cURL有效，但PHP cURL无法上网

Question

Trying to diagnose an issue using PHP to cURL to an Internet location on a RedHat Linux server.

cURL is installed and working, and:

<?php var_dump(curl_version()); ?>

shows all the correct information in the output. The issue is I can use PHP to cURL to localhost on the box itself, but not the Internet (see below).

Normally I'd suspect the firewall, but I can cURL from the command line to the Internet without a problem. The box can also update it's own software packages, etc.

What am I missing? My test is:

<?php 
    function http_head_curl($url,$timeout=30)
    {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_TIMEOUT, $timeout);
        curl_setopt($ch, CURLOPT_HEADER, 1);
        curl_setopt($ch, CURLOPT_NOBODY, 1);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        $res = curl_exec($ch);
        if ($res === false) {
            throw new RuntimeException("cURL exception: ".curl_errno($ch).": ".curl_error($ch));
        }
        return trim($res);
    }

    // Succeeds, displaying headers
    echo(http_head_curl('localhost'));

    // Fails:
    echo(http_head_curl('www.google.com'));
?>

Answer 1

Are you having DNS resolution issues on the server? It will always be able to resolve localhost but may not be able to resolve www.google.com. Try this:

var_dump(dns_get_record('www.google.com'));

If DNS if not resolving, you should get:

array(0) {}

If DNS is working, you should get an array something like this:

array(6) {
  [0]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(13) "74.125.201.99"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
  [1]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(14) "74.125.201.105"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
  [2]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(14) "74.125.201.104"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
  [3]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(14) "74.125.201.106"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
  [4]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(14) "74.125.201.103"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
  [5]=>
  array(5) {
    ["host"]=>
    string(14) "www.google.com"
    ["type"]=>
    string(1) "A"
    ["ip"]=>
    string(14) "74.125.201.147"
    ["class"]=>
    string(2) "IN"
    ["ttl"]=>
    int(375)
  }
}