QFtp Class Reference
^{[QtNetwork module]}

Detailed Description

The QFtp class provides an implementation of the client side of FTP protocol.

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:

 QFtp *ftp = new QFtp(parent);
 ftp->connectToHost("ftp.trolltech.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 Trolltech's FTP server, you would write this:

 ftp->connectToHost("ftp.trolltech.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 read() 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.

For file transfer, QFtp can use both active or passive mode, and it uses passive file transfer mode by default; see the documentation for setTransferMode() for more details about this.

Call setProxy() to make QFtp connect via an FTP proxy server.

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.

If you are an experienced network programmer and want to have complete control you can use rawCommand() to execute arbitrary FTP commands.

Warning: The current version of QFtp doesn't fully support non-Unix FTP servers. We hope to fix this in a future version of Qt.

See also QHttp and FTP Example.

Member Type Documentation

enum QFtp::Command

This enum is used as the return value for the currentCommand() function. This allows you to perform specific actions for particular commands, e.g. in a FTP client, you might want to clear the directory view when a list() command is started; in this case you can simply check in the slot connected to the start() signal if the currentCommand() is List.

See also currentCommand().

enum QFtp::Error

This enum identifies the error that occurred.

See also error().

enum QFtp::State

This enum defines the connection state:

See also stateChanged() and state().

enum QFtp::TransferMode

FTP works with two socket connections; one for commands and another for transmitting data. While the command connection is always initiated by the client, the second connection can be initiated by either the client or the server.

This enum defines whether the client (Passive mode) or the server (Active mode) should set up the data connection.

enum QFtp::TransferType

This enum identifies the data transfer type used with get and put commands.

Member Function Documentation

QFtp::QFtp ( QObject * parent = 0 )

Constructs a QFtp object with the given parent.

QFtp::~QFtp ()   [virtual]

Destructor.

void QFtp::abort ()   [slot]

Aborts the current command and deletes all scheduled commands.

If there is an unfinished command (i.e. a command for which the commandStarted() signal has been emitted, but for which the commandFinished() signal has not been emitted), this function sends an ABORT command to the server. When the server replies that the command is aborted, the commandFinished() signal with the error argument set to true is emitted for the command. Due to timing issues, it is possible that the command had already finished before the abort request reached the server, in which case, the commandFinished() signal is emitted with the error argument set to false.

For all other commands that are affected by the abort(), no signals are emitted.

If you don't start further FTP commands directly after the abort(), there won't be any scheduled commands and the done() signal is emitted.

Warning: Some FTP servers, for example the BSD FTP daemon (version 0.3), wrongly return a positive reply even when an abort has occurred. For these servers the commandFinished() signal has its error flag set to false, even though the command did not complete successfully.

See also clearPendingCommands().

qint64 QFtp::bytesAvailable () const

Returns the number of bytes that can be read from the data socket at the moment.

See also get(), readyRead(), read(), and readAll().

int QFtp::cd ( const QString & dir )

Changes the working directory of the server to dir.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

void QFtp::clearPendingCommands ()

Deletes all pending commands from the list of scheduled commands. This does not affect the command that is being executed. If you want to stop this this as well, use abort().

See also hasPendingCommands() and abort().

int QFtp::close ()

Closes the connection to the FTP server.

The stateChanged() signal is emitted when the state of the connecting process changes, e.g. to Closing, then Unconnected.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also stateChanged(), commandStarted(), and commandFinished().

void QFtp::commandFinished ( int id, bool error )   [signal]

This signal is emitted when processing the command identified by id has finished. error is true if an error occurred during the processing; otherwise error is false.

See also commandStarted(), done(), error(), and errorString().

void QFtp::commandStarted ( int id )   [signal]

This signal is emitted when processing the command identified by id starts.

See also commandFinished() and done().

int QFtp::connectToHost ( const QString & host, quint16 port = 21 )

Connects to the FTP server host using port port.

The stateChanged() signal is emitted when the state of the connecting process changes, e.g. to HostLookup, then Connecting, then Connected.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also stateChanged(), commandStarted(), and commandFinished().

Command QFtp::currentCommand () const

Returns the command type of the FTP command being executed or None if there is no command being executed.

See also currentId().

QIODevice * QFtp::currentDevice () const

Returns the QIODevice pointer that is used by the FTP command to read data from or store data to. If there is no current FTP command being executed or if the command does not use an IO device, this function returns 0.

This function can be used to delete the QIODevice in the slot connected to the commandFinished() signal.

See also get() and put().

int QFtp::currentId () const

Returns the identifier of the FTP command that is being executed or 0 if there is no command being executed.

See also currentCommand().

void QFtp::dataTransferProgress ( qint64 done, qint64 total )   [signal]

This signal is emitted in response to a get() or put() request to indicate the current progress of the download or upload.

done is the amount of data that has already been transferred and total is the total amount of data to be read or written. It is possible that the QFtp class is not able to determine the total amount of data that should be transferred, in which case total is 0. (If you connect this signal to a QProgressBar, the progress bar shows a busy indicator if the total is 0).

Warning: done and total are not necessarily the size in bytes, since for large files these values might need to be "scaled" to avoid overflow.

See also get(), put(), and QProgressBar.

void QFtp::done ( bool error )   [signal]

This signal is emitted when the last pending command has finished; (it is emitted after the last command's commandFinished() signal). error is true if an error occurred during the processing; otherwise error is false.

See also commandFinished(), error(), and errorString().

Error QFtp::error () const

Returns the last error that occurred. This is useful to find out what went wrong when receiving a commandFinished() or a done() signal with the error argument set to true.

If you start a new command, the error status is reset to NoError.

QString QFtp::errorString () const

Returns a human-readable description of the last error that occurred. This is useful for presenting a error message to the user when receiving a commandFinished() or a done() signal with the error argument set to true.

