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diff --git a/doc/network.doc b/doc/network.doc new file mode 100644 index 0000000..f6b986d --- /dev/null +++ b/doc/network.doc @@ -0,0 +1,522 @@ +/**************************************************************************** +** +** Documentation for network programming +** +** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved. +** +** This file is part of the Qt GUI Toolkit. +** +** This file may be used under the terms of the GNU General +** Public License versions 2.0 or 3.0 as published by the Free +** Software Foundation and appearing in the files LICENSE.GPL2 +** and LICENSE.GPL3 included in the packaging of this file. +** Alternatively you may (at your option) use any later version +** of the GNU General Public License if such license has been +** publicly approved by Trolltech ASA (or its successors, if any) +** and the KDE Free Qt Foundation. +** +** Please review the following information to ensure GNU General +** Public Licensing requirements will be met: +** http://trolltech.com/products/qt/licenses/licensing/opensource/. +** If you are unsure which license is appropriate for your use, please +** review the following information: +** http://trolltech.com/products/qt/licenses/licensing/licensingoverview +** or contact the sales department at sales@trolltech.com. +** +** This file may be used under the terms of the Q Public License as +** defined by Trolltech ASA and appearing in the file LICENSE.QPL +** included in the packaging of this file. Licensees holding valid Qt +** Commercial licenses may use this file in accordance with the Qt +** Commercial License Agreement provided with the Software. +** +** This file is provided "AS IS" with NO WARRANTY OF ANY KIND, +** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR +** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted +** herein. +** +**********************************************************************/ + +/* + The text here is due to be replaced by networking.doc, once that's + ready. +*/ + +/*! +\page network.html + +\title Network Module + +\if defined(commercial) +This module is part of the \link commercialeditions.html Qt Enterprise Edition \endlink. +\endif + +\tableofcontents + + +\section1 Introduction + +The network module offers classes to make network programming easier +and portable. Essentially, there are three sets of classes, first low +level classes like \l QSocket, \l QServerSocket, \l QDns, etc. which +allow you to work in a portable way with TCP/IP sockets. In addition, +there are classes like \l QNetworkProtocol, \l QNetworkOperation in +the Qt base library, which provide an abstract layer for implementing +network protocols and \c QUrlOperator which operates on such network +protocols. Finally the third set of network classes are the passive +ones, specifically \c QUrl and \c QUrlInfo which do URL parsing and +similar. + +The first set of classes (\l QSocket, \l QServerSocket, \l QDns, \l +QFtp, etc.) are included in Qt's "network" module. + +The QSocket classes are not directly related to the QNetwork classes, +but QSocket should and will be used for implementing network +protocols, which are directly related to the QNetwork classes. For +example, the QFtp class (which implements the FTP protocol) uses +QSockets. But QSockets don't need to be used for protocol +implementations, e.g. QLocalFs (which is an implementation of the +local filesystem as network protocol) uses QDir and doesn't use +QSocket. Using QNetworkProtocols you can implement everything which +fits into a hierarchical structure and can be accessed using URLs. +This could be, for example, a protocol which can read pictures from a +digital camera using a serial connection. + + +\section1 Working Network Protocol independently with QUrlOperator and QNetworkOperation + +It is quite easy to just use existing network protocol implementations +and operate on URLs. For example, downloading a file from an FTP +server to the local filesystem can be done with following code: + +\code + QUrlOperator op; + op.copy( "ftp://ftp.trolltech.com/qt/source/qt-2.1.0.tar.gz", "file:/tmp", FALSE ); +\endcode + +And that's all! Of course an implementation of the FTP protocol has to +be available and registered for doing that. More information on that +later. + +You can also do things like creating directories, removing files, +renaming, etc. For example, to create a folder on a private FTP +account do + +\code + QUrlOperator op( "ftp://username:password@host.domain.no/home/username" ); + op.mkdir( "New Directory" ); +\endcode + +To see all available operations, look at the \c QUrlOperator class +documentation. + +Since networking works asynchronously, the function call for an +operation will normally return before the operation has been +completed. This means that the function cannot return a value +indicating failure or success. Instead, the return value always is a +pointer to a \c QNetworkOperation, and this object stores +all the information about the operation. + +For example, \c QNetworkOperation has a method which returns the state +of this operation. Using this you can find out the state of the +operation at any time. The object also makes available the arguments +you passed to the \c QUrlOperator method, the type of the