CURL and HTTPS, "Cannot resolve host"

Question

I'm trying to fetch the contents of a page using CURL. The page that is doing the fetching is https and the page it is trying to fetch is also https. I'm getting an error "Couldn't resolve host" with all of the settings I try.

$c=curl_init();
curl_setopt($c, CURLOPT_URL,$url);
//curl_setopt($c, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:x.x.x) Gecko/20041107 Firefox/x.x");
curl_setopt ($c, CURLOPT_RETURNTRANSFER, TRUE);
//curl_setopt($c, CURLOPT_SSL_VERIFYPEER, TRUE);
//curl_setopt($c, CURLOPT_SSL_VERIFYHOST, TRUE);
curl_setopt($c, CURLOPT_HEADER, FALSE);

$html=curl_exec($c);

if($html === false) {
    echo curl_error($c);
}
else {
    echo 'Operation completed without any errors';
}   


curl_close($c);

Any ideas?

Answer 1

I found that curl can decide to use IPv6, in which case it tries to resolve but doesn't get an IPv6 answer (or something to that effect) and times out.

You can try the curl command line switch -4 to test this out:

curl -4 http://x.com

In PHP, you can configure this line by setting this:

curl_setopt($c, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);

Official manual page for this option: https://curl.se/libcurl/c/CURLOPT_IPRESOLVE.html

Answer 2

Maybe a DNS issue?

Try your URL against this code:

$_h = curl_init();
curl_setopt($_h, CURLOPT_HEADER, 1);
curl_setopt($_h, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($_h, CURLOPT_HTTPGET, 1);
curl_setopt($_h, CURLOPT_URL, 'YOUR_URL' );
curl_setopt($_h, CURLOPT_DNS_USE_GLOBAL_CACHE, false );
curl_setopt($_h, CURLOPT_DNS_CACHE_TIMEOUT, 2 );

var_dump(curl_exec($_h));
var_dump(curl_getinfo($_h));
var_dump(curl_error($_h)); 

Answer 3

I had the same problem. Coudn't resolve google.com. There was a bug somewhere in php fpm, which i am using. Restarting php-fpm solved it for me.

Answer 4

Just a note which may be helpful- I was having this trouble with Apache on my laptop (which connects by wifi AFTER startup), and restarting the server (after connect) fixed the issue. I guess in my case this may be to do with apache starting offline and perhaps there noting that DNS lookups fail?

Answer 5

There is a current bug in glibc on Ubuntu which can have this effect: https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1674733

To resolve it, update libc and all related (Packages that will be upgraded: libc-bin libc-dev-bin libc6 libc6-dev libfreetype6 libfreetype6-dev locales multiarch-support) and restart the server.