Q3Ftp Class Reference
[Qt3Support module]

Detailed Description

The Q3Ftp class provides an implementation of the FTP protocol.

This class provides two different interfaces: one is the QNetworkProtocol interface that allows you to use FTP through the QUrlOperator abstraction. The other is a direct interface to FTP that gives you lower-level access to the FTP protocol for finer control. Using the direct interface you can also execute arbitrary FTP commands.

Don't mix the two interfaces, since the behavior is not well-defined.

If you want to use Q3Ftp with the QNetworkProtocol interface, you do not use it directly, but rather through a QUrlOperator, for example:

 QUrlOperator op( "ftp://ftp.qt.nokia.com" );
 op.listChildren(); // Asks the server to provide a directory listing

This code will only work if the Q3Ftp class is registered; to register the class, you must call q3InitNetworkProtocols() before using a QUrlOperator with Q3Ftp.

The rest of this descrption describes the direct interface to FTP.

The class works asynchronously, so there are no blocking functions. If an operation cannot be executed immediately, the function will still return straight away and the operation will be scheduled for later execution. The results of scheduled operations are reported via signals. This approach depends on the event loop being in operation.

The operations that can be scheduled (they are called "commands" in the rest of the documentation) are the following: connectToHost(), login(), close(), list(), cd(), get(), put(), remove(), mkdir(), rmdir(), rename() and rawCommand().

All of these commands return a unique identifier that allows you to keep track of the command that is currently being executed. When the execution of a command starts, the commandStarted() signal with the command's identifier is emitted. When the command is finished, the commandFinished() signal is emitted with the command's identifier and a bool that indicates whether the command finished with an error.

In some cases, you might want to execute a sequence of commands, e.g. if you want to connect and login to a FTP server. This is simply achieved:

 Q3Ftp *ftp = new Q3Ftp( this ); // this is an optional QObject parent
 ftp->connectToHost( "ftp.qt.nokia.com" );
 ftp->login();

In this case two FTP commands have been scheduled. When the last scheduled command has finished, a done() signal is emitted with a bool argument that tells you whether the sequence finished with an error.

If an error occurs during the execution of one of the commands in a sequence of commands, all the pending commands (i.e. scheduled, but not yet executed commands) are cleared and no signals are emitted for them.

Some commands, e.g. list(), emit additional signals to report their results.

Example: If you want to download the INSTALL file from the Qt FTP server, you would write this:

 ftp->connectToHost( "ftp.qt.nokia.com" );   // id == 1
 ftp->login();                               // id == 2
 ftp->cd( "qt" );                            // id == 3
 ftp->get( "INSTALL" );                      // id == 4
 ftp->close();                               // id == 5

For this example the following sequence of signals is emitted (with small variations, depending on network traffic, etc.):

 start( 1 )
 stateChanged( HostLookup )
 stateChanged( Connecting )
 stateChanged( Connected )
 finished( 1, false )

 start( 2 )
 stateChanged( LoggedIn )
 finished( 2, false )

 start( 3 )
 finished( 3, false )

 start( 4 )
 dataTransferProgress( 0, 3798 )
 dataTransferProgress( 2896, 3798 )
 readyRead()
 dataTransferProgress( 3798, 3798 )
 readyRead()
 finished( 4, false )

 start( 5 )
 stateChanged( Closing )
 stateChanged( Unconnected )
 finished( 5, false )

 done( false )

The dataTransferProgress() signal in the above example is useful if you want to show a progress bar to inform the user about the progress of the download. The readyRead() signal tells you that there is data ready to be read. The amount of data can be queried then with the bytesAvailable() function and it can be read with the readBlock() or readAll() function.

If the login fails for the above example, the signals would look like this:

 start( 1 )
 stateChanged( HostLookup )
 stateChanged( Connecting )
 stateChanged( Connected )
 finished( 1, false )

 start( 2 )
 finished( 2, true )

 done( true )

You can then get details about the error with the error() and errorString() functions.

The functions currentId() and currentCommand() provide more information about the currently executing command.

The functions hasPendingCommands() and clearPendingCommands() allow you to query and clear the list of pending commands.

The safest and easiest way to use the FTP protocol is to use QUrlOperator() or the FTP commands described above. If you are an experienced network programmer and want to have complete control you can use rawCommand() to execute arbitrary FTP commands.

See also Q3NetworkProtocol, Q3UrlOperator, and Q3Http.

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