Copyright 2020-2024 Kevin Backhouse.

DBusParse

DBusParse is a C++ library for parsing D-Bus messages. It can also serialize a D-Bus message to an array of bytes, ready for sending. DBusParse includes some simple utility functions for sending and receiving D-Bus messages, but is not intended to be a fully fledged D-Bus message handler. For example, it does not include logic for generating message serial numbers. However, it is certainly suitable to be used as a sub-component of a complete D-Bus implementation.

The parser is designed to be able to parse an incomplete input. You can feed it some bytes, then save its state until you have received more bytes. This is handy when reading bytes from a socket, because you might not receive the complete message in a single read. It means, for example, that the parser is well-suited for use in an epoll event loop. The parser implementation uses continuation-passing style. The parser state includes a continuation function, which is invoked when more bytes are received.

I wrote DBusParse because I was doing security research on dbus-daemon and several D-Bus services, and wanted to gain a thorough understanding of the message format. I also, stupidly, thought that it wouldn't be much work. Initially, I only needed the ability to send messages and I wasn't aware of the dbus-send tool, so I wrote a serializer. But I quickly discovered that I also needed to parse the reply messages, so I started implementing a parser too. Now that it has grown into a complete implementation, I figure I might as well make it open source.

Usage

DBusParse is a library. For an example of how to use it in a simple application, please see the DBusParseDemo demo repository.

Building

On Linux, you can build DBusParse as follows:

mkdir build
cd build
cmake ..
make

To run the tests:

make test

You can install DBusParse on your system like this:

sudo make install

However, if you are not keen to use sudo to modify your system, you can instead use DBusParse by including it as a sub-module in your project. The DBusParseDemo project does exactly that.

Design notes

dbus.hpp defines a class named DBusType with sub-types such as DBusTypeInt32 and DBusTypeArray. Similarly, it defines a class named DBusObject with sub-types such as DBusObjectInt32 and DBusObjectArray. These class hierarchies correspond to the types and objects defined in the D-Bus specification.

Smart pointers are used to manage memory automatically. For example, composite objects such as DBusObjectStruct use std::unique_ptr to point to their child objects.