PHP: checking the returned XML for errors

Question

Using the code below, I get an XML with the exchange rate on a given date. However, sometimes there are no quotes for a given date and an error is returned to me. In such cases, I would like to do minus one day by a given date and get the data again. If there is another error, again minus one day. As soon as the correct XML is obtained, we cache it (now I cache everything received for 6 hours).

function get_currency($currency_code, $setDate, $format)
{
    $date = $setDate;
    $cache_time_out = '21600';
    $filename = date('d-m-Y', strtotime($date)) . '.xml';

    $file_currency_cache = __DIR__ . '/cache/' . $filename;

    if (!is_file($file_currency_cache) || filemtime($file_currency_cache) < (time() - $cache_time_out)) {

        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, 'https://www.cbr-xml-daily.ru/archive/' . $date . '/daily_utf8.xml');
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_HEADER, false);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 0);
        curl_setopt($ch, CURLOPT_TIMEOUT, 50);

        $out = curl_exec($ch);

        curl_close($ch);

        file_put_contents($file_currency_cache, $out);
    }

    $content_currency = simplexml_load_file($file_currency_cache);

    return number_format(str_replace(',', '.', $content_currency->xpath('Valute[CharCode="' . $currency_code . '"]')[0]->Value), $format);
}

I show the result of parsing on the site like this:

$date = '2014/06/02';
$ex_rate_usd = get_currency('USD', $date, 3);
echo $ex_rate_usd;

I found this code on the web and it works correctly, but problems with the lack of currency quotes for some dates break everything. I will be grateful for any help in this matter.

$date = 2014/06/02; would give 167.83333333333 and not a date. — Markus Zeller
– Markus Zeller, Commented May 17, 2022 at 8:30
Sorry, I corrected it, I have a variable with a date there). $date = '2014/06/02'; — Sergey Pervushin
– Sergey Pervushin, Commented May 17, 2022 at 8:31

ThW · Accepted Answer · 2022-05-17 14:56:41Z

1

SimpleXMLElement->xpath() always returns an array (for a valid Xpath expression). But this array can be empty. You access a property of the first element of the result array without validating that it exists.

$valute = $content_currency->xpath('Valute[CharCode="'.$currency_code.'"]')[0]
$rate = $valute ? $valute->value : null;

If you select an attribute with the xpath expression then you can simplify this a little:

$rate = (string)(
  $content_currency->xpath('Valute[CharCode="'.$currency_code.'"]/@value')[0] ?? ''
)

With DOM Xpath can return scalar values:

$document = new DOMDocument();
$document->loadXML($file_currency_cache);
$xpath = new DOMXpath($document);

$rate = $xpath->evaluate(
  'number(//Valute[CharCode="'.$currency_code.'"]/@value)'
);

edited May 17, 2022 at 14:56

answered May 17, 2022 at 10:08

ThW

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