How PHP obtains client IP

/** * Get client IP address * @param integer $type return type 0 return IP address 1 return IPV4 address number * @return mixed */function get_client_ip ($type = 0) {
  $type       =  $type? 1:0;    static $ip  =   NULL;    if ($ip!== NULL) return $ip [$type];    if (Isset ($_server[' http_x_forwarded_for ')) {        $arr    =   explode (', ', $_server[' http_x_forwarded_for ')) ;        $pos    =   array_search (' unknown ', $arr);        if (false!== $pos) unset ($arr [$pos]);        $ip     =   Trim ($arr [0]);    } ElseIf (Isset ($_server[' http_client_ip ')) {        $ip     =   $_server[' http_client_ip '];    } ElseIf (Isset ($_server[' remote_addr ')) {        $ip     =   $_server[' remote_addr '];    }    IP Address valid authentication    $long = sprintf ("%u", Ip2long ($IP));    $ip   = $long? Array ($ip, $long): Array (' 0.0.0.0 ', 0);    return $ip [$type];}

The above is the thinkphp framework comes with a function to get the client IP address, calling the method

Get_client_ip ();

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