c# - FTP文件下载C#

Question

在我的代码中，我想从 FTP 服务器下载一个特定的文件到我的本地机器。我得到一个如下所示的异常

System.InvalidCastException: Unable to cast object of type: 'System.Net.HttpWebRequest' to type 'System.Net.FtpWebRequest' at FTPapp.ftpdownload.Download(String remoteFile, String localFile)

我的代码：

namespace FTPapp
            {
                public partial class ftpdownload : Form
                {
                    private string Host = null;
                    private string user = null;
                    private string pass = null;
                    private string SSH = null;
                    private FtpWebRequest ftprequest = null;
                    private FtpWebResponse ftpresponse = null;
                    private Stream ftpStream = null;
                    private int buffersize = 2048;
                    public ftpdownload()
                    {
                        InitializeComponent();
                    }

                    public ftpdownload(string hostIP, string username, string password ,string SSHkey)
                    {
                        Host = hostIP;
                        user = username;
                        pass = password;
                        SSH = SSHkey;

                    }
                    public void Download(string remoteFile, string localFile)
                    {
                        try
                        {

                            ftprequest = (FtpWebRequest)FtpWebRequest.Create(Host + "/" + remoteFile);
                            ftprequest.Credentials = new NetworkCredential(user, pass ,SSH);
                            ftprequest.UseBinary = true;
                            ftprequest.UsePassive = true;
                            ftprequest.KeepAlive = true;

                            ftprequest.Method = WebRequestMethods.Ftp.DownloadFile;
                            ftpresponse = (FtpWebResponse)ftprequest.GetResponse();
                            ftpStream = ftpresponse.GetResponseStream();
                            FileStream localFileStream = new FileStream(localFile, FileMode.Create);
                            byte[] byteBuffer = new byte[buffersize];
                         `enter code here`   int bytesRead = ftpStream.Read(byteBuffer, 0, buffersize);

                            try
                            {
                                while (bytesRead > 0)
                                {
                                    localFileStream.Write(byteBuffer, 0, bytesRead);
                                    bytesRead = ftpStream.Read(byteBuffer, 0, buffersize);
                                }
                            }
                            catch (Exception ex)
                            {
                                Console.WriteLine(ex.ToString());

                            }
                            localFileStream.Close();
                            ftpStream.Close();
                            ftpresponse.Close();
                            ftprequest= null;
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine(ex.ToString());
                            MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);

                        }
                    }

                    private void BackgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
                    {

                    }

                    private void Form1_Load(object sender, EventArgs e)
                    {
                        txtServer.Text = "http://ftpsite.com";
                        txtUsername.Text = "";
                        txtPassword.Text = @"";
                        txtFilename.Text = @"";
                        txtSSHKey.Text = "";
                    }

                    private void BtnDownload_Click(object sender, EventArgs e)
                    {
                        ftpdownload ftp = new ftpdownload("http://ftpsite.com" ,"","","");
                        ftp.Download(@"Remotepath", @"local path");
                    }


                }
            }

标签： c#visual-studioftp

Answer 1

如果不检查，我们无法确定该链接是 FTP Uri。

如microsoft 文档中所述，您需要ftp://在主机名之前使用，例如：ftp://contoso.com/someFile.txt.

那么，如何解决您的问题呢？

首先，您应该添加ftp://到您的链接。之后，您可以创建一个Uri对象并检查它的方案是否为Uri.UriSchemeFtp. 如果没有，请返回。