Ftplet

Overview

The Ftplet API is a simple API used to handle different FtpServer notifications. Apache FtpServer is a Ftplet container, allowing administrators to deploy Ftplet to carry out a variety of complex FTP event handler tasks.

Implementing a custom Ftplet is generally a simple task, most of whose complexity lies in coding the actual work to be done by the Ftplet. This is largely due to the simplicity of the Ftplet interface and the fact that a DefaultFtplet class is provided as part of the Ftplet package.

The Ftplet interface supports two lifecycle methods to provide initialization (the init() method) and shutdown (the destroy() method). Main processing is done in different notification methods, which take a FtpSession object and a FtpRequest object. All the notification methods return FtpletResult object to indicate the future action.

There will be one instance of Ftplet object. Notification methods will be called from different connections running in different threads. So Ftplet implementation has to be thread-safe. Each connection will have its own request (FtpRequest) and session (FtpSession) objects.

Main Classes

FtpletResult

This class encapsulates the return values of the ftplet methods. There are four static FtpletResult values.

  • DEFAULT : This return value indicates that the next ftplet method will be called. If no other ftplet is available, the FtpServer will process the request.
  • NO_FTPLET : This return value indicates that the other ftplet methods will not be called but the FtpServer will continue processing this request.
  • SKIP : It indicates that the server will skip everything. No further processing will be done for this request.
  • DISCONNECT : It indicates that the server will skip and disconnect the client. No other request from the same client will be served.

So, DEFAULT < NO_FTPLET < SKIP > DISCONNECT. If the Ftplet returns null, DEFAULT is assumed.

FtpSession

The session object is kept for the entire user session. So the attributes set by setAttribute() will be always available later unless that attribute is removed. Different session will have different FtpSession objects. From here we can get user information, data streams, user file system view etc.

Ftplets can use this to send custom codes and messages to client.

FtpRequest

Provides the client request information to a ftplet. Contains the FTP command and argument.

Ftplet

There will be only one instance of Ftplet. During startup the Ftplets will be initialized. The initialization sequence is same as the Ftplet sequence in the configuration. Then all notification methods will be called and when the FtpServer goes down, the Ftplet will be destroyed. The following method describes all the notification methods.

Method Description
onConnect Client connect notification method. This is the first method FtpServer will call. If it returns SKIP, IP restriction check, connection limit check will not be performed and the server will not send the welcome message (220).
onDisconnect Client disconnect notification method. This is the last method FtpServer will call. Whatever it returns, the client connection will be closed.
beforeCommand Called before the server invoke the command.
afterCommand Called after the server as invoked the command.

DefaultFtplet

DefaultFtplet provides some convenience methods for common FTP commands. Users can easily extend the DefaultFtplet class and choose what methods to override and handle.

Method Description
onLogin Client login notification method. This will be called after the user authentication. In this case the FtpServer has already sent the login OK (230) reply. This is called during FTP PASS request. The FTP session will be disconnected in the return value is FtpletResult.DISCONNECT.
onDeleteStart Before file deletion this method will be called. Before this FtpServer will not check anything like file existence or permission. The requested file name can be get from request argument. We can get the file object from the request file system view. This is called in DELE FTP command. The method should send some responses (like 250, 450, 550) in case of SKIP return value. In this case, the server will skip the command processing and the ftplet has to send appropriate response values.
onDeleteEnd This method will be called after the file deletion, successful or not. In this case the FtpServer has already sent the reply message. This is called in DELE FTP command.
onUploadStart This method will be called before the file upload. The file name can be get from the request argument. We can get the data input stream from request. This will be called before the permission check. This is called during STOR command. If the method returns SKIP, it has to send responses before and after processing. For example, before opening the data input stream, the method has to notify the client with a response code 150. Similarly, after the data transfer, the method has to notify the client with a response code 226. In case of any error, the method should send different response codes like 450, 425, 426, 551.
onUploadEnd This notification method will be called to indicate that the file transfer is successful and the server has send the replies. In case of any error this method will not be called. This is called in STOR command.
onDownloadStart This is file download request notification method called during RETR command. This will be called before the file download. We can get the file name argument from request. Similarly, the data output stream can be get from the request. This will be called before the file existence and permission check. If the method returns SKIP, it has to send responses before and after processing. For example, before opening the data output stream, the method has to notify the client with a response code 150. Similarly, after the data transfer, the method has to notify the client with a response code 226. In case of any error, the method should send different response codes like 450, 425, 426, 551.
onDownloadEnd This notification method will be called to indicate that the file transfer is successful and the server has send the replies in RETR command.
onRmdirStart Before directory deletion this method will be called during RMD command. Before this FtpServer will not check anything like directory existence or permission. The requested directory name can be get from request argument. If the method returns the SKIP, it has to send appropriate response codes to clients like 250, 450, 550.
onRmdirEnd This method will be called after the invocation of the RMD command. In this case the FtpServer has already sent the reply message.
onMkdirStart Before directory creation this method will be called during MKD command. Before this FtpServer will not check anything like directory existence or permission. The requested directory name can be get from request argument. If it returns SKIP, it has to send appropriate response codes to clients like 250, 550.
onMkdirEnd This method will be called if the directory creation is successful in MKD command. In this case the FtpServer has already sent the reply message.
onAppendStart This is file append request notification method called in APPE command. The file name can be get from the request argument. We can get the data input stream from request. This will be called before the permission check. If the method returns SKIP, it has to send responses before and after processing. For example, before opening the data input stream, the method has to notify the client with a response code 150. Similarly, after the data transfer, the method has to notify the client with a response code 226. In case of any error, the method should send different response codes like 450, 425, 426, 551.
onAppendEnd This is file append success notification method called in APPE command.
onUploadUniqueStart This is unique file create request notification method called in STOU command. We can get the data input stream from request. This will be called before the permission check. If the method returns SKIP, it has to send responses before and after processing. For example, before opening the data input stream, the method has to notify the client with a response code 150. Similarly, after the data transfer, the method has to notify the client with a response code 226. In case of any error, the method should send different response codes like 450, 425, 426, 551.
onUploadUniqueEnd This is unique file create success notification method called in STOU command. This notification method will be called to indicate the the server has send the replies.
onRenameStart This is file rename start notification method called in RNTO command. This will be called before the file existence or permission check. The “rename from” file object can be get from request object. If it returns SKIP, it has to send appropriate response codes like 503, 553, 250.
onRenameEnd This is file rename success notification method called in RNFR command. This will be called before the file existence or permission check. The “rename from” file object an be get from request object. This notification method will be called after the invocation of the RNTO command and the server has send the reply message.
onSite This is SITE command start notification method. It gives a chance to implement custom SITE command. If this method returns SKIP or DISCONNECT, the existing SITE commands will not be executed.

