具体如下：

m_url = $url;
    if(is_array($urls)) {
      $this->m_host = $urls["host"];
      if(!empty($urls["scheme"])) $this->m_scheme = $urls["scheme"];
      if(!empty($urls["user"])) $this->m_user = $urls["user"];
      if(!empty($urls["pass"])) $this->m_pass = $urls["pass"];
      if(!empty($urls["port"])) $this->m_port = $urls["port"];
      if(!empty($urls["path"])) $this->m_path = $urls["path"];
      $this->m_urlpath = $this->m_path;
      if(!empty($urls["query"])) {
        $this->m_query = $urls["query"];
        $this->m_urlpath .= "?".$this->m_query;
      }
    }
  }
  /**
  * 打开指定网址
  */
  function OpenUrl($url) {
    #重设各参数
    $this->m_url = "";
    $this->m_urlpath = "";
    $this->m_scheme = "http";
    $this->m_host = "";
    $this->m_port = "80";
    $this->m_user = "";
    $this->m_pass = "";
    $this->m_path = "/";
    $this->m_query = "";
    $this->m_error = "";
    $this->m_httphead = "" ;
    $this->m_html = "";
    $this->Close();
    #初始化系统
    $this->PrivateInit($url);
    $this->PrivateStartSession();
  }
  /**
  * 获得某操作错误的原因
  */
  public function printError() {
    echo "错误信息：".$this->m_error;
    echo "具体返回头：
";
    foreach($this->m_httphead as $k=>$v) {
      echo "$k => $v 
\r\n";
    }
  }
  /**
  * 判别用Get方法发送的头的应答结果是否正确
  */
  public function IsGetOK() {
    if( ereg("^2",$this->GetHead("http-state")) ) {
      return true;
    } else {
      $this->m_error .= $this->GetHead("http-state")." - ".$this->GetHead("http-describe")."
";
      return false;
    }
  }
  /**
  * 看看返回的网页是否是text类型
  */
  public function IsText() {
    if (ereg("^2",$this->GetHead("http-state")) && eregi("^text",$this->GetHead("content-type"))) {
      return true;
    } else {
      $this->m_error .= "内容为非文本类型
";
      return false;
    }
  }
  /**
  * 判断返回的网页是否是特定的类型
  */
  public function IsContentType($ctype) {
    if (ereg("^2",$this->GetHead("http-state")) && $this->GetHead("content-type") == strtolower($ctype)) {
      return true;
    } else {
      $this->m_error .= "类型不对 ".$this->GetHead("content-type")."
";
      return false;
    }
  }
  /**
  * 用 HTTP 协议下载文件
  */
  public function SaveToBin($savefilename) {
    if (!$this->IsGetOK()) return false;
    if (@feof($this->m_fp)) {
      $this->m_error = "连接已经关闭！";
      return false;
    }
    $fp = fopen($savefilename,"w") or die("写入文件 $savefilename 失败！");
    while (!feof($this->m_fp)) {
      @fwrite($fp,fgets($this->m_fp,256));
    }
    @fclose($this->m_fp);
    return true;
  }
  /**
  * 保存网页内容为 Text 文件
  */
  public function SaveToText($savefilename) {
    if ($this->IsText()) {
      $this->SaveBinFile($savefilename);
    } else {
      return "";
    }
  }
  /**
  * 用 HTTP 协议获得一个网页的内容
  */
  public function GetHtml() {
    if (!$this->IsText()) return "";
    if ($this->m_html!="") return $this->m_html;
    if (!$this->m_fp||@feof($this->m_fp)) return "";
    while(!feof($this->m_fp)) {
      $this->m_html .= fgets($this->m_fp,256);
    }
    @fclose($this->m_fp);
    return $this->m_html;
  }
  /**
  * 开始 HTTP 会话
  */
  public function PrivateStartSession() {
    if (!$this->PrivateOpenHost()) {
      $this->m_error .= "打开远程主机出错!";
      return false;
    }
    if ($this->GetHead("http-edition")=="HTTP/1.1") {
      $httpv = "HTTP/1.1";
    } else {
      $httpv = "HTTP/1.0";
    }
    fputs($this->m_fp,"GET ".$this->m_urlpath." $httpv\r\n");
    fputs($this->m_fp,"Host: ".$this->m_host."\r\n");
    fputs($this->m_fp,"Accept: */*\r\n");
    fputs($this->m_fp,"User-Agent: Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.2)\r\n");
    #HTTP1.1协议必须指定文档结束后关闭链接,否则读取文档时无法使用feof判断结束
    if ($httpv=="HTTP/1.1") {
      fputs($this->m_fp,"Connection: Close\r\n\r\n");
    } else {
      fputs($this->m_fp,"\r\n");
    }
    $httpstas = fgets($this->m_fp,256);
    $httpstas = split(" ",$httpstas);
    $this->m_httphead["http-edition"] = trim($httpstas[0]);
    $this->m_httphead["http-state"] = trim($httpstas[1]);
    $this->m_httphead["http-describe"] = "";
    for ($i=2;$im_httphead["http-describe"] .= " ".trim($httpstas[$i]);
    }
    while (!feof($this->m_fp)) {
      $line = str_replace("\"","",trim(fgets($this->m_fp,256)));
      if($line == "") break;
      if (ereg(":",$line)) {
        $lines = split(":",$line);
        $this->m_httphead[strtolower(trim($lines[0]))] = trim($lines[1]);
      }
    }
  }
  /**
  * 获得一个Http头的值
  */
  public function GetHead($headname) {
    $headname = strtolower($headname);
    if (isset($this->m_httphead[$headname])) {
      return $this->m_httphead[$headname];
    } else {
      return "";
    }
  }
  /**
  * 打开连接
  */
  public function PrivateOpenHost() {
    if ($this->m_host=="") return false;
    $this->m_fp = @fsockopen($this->m_host, $this->m_port, &$errno, &$errstr,10);
    if (!$this->m_fp){
      $this->m_error = $errstr;
      return false;
    } else {
      return true;
    }
  }
  /**
  * 关闭连接
  */
  public function Close(){
    @fclose($this->m_fp);
  }
}
#两种使用方法，分别如下：
#打开网页
$httpdown = new HttpDownload();
$httpdown->OpenUrl("http://www.google.com.hk");
echo $httpdown->GetHtml();
$httpdown->Close();
#下载文件
$file = new HttpDownload(); # 实例化类
$file->OpenUrl("http://www.ti.com.cn/cn/lit/an/rust020/rust020.pdf"); # 远程文件地址
$file->SaveToBin("rust020.pdf"); # 保存路径及文件名
$file->Close(); # 释放资源
?>