[Development] QDataStream: blackbox or document all versions?

Thiago Macieira thiago.macieira at intel.com
Sun Sep 25 05:58:38 CEST 2016

A thread[1] on the interest mailing list started when someone asked for the 
docs for the current format of the QDataStream wire protocol, to which I 
replied that it doesn't exist as we don't maintain such docs.

Long story short, we have two options:

Option 1: claim QDataStream is a blackbox and tell people that the only thing 
that can read QDataStream is QDataStream. That means removing the 
documentation file src/corelib/doc/src/datastreamformat.qdoc, as we don't want 
people getting any ideas that they could write their own decoders or encoders.

Option 2: the opposite, saying that reading QDataStream's output is fine from 
non-Qt code and it's fine to write data that QDataStream should read. This 
means extending the documentation to cover ALL 17 wire formats (including 
bugs) and keeping it up to date whenever someone modifies the format.

I am in favour of Option 1 because I really don't think QDataStream is a good 
format for exchanging data with non-Qt code. It's designed first and foremost 
for Qt's own internal data formats (sometimes even depending on internal 
details), the marshalling of certain types in certain versions is buggy and 
lossy. Instead, people should find a better transport format for their data, of 
which we already have in Qt:

	QSettings (to an extent)

And I can add CBOR support if we want to.

[1] http://lists.qt-project.org/pipermail/interest/2016-September/024387.html
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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