[RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

* v1: 
    - Added back the "Value" property. Changed its meaning so that the property
      represents the cached characteristic/descriptor value and there are no
      read/write request semantics tied to Get/Set. PropertiesChanged is sent on
      notifications/indications and after successful read requests. The property
      is now read-only and optional, i.e. it won't be present until a read
      request or a not/ind.

    - Replaced the "Authentication", "Authorization", and "Encryption" errors
      with a simpler "NotPaired" error, since there's not much the external
      application can do on these errors other than try to pair. bluetoothd will
      automatically attempt to raise the security level of the connection on
      these errors.

Arman Uguray (1):
  doc/gatt-api: New API properties and methods for the GATT D-Bus API.

 doc/gatt-api.txt | 118 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 106 insertions(+), 12 deletions(-)

-- 
2.0.0.526.g5318336

[RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

This patch proposes changes to the currently unimplemented GATT D-Bus API for
desktop bluetoothd. This is the first step in implementing a GATT client layer
for bluetoothd that will change the way remote attributes are accessed via
bluetoothd plugins and external applications.
---
 doc/gatt-api.txt | 118 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 106 insertions(+), 12 deletions(-)

diff --git a/doc/gatt-api.txt b/doc/gatt-api.txt
index 8c7975c..741bd18 100644
--- a/doc/gatt-api.txt
+++ b/doc/gatt-api.txt
@@ -32,6 +32,25 @@ Properties	string UUID [read-only]
 
 			128-bit service UUID.
 
+		boolean Primary [read-only]
+
+			Indicates whether or not this GATT service is a
+			primary service. If false, the service is secondary.
+
+		object Device [read-only, optional]
+
+			Object path of the Bluetooth device the service
+			belongs to. Only present on services from remote
+			devices.
+
+		array{object} Characteristics [read-only]
+
+			Array of object paths representing the characteristics
+			of this service. This property is set only when the
+			characteristic discovery has been completed, however the
+			characteristic objects will become available via
+			ObjectManager as soon as they get discovered.
+
 		array{object} Includes [read-only]: Not implemented
 
 			Array of object paths representing the included
@@ -48,6 +67,47 @@ Service		org.bluez
 Interface	org.bluez.GattCharacteristic1 [Experimental]
 Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY
 
+Methods		array{byte} ReadValue()
+
+			Issues a request to read the value of the
+			characteristic and returns the value if the
+			operation was successful.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.ReadNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void WriteValue(array{byte} value)
+
+			Issues a request to write the value of the
+			characteristic.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.WriteNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void StartNotify()
+
+			Starts a notification session from this characteristic
+			if it supports value notifications or indications.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.NotSupported
+
+		void StopNotify()
+
+			This method will cancel any previous StartNotify
+			transaction. Note that notifications from a
+			characteristic are shared between sessions thus
+			calling StopNotify will release a single session.
+
+			Possible Errors: org.bluez.Error.Failed
+
 Properties	string UUID [read-only]
 
 			128-bit characteristic UUID.
@@ -57,12 +117,19 @@ Properties	string UUID [read-only]
 			Object path of the GATT service the characteristc
 			belongs to.
 
-		array{byte} Value [read-write]
+		array{byte} Value [read-only, optional]
+
+			The cached value of the characteristic. This property
+			gets updated only after a successful read request and
+			when a notification or indication is received, upon
+			which a PropertiesChanged signal will be emitted.
 
-			Value read from the remote Bluetooth device or from
-			the external application implementing GATT services.
+		boolean Notifying [read-only]
 
-		array{string} Flags [read-only, optional]
+			True, if notifications or indications on this
+			characteristic are currently enabled.
+
+		array{string} Flags [read-only]
 
 			Defines how the characteristic value can be used. See
 			Core spec "Table 3.5: Characteristic Properties bit
@@ -79,6 +146,14 @@ Properties	string UUID [read-only]
 				"reliable-write"
 				"writable-auxiliaries"
 
+		array{object} Descriptors [read-only]
+
+			Array of object paths representing the descriptors
+			of this service. This property is set only when the
+			descriptor discovery has been completed, however the
+			descriptor objects will become available via
+			ObjectManager as soon as they get discovered.
+
 
