delphi 利用TIdHttp实现文件下载的分块断点续传

环境delphi2007 + indy
网上有大量利用TIdHttp控件下载并支持断点续传的例子，但在delphi2007环境下运行都不成功。最近应为项目需要编写了一个测试程序，可以成功实现分块断点续传，并支持链接重定向后，自动获得真实的下载文件名。供大家参考。
（想修改成多线程下载也只是增加一些逻辑就可以了。）

procedure TForm3.RzButton1Click(Sender: TObject);
var
  IdHttp: TIdHttp;
  MemStream: TMemoryStream;
  UrlStr,
  DFileName: string;
  FilePosition: int64;
  FileSize: integer;
begin
  //初始化进度条
  RzProgressBar1.TotalParts    := 0;
  RzProgressBar1.PartsComplete := 0;
  //获取下载地址
  UrlStr := trim(RzEditUrl.Text);

  IdHttp := tIdHttp.Create(nil);
  IdHttp.ProtocolVersion := pv1_1 ;
  //IdHttp.RecvBufferSize := 1024 ;
  IdHttp.HandleRedirects := true;
  try
    //获取重定向后的下载地址和文件大小
    IdHttp.Head(UrlStr);
    FileSize := IdHttp.Response.ContentLength;
    DFileName := idhttp.URL.URI;
    //由下载地址转换为保存文件名
    while pos('/',DFileName) > 0 do
    begin
      delete(DFileName, 1, pos('/',DFileName));
    end;
    while pos('/',DFileName) > 0 do
    begin
      delete(DFileName, 1, pos('/',DFileName));
    end;
    if DFileName = '' then
      exit;

    FilePosition := 0;
    MemStream := TMemoryStream.Create;
    if FileExists(ExtractFilePath(Application.ExeName) + DFileName) then
    begin
      try
        MemStream.LoadFromFile(ExtractFilePath(Application.ExeName) + DFileName);
        MemStream.Seek(0, soFromEnd);
        FilePosition := MemStream.Size;
      except
        MemStream.Free;
        RzMemo1.lines.Add(Format('Open file "%S" failed!', [DFileName]));
        exit;
      end;
    end;
    //初始化进度条
    RzProgressBar1.TotalParts    := FileSize;
    RzProgressBar1.PartsComplete := FilePosition;
    RzMemo1.Lines.Add('FileName:' + DFileName);
    RzMemo1.Lines.Add('FileSize:' + IntToStr(RzProgressBar1.TotalParts));
    while FilePosition < FileSize do
    begin
      //方法1：未验证
      //IdHttp.Request.ContentRangeStart := FilePosition;
      //IdHttp.Request.ContentRangeEnd   := FilePosition + 1024;
      //方法2：已验证
      IdHttp.Request.Range := IntToStr(FilePosition) + '-' ;
      if FilePosition + 10240 < FileSize then
        IdHttp.Request.Range := IdHttp.Request.Range + IntToStr(FilePosition + 10239);
       
      IdHttp.get(idhttp.URL.URI, MemStream);
      //MemStream.LoadFromStream(IdHttp.Response.ContentStream);
      MemStream.SaveToFile(ExtractFilePath(Application.ExeName) + DFileName);
      FilePosition := MemStream.Size;
      //刷新进度条
      RzProgressBar1.PartsComplete := FilePosition;
      Application.ProcessMessages;
      //sleep(50);      //为确保能够看到下载过程，添加此延时
    end;
  finally
    IdHttp.Free;
    MemStream.Free;
  end;
end;

来源 http://blog.csdn.net/arbin_he/article/details/6325708