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I am starting to create a dbus application in C to interface with bluez. I am new to dbus and I am a little confused as how to correctly structure my application with dbus.

The first question is related to the Service, Interface, and Object path in dbus. Bluez Adapter API has the org.bluez service, a org.bluez.Adapter1 interface, and a number of methods and properties. If I wanted to call the void StopDiscovery() method, would the following be the correct call?

DBusPendingCall * pending;
// create a new method call and check for errors
msg = dbus_message_new_method_call("org.bluez",
    "/", // object to call on
    "org.bluez.Adapter1", // interface to call on
    "StopDiscovery"); // method name
// send message and get a handle for a reply
if (!dbus_connection_send_with_reply (m_dbus_conn, msg, &pending, -1))
{
     //err
}

If this is the case, when does the object path come into play?

The follow on to this is how to go about receiving information back from dbus. I've seen a few examples with a DBusPendingCall * however the function has dbus_pending_call_block() so the function blocks until the data is returned. If I wanted to do multiple calls and not block I would need to make a list of DBPendingCall pointers and check each one? Are there any callbacks?

Thanks

protological
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2 Answers2

2

I did create an example showing the non-blocking call based on the dbus watch and timeout mechanism, in response to the SO question dbus watch and timeout examples. Basically you run a unix select() loop and everything is dispatched around it.

And I did not touch the multiple outstanding pending-call part. I assume one way is to check each pending-call to see whether it is completed when the watched event is received. Checking pending complete is non-blocking. If you keep a small number of outstanding pending calls it should be ok, though that is not an efficient solution if the number becomes big.

It looks like according to the API document, a better solution is to use dbus_pending_call_set_notify() to register a callback to a pending call.

Community
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minghua
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1

So it appears that both the object path and the interface are required when talking to bluez over dbus.

// create a new method call for the adapter
msg = dbus_message_new_method_call("org.bluez",
"/org/bluez/hci0", // object to call on
"org.bluez.Adapter1", // interface to call on
"StopDiscovery"); // method name


// create a new method call for a characteristic on
// a given service 
msg = dbus_message_new_method_call("org.bluez",
"/org/bluez/hci0/dev_12_34_56_78_9A_BC/service0010/char0011",
"org.bluez.GattCharacteristic1",
"StartNotify");

The select on Unix sockets for pending looks like a solid, scaleable way to go, I will consider this architecture as the application grows

protological
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