceError("client is not allowed to access this lecture: $lecture");
}

if ($resource === 'vmx') {
    echo getVMX($lecture);
} else if ($resource === 'test') {
    echo "Here's your special test data!";
} else {
    echo "I don't know how to give you that resource";
}