curl Time Out Problem and Solution

If you want cURL to timeout in less than one second, you can use CURLOPT_TIMEOUT_MS, although there is a bug/”feature”  on “Unix-like systems” that causes libcurl to timeout immediately if the value is < 1000 ms with the error “cURL Error (28): Timeout was reached”.  The explanation for this behavior is:

“If libcurl is built to use the standard system name resolver, that portion of the transfer will still use full-second resolution for timeouts with a minimum timeout allowed of one second.”

What this means to PHP developers is “You can use this function without testing it first, because you can’t tell if libcurl is using the standard system name resolver (but you can be pretty sure it is)”

The problem is that on (Li|U)nix, when libcurl uses the standard name resolver, a SIGALRM is raised during name resolution which libcurl thinks is the timeout alarm.

The solution is to disable signals using CURLOPT_NOSIGNAL.  Here’s an example script that requests itself causing a 10-second delay so you can test timeouts:

if (!isset($_GET['foo'])) {
// Client
$ch = curl_init('http://localhost/test/test_timeout.php?foo=bar');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_NOSIGNAL, 1);
curl_setopt($ch, CURLOPT_TIMEOUT_MS, 200);
$data = curl_exec($ch);
$curl_errno = curl_errno($ch);
$curl_error = curl_error($ch);

if ($curl_errno > 0) {
echo "cURL Error ($curl_errno): $curl_error\n";
} else {
echo "Data received: $data\n";
} else {
// Server
echo "Done.";