Response Codes

This section gives an overview on different response codes which might be useful in developing custom ftplet. These commands might be used when the ftplet method return value is SKIP.

Method Response Code Description
onConnect 220 Service ready for new user.
onConnect 530 No server access from the IP.
onConnect 530 Maximum server connection has been reached.
onDisconnect    
onLogin    
onDeleteStart 250 Requested file action okay
onDeleteStart 450 No permission to delete.
onDeleteStart 550 Not a valid file.
onDeleteStart 450 Can’t delete file.
onDeleteEnd    
onUploadStart 150 File status okay; about to open data connection.
onUploadStart 226 Transfer complete.
onUploadStart 550 Invalid path.
onUploadStart 550 Permission denied.
onUploadStart 425 Can’t open data connection.
onUploadStart 426 Data connection error.
onUploadStart 551 Error on output file.
onUploadEnd    
onDownloadStart 150 File status okay; about to open data connection.
onDownloadStart 226 Transfer complete.
onDownloadStart 550 No such file or directory.
onDownloadStart 550 Not a plain file.
onDownloadStart 550 Permission denied.
onDownloadStart 425 Can’t open data connection.
onDownloadStart 426 Data connection error.
onDownloadStart 551 Error on input file.
onDownloadEnd    
onRmdirStart 250 Directory removed.
onRmdirStart 550 Not a valid directory.
onRmdirStart 550 Permission denied.
onRmdirStart 550 Can’t remove directory.
onRmdirEnd    
onMkdirStart 250 Directory created.
onMkdirStart 550 Not a valid file.
onMkdirStart 550 Permission denied
onMkdirStart 550 Directory already exists.
onMkdirStart 550 Can’t create directory.
onMkdirEnd    
onAppendStart 150 File status okay; about to open data connection.
onAppendStart 226 Transfer complete.
onAppendStart 550 Not a plain file.
onAppendStart 550 Permission denied.
onAppendStart 425 Can’t open data connection.
onAppendStart 426 Data connection error.
onAppendStart 551 Error on output file.
onAppendEnd    
onUploadUniqueStart 150 File status okay; about to open data connection.
onUploadUniqueStart 250 filename: Transfer started.
onUploadUniqueStart 226 filename: Transfer complete.
onUploadUniqueStart 550 Unique file name error.
onUploadUniqueStart 550 Permission denied.
onUploadUniqueStart 425 Can’t open data connection.
onUploadUniqueStart 426 Data connection error.
onUploadUniqueStart 551 Error on output file.
onUploadUniqueEnd    
onRenameStart 250 Requested file action okay, file renamed.
onRenameStart 503 Can’t find the file which has to be renamed.
onRenameStart 553 Not a valid file name.
onRenameStart 553 Permission denied.
onRenameStart 553 No such file or directory.
onRenameStart 553 Can’t rename file.
onRenameEnd    
onSite 200 Command SITE okay.
onSite 530 Permission denied.
onSite 502 Not implemented.
onSite 500 Execution failed.

Configuration

Ftplet will get the Ftplet specific configuration as the init() method argument.

Implementation

Ftplets are regular POJOs. If running the server as embedded they can be added to the FtpletContainer as normal instances of the object. If using the XML configuration, they are configured and Spring beans within the ftplets element. Here’s an example:

<ftplets>
    <ftplet name="ftplet1">
        <beans:bean class="org.apache.ftpserver.examples.MyFtplet">
            <beans:property name="foo" value="123" />
        </beans:bean>
    </ftplet>
</ftplets>

Deployment

The Ftplet must be added to Apache FtpServer classpath so that the Ftplet can be loaded. There are three ways you can do that.

  1. Modify your system CLASSPATH environment variable to include your ftplet classes.
  2. Copy your ftplet class files (unpacked) in the common/classes directory of the FtpServer installation.
  3. Place a jar file containing the custom ftplet class files in the common/lib subdirectory of the FtpServer installation.