FtpWebRequest 下载文件大小不正确

问题描述

我正在使用以下代码从远程 ftp 服务器下载文件:

I’m using the following code to download a file from a remote ftp server:

        FtpWebRequest request = (FtpWebRequest)WebRequest.Create(serverPath);

        request.KeepAlive = true;
        request.UsePassive = true;
        request.UseBinary = true;

        request.Method = WebRequestMethods.Ftp.DownloadFile;
        request.Credentials = new NetworkCredential(userName, password);                

        using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
        using (Stream responseStream = response.GetResponseStream())
        using (StreamReader reader = new StreamReader(responseStream))
        using (StreamWriter destination = new StreamWriter(destinationFile))
        {
            destination.Write(reader.ReadToEnd());
            destination.Flush();
        }

我正在下载的文件是一个 dll，我的问题是它被这个过程以某种方式改变了.我知道这是因为文件大小在增加.我怀疑这部分代码有问题:

The file that I’m downloading is a dll and my problem is that it is being altered by this process in some way. I know this because the file size is increasing. I have a suspicion that this section of code is at fault:

        destination.Write(reader.ReadToEnd());
        destination.Flush();

任何人都可以就可能出现的问题提供任何想法吗?

Can anyone offer any ideas as to what may be wrong?

推荐答案

StreamReader 和 StreamWriter 处理字符数据，因此您正在将流从字节解码为字符并然后再次将其编码回字节.dll 文件包含二进制数据，因此这种往返转换会引入错误.您想直接从 responseStream 对象读取字节并写入未包装在 StreamWriter 中的 FileStream.

StreamReader and StreamWriter work with character data, so you are decoding the stream from bytes to characters and then encoding it back to bytes again. A dll file contains binary data, so this round-trip conversion will introduce errors. You want to read bytes directly from the responseStream object and write to a FileStream that isn't wrapped in a StreamWriter.

如果您使用的是 .NET 4.0，则可以使用 Stream.CopyTo，否则您将不得不手动复制流.这个StackOverflow问题有一个很好的复制流的方法:

If you are using .NET 4.0 you can use Stream.CopyTo, but otherwise you will have to copy the stream manually. This StackOverflow question has a good method for copying streams:

public static void CopyStream(Stream input, Stream output)
{
    byte[] buffer = new byte[32768];
    while (true)
    {
        int read = input.Read(buffer, 0, buffer.Length);
        if (read <= 0)
            return;
        output.Write(buffer, 0, read);
    }
}

因此，您的代码将如下所示:

So, your code will look like this:

using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
using (Stream responseStream = response.GetResponseStream())
using (FileStream destination = File.Create(destinationFile))
{
    CopyStream(responseStream, destination);
}

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