The error string is often (but not always) the reply from the server, so it is not always possible to translate the string. If the message comes from Qt, the string has already passed through tr().

int QFtp::get ( const QString & file, QIODevice * dev = 0, TransferType type = Binary )

Downloads the file file from the server.

If dev is 0, then the readyRead() signal is emitted when there is data available to read. You can then read the data with the read() or readAll() functions.

If dev is not 0, the data is written directly to the device dev. Make sure that the dev pointer is valid for the duration of the operation (it is safe to delete it when the commandFinished() signal is emitted). In this case the readyRead() signal is not emitted and you cannot read data with the read() or readAll() functions.

If you don't read the data immediately it becomes available, i.e. when the readyRead() signal is emitted, it is still available until the next command is started.

For example, if you want to present the data to the user as soon as there is something available, connect to the readyRead() signal and read the data immediately. On the other hand, if you only want to work with the complete data, you can connect to the commandFinished() signal and read the data when the get() command is finished.

The data is transferred as Binary or Ascii depending on the value of type.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

commandFinished()

See also readyRead(), dataTransferProgress(), and commandStarted().

bool QFtp::hasPendingCommands () const

Returns true if there are any commands scheduled that have not yet been executed; otherwise returns false.

The command that is being executed is not considered as a scheduled command.

See also clearPendingCommands(), currentId(), and currentCommand().

int QFtp::list ( const QString & dir = QString() )

Lists the contents of directory dir on the FTP server. If dir is empty, it lists the contents of the current directory.

The listInfo() signal is emitted for each directory entry found.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also listInfo(), commandStarted(), and commandFinished().

void QFtp::listInfo ( const QUrlInfo & i )   [signal]

This signal is emitted for each directory entry the list() command finds. The details of the entry are stored in i.

See also list().

int QFtp::login ( const QString & user = QString(), const QString & password = QString() )

Logs in to the FTP server with the username user and the password password.

The stateChanged() signal is emitted when the state of the connecting process changes, e.g. to LoggedIn.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

int QFtp::mkdir ( const QString & dir )

Creates a directory called dir on the server.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

int QFtp::put ( QIODevice * dev, const QString & file, TransferType type = Binary )

Reads the data from the IO device dev, and writes it to the file called file on the server. The data is read in chunks from the IO device, so this overload allows you to transmit large amounts of data without the need to read all the data into memory at once.

The data is transferred as Binary or Ascii depending on the value of type.

Make sure that the dev pointer is valid for the duration of the operation (it is safe to delete it when the commandFinished() is emitted).

int QFtp::put ( const QByteArray & data, const QString & file, TransferType type = Binary )

This is an overloaded member function, provided for convenience.

Writes a copy of the given data to the file called file on the server. The progress of the upload is reported by the dataTransferProgress() signal.

The data is transferred as Binary or Ascii depending on the value of type.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

Since this function takes a copy of the data, you can discard your own copy when this function returns.

See also dataTransferProgress(), commandStarted(), and commandFinished().

int QFtp::rawCommand ( const QString & command )

Sends the raw FTP command command to the FTP server. This is useful for low-level FTP access. If the operation you wish to perform has an equivalent QFtp function, we recommend using the function instead of raw FTP commands since the functions are easier and safer.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also rawCommandReply(), commandStarted(), and commandFinished().

void QFtp::rawCommandReply ( int replyCode, const QString & detail )   [signal]

This signal is emitted in response to the rawCommand() function. replyCode is the 3 digit reply code and detail is the text that follows the reply code.

See also rawCommand().

qint64 QFtp::read ( char * data, qint64 maxlen )

Reads maxlen bytes from the data socket into data and returns the number of bytes read. Returns -1 if an error occurred.

See also get(), readyRead(), bytesAvailable(), and readAll().

QByteArray QFtp::readAll ()

Reads all the bytes available from the data socket and returns them.

See also get(), readyRead(), bytesAvailable(), and read().

void QFtp::readyRead ()   [signal]

This signal is emitted in response to a get() command when there is new data to read.

If you specify a device as the second argument in the get() command, this signal is not emitted; instead the data is written directly to the device.

You can read the data with the readAll() or read() functions.

This signal is useful if you want to process the data in chunks as soon as it becomes available. If you are only interested in the complete data, just connect to the commandFinished() signal and read the data then instead.

See also get(), read(), readAll(), and bytesAvailable().

int QFtp::remove ( const QString & file )

Deletes the file called file from the server.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

int QFtp::rename ( const QString & oldname, const QString & newname )

Renames the file called oldname to newname on the server.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

int QFtp::rmdir ( const QString & dir )

Removes the directory called dir from the server.

The function does not block and returns immediately. The command is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by commandStarted() and commandFinished().

When the command is started the commandStarted() signal is emitted. When it is finished the commandFinished() signal is emitted.

See also commandStarted() and commandFinished().

int QFtp::setProxy ( const QString & host, quint16 port )

Enables use of the FTP proxy on host host and port port. Calling this function with host empty disables proxying.

QFtp does not support FTP-over-HTTP proxy servers. Use QHttp for this.

int QFtp::setTransferMode ( TransferMode mode )

Sets the current FTP transfer mode to mode. The default is QFtp::Passive.

See also QFtp::TransferMode.

State QFtp::state () const

Returns the current state of the object. When the state changes, the stateChanged() signal is emitted.

See also State and stateChanged().

void QFtp::stateChanged ( int state )   [signal]

This signal is emitted when the state of the connection changes. The argument state is the new state of the connection; it is one of the State values.

It is usually emitted in response to a connectToHost() or close() command, but it can also be emitted "spontaneously", e.g. when the server closes the connection unexpectedly.

See also connectToHost(), close(), state(), and State.