This users guide will go through some of the basic steps that one might take in order to create an FTP client application in VS.Net. The full source code for this client is available for download with any of the IPWorks! Editions.
In this guide, we will make use of the FTP component included in the IP*Works! .Net Edition. If you do not have this toolkit, or would like to download it for free, please visit our download site and do so. For the purposes of this document, we will assume that IP*Works! .Net Edition has already been installed on the readers computer. The .Net Edition includes sample code for both VB.Net and C#, but here we will be coding in VB.Net. If you would like code samples in a particular language, please contact support@nsoftware.com, or look through the demos available in the free fully functional trial versions of IP*Works! which is downloadable at http://www.nsoftware.com/download.asp. IP*Works! is available for many different languages and platforms.
Getting Connected
Begin by placing the FTP component on the form IP*Works! will provide you with the option of creating an IP*Works! toolbar in your VS.Net toolbox when you install Simply select the component from there The first thing we want to do is have the ability to logon to an FTP server, right? We'll put a Connect button, and textboxes for user input in order to get the name of the FTP server, the user name, and the password for that user.
Once we have gathered this information “we can connect to the server. Simply assign the RemoteHost, User, and Password properties and call the Logon method.
FTP1.RemoteHost = txtServer.Text
FTP1.User = txtUser.Text
FTP1.Password = txtPassword.Text
FTP1.Logon()
What About Connection Errors?
If the server is not reachable or if the connection is refused by the server, the component will generate an exception. This error would be a standard exception, caught with traditional error catching routines (ie in VB.Net, an On Error statement). As for slow connections, or established connections that experience problems later, you can set an optional timeout value using the Timeout property if you like. The Timeout will fire an error if the method (in this case the logon method) does not return in Timeout seconds.
Now that we are connected what are we to do? The first thing we'll want to do obviously in an FTP client application is display a listing of files on the client and the server. In order to display the client side files, you'd want to use some file object library. You can use the VS.Net System.IO classes for this. The remote file listing can be obtained by using the ListDirectory or ListDirectoryLong methods of the FTP component. The difference is that the ListDirectory method will only return the filenames of the remote directory. The ListDirectoryLong method returns the filename, size, modification date, etc. The results from the methods will be returned in the DirList event. You'll need to overwrite this event in order to retrieve the results.
We’ll use a listbox and combo box for both the client and server side to hold the file listings and the working directory. The RemotePath and RemoteFile properties are very important to the ListDirectory method (and any other FTP method that handles files). The directory listing will be performed on the remote path that is contained in the RemotePath property, and with the filemask contained in RemoteFile. If RemoteFile is empty, all files will be returned.
After the Logon method, the RemotePath will automatically be updated with the home directory of the user, ie generally “/home/username”. But you must be very careful to keep up with what the RemotePath is during your connection.
FTP1.RemotePath = “/home/username”
FTP1.RemoteFile = “”
FTP1.ListDirectory()
These three simple lines will retrieve a directory listing of all files in the remote path /home/username. We’ll grab this data from the DirList event and insert it into the remote file listbox called lstRemote. The DirList event will fire one time for each file on the server that matches the filemask for the directory list request.
Private Sub Ftp1_OnDirList(ByVal sender As System.Object, ByVal e As nsoftware.IPWorks.FtpDirListEventArgs) Handles Ftp1.OnDirList
If e.IsDir Then
lstRemote.Items.Add( "<Dir> " & e.FileName)
Else
lstRemote.Items.Add(e.FileName)
End If
End Sub
Here, the parameter DirEntry contains the exact directory entry response from the server, exactly as the server sent it, ie:
-rw-r--r-- 1 group username 4557 Aug 29 2001 .Xdefaults
FileName is a string parameter containing the name of the file itself, ie .Xdefaults.
IsDir is a Boolean value. IsDir will be true if this particular DirEntry is a directory.
FileSize is a long containing the size of the file on the remote server.
FileTime is a string containing the last modified date of the file on the server.
File Transfers: Upload and Download
Now we’ll add Upload and Download capabilities. To do this, we’ll need to set the RemotePath, RemoteFile, LocalPath, and LocalFile properties before attempting a transfer. We’ll use our two listboxes and comboboxes to determine that information.
The value in our client combobox cbClient is “C:/”. The selected item in our client listbox lstClient is “test.txt”. So we’ll set:
FTP1.LocalPath = cbClient.Items(cbClient.SelectedIndex)
FTP1.LocalFile = lstClient.Items(lstClient.Selectedindex)
This will point the FTP component to the local file we want to upload. Now we’ll name the file the same thing on the client side, and we’ll keep track of the remote path in the server combobox, cbServer, ie:
FTP1.RemotePath = cbServer.Items(cbServer.SelectedIndex)
FTP1.RemoteFile = lstClient.Items(lstClient.SelectedIndex)
And now perform the upload:
FTP1.Upload()
Other Methods
For other miscellaneous functions of the FTP component, there are many useful methods:
Append, much like Upload, except if the remote file already exists, the file is appended to rather than overwritten. DeleteFile, attempts to delete the remote file from the server. Logoff, log off the server. MakeDirectory, create the directory specified by RemoteFile on the server. RemoveDirectory, remove the directory specified by RemoteFile on the server. This will not remove files within the directory automatically, that would have to be done using DeleteFile before removing the directory. RenameFile, renames the file specified in RemoteFile to the value specified in the AltValue property. StoreUnique - much like Upload, except that the remote server decides the remote file name itself such that the file name is a unique one. The file name that the server writes to will be sent to the client. You can determine that filename by examining the LastReply property, which always contains the last reply from the server.
Percent Transferred
OK, so now we are transferring files. How do I know the status of the file transfer? First of all, when the transfer is first begun, a StartTransfer event will fire. During the transfer, a Transfer event will fire, and after the transfer is finished, an EndTransfer event will fire. You can use the BytesTransferred property that is available in the Transfer event of the FTP component to keep track of how many bytes have been transferred so far in the current transfer. This information will allow you to create a progress bar. In order to do the math, you will of course need to know the file size. If you are uploading a file to the server, you already know the file size since its local (Use a File system object). If you are downloading a remote file from the server, you’ll need to ask the server how large the file is before initiating the download, by setting the RemoteFile property to the appropriate file and issuing a ListDirectoryLong. Then the DirList event will be fired once for the file you have specified and you can get the filesize parameter of the DirList event.
Debugging
The most powerful debugging tool of the FTP component is the PITrail event. The PITrail event shows you all of the communication that is happening between the client and the server.
Private Sub Ftp1_OnPITrail(ByVal sender As System.Object, ByVal e As nsoftware.IPWorks.FtpPITrailEventArgs) Handles Ftp1.OnPITrail
txtPITrail.AppendText(e.Direction & ": " & e.Message & VbCrLf)
End Sub
The Direction parameter of the event tells you in what direction the message is traveling, from the client to the server or server to the client. If the value of Direction is 0, the Message is being sent by the client. If the value of Direction is 1, the Message is being sent by the server.
For the full source of this fully implemented FTP Client, download an IP*Works! trial Edition from www.nsoftware.com/download.asp.
More Information
For more information about IP*Works! or the FTP component, please visit www.nsoftware.com. There you will find access to our online Knowledge Base, access to free email technical support, and much more valuable information. Included in each edition of IP*Works! are many demo applications that show the power and flexibility of the toolkit. If you need more specific guidance, please feel free to email our technical support department via the online support form at www.nsoftware.com/support/request.asp.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
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