Curl an unresolvable host?

Question

I need to Curl from a PHP website to a host that's unresolvable from the target machine (curl_error returns (6) couldn't resolve host). It's resolvable just fine on my local machine though, so after some web searching I figured it might be a DNS caching issue.
I only have FTP access to this webserver, so I can't restart Apache or edit the r.conf file.
I tried Curling using the IP address I got from pinging the domain, but unfortunately I need to make requests to a subdomain (e.g., api.domain.com), and requests to the IP address directly get handled differently.

I had hoped I could specify the subdomain+domain in the Host header (see below), but this doesn't work either.

$curl = curl_init();

$opt = array(
    CURLOPT_URL => 'http://11.22.33.44/handler.php?params=1',
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_HTTPHEADER => array('Host: subdomain.domain.com')
);
curl_setopt_array($curl, $opt);
$output = curl_exec($curl);

It doesn't work, as it seems as if the Host header is ignored. I get the same result without it. — Protector one
– Protector one, Commented Nov 17, 2014 at 10:53

Daniel Stenberg · Accepted Answer · 2014-11-17 10:56:18Z

1

An alternative way to the Host: fiddling (if you use a new enough PHP version, apparently this is in 5.5 or later) is to pre-populate the libcurl DNS cache with a "fake" entry for the host name and then you can use the host name in the URL.

See the CURLOPT_RESOLVE option which seems badly documented in the PHP docs but can be found out about in the bug tracker: https://bugs.php.net/bug.php?id=63488&edit=1

The underlying libcurl option CURLOPT_RESOLVE is documented on the curl web site.

answered Nov 17, 2014 at 10:56

Daniel Stenberg

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4 Comments

Protector one Over a year ago

Badly documented indeed, but this looks promising!

Protector one Over a year ago

Unfortunately, using CURLOPT_RESOLVE I still get the same Curl error. I used the code snippet on that bug tracker page—once with the subdomain and once without—but neither had any noticeable effect.

Daniel Stenberg Over a year ago

Then investigate exactly how the request looks like and make sure it is correct, because both these methods should work

Protector one Over a year ago

Thanks to that suggestion, I got it to work with the Host: fiddling! Still no idea why CURLOPT_RESOLVE does nothing, but if you hadn't said the Host header should work too, I might have given up! Thank you

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