FileSystemWatcher for FTP

问题:

How can I implement a FileSystemWatcher for an FTP location (in C#). The idea is whenever anything gets added in the FTP location I wish to copy it to my local machine. Any ideas will be helpful.

This is a follow up of my previous question Selective FTP download using .NET.

回答1:

You're going to have to implement a polling solution, where you keep asking for the directory content periodically. Compare this to a cached list from the previous call and determine what happened that way.

There's nothing in the FTP protocol that will help you with this unfortunately.

回答2:

The FileSystemWatcher class works by registering for events with the host Windows operating system. As such, it is limited to working on local paths and UNC paths to directories hosted on Windows systems. The MSDN documentation on FileSystemWatcher explains the paths which you can use and some of the potential problems with using the class.

If you are looking to be alerted to changes on an FTP site, you will have to use a polling mechanism to ask for the current status of files or folders you are interested in monitoring. You will be able to see when files are added and removed by comparing snapshots of the FTP site for changes and raising similar events when you detect changes. Unfortunately you wont be able to detect rename events, but other changes should be simple to monitor this way.

回答3:

You cannot use the FileSystemWatcher or any other way, because the FTP protocol does not have any API to notify a client about changes in the remote directory.

All you can do is to periodically iterate the remote tree and find changes.

It's actually rather easy to implement, if you use an FTP client library that supports recursive listing of a remote tree. Unfortunately, the built-in .NET FTP client, the FtpWebRequest does not. But for example with WinSCP .NET assembly version 5.9 (or newer), you can use the Session.EnumerateRemoteFiles method.

See the article Watching for changes in SFTP/FTP server:

// Setup session options
SessionOptions sessionOptions = new SessionOptions
{
    Protocol = Protocol.Ftp,
    HostName = "example.com",
    UserName = "user",
    Password = "password",
};

using (Session session = new Session())
{
    // Connect
    session.Open(sessionOptions);

    List<string> prevFiles = null;

    while (true)
    {
        // Collect file list
        List<string> files =
            session.EnumerateRemoteFiles(
                "/remote/path", "*.*", EnumerationOptions.AllDirectories)
            .Select(fileInfo => fileInfo.FullName)
            .ToList();
        if (prevFiles == null)
        {
            // In the first round, just print number of files found
            Console.WriteLine("Found {0} files", files.Count);
        }
        else
        {
            // Then look for differences against the previous list
            IEnumerable<string> added = files.Except(prevFiles);
            if (added.Any())
            {
                Console.WriteLine("Added files:");
                foreach (string path in added)
                {
                    Console.WriteLine(path);
                }
            }

            IEnumerable<string> removed = prevFiles.Except(files);
            if (removed.Any())
            {
                Console.WriteLine("Removed files:");
                foreach (string path in removed)
                {
                    Console.WriteLine(path);
                }
            }
        }

        prevFiles = files;

        Console.WriteLine("Sleeping 10s...");
        Thread.Sleep(10000);
    }
}

(I'm the author of WinSCP)

---

Though, if you actually want to just download the changes, it's a way easier. Just use the Session.SynchronizeDirectories in the loop.

session.SynchronizeDirectories(
    SynchronizationMode.Local, "/remote/path", @"C:\local\path", true).Check();

---

If you do not want to use a 3rd party library, you have to do with limitations of the FtpWebRequest. For an example how to recursively list a remote directory tree with the FtpWebRequest, see my answer to C# Download all files and subdirectories through FTP.

回答4:

Write a simple service to create FileSystemWatcher, pointing at your ftp location.

Then when a file is uploaded or modified, an event will be fired in your service, which you can then use to copy the file to your local machine.
File.Copy etc.

Hav a look at: this blog

回答5:

You can monitor the FTP location by following method:

public class FtpFileSystemWatcher
{

    public bool IsRunning
    {
        get;
        private set;
    }
    public string FtpUserName
    {
        get;
        set;
    }
    public string FtpPassword
    {
        get;
        set;
    }
    public string FtpLocationToWatch
    {
        get;
        set;
    }
    public string DownloadTo
    {
        get;
        set;
    }
    public bool KeepOrignal
    {
        get;
        set;
    }
    public bool OverwriteExisting
    {
        get;
        set;
    }
    public int RecheckIntervalInSeconds
    {
        get;
        set;
    }
    private bool DownloadInprogress
    {
        get;
        set;
    }

    private System.Timers.Timer JobProcessor;

    public FtpFileSystemWatcher(string FtpLocationToWatch = "", string DownloadTo = "", int RecheckIntervalInSeconds = 1, string UserName = "", string Password = "", bool KeepOrignal = false, bool OverwriteExisting = false)
    {
        this.FtpUserName = UserName;
        this.FtpPassword = Password;
        this.FtpLocationToWatch = FtpLocationToWatch;
        this.DownloadTo = DownloadTo;
        this.KeepOrignal = KeepOrignal;
        this.RecheckIntervalInSeconds = RecheckIntervalInSeconds;
        this.OverwriteExisting = OverwriteExisting;

        if (this.RecheckIntervalInSeconds < 1) this.RecheckIntervalInSeconds = 1;
    }

    public void StartDownloading()
    {

        JobProcessor = new Timer(this.RecheckIntervalInSeconds * 1000);
        JobProcessor.AutoReset = false;
        JobProcessor.Enabled = false;
        JobProcessor.Elapsed += (sender, e) =>
        {
            try
            {

                this.IsRunning = true;

                string[] FilesList = GetFilesList(this.FtpLocationToWatch, this.FtpUserName, this.FtpPassword);

                if (FilesList == null || FilesList.Length < 1)
                {
                    return;
                }

                foreach (string FileName in FilesList)
                {
                    if (!string.IsNullOrWhiteSpace(FileName))
                    {
                        DownloadFile(this.FtpLocationToWatch, this.DownloadTo, FileName.Trim(), this.FtpUserName, this.FtpPassword, this.OverwriteExisting);