 Characteristic Descriptors hierarchy
 ====================================
@@ -89,6 +164,29 @@ Service		org.bluez
 Interface	org.bluez.GattDescriptor1 [Experimental]
 Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY/descriptorZZZ
 
+Methods		array{byte} ReadValue()
+
+			Issues a request to read the value of the
+			characteristic and returns the value if the
+			operation was successful.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.ReadNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void WriteValue(array{byte} value)
+
+			Issues a request to write the value of the
+			characteristic.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.WriteNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
 Properties	string UUID [read-only]
 
 			128-bit descriptor UUID.
@@ -98,16 +196,12 @@ Properties	string UUID [read-only]
 			Object path of the GATT characteristc the descriptor
 			belongs to.
 
-		array{byte} Value [read-write]
-
-			Raw characteristic descriptor value read from the
-			remote Bluetooth device or from the external
-			application implementing GATT services.
+		array{byte} Value [read-only, optional]
 
-		string Permissions [read-only]: To be defined
+			The cached value of the descriptor. This property
+			gets updated only after a successful read request, upon
+			which a PropertiesChanged signal will be emitted.
 
-			Defines read/write authentication and authorization
-			requirements.
 
 Service Manager hierarchy
 =============================
-- 
2.0.0.526.g5318336

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[guchaojie]

On Mon, Jul 21, 2014 at 04:40:34PM -0700, Arman Uguray wrote:
Through the disscussion , I think this proposal make lots of sense. Below is my
thought about new property and method.
> This patch proposes changes to the currently unimplemented GATT D-Bus API for
> desktop bluetoothd. This is the first step in implementing a GATT client layer
> for bluetoothd that will change the way remote attributes are accessed via
> bluetoothd plugins and external applications.
> ---
>  doc/gatt-api.txt | 118 +++++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 106 insertions(+), 12 deletions(-)
> 
> diff --git a/doc/gatt-api.txt b/doc/gatt-api.txt
> index 8c7975c..741bd18 100644
> --- a/doc/gatt-api.txt
> +++ b/doc/gatt-api.txt
> @@ -32,6 +32,25 @@ Properties	string UUID [read-only]
>  
>  			128-bit service UUID.
>  
> +		boolean Primary [read-only]
> +
> +			Indicates whether or not this GATT service is a
> +			primary service. If false, the service is secondary.
> +
This is useful to help user differenciate between primary and secondary.
> +		object Device [read-only, optional]
> +
> +			Object path of the Bluetooth device the service
> +			belongs to. Only present on services from remote
> +			devices.
This property is to get which service belong to which device, just like other
hierachy interfaces do, such as org.bluez.Device1, org.bluez.GattService1 ...
> +		array{object} Characteristics [read-only]
> +
> +			Array of object paths representing the characteristics
> +			of this service. This property is set only when the
> +			characteristic discovery has been completed, however the
> +			characteristic objects will become available via
> +			ObjectManager as soon as they get discovered.
For this new property, I think there is not essential as other property,
because when characteristic discovery happen , all the object path will setup
on DBus Hierarchy. And user can get all the characteristic by ObjectManger.
Through this, User can use their own structure to get this array of object.
That is also why we need object property such as Device, Service and so on.

And another reason , it have to wait for characteristic discovery completed, it
also can say that it have to wait for characteristic setup DBus Hirarchy is
ready. There exists asynchronous issues, if user get this property operation
before all the characteristic DBus setup is ready, it will make a mistake.

Let user get all the characteristics under the service by DBus Hierarchy, it
will be no problem.

All in one, I think this property that user can get by existing DBus
Information already .

>  		array{object} Includes [read-only]: Not implemented
>  
>  			Array of object paths representing the included
> @@ -48,6 +67,47 @@ Service		org.bluez
>  Interface	org.bluez.GattCharacteristic1 [Experimental]
>  Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY
>  
> +Methods		array{byte} ReadValue()
> +
> +			Issues a request to read the value of the
> +			characteristic and returns the value if the
> +			operation was successful.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +					 org.bluez.Error.InProgress
> +					 org.bluez.Error.ReadNotPermitted
> +					 org.bluez.Error.NotPaired
> +					