PHP下载远程文件到本地存储的方法

<?php
function grabimage($url,$filename="") {
  if($url=="") return false;
  if($filename=="") {
    $ext=strrchr($url,".");
    if($ext!=".gif" && $ext!=".jpg") return false;
    $filename=date("dmyhis").$ext;
  }
  ob_start();
  readfile($url);
  $img = ob_get_contents();
  ob_end_clean();
  $size = strlen($img);
  $fp2=@fopen($filename, "a");
  fwrite($fp2,$img);
  fclose($fp2);
  return $filename;
}
function gethttpimage($url){ 
  if(!empty($url)){ 
    $filename=uniqid().strrchr($url,"."); 
    echo $filename;
    $get_file=@file_get_contents($url); 
    if($get_file){ 
      $fp=@fopen($filename,"w"); 
      @fwrite($fp,$get_file); 
      @fclose($fp); 
    } 
    return $imgurl; 
  }else{ 
    return false; 
  } 
} 
//$img=grabimage("//www.jb51.net/images/logo.gif","");
$img=gethttpimage("//www.jb51.net/images/logo.gif","");
if($img) echo '<pre><img src="'.$img.'"></pre>';
else echo "false";
?>