Changes to Qt Network

Qt 6 is a result of the conscious effort to make the framework more efficient and easy to use.

We try to maintain binary and source compatibility for all the public APIs in each release. But some changes were inevitable in an effort to make Qt a better framework.

In this topic we summarize those changes in Qt Network, and provide guidance to handle them.

API changes

Ambiguous name overloads

Several ambiguous overloaded functions are removed. The error() signal is replaced by errorOccurred() in QAbstractSocket and its heirs (QTcpSocket, QUdpSocket, QLocalSocket, and QSslSocket), and in QNetworkReply. Code such as:

connect(socket, qOverload<QAbstractSocket::SocketError>(&QAbstractSocket::error),
        this, &SomeClass::errorSlot);

must therefore be changed to:

connect(socket, &QAbstractSocket::errorOccurred, this, &SomeClass::errorSlot);

In QSslSocket, the function that returns a list of errors encountered during the TLS handshake:

QList<QSslError> sslErrors() const;

is renamed to sslHandshakeErrors():

const auto tlsErrors = socket.sslHandshakeErrors();

Bearer management is removed

The classes QNetworkConfiguration and QNetworkConfigurationManager are removed in Qt 6. Consequently, the following member functions of QNetworkAccessManager are also removed:

void setConfiguration(const QNetworkConfiguration &config);
QNetworkConfiguration configuration() const;
QNetworkConfiguration activeConfiguration() const;
void setNetworkAccessible(NetworkAccessibility accessible);
NetworkAccessibility networkAccessible() const;
void networkSessionConnected();

QNetworkInformation, initially introduced in Qt 6.1, aims to replace some aspects of the bearer management API. It works by providing a unified API which subscribes to changes to the network as notified by the operating system.

QNetworkInformation::reachability(), introduced in Qt 6.1, replaces the QNetworkAccessManager::networkAccessible() function, while adding more detailed information about the reachability of the network. See its documentation for more details.

In Qt 6.2 QNetworkInformation gained the ability to detect captive portals.

In Qt 6.3 QNetworkInformation gained QNetworkInformation::transportMedium() and QNetworkInformation::isMetered().

Deleted enumerators

Several enumerators are removed in QtNetwork. This includes constants for no longer supported protocols and functionality:

• QSsl::SslV2;
• QSsl::SslV3;
• QSsl::TlsV1SslV3;
• QNetworkRequest::SpdyAllowedAttribute;
• QNetworkRequest::SpdyWasUsedAttribute;
• QNetworkAccessManager::UnknownAccessibility;
• QNetworkAccessManager::NotAccessible;
• QNetworkAccessManager::Accessible

and enumerators whose names did not follow proper naming conventions:

• QSsl::TlsV1 (QSsl::TlsV1_0 is the proper name);
• QNetworkRequest::HTTP2AllowedAttribute (use QNetworkRequest::Http2AllowedAttribute);
• QNetworkRequest::HTTP2WasUsedAttribute (use QNetworkRequest::Http2WasUsedAttribute).

QNetworkRequest::FollowRedirectsAttribute is removed in Qt 6, see the section about redirects handling below.

Configuring QSslSocket

The following deprecated functions are removed in Qt 6:

QList<QSslCipher> ciphers() const;
void setCiphers(const QList<QSslCipher> &ciphers);
void setCiphers(const QString &ciphers);
static void setDefaultCiphers(const QList<QSslCipher> &ciphers);
static QList<QSslCipher> defaultCiphers();
static QList<QSslCipher> supportedCiphers();
QList<QSslCipher> ciphers() const;
void setCiphers(const QList<QSslCipher> &ciphers);
void setCiphers(const QString &ciphers);
static void setDefaultCiphers(const QList<QSslCipher> &ciphers);
static QList<QSslCipher> defaultCiphers();
static QList<QSslCipher> supportedCiphers();
bool addCaCertificates(const QString &path, QSsl::EncodingFormat format = QSsl::Pem,
                       QRegExp::PatternSyntax syntax = QRegExp::FixedString);
void addCaCertificate(const QSslCertificate &certificate);
void addCaCertificates(const QList<QSslCertificate> &certificates);
void setCaCertificates(const QList<QSslCertificate> &certificates);
QList<QSslCertificate> caCertificates() const;
static bool addDefaultCaCertificates(const QString &path, QSsl::EncodingFormat format = QSsl::Pem,
                                     QRegExp::PatternSyntax syntax = QRegExp::FixedString);
static void addDefaultCaCertificate(const QSslCertificate &certificate);
static void addDefaultCaCertificates(const QList<QSslCertificate> &certificates);
static void setDefaultCaCertificates(const QList<QSslCertificate> &certificates);
static QList<QSslCertificate> defaultCaCertificates();
static QList<QSslCertificate> systemCaCertificates();

Use QSslConfiguration and its member functions to set these parameters, e.g.:

auto sslConfiguration = QSslConfiguration::defaultConfiguration();
sslConfiguration.setCiphers("ECDHE-ECDSA-AES256-SHA384");
// Set other parameters here ...
socket.setSslConfiguration(sslConfiguration);

Changes in QNetworkAccessManager's default behavior

Redirect policies

In Qt 6, the default redirect policy has changed from manual to QNetworkRequest::NoLessSafeRedirectPolicy. If your application relies on manual redirect handling (it connects its slot to the QNetworkReply::redirected signal), you have to explicitly set this policy when creating a request:

request.setAttribute(QNetworkRequest::RedirectPolicyAttribute, QNetworkRequest::ManualRedirectPolicy);

HTTP/2 is enabled by default

In Qt 6 QNetworkAccessManager enables HTTP/2 protocol by default. Depending on the scheme ("https" or "http"), QNetworkAccessManager will use the Application Layer Protocol Negotiation TLS extension or "protocol upgrade" HTTP header to negotiate HTTP/2. If HTTP/2 cannot be negotiated, the access manager will fall back to using HTTP/1.1. If your application can only use HTTP/1.1, you have to disable HTTP/2 manually on a new request:

request.setAttribute(QNetworkRequest::Http2AllowedAttribute, false);

QNetworkAccessManager now guards against archive bombs

Starting with Qt 6.2 QNetworkAccessManager will guard against compressed files that decompress to files which are much larger than their compressed form by erroring out the reply if the decompression ratio exceeds a certain threshold. This check is only applied to files larger than a certain size, which can be customized (or disabled by passing -1) by calling QNetworkRequest::setDecompressedSafetyCheckThreshold().