問題描述

我正在使用以下代碼從遠程 ftp 服務器下載文件:

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();
        }

我正在下載的文件是一個 dll，我的問題是它被這個過程以某種方式改變了.我知道這是因為文件大小在增加.我懷疑這部分代碼有問題:

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現的問題提供任何想法嗎?

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

推薦答案

StreamReader 和 StreamWriter 處理字符數據，因此您正在將流從字節解碼為字符并然后再次將其編碼回字節.dll 文件包含二進制數據，因此這種往返轉換會引入錯誤.您想直接從 responseStream 對象讀取字節并寫入未包裝在 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，則可以使用 Stream.CopyTo，否則您將不得不手動復制流.這個StackOverflow問題有一個很好的復制流的方法:

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，您的代碼將如下所示:

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);
}

這篇關于FtpWebRequest 下載文件大小不正確的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！