[Interest] QML Debug API

Ulf Hermann

2018-11-09 08:07:46 UTC

Hi Nils,

Post by Nils Schlemminger
I have read that QML offers a binary debug protocol that is used by
several tools to to gain insights into QML applications. I read about
this interface here: http://doc.qt.io/qt-5/qtquick-debugging.html
It is stated that: "The Qt QML module provides services for debugging,
inspecting, and profiling applications via a TCP port."

In fact you can also use a local socket or (with restrictions) the
native debugger as connection mechanism.

Post by Nils Schlemminger
I'm planning to build my own tool on top of that API. I searched around
for the description and details about this protocol for a while but
couldn't find much beside the qtdeclarative git repository which seems
to contain the implementation.
Do I have to reverese engeneer the API from the source code or is there
some form of documentation that I wasn't able to find?

There is private API for interacting with the various debug services.
Take a look at src/qmldebug in qtdeclarative. The code results in a
static library called QtQmlDebug. You can either link against that (with
the usual caveats of using private API), or you can use the code to
figure out how the protocol works.

There is QQmlDebugConnection to establish a connection to the target
application, QV4DebugClient for JavaScript debugging,
QQmlEngineDebugClient and QQmlInspectorClient for QML debugging,
QQmlProfilerClient for profiling, QQmlEngineControlClient for
synchronizing the profiler in case of multiple QML engines, and
QQmlDebugMessageClient to receive debug messages through the connection.
I'm thinking about adding QQmlDebugProcess to QtQmlDebug, so that you
get an easy way to start a process and directly connect to it. That
class so far is in tests/auto/qml/debugger/shared in qtdeclarative.

If there is demand for this, I would consider making it public. It
probably needs some more cleanup, but generally the client interfaces
look good.

Ulf