SimpleXMLElement failure workaround

nuts

Hello

I have a script that uses SimpleXMLElement to access an API from an external provider. The same script is used on many websites to provide real-time content.

It works well almost all the time, however when the external provider has an occasional problem, it prevents my page from loading properly, and causes server overload because multiple httpd processes never finish.

The code in question is

 $pFile = new SimpleXMLElement('http://api.XXX.com/a/XXX-api/xml-v2/ws-'.$number.'/q-'.$terms.'?pshid=XXX&ssty=1&cflg=r', null, true);

For example, last night for about 2 hours the API access string typed into a browser produced the following error:

502 Bad Gateway
nginx

I have tried entering the following snippet into the script but it didn't work:

libxml_use_internal_errors(true);
if (!$pFile) {
    echo "Failed loading XML\n";
    foreach(libxml_get_errors() as $error) {
        echo "\t", $error->message;
    }
}

I have also been playing around with curl, however that would mean accessing the API twice, and there are already thousands of hits per day.

Any suggestions will be much appreciated.

Thanks
Mike

dalecosp

Is there a way to test the availability of the external resource and place the call to it in a conditional based on that result?

On my servers I often use "tcping" to test for an open socket. I suppose in PHP you might try [man]fsockopen/man or similar?

nuts

Thanks for the comment

I have found a partial solution. This uses curl to test if the api is returning results. The downside is it calls the api twice.

function remoteFileExists($url) {
    $curl = curl_init($url);

//don't fetch the actual page, you only want to check the connection is ok
curl_setopt($curl, CURLOPT_NOBODY, true);

//do request
$result = curl_exec($curl);

$ret = false;

//if request did not fail
if ($result !== false) {
    //if request was ok, check response code
    $statusCode = curl_getinfo($curl, CURLINFO_HTTP_CODE);

    if ($statusCode == 200) {
        $ret = true;
    }
}

curl_close($curl);

return $ret;
}
$exists = remoteFileExists('http://api.XXX.com/a/XXX-api/xml-v2/ws-'.$number.'/q-'.$terms.'?pshid=XXX&ssty=1&cflg=r');

if (!$exists) {
    echo 'no jobs returned, please try later';
} else {

$c = 0;
do {
 $pFile = new SimpleXMLElement('http://api.XXX.com/a/XXX-api/xml-v2/ws-'.$number.'/q-'.$terms.'?pshid=XXX&ssty=1&cflg=r', null, true);

I tried the following suggestion from the devnetwork.net forum, and it works fine when the api is working.

However, when I change the url to a non-existent location to approximate a fail condition, the simplexml script does not return the default error message, and also seems to break page load and stop every include coming after it.

function getRemoteFile($url) {
    $curl = curl_init($url);

//fetch the actual page
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

//do request
$result = curl_exec($curl);
if ((false !== $result) && 200 != curl_getinfo($curl, CURLINFO_HTTP_CODE)) {
     $result = false;
}
curl_close($curl);
return $result;
}
$response = getRemoteFile('http://api.XXX.com/a/XXX-api/xml-v2/ws-'.$number.'/q-'.$terms.'?pshid=XXX&ssty=1&cflg=r');

if (false === $response) {
    echo 'no jobs returned, please try later';
} else {  

     $pFile = new SimpleXMLElement($response);
}

johanafm

Is error_reporting turned on and are you displaying and/or logging errors? It looks as if what you have should work, with one possible exception in unposted code

if (false === $response) {
    echo 'no jobs returned, please try later';
} else {  

     $pFile = new SimpleXMLElement($response);
}
# If you start using $pFile here, you will encounter errors here if $response === false...