c# BinaryReader“流不支持查找操作”

I am trying to download files from an ftp server using C# and ftpwebrequest. I can get the bytes using BinaryReader, but when I try to read the stream using br.ReadBytes(int), I get an error that BinaryReader does not support seek operations.

我正在尝试用c#和ftpwebrequest从一个ftp服务器下载文件。我可以使用BinaryReader来获取字节，但是当我尝试使用br.ReadBytes(int)读取流时，我得到一个错误，即BinaryReader不支持查找操作。

Does anyone know how best to read the bytes so I can write them to a file?

有没有人知道如何最好地读取字节，这样我就可以将它们写入文件?

Here's the full method:

这是完整的方法:

    public void DownloadFile(String fileName)
    {
        Logger.Info("starting to download file: " + fileName);

        try
        {
            var downloadFileRequest = (FtpWebRequest)WebRequest.Create(FtpServer + "//" + fileName);
            downloadFileRequest.Credentials = new NetworkCredential(FtpUsername,FtpPassword);
            downloadFileRequest.Method = WebRequestMethods.Ftp.DownloadFile;
            downloadFileRequest.UseBinary = true;

            ServicePoint sp = downloadFileRequest.ServicePoint;
            sp.ConnectionLimit = 2;

            Logger.Info("getting ftp response for download file for " + fileName);

            try
            {
                var downloadResponse = (FtpWebResponse)downloadFileRequest.GetResponse();

                Logger.Info("getting ftp response stream for " + fileName);

                try
                {
                    Stream downloadStream = downloadResponse.GetResponseStream();

                    Logger.Info("File Download status: {0}", downloadResponse.StatusDescription.Trim());

                    Logger.Info("getting binary reader for " + fileName);

                    try
                    {
                       using ( var downloadReader = new BinaryReader(downloadStream))
                       {
                           String destinationFilePath= Path.Combine(LocalFolder, fileName);

                           Logger.Info("writing response stream to " + destinationFilePath);

                           try
                           {
                               using (var downloadWriter = new BinaryWriter(System.IO.File.Open(destinationFilePath, FileMode.Create)))
                               {
                                   downloadWriter.Write(downloadReader.ReadBytes((int)downloadStream.Length));
                               }

                               Logger.Info("successfully saved " + destinationFilePath);

                            }
                            catch (Exception ex)
                            {
                                Logger.Info("could not save " + destinationFilePath+ " b/c: " + ex.Message);
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        Logger.Info("could not read " + fileName + " b/c: " + ex.Message);
                    }
                }
                catch (Exception ex)
                {
                    Logger.Info("could not open download stream for " + fileName + " b/c: " + ex.Message);
                }
                finally
                {
                    downloadResponse.Close();
                }
            }
            catch (Exception ex)
            {
                Logger.Info("could not get ftp response stream for " + fileName + " b/c: " + ex.Message);
            }
        }
        catch (Exception ex)
        {
            Logger.Info("could not get ftp request stream for " + fileName + " b/c: " + ex.Message);
        }
    }

This runs as part of an ongoing service, so I don't want to throw errors that would stop the service. Instead, I'm writing to a log. Here are the contents of the log for this method:

这是正在运行的服务的一部分，所以我不想抛出会停止服务的错误。相反，我在写日志。下面是该方法的日志内容:

2009-10-07 16:33:29.1421|INFO|xxx.Web.Controllers.FtpController|starting to download file: 2009-10-06155728Z_metadata.txt
2009-10-07 16:33:29.1421|INFO|xxx.Web.Controllers.FtpController|getting ftp response for download file for 2009-10-06155728Z_metadata.txt
2009-10-07 16:33:29.6661|INFO|xxx.Web.Controllers.FtpController|getting ftp response stream for 2009-10-06155728Z_metadata.txt
2009-10-07 16:33:29.6661|INFO|xxx.Web.Controllers.FtpController|File Download status: 125 Data connection already open; Transfer starting.
2009-10-07 16:33:29.6721|INFO|xxx.Web.Controllers.FtpController|getting binary reader for 2009-10-06155728Z_metadata.txt
2009-10-07 16:33:29.6721|INFO|xxx.Web.Controllers.FtpController|writing response stream to C:\\Resumes\\2009-10-06155728Z_metadata.txt
2009-10-07 16:33:29.6951|INFO|xxx.Web.Controllers.FtpController|could not save C:\\Resumes\\2009-10-06155728Z_metadata.txt b/c: This stream does not support seek operations.

I've been working on this way too long, so any help would be appreciated!

我在这方面工作太久了，所以任何帮助都是值得感激的!

Thanks!!

谢谢! !

2 个解决方案

#1

You shouldn't rely on Stream.Length, its possible it could be wrong. You just need to read all of the bytes in a while loop until there are no more bytes to read.

你不应该依赖于流。长度，可能是错的。您只需要在一个while循环中读取所有的字节，直到没有更多的字节来读取。

MemoryStream ms = new MemoryStream();
byte[] chunk = new byte[4096];
int bytesRead;
while ((bytesRead = downloadStream.Read(chunk, 0, chunk.Length)) > 0)
{
     ms.Write(chunk, 0, bytesRead);
}

From there, all the read data is in the MemoryStream, and you can initialize the BinaryReader with that.

从那里，所有读取数据都在MemoryStream中，您可以使用它初始化BinaryReader。

#2

Darkassassin's answer works great! Here's the code I finally got to work before I saw his post. It's slightly different b/c it writes directly to the file rather than to the memory stream.

Darkassassin回答的作品太棒了!在我看到他的帖子之前，我终于开始工作了。它是稍微不同的b/c，它直接写入文件而不是内存流。

I replaced this line:

我更换这条线:

downloadWriter.Write(downloadReader.ReadBytes((int)downloadStream.Length));

with this:

用这个:

var buffer = new byte[BufferSize];
int readCount = downloadStream.Read(buffer, 0, BufferSize);
while (readCount > 0)
{
    downloadWriter.Write(buffer, 0, readCount);
    readCount = downloadStream.Read(buffer, 0, BufferSize);
}

(BufferSize = 4096)

Thanks again for the quick help!!

再次感谢您的快速帮助!!

#1