Alban’s blog

DBusMessagesBox.py can monitor messages going through a D-Bus message bus and display message sequence chart with Mscgen. It connects to dbus-daemon with dbus-python.

Example of PNG output

When Rhythmbox plays a song, it prevents the power manager to suspend or hibernate (method call #13). The user is notified (method call #14). See GNOME Power Management Specification.

Example of HTML output

A video conference with Empathy involves several Telepathy components. They communicates together via D-Bus messages.

Telepathy D-Bus messages when starting a video conference

How to try it

• You need a patched version of Mscgen. Download Mscgen sources and the signal patch. Or use the signal branch of my git repository. Install it.
• Then get DBusMessagesBox.py (also available in git).
• In the __name__ function, changes the variable skip_entities.
• Start DBusMessagesBox.py in a console.
• Stop it with Ctrl-c.
• Look at the output files dbus_output.*

Features

• Call the dbus-daemon to know the names of connections (GetNameOwner).
• PNG and HTML/javascript output.
• Filter the connections to display (see skip_entities in the source).
• Method calls and returns are linked together in the HTML version.
• When connections want to receive signals from dbus-daemon, DBusMessagesBox.py knows it and displays which connections receives the signal.

Bugs

• Most bugs are silently ignored because of Bug fd.o #9980.
• When there is several recipients for a signal, there are not displayed correctly. Mscgen needs a patch for that.
• The code needs clean up and a better API to use DBusMessagesBox.py in other python programs.

API

The class DBusMessagesBox has some functions like start_recording(), stop_recording(), parse_to_mscfile(). But a lot is hardcoded and need clean up.

See also

• D-Bus Spy
• Bustle