QHttp Class Reference
[QtNetwork module]

Detailed Description

The QHttp class provides an implementation of the HTTP protocol.

This class provides a direct interface to HTTP that allows you to have more control over the requests and that allows you to access the response header fields. However, for new applications, it is recommended to use QNetworkAccessManager and QNetworkReply, as those classes possess a simpler, yet more powerful API.

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 "requests" in the rest of the documentation) are the following: setHost(), get(), post(), head() and request().

All of these requests return a unique identifier that allows you to keep track of the request that is currently executed. When the execution of a request starts, the requestStarted() signal with the identifier is emitted and when the request is finished, the requestFinished() signal is emitted with the identifier and a bool that indicates if the request finished with an error.

To make an HTTP request you must set up suitable HTTP headers. The following example demonstrates, how to request the main HTML page from the Trolltech home page (i.e., the URL http://www.trolltech.com/index.html):

 QHttpRequestHeader header("GET", QUrl::toPercentEncoding("/index.html"));
 header.setValue("Host", "www.trolltech.com");
 http->setHost("www.trolltech.com");
 http->request(header);

For the common HTTP requests GET, POST and HEAD, QHttp provides the convenience functions get(), post() and head(). They already use a reasonable header and if you don't have to set special header fields, they are easier to use. The above example can also be written as:

 http->setHost("www.trolltech.com");                // id == 1
 http->get(QUrl::toPercentEncoding("/index.html")); // id == 2

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

 requestStarted(1)
 requestFinished(1, false)

 requestStarted(2)
 stateChanged(Connecting)
 stateChanged(Sending)
 dataSendProgress(77, 77)
 stateChanged(Reading)
 responseHeaderReceived(responseheader)
 dataReadProgress(5388, 0)
 readyRead(responseheader)
 dataReadProgress(18300, 0)
 readyRead(responseheader)
 stateChanged(Connected)
 requestFinished(2, false)

 done(false)

 stateChanged(Closing)
 stateChanged(Unconnected)

The dataSendProgress() and dataReadProgress() signals in the above example are useful if you want to show a progress bar to inform the user about the progress of the download. The second argument is the total size of data. In certain cases it is not possible to know the total amount in advance, in which case the second argument is 0. (If you connect to a QProgressBar a total of 0 results in a busy indicator.)

When the response header is read, it is reported with the responseHeaderReceived() signal.

The readyRead() signal tells you that there is data ready to be read. The amount of data can then be queried with the bytesAvailable() function and it can be read with the read() or readAll() functions.

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.

For example, if you have the following sequence of requests

 http->setHost("www.foo.bar");       // id == 1
 http->get("/index.html");           // id == 2
 http->post("register.html", data);  // id == 3

and the get() request fails because the host lookup fails, then the post() request is never executed and the signals would look like this:

 requestStarted(1)
 requestFinished(1, false)

 requestStarted(2)
 stateChanged(HostLookup)
 requestFinished(2, true)

 done(true)

 stateChanged(Unconnected)

You can then get details about the error with the error() and errorString() functions. Note that only unexpected behavior, like network failure is considered as an error. If the server response contains an error status, like a 404 response, this is reported as a normal response case. So you should always check the status code of the response header.

The functions currentId() and currentRequest() provide more information about the currently executing request.

The functions hasPendingRequests() and clearPendingRequests() allow you to query and clear the list of pending requests.

See also QFtp, QNetworkAccessManager, QNetworkRequest, QNetworkReply, HTTP Example, and Torrent Example.

Member Type Documentation

enum QHttp::ConnectionMode

This enum is used to specify the mode of connection to use:

When using the Https mode, care should be taken to connect to the sslErrors signal, and handle possible Ssl errors.

This enum was introduced in Qt 4.3.

See also QSslSocket.

enum QHttp::Error

This enum identifies the error that occurred.

See also error().

enum QHttp::State

This enum is used to specify the state the client is in:

See also stateChanged() and state().

Member Function Documentation

QHttp::QHttp ( QObject * parent = 0 )

Constructs a QHttp object. The parent parameter is passed on to the QObject constructor.

QHttp::QHttp ( const QString & hostName, quint16 port = 80, QObject * parent = 0 )

Constructs a QHttp object. Subsequent requests are done by connecting to the server hostName on port port.

The parent parameter is passed on to the QObject constructor.

See also setHost().

QHttp::QHttp ( const QString & hostName, ConnectionMode mode, quint16 port = 0, QObject * parent = 0 )

Constructs a QHttp object. Subsequent requests are done by connecting to the server hostName on port port using the connection mode mode.

If port is 0, it will use the default port for the mode used (80 for Http and 443 for Https).

