This software is a framework that enables a Java based application to interact with a D-Bus instance in the role of a client. The D-Bus instance can be a system or session bus. As of now, only Unix sockets are supported as transport by this framework. The type system, the wire format and the message protocol are fully implemented as of D-Bus Specification 0.41.
D-Bus is a bus system commonly found on the Linux desktop. It enables applications to communicate with each other indirectly via a bus. Applications can use this bus to signal state changes to or exchange information with other applications. Since D-Bus defines a marshalling format for its type system, an application written in Java can talk to an application written in C via D-Bus. For in depth information about D-Bus, please visit https://www.freedesktop.org/wiki/Software/dbus/.
This D-Bus framework is written from scratch and doesn't suffer the same architectural decisions as the reference implementation. Furthermore, it can handle empty responses, and both byte orders (little and big endian) on the wire format of D-Bus.
This framework is based on a non-blocking I/O framework called Netty. Therefore its an asynchronous event-driven network application framework.
The application needs to implement specific handlers that will get called by this framework. Those handlers must be programmed in a non-blocking fashion. Using Future and CompletionStage is a good way to do so.
The type system of D-Bus is implemented by introducing facades to the data types of Java (Facade Design Pattern). This choice makes the framework a bit more robust and the use of this framework approachable.
- Java Runtime 8 or higher
- D-Bus 1.12 or higher
String userId = "1000";
String cookiePath = "~/.dbus-keyrings/";
String socketPath = "/var/run/dbus/system_bus_socket";
ConnectionFactory factory = new UnixSocketConnectionFactory(userId, cookiePath, socketPath);
PipelineInitializer initializer = pipeline ->
pipeline.addLast(EXAMPLE_HANDLER, new ExampleHandler());
CompletionStage<Connection> connStage = factory.create(initializer);
UInt32 serial = pipeline.getConnection().getNextSerial();
DBusString destination = DBusString.valueOf("org.bluez");
ObjectPath path = ObjectPath.valueOf("/");
DBusString name = DBusString.valueOf("GetManagedObjects");
OutboundMethodCall msg = new OutboundMethodCall(serial, destination, path, name);
DBusString iface = DBusString.valueOf("org.freedesktop.DBus.ObjectManager");
msg.setInterfaceName(iface);
pipeline.passOutboundMessage(msg);
In this example, the handler implements the org.freedesktop.DBus.Peer interface,
in order to respond to a ping request and/or to a request to return the machine-id.
public final class DbusPeerHandler implements Handler {
private static final DBusString INTERFACE = DBusString.valueOf("org.freedesktop.DBus.Peer");
private final UUID machineId;
public DbusPeerHandler(final UUID machineId) {
this.machineId = Objects.requireNonNull(machineId);
}
private static void respondToPing(final HandlerContext ctx, final InboundMethodCall methodCall) {
final DBusString destination = methodCall.getSender();
final UInt32 serial = ctx.getPipeline().getConnection().getNextSerial();
final UInt32 replySerial = methodCall.getSerial();
final OutboundMethodReturn methodReturn = new OutboundMethodReturn(destination, serial, replySerial);
ctx.passOutboundMessage(methodReturn);
}
private void handleInboundMethodCall(final HandlerContext ctx, final InboundMethodCall methodCall) {
if (methodCall.getInterfaceName().orElse(DBusString.valueOf("")).equals(INTERFACE)) {
if (methodCall.getName().equals(DBusString.valueOf("Ping"))) {
respondToPing(ctx, methodCall);
} else if (methodCall.getName().equals(DBusString.valueOf("GetMachineId"))) {
respondWithMachineId(ctx, methodCall);
} else {
ctx.passInboundMessage(methodCall);
}
} else {
ctx.passInboundMessage(methodCall);
}
}
private void respondWithMachineId(final HandlerContext ctx, final InboundMethodCall methodCall) {
final DBusString destination = methodCall.getSender();
final UInt32 serial = ctx.getPipeline().getConnection().getNextSerial();
final UInt32 replySerial = methodCall.getSerial();
final OutboundMethodReturn methodReturn = new OutboundMethodReturn(destination, serial, replySerial);
final List<DBusType> payload = new ArrayList<>();
payload.add(DBusString.valueOf(machineId.toString()));
methodReturn.setPayload(payload);
ctx.passOutboundMessage(methodReturn);
}
@Override
public void onInboundMessage(final HandlerContext ctx, final InboundMessage msg) {
if (msg instanceof InboundMethodCall) {
handleInboundMethodCall(ctx, (InboundMethodCall) msg);
} else {
ctx.passInboundMessage(msg);
}
}
}Participation is welcome and endorsed by the chosen license and a simplified contributor agreement.
As the chosen open source license implicitly serves as both the inbound (from contributors) and outbound (to other contributors and users) license, there's no need for an additional contributor agreement.
But to be super safe, this project requires developers to state that each commit they make is authorized. A Developer Certificate of Origin requirement is how many projects achieve this.
By making a contribution to this project, I certify that:
a. The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or
b. The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or
c. The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.
d. I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.
Therefore the contributors to this project sign-off that they adhere to these requirements by adding a Signed-off-by line to commit messages.
This is an example commit message.
Signed-off-by: Peter Peterson <[email protected]>
Copyright 2021 Lucimber UG
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.