[Interest] [Qt 4.8] Subclassing QAbstractSocket (for ICMP)

[Jason Cipriani]

Excellent, thanks for the quick response and solid information. I will
abandon the QAbstractSocket approach and start from scratch.

Just out of curiosity, what is the purpose of UnknownSocketType? Is it
meant only for stream and datagram (not raw) sockets that use other
protocols besides TCP or UDP?

Thanks,
Jason


On Mon, Jan 28, 2013 at 1:58 AM, Thiago Macieira
<thiago.macieira at intel.com>wrote:

> On domingo, 27 de janeiro de 2013 22.02.01, Jason Cipriani wrote:
> > I am writing an application that has to send and receive ICMP messages.
>
> That means you're running as root and you're using raw sockets. Please
> continue using raw sockets, not QAbstractSocket.
>
> QAbsractSocket::setSocketDescriptor requires a socket of type SOCK_STREAM
> or
> SOCK_DGRAM. If you pass anything else (like ICMP raw sockets), funny things
> will happen.
>
> My suggestion: abandon your approach and create your class that is
> independent
> of QAbstractSocket.
>
> >   1) I needed to call WSAStartup/WSACleanup. I feel that Qt is already
> > doing this somewhere and I'd like to use Qt's platform-independent
> > initialization instead.
>
> That's done automatically when the QNativeSocketEngine is created. If you
> create your socket before calling setSocketDescriptor (which you usually
> do),
> you need to call it yourself. You can also just create a dummy socket and
> try
> to connect somewhere, or create a UDP socket and just bind it.
>
> >   2) QAbstractSocket doesn't really provide a public way to send data to
> a
> > specific host (ICMP is connectionless).
>
> Correct. As I said, it's not meant to do ICMP. You need to add your own
> methods, preferably to your own class.
>
> >   3) I tried setSocketDescriptor + UnconnectedState then a call to
> > connectToHost anyways, but the call was unsuccessful.
>
> connectToHost makes no sense for ICMP. Besides, there's a long-standing
> bug in
> setSocketDescriptor in unconnected state + connectToHost. If you do that,
> it'll close your socket and create a new one.
>
> >   1) Is creating a socket and calling setSocketDescriptor in the
> > constructor the right approach? Will QAbstractSocket then manage the
> > descriptor from here on out?
>
> No and no.
>
> >   2) QUdpSocket/QTcpSocket use an underlying socket engine for many
> things
> > (e.g. platform-independent error codes to strings, initialization,
> etc.). I
> > don't know how to access the socket engine. QUdpSocket/QTcpSocket have a
> > private object, but in order to use QAbstractSocketPrivate, I have to
> have
> > qabstractsocket_p.h installed locally. It *seems* like I should be able
> to
> > do this without the Qt source installed, but I may be wrong. How can I
> > access the features of the underlying socket engine? Do I have to build
> > against the Qt source?
>
> You can only do it from inside QtNetwork. The classes are not exported.
>
> You must modify the sources and add the feature inside QtNetwork itself.
> Then
> rebuild Qt.
>
> >   3) On Windows, can I accomplish this without calling WSAStartup()
> > explicitly? Is there a platform-independent method of initializing the
> > network subsystem? The above code fails as-is because WSAStartup has not
> > been called (I had hoped QAbstractSocket's constructor to indirectly lead
> > to network initialization but it does not).
>
> There's QWindowsSockInit. If you're modifying QtNetwork, you have access to
> it. If you're not modifying it, then you can't access it and there's
> nothing
> cross-platform.
>
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel Open Source Technology Center
>
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>
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