operation +and some more information. For more details see the class +documentation of \c QNetworkOperation. + +The \c QUrlOperator emits signals to inform you about the progress of +the operations. As you can call many methods which operate on a \c +QUrlOperator's URL, it queues up all the operations. So you can't know +which operation the \c QUrlOperator just processed. Clearly you will +want to know which operation just took place, so each signal's last +argument is a pointer to the \c QNetworkOperation object which was +just processed and which caused the signal to be emitted. + +Some of these operations send a \c start() signal at the beginning (if +this makes sense), and some of them send some signals during +processing. All operations send a \c finished() signal after they are +done. To find that out if an operation finished successfully you can +use the \c QNetworkOperation pointer you got with the \c finished() +signal. If \c QNetworkOperation::state() equals \c +QNetworkProtocol::StDone the operation finished successfully, if it is +\c QNetworkProtocol::StFailed the operation failed. + +Example: A slot which you might connect to the +\c{QUrlOperator::finished( QNetworkOperation * )} +\code +void MyClass::slotOperationFinished( QNetworkOperation *op ) +{ + switch ( op->operation() ) { + case QNetworkProtocol::OpMkDir: + if ( op->state() == QNetworkProtocol::StFailed ) + qDebug( "Couldn't create directory %s", op->arg( 0 ).latin1() ); + else + qDebug( "Successfully created directory %s", op->arg( 0 ).latin1() ); + break; + // ... and so on + } +} +\endcode + +As mentioned earlier, some operations send other signals too. Let's +take the list children operation as an example (e.g. read a directory +on a FTP server): + +\code +QUrlOperator op; + +MyClass::MyClass() : QObject(), op( "ftp://ftp.trolltech.com" ) +{ + connect( &op, SIGNAL( newChildren( const QValueList<QUrlInfo> &, QNetworkOperation * ) ), + this, SLOT( slotInsertEntries( const QValueList<QUrlInfo> &, QNetworkOperation * ) ) ); + connect( &op, SIGNAL( start( QNetworkOperation * ) ), + this, SLOT( slotStart( QNetworkOperation *) ) ); + connect( &op, SIGNAL( finished( QNetworkOperation * ) ), + this, SLOT( slotFinished( QNetworkOperation *) ) ); +} + +void MyClass::slotInsertEntries( const QValueList<QUrlInfo> &info, QNetworkOperation * ) +{ + QValueList<QUrlInfo>::ConstIterator it = info.begin(); + for ( ; it != info.end(); ++it ) { + const QUrlInfo &inf = *it; + qDebug( "Name: %s, Size: %d, Last Modified: %s", + inf.name().latin1(), inf.size(), inf.lastModified().toString().latin1() ); + } +} + +void MyClass::slotStart( QNetworkOperation * ) +{ + qDebug( "Start reading '%s'", op.toString().latin1() ); +} + +void MyClass::slotFinished( QNetworkOperation *operation ) +{ + if ( operation->operation() == QNetworkProtocol::OpListChildren ) { + if ( operation->state() == QNetworkProtocol::StFailed ) + qDebug( "Couldn't read '%s'! Following error occurred: %s", + op.toString().latin1(), operation->protocolDetail().latin1() ); + else + qDebug( "Finished reading '%s'!", op.toString().latin1() ); + } +} + +\endcode + +These examples demonstrate now how to use the \c QUrlOperator and \c +QNetworkOperations. The network extension also contains useful example +code. + + +\section2 Implementing your own Network Protocol + +\c QNetworkProtocol provides a base class for implementations +of network protocols and an architecture for the a dynamic +registration and de-registration of network protocols. If you use this +architecture you don't need to care about asynchronous programming, as +the architecture hides this and does all the work for you. + +\e{Note} It is difficult to design a base class for network protocols +which is useful for all network protocols. The architecture described +here is designed to work with all kinds of hierarchical structures, +like filesystems. So everything which can be interpreted as +hierarchical structure and accessed via URLs, can be implemented as +network protocol and easily used in Qt. This is not limited to +filesystems only! + +To implement a network protocol create a class derived from +\c QNetworkProtocol. + +Other classes will use this network protocol implementation +to operate on it. So you should reimplement following protected members + +\code + void QNetworkProtocol::operationListChildren( QNetworkOperation *op ); + void QNetworkProtocol::operationMkDir( QNetworkOperation *op ); + void QNetworkProtocol::operationRemove( QNetworkOperation *op ); + void QNetworkProtocol::operationRename( QNetworkOperation *op ); + void QNetworkProtocol::operationGet( QNetworkOperation *op ); + void QNetworkProtocol::operationPut( QNetworkOperation *op ); +\endcode + +Some notes on reimplementing these methods: You always get a pointer +to a \c QNetworkOperation as argument. This pointer holds all the +information about the operation in the current state. If you start +processing such an operation, set the state to \c +QNetworkProtocol::StInProgress. If you finished processing the +operation, set the state to \c QNetworkProtocol::StDone if it was +successful or \c QNetworkProtocol::StFailed if an error occurred. If +an error occurred you must set an error code (see +\c{QNetworkOperation::setErrorCode()}) and if you know some details +(e.g. an error