使用FtpWebRequest下载文件

Question

我正在尝试使用FtpWebRequest下载文件。

private void DownloadFile(string userName, string password, string ftpSourceFilePath, string localDestinationFilePath)
{
    int bytesRead = 0;
    byte[] buffer = new byte[1024];

    FtpWebRequest request = CreateFtpWebRequest(ftpSourceFilePath, userName, password, true);
    request.Method = WebRequestMethods.Ftp.DownloadFile;

    Stream reader = request.GetResponse().GetResponseStream();
    BinaryWriter writer = new BinaryWriter(File.Open(localDestinationFilePath, FileMode.CreateNew));

    while (true)
    {
        bytesRead = reader.Read(buffer, 0, buffer.Length);

        if (bytesRead == 0)
            break;

        writer.Write(buffer, 0, bytesRead);
    }        
}

它使用我创建的这个CreateFtpWebRequest方法：

private FtpWebRequest CreateFtpWebRequest(string ftpDirectoryPath, string userName, string password, bool keepAlive = false)
{
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create(new Uri(ftpDirectoryPath));

    //Set proxy to null. Under current configuration if this option is not set then the proxy that is used will get an html response from the web content gateway (firewall monitoring system)
    request.Proxy = null;

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

    request.Credentials = new NetworkCredential(userName, password);

    return request;
}

它会下载它。但是信息总是被破坏的。有人知道是怎么回事吗？

Answer 1

我就想明白了：

    private void DownloadFile(string userName, string password, string ftpSourceFilePath, string localDestinationFilePath)
    {
        int bytesRead = 0;
        byte[] buffer = new byte[2048];

        FtpWebRequest request = CreateFtpWebRequest(ftpSourceFilePath, userName, password, true);
        request.Method = WebRequestMethods.Ftp.DownloadFile;

        Stream reader = request.GetResponse().GetResponseStream();
        FileStream fileStream = new FileStream(localDestinationFilePath, FileMode.Create);

        while (true)
        {
            bytesRead = reader.Read(buffer, 0, buffer.Length);

            if (bytesRead == 0)
                break;

            fileStream.Write(buffer, 0, bytesRead);
        }
        fileStream.Close();       
    }

不得不改用FileStream。

Answer 2

最简单的方法

使用.NET框架从FTP服务器下载文件最简单的方法就是使用WebClient.DownloadFile method

WebClient client = new WebClient();
client.Credentials = new NetworkCredential("username", "password");
client.DownloadFile(
    "ftp://ftp.example.com/remote/path/file.zip", @"C:\local\path\file.zip");

高级选项

使用FtpWebRequest class，如果你只需要一个更大的控制，WebClient类不提供(如TLS/SSL encryption，进度监控，ascii/文本传输模式，resuming transfers等)。一种简单的方法是使用Stream.CopyTo方法将FTP响应流复制到FileStream：

FtpWebRequest request =
    (FtpWebRequest)WebRequest.Create("ftp://ftp.example.com/remote/path/file.zip");
request.Credentials = new NetworkCredential("username", "password");
request.Method = WebRequestMethods.Ftp.DownloadFile;

using (Stream ftpStream = request.GetResponse().GetResponseStream())
using (Stream fileStream = File.Create(@"C:\local\path\file.zip"))
{
    ftpStream.CopyTo(fileStream);
}

进度监控

如果您需要监控下载进度，您必须自己按块复制内容：

FtpWebRequest request =
    (FtpWebRequest)WebRequest.Create("ftp://ftp.example.com/remote/path/file.zip");
request.Credentials = new NetworkCredential("username", "password");
request.Method = WebRequestMethods.Ftp.DownloadFile;

using (Stream ftpStream = request.GetResponse().GetResponseStream())
using (Stream fileStream = File.Create(@"C:\local\path\file.zip"))
{
    byte[] buffer = new byte[10240];
    int read;
    while ((read = ftpStream.Read(buffer, 0, buffer.Length)) > 0)
    {
        fileStream.Write(buffer, 0, read);
        Console.WriteLine("Downloaded {0} bytes", fileStream.Position);
    }
}

有关图形用户界面进度(WinForms ProgressBar)，请参阅：

FtpWebRequest FTP download with ProgressBar

正在下载文件夹

如果要从远程文件夹下载所有文件，请参见

C# Download all files and subdirectories through FTP。