We're hiring!
*

Checking D-Bus API stability

Philip Withnall avatar

Philip Withnall
June 02, 2015

Share this post:

Announcing dbus-deviation, a small tool and set of libraries for automatically checking whether a D-Bus interface has broken API between two releases of a piece of software, developed as part of my work at Collabora.

Why?

If you have a large software project, worked on by multiple developers, it might not be clear when D-Bus interfaces change. For example, they might be pulled in from another repository, or might be accidentally changed without anyone noticing.

Breaks in the D-Bus API of a project (when it’s supposed to be stable) are potentially worse than breaks in its C API, because they can only be detected at runtime — when client applications suddenly error out half-way through an operation because they’ve called a D-Bus method with the wrong argument type. At least with C API breaks, the compiler will catch the break.

(In this respect, I guess D-Bus APIs are actually a form of ABI — a runtime interface, rather than a compile-time interface.)

How?

dbus-deviation provides a utility called dbus-interface-diff, plus some GNU Make glue to plug it into your build system. It only works with git: for each tagged release of your project, it uses git-notes to store copies of all the D-Bus interfaces you care about, in their state at the time of that release. They’re stored as introspection XML; if you have that XML committed into the repository anyway, the git-note becomes a ref to the existing file blob, and takes up virtually no space at all. The dbus-interface-diff tool then does a diff between two XML files (for example, one stored for the most recent release, and the one currently in your working tree), and flags up any forwards- or backwards-incompatibilities.

What?

A backwards-incompatibility, as far as dbus-deviation is concerned, is one where existing clients will not work against new versions of the D-Bus service, for example because a method they use has been removed.

A forwards-incompatibility is one where new versions of clients may not work against old versions of the D-Bus service, for example because they use a method which has been added in a new version of the API.

Traditionally, projects care about preventing backwards-incompatible API changes, and don’t care so much about forwards-incompatibilities. dbus-deviation lets you set your desired stability policy.

Where?

dbus-deviation has a spartan website, a git repository, and bugs are stored using Bugs Everywhere in git; contact me in the comments or by e-mail if you want to report something.API documentation is available for the Python libraries underpinning it, which provide an AST and diff methods for D-Bus APIs.

To get using it, follow the instructions in the README file!

All feedback is very much welcome. One area I feel is still a little awkward is how dbus-deviation integrates with make dist — it forces use of a pre-push git hook to update the remote git-notes for the API signatures of newly pushed release tags. That needs to be set up by each developer who releases a project (using make dist) — any suggestions for improving this are welcome.

What next?

API stability checking for GIR APIs, perhaps? This one needs some more work.

Original post

Related Posts

Related Posts

Comments (0)


Add a Comment






Allowed tags: <b><i><br>Add a new comment:


Search the newsroom

Latest Blog Posts

Empathy first: Driving growth through people leadership

30/11/2020

This year, the global pandemic has put a strain on us all. Motivation can become hard to maintain, worries can cloud our minds. Now more…

Developing Wayland Color Management and High Dynamic Range

19/11/2020

Wayland is still lacking proper consideration for color management & support for high dynamic range (HDR) imagery. However, a group of renegade…

A summer sprint: bringing near-native performance to Zink

06/11/2020

This week marks two years since the OpenGL implementation on Vulkan was initially announced. Since then, and especially over the past few…

From Panfrost to production, a tale of Open Source graphics

03/11/2020

Since our previous update on Panfrost, the open source stack for Arm's Mali Midgard and Bifrost GPUs, we've focused on taking our driver…

Engaging in an "Open First" remote internship at Collabora

20/10/2020

The concept of a remote internship may raise some doubts, or even red flags, for many students, as would remote jobs for professionals.…

Building GStreamer text rendering and overlays on Windows with gst-build

28/09/2020

GStreamer relies on various 2D font rendering and layout libraries such as Pango and Cairo to generate text for the Pango plugin, which…

Open Since 2005 logo

We use cookies on this website to ensure that you get the best experience. By continuing to use this website you are consenting to the use of these cookies. To find out more please follow this link.

Collabora Ltd © 2005-2020. All rights reserved. Privacy Notice. Sitemap.