message) you can also set this message to the operation +pointer (see \c{QNetworkOperation::setProtocolDetail()}). Also you get +all the relevant information (type, arguments, etc.) about the +operation from the \c QNetworkOperation pointer. For details about +which arguments you can get and set look at \c{QNetworkOperation}'s +class documentation. + +If you reimplement an operation function, it's very important to emit +the correct signals at the correct time: In general always emit \c +finished() at the end of an operation (when you either successfully +finished processing the operation or an error occurred) with the +network operation as argument. The whole network architecture relies +on correctly emitted \c finished() signals! Then there are some more +specialized signals which are specific to operations: +\list + \i Emit in \c operationListChildren: + \list + \i \c start() just before starting to list the children + \i \c newChildren() when new children are read + \endlist + \i Emit in \c operationMkDir: + \list + \i \c createdDirectory() after the directory has been created + \i \c newChild() (or newChildren()) after the directory has been + created (since a new directory is a new child) + \endlist + \i Emit in \c operationRemove: + \list + \i \c removed() after a child has been removed + \endlist + \i Emit in \c operationRename: + \list + \i \c itemChanged() after a child has been renamed + \endlist + \i Emit in \c operationGet: + \list + \i \c data() each time new data has been read + \i \c dataTransferProgress() each time new data has been read to + indicate how much of the data has been read now. + \endlist + \i Emit in \c operationPut: + \list + \i \c dataTransferProgress() each time data has been written to + indicate how much of the data has been written. Although you + know the whole data when this operation is called, it's + suggested not to write the whole data at once, but to do it + step by step to avoid blocking the GUI. Doing things + incrementally also means that progress can be made visible + to the user. + \endlist +\endlist + +And remember, always emit the \c finished() signal at the end! + +For more details about these signals' arguments look at the \c +QNetworkProtocol class documentation. + +Here is a list of which \c QNetworkOperation arguments you can get and +which you must set in which function: + +(To get the URL on which you should work, use the \c +QNetworkProtocol::url() method which returns a pointer to the URL +operator. Using that you can get the path, host, name filter, etc.) + +\list + \i In \c operationListChildren: + \list + \i Nothing. + \endlist + \i In \c operationMkDir: + \list + \i \c QNetworkOperation::arg( 0 ) contains the name of the directory which should be created + \endlist + \i In \c operationRemove: + \list + \i \c QNetworkOperation::arg( 0 ) contains the name of the file + which should be removed. Normally this is a relative name. But + it could be absolute. Use QUrl( op->arg( 0 ) ).fileName() + to get the filename. + \endlist + \i In \c operationRename: + \list + \i \c QNetworkOperation::arg( 0 ) contains the name of the file + which should be renamed + \i \c QNetworkOperation::arg( 1 ) contains the name to which it + should be renamed. + \endlist + \i In \c operationGet: + \list + \i \c QNetworkOperation::arg( 0 ) contains the full URL of the + file which should be retrieved. + \endlist + \i In \c operationPut: + \list + \i \c QNetworkOperation::arg( 0 ) contains the full URL of the + file in which the data should be stored. + \i \c QNetworkOperation::rawArg( 1 ) contains the data which + should be stored in \c QNetworkOperation::arg( 0 ) + \endlist +\endlist + +In summary: If you reimplement an operation function, you must emit +some special signals and at the end you must \e always emit a \c +finished() signal, regardless of success or failure. Also you must +change the state of the \c QNetworkOperation during processing. You +can also get and set \c QNetworkOperation arguments as the operation +progresses. + +It may occur that the network protocol you implement only requires a +subset of these operations. In such cases, simply reimplement the +operations which are supported by the protocol. Additionally you must +specify which operations you support. This is achieved by +reimplementing + +\code + int QNetworkProtocol::supportedOperations() const; +\endcode + +In your implementation of this method return an \c int value +which is constructed by OR-ing together the correct values +(supported operations) of the following enum (of \c QNetworkProtocol): + +\list +\i \c OpListChildren +\i \c OpMkDir +\i \c OpRemove +\i \c OpRename +\i \c OpGet +\i \c OpPut +\endlist + +For example, if your protocol supports listing children and renaming +them, your implementation of \c supportedOperations() should do this: + +\code + return OpListChildren | OpRename; +\endcode + +The last method you must reimplement is + +\code + bool QNetworkProtocol::checkConnection( QNetworkOperation *op ); +\endcode + +Here you must return TRUE, if the connection is up and okay (this means +operations on the protocol can be done). If the connection is not okay, +return FALSE and start to try opening it. If you cannot open the +connection at all (e.g. because the host is not found), emit a \c