The parent parameter is passed on to the QObject constructor.

See also setHost().

QHttp::~QHttp ()   [virtual]

Destroys the QHttp object. If there is an open connection, it is closed.

void QHttp::abort ()   [slot]

Aborts the current request and deletes all scheduled requests.

For the current request, the requestFinished() signal with the error argument true is emitted. For all other requests that are affected by the abort(), no signals are emitted.

Since this slot also deletes the scheduled requests, there are no requests left and the done() signal is emitted (with the error argument true).

See also clearPendingRequests().

void QHttp::authenticationRequired ( const QString & hostname, quint16 port, QAuthenticator * authenticator )   [signal]

This signal can be emitted when a web server on a given hostname and port requires authentication. The authenticator object can then be filled in with the required details to allow authentication and continue the connection.

Note: It is not possible to use a QueuedConnection to connect to this signal, as the connection will fail if the authenticator has not been filled in with new information when the signal returns.

This function was introduced in Qt 4.3.

See also QAuthenticator and QNetworkProxy.

qint64 QHttp::bytesAvailable () const

Returns the number of bytes that can be read from the response content at the moment.

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

void QHttp::clearPendingRequests ()

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

See also hasPendingRequests() and abort().

int QHttp::close ()

Closes the connection; this is useful if you have a keep-alive connection and want to close it.

For the requests issued with get(), post() and head(), QHttp sets the connection to be keep-alive. You can also do this using the header you pass to the request() function. QHttp only closes the connection to the HTTP server if the response header requires it to do so.

The function does not block; instead, it returns immediately. The request is scheduled, and its execution is performed asynchronously. The function returns a unique identifier which is passed by requestStarted() and requestFinished().

When the request is started the requestStarted() signal is emitted. When it is finished the requestFinished() signal is emitted.

If you want to close the connection immediately, you have to use abort() instead.

See also stateChanged(), abort(), requestStarted(), requestFinished(), and done().

QIODevice * QHttp::currentDestinationDevice () const

Returns the QIODevice pointer that is used as to store the data of the HTTP request being executed. If there is no current request or if the request does not store the data to an IO device, this function returns 0.

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

See also currentSourceDevice(), get(), post(), and request().

int QHttp::currentId () const

Returns the identifier of the HTTP request being executed or 0 if there is no request being executed (i.e. they've all finished).

See also currentRequest().

QHttpRequestHeader QHttp::currentRequest () const

Returns the request header of the HTTP request being executed. If the request is one issued by setHost() or close(), it returns an invalid request header, i.e. QHttpRequestHeader::isValid() returns false.

See also currentId().

QIODevice * QHttp::currentSourceDevice () const

Returns the QIODevice pointer that is used as the data source of the HTTP request being executed. If there is no current request or if the request does not use an IO device as the data source, this function returns 0.

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

See also currentDestinationDevice(), post(), and request().

void QHttp::dataReadProgress ( int done, int total )   [signal]

This signal is emitted when this object reads data from a HTTP server to indicate the current progress of the download.

done is the amount of data that has already arrived and total is the total amount of data. It is possible that the total amount of data that should be transferred cannot be determined, in which case total is 0.(If you connect 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 dataSendProgress(), get(), post(), request(), and QProgressBar.

void QHttp::dataSendProgress ( int done, int total )   [signal]

This signal is emitted when this object sends data to a HTTP server to inform it about the progress of the upload.

done is the amount of data that has already arrived and total is the total amount of data. It is possible that the total amount of data that should be transferred cannot be determined, in which case total is 0.(If you connect 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 dataReadProgress(), post(), request(), and QProgressBar.

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

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

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

Error QHttp::error () const

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

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

QString QHttp::errorString () const

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

int QHttp::get ( const QString & path, QIODevice * to = 0 )

Sends a get request for path to the server set by setHost() or as specified in the constructor.

path must be a absolute path like /index.html or an absolute URI like http://www.trolltech.com/index.html and must be encoded with either QUrl::toPercentEncoding() or QUrl::encodedPath().

If the IO device to is 0 the readyRead() signal is emitted every time new content data is available to read.

If the IO device to is not 0, the content data of the response is written directly to the device. Make sure that the to pointer is valid for the duration of the operation (it is safe to delete it when the requestFinished() signal is emitted).

 void Ticker::getTicks()
 {
   http = new QHttp(this);
   connect(http, SIGNAL(done(bool)), this, SLOT(showPage()));
   http->setProxy("proxy.example.com", 3128);
   http->setHost("ticker.example.com");
   http->get("/ticks.asp");
 }

 void Ticker::showPage()
 {
   display(http->readAll());
 }