curl_getinfo returning -1 as content-length

I am building a website crawler and using a cURL class with these options for getting headers, so that I can extract their mime/type and c开发者_如何学运维ontent-length before downloading full site to very it as text/html and below specified size limits.

these are my curl options

$c->setopt(CURLOPT_URL, $theURL);
$c->setopt(CURLOPT_HEADER, false);
$c->setopt(CURLOPT_RETURNTRANSFER, true);
$c->setopt(CURLOPT_TIMEOUT, 10);
$c->setopt(CURLOPT_CONNECTTIMEOUT, 10);
$c->setopt(CURLOPT_NOBODY, TRUE);
$c->setopt(CURLOPT_FOLLOWLOCATION, TRUE);
$c->setopt(CURLOPT_MAXREDIRS, 2);

// Within Class
$theReturnValue = curl_exec($this->m_handle);
$this->m_status = curl_getinfo($this->m_handle) ;

but it always return [download_content_length] => -1 even without CURLOPT_NOBODY however the data (whole file) retrived is correct.

The libcurl docs for CURLINFO_CONTENT_LENGTH_DOWNLOAD (which is what the PHP binding is using) says:

"this returns -1 if the size isn't known"