finished() +signal and set an error code and the \c QNetworkProtocol::StFailed state to +the \c QNetworkOperation pointer you get here. + +Now, you never need to check before doing an operation yourself, if +the connection is okay. The network architecture does this, which +means it uses \c checkConnection() to see if an operation can be done +and if not, it tries it again and again for some time, only calling an +operation function if the connection is okay. + +To be able to use a network protocol with a QUrlOperator (and so, for +example, in the QFileDialog), you must register the network +protocol implementation. This can be done like this: + +\code + QNetworkProtocol::registerNetworkProtocol( "myprot", new QNetworkProtocolFactory<MyProtocol> ); +\endcode + +In this case \c MyProtocol would be a class you implemented as +described here (derived from \c QNetworkProtocol) and the name of the +protocol would be "myprot". So to use it, you would do something like + +\code + QUrlOperator op( "myprot://host/path" ); + op.listChildren(); +\endcode + +Finally, as example of a network protocol implementation you could +look at the implementation of QLocalFs. The network extension also +contains an example implementation of a network protocol. + + +\section2 Error Handling + +Error handling is important for both implementing new network +protocols for and using them (through \c QUrlOperator). + +After processing an operation has been finished the network operation +the QUrlOperator emits the \c finished() signal. This has as argument +a pointer to the processed \c QNetworkOperation. If the state of this +operation is \c QNetworkProtocol::StFailed, the operation contains +some more information about this error. The following error codes are +defined in \c QNetworkProtocol: + +\table +\header \i Error \i Meaning +\row \i \c QNetworkProtocol::NoError + \i No error occurred +\row \i \c QNetworkProtocol::ErrValid + \i The URL you are operating on is not valid +\row \i \c QNetworkProtocol::ErrUnknownProtocol + \i There is no protocol implementation available for the protocol + of the URL you are operating on (e.g. if the protocol is http + and no http implementation has been registered) +\row \i \c QNetworkProtocol::ErrUnsupported + \i The operation is not supported by the protocol +\row \i \c QNetworkProtocol::ErrParse + \i Parse error of the URL +\row \i \c QNetworkProtocol::ErrLoginIncorrect + \i You needed to login but the username or password are wrong +\row \i \c QNetworkProtocol::ErrHostNotFound + \i The specified host (in the URL) couldn't be found +\row \i \c QNetworkProtocol::ErrListChildren + \i An error occurred while listing the children +\row \i \c QNetworkProtocol::ErrMkDir + \i An error occurred when creating a directory +\row \i \c QNetworkProtocol::ErrRemove + \i An error occurred while removing a child +\row \i \c QNetworkProtocol::ErrRename + \i An error occurred while renaming a child +\row \i \c QNetworkProtocol::ErrGet + \i An error occurred while getting (retrieving) data +\row \i \c QNetworkProtocol::ErrPut + \i An error occurred while putting (uploading) data +\row \i \c QNetworkProtocol::ErrFileNotExisting + \i A file which is needed by the operation doesn't exist +\row \i \c QNetworkProtocol::ErrPermissionDenied + \i The permission for doing the operation has been denied +\endtable + +\c QNetworkOperation::errorCode() returns one of these codes or +perhaps a different one if you use your an own network protocol +implementation which defines additional error codes. + +\c QNetworkOperation::protocolDetails() may also return a string which +contains an error message then which might be suitable for display to +the user. + +If you implement your own network protocol, you must report any +errors which occurred. First you always need to be able to +access the \c QNetworkOperation which is being processed at the +moment. This is done using \c +QNetworkOperation::operationInProgress(), which returns a pointer to +the current network operation or 0 if no operation is processed at the +moment. + +Now if an error occurred and you need to handle it, do this: +\code + if ( operationInProgress() ) { + operationInProgress()->setErrorCode( error_code_of_your_error ); + operationInProgress()->setProtocolDetails( detail ); // optional + emit finished( operationInProgress() ); + return; + } +\endcode + +That's all. The connection to the \c QUrlOperator and so on is done +automatically. Additionally, if the error was really bad so that no +more operations can be done in the current state (e.g. if the host +couldn't be found), call \c QNetworkProtocol::clearOperationStack() \e +before emitting \c finished(). + +Ideally you should use one of the predefined error codes of \c +QNetworkProtocol. If this is not possible, you can add own error codes +- they are just normal \c{int}s. Just be careful that the value of the +error code doesn't conflict with an existing one. + +An example to look at is in qt/examples/network/ftpclient. +This is the implementation of a fairly complete FTP client, which +supports uploading and downloading files, making directories, etc., +all done using \c QUrlOperators. + +You might also like to look at QFtp (in qt/src/network/qftp.cpp) or at +the example in qt/examples/network/networkprotocol/nntp.cpp. + +*/ |