Qt5.5以来对Network的改进（包括对SSL的功能支持，HTTP的重定向等等）

Qt Network

New SSL back-end for iOS and OS X based on Secure Transport. Note that in Qt 5.6 this will become the default SSL: back-end on these platforms.

Support for libproxy

Support for TLS PSK ciphersuites

Support for elliptic curve certificates

Ability to select specific curves when using elliptic curve ciphersuites.
http://wiki.qt.io/New_Features_in_Qt_5.5
Qt Network

Added QHostAddress::isMulticast()

Support HTTP redirection in QNetworkAccessManager
http://wiki.qt.io/New_Features_in_Qt_5.6
Qt Network

Support for TLS PSK ciphersuites on server side

Support for configurable diffie hellman parameters

Support for HTTP/2 in Network Access Manager
http://wiki.qt.io/New_Features_in_Qt_5.8
Qt Network

Added HSTS support (HTTP Strict Transport Security) to QNetworkAccessManager

Added redirects policy to QNetworkAccessManager (ManulRedirectsPolicy, NoLessSafeRedirectsPolicy, SameOriginRedirectsPolicy, UserVerifiedRedirectsPolicy)
http://wiki.qt.io/New_Features_in_Qt_5.9