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From: Martin Woolley <>
To: "" <>
Subject: Comments on the ConnectDevice API function
Date: Fri, 22 May 2020 08:22:12 +0000
Message-ID: <> (raw)


I've recently been working with BlueZ via D-Bus and have a situation which requires me to be able to connect to a device whose Bluetooth device address is known, but without first scanning. This is a link layer state transition with the specification allows.

BlueZ currently supports this via an API adapter function called ConnectDevice, whose status is currently "experimental". From my experience of using this function, it seems to behave like this:

If the BlueZ instance has not scanned yet, so that the target device is not known to it, the ConnectDevice call results in scanning taking place and then if the target device is found, it is connected to. Success!

But if scanning has previously been performed, regardless of the state of the actual device (e.g. advertising and ready to accept connections), an exception is thrown with a message whose text value is "Already Exists".

I was wondering if I could influence the design of the API before the ConnectDevice experimental status is removed? 

I would like to suggest that there should be no need for a special API to connect directly to a device without first scanning. Why burden the application developer needing to call it just in case this condition applies, catching the BlueZ exception ("Already Exists") and responding by then calling the normal Connect API? 

An alternative would be to accommodate this special case (not scanned before) in the implementation of the standard device Connect(bdaddr) function or if that makes no sense because Device objects must correspond to previously discovered, physical devices, then at least the adapter ConnectDevice function could take care of the two possible paths and simplify matters for the application developer. 

Thanks in anticipation.

Martin Woolley 
Senior Developer Relations Manager, EMEA  |  Bluetooth Special Interest Group, Inc.

             reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-22  8:22 Martin Woolley [this message]
2020-05-22 17:48 ` Luiz Augusto von Dentz
2020-05-27 13:41   ` Martin Woolley
2020-05-27 14:10     ` Szymon Janc
2020-05-27 15:38       ` Luiz Augusto von Dentz
2020-05-27 16:10         ` Martin Woolley
2020-05-27 16:32           ` Martin Woolley

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