                        if (!this.KeepOrignal)
                        {
                            DeleteFile(Path.Combine(this.FtpLocationToWatch, FileName.Trim()), this.FtpUserName, this.FtpPassword);
                        }
                    }
                }

                this.IsRunning = false;
                JobProcessor.Enabled = true;                    
            }

            catch (Exception exp)
            {
                this.IsRunning = false;
                JobProcessor.Enabled = true;
                Console.WriteLine(exp.Message);
            }
        };

        JobProcessor.Start();
    }

    public void StopDownloading()
    {
        try
        {
            this.JobProcessor.Dispose();
            this.IsRunning = false;
        }
        catch { }
    }

    private void DeleteFile(string FtpFilePath, string UserName, string Password)
    {
        FtpWebRequest FtpRequest;
        FtpRequest = (FtpWebRequest)FtpWebRequest.Create(new Uri(FtpFilePath));
        FtpRequest.UseBinary = true;
        FtpRequest.Method = WebRequestMethods.Ftp.DeleteFile;

        FtpRequest.Credentials = new NetworkCredential(UserName, Password);
        FtpWebResponse response = (FtpWebResponse)FtpRequest.GetResponse();
        response.Close();

    }
    private void DownloadFile(string FtpLocation, string FileSystemLocation, string FileName, string UserName, string Password, bool OverwriteExisting)
    {
        try
        {
            const int BufferSize = 2048;
            byte[] Buffer = new byte[BufferSize];

            FtpWebRequest Request;
            FtpWebResponse Response;

            if (File.Exists(Path.Combine(FileSystemLocation, FileName)))
            {
                if (OverwriteExisting)
                {
                    File.Delete(Path.Combine(FileSystemLocation, FileName));
                }
                else
                {
                    Console.WriteLine(string.Format("File {0} already exist.", FileName));
                    return;
                }
            }

            Request = (FtpWebRequest)FtpWebRequest.Create(new Uri(Path.Combine(FtpLocation, FileName)));
            Request.Credentials = new NetworkCredential(UserName, Password);
            Request.Proxy = null;
            Request.Method = WebRequestMethods.Ftp.DownloadFile;
            Request.UseBinary = true;

            Response = (FtpWebResponse)Request.GetResponse();

            using (Stream s = Response.GetResponseStream())
            {
                using (FileStream fs = new FileStream(Path.Combine(FileSystemLocation, FileName), FileMode.CreateNew, FileAccess.ReadWrite))
                {
                    while (s.Read(Buffer, 0, BufferSize) != -1)
                    {
                        fs.Write(Buffer, 0, BufferSize);
                    }
                }
            }
        }
        catch { }

    }
    private string[] GetFilesList(string FtpFolderPath, string UserName, string Password)
    {
        try
        {
            FtpWebRequest Request;
            FtpWebResponse Response;

            Request = (FtpWebRequest)FtpWebRequest.Create(new Uri(FtpFolderPath));
            Request.Credentials = new NetworkCredential(UserName, Password);
            Request.Proxy = null;
            Request.Method = WebRequestMethods.Ftp.ListDirectory;
            Request.UseBinary = true;

            Response = (FtpWebResponse)Request.GetResponse();
            StreamReader reader = new StreamReader(Response.GetResponseStream());
            string Data = reader.ReadToEnd();

            return Data.Split('\n');
        }
        catch
        {
            return null;
        }
    }


}

回答6:

The way I handle this is to upload a one element byte array, named ".ftpComplete". The FileSystemWatcher only watches for ".ftpComplete" files, and strips that off the end to know the actual file uploaded. Since the".ftpComplete" file is only 1 byte, it uploads about as fast as it is created on the FTP server, so it can be deleted once you do whatever you need to with the main uploaded file

        FtpWebRequest request = (FtpWebRequest)FtpWebRequest.Create(
            FTPAddress + "/" + Path.GetFileName(filePath) + ".ftpComplete");
        request.Method = WebRequestMethods.Ftp.UploadFile;
        request.Credentials = new NetworkCredential(username, password);
        request.UsePassive = true;
        request.UseBinary = true;
        request.KeepAlive = false;
        byte[] buffer = new byte[1];
        Stream reqStream = request.GetRequestStream();
        reqStream.Write(buffer, 0, buffer.Length);
        reqStream.Close();

回答7:

You could use a Robo-FTP script to monitor the FTP site for changes. Here is a link to a sample script that sends an email whenever a change is detected: http://kb.robo-ftp.com/script_library/show/40

I looked at the previous question that you linked. I think you should be able to modify the Robo-FTP sample and use the SETLEFT command with the /split option to make it parse the folder name and ISO file number of the changed file and then move the file to the proper location.