Random 500 errors in a multi CURL request - php

Question

I am trying to get some hal+json data from a web service through a curl_multi to fill in a Bootstrap Typeahead. Every time I run this code, some of my requests in the curl_multi will be 500, and some will return the data I need. The ones that are 500 are completely random; the next time I load the page different queries will be 500 instead (And I get no errors). Why does that keep happening?
<?php
$curlurl = 'https://service.domain.com/'.$_POST['customer-name'].'/contact?callback=?';
$cuurl = singleRequest($curlurl);
global $contacts_typeahead_data;
$contacts_typeahead_data = array();
$clinks = $cuurl['_links']['https://service.domain.com/rel/contacts'];
for ($i=0; $i < count($clinks); $i++) {
$data[] = 'https://service.domain.com'.$clinks[$i]['href'].'?callback=?';
};
print_r($data);
$datar = multiRequest($data);
print_r($datar);
foreach($datar as $c){
$cs = json_decode($c, true);?>
<option value="<?php echo $cs['id']; ?>"><?php echo $cs['id'].' ('.$cs['info'][0]['name'].')'; ?></option>
<?php $contacts_typeahead_data[] = $cs['id'].' ('.$cs['info'][0]['name'].')';
}?>
And here is the code to the singleRequest and multiRequest, which is based on http://www.phpied.com/simultaneuos-http-requests-in-php-with-curl/:
function multiRequest($data, $options = array()) {
// array of curl handles
$curly = array();
// data to be returned
$result = array();
// multi handle
$mh = curl_multi_init();
// loop through $data and create curl handles
// then add them to the multi-handle
foreach ($data as $id => $d) {
$curly[$id] = curl_init();
$url = (is_array($d) && !empty($d['url'])) ? $d['url'] : $d;
$username = base64_encode('username');
$password2 = 'password';
$auth_token = $username . $password2 . 'QQ==';
curl_setopt($curly[$id], CURLOPT_URL, $url);
curl_setopt($curly[$id], CURLOPT_HEADER, 0);
curl_setopt($curly[$id], CURLOPT_RETURNTRANSFER, 1);
curl_setopt($curly[$id], CURLOPT_USERPWD, "$username:$password2");
curl_setopt($curly[$id], CURLOPT_SSLVERSION,3);
curl_setopt($curly[$id], CURLOPT_HTTPHEADER, array(
'Accept: application/hal+json',
'Access-Control-Allow-Origin: *',
'Content-Type: application/hal+json',
'Authorization: Basic ' . $auth_token
));
curl_setopt($curly[$id], CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($curly[$id], CURLOPT_CONNECTTIMEOUT, 0);
curl_setopt($curly[$id], CURLOPT_TIMEOUT, 30);
curl_setopt($curly[$id], CURLOPT_PORT, 443);
curl_setopt($curly[$id], CURLOPT_REFERER, $_SERVER['HTTP_REFERER']);
curl_setopt($curly[$id], CURLOPT_USERAGENT, 'Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)');
curl_setopt($curly[$id], CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curly[$id], CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curly[$id], CURLOPT_COOKIE, 'cert_url=https://service.domain.com/cert/yagowyefayygwflagliwygelifyaigwepifgpai');
// post?
if (is_array($d)) {
if (!empty($d['post'])) {
curl_setopt($curly[$id], CURLOPT_POST, 1);
curl_setopt($curly[$id], CURLOPT_POSTFIELDS, $d['post']);
}
}
// extra options?
if (!empty($options)) {
curl_setopt_array($curly[$id], $options);
}
curl_multi_add_handle($mh, $curly[$id]);
}
// execute the handles
$running = null;
do {
curl_multi_exec($mh, $running);
} while($running > 0);
// get content and remove handles
foreach($curly as $id => $c) {
// cURL error number
$curl_errno = curl_errno($c);
// cURL error message
$curl_error = curl_error($c);
// output if there was an error
if ($curl_error) {
echo " *** cURL error: (".$curl_errno.") ".$curl_error;
} else {
$result[$id] = curl_multi_getcontent($c);
}
curl_multi_remove_handle($mh, $c);
}
// all done
curl_multi_close($mh);
return $result;
}
function singleRequest($curlurl){
$username = base64_encode('username');
$password2 = 'password';
$auth_token = $username . $password2 . 'QQ==';
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_USERPWD, "$username:$password2");
curl_setopt($ch, CURLOPT_SSLVERSION,3);
curl_setopt($ch, CURLOPT_HEADER, false);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Accept: application/hal+json',
'Access-Control-Allow-Origin: *',
'Content-Type: application/hal+json',
'Authorization: Basic ' . $auth_token
));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_COOKIE, 'cert_url=https://service.domain.com/cert/yagowyefayygwflagliwygelifyaigwepifgpai');
$result = curl_exec($ch);
if($result === false){
echo 'Curl error: ' . curl_error($ch). '<br><br>';
print_r(error_get_last());
}
$response = json_decode($result, true);
curl_close($ch);
return $response;
}
Edit Added error check

Answer 1

Why does that keep happening?
The server you send the request to makes this happen. It is just that requests can fail.
Deal with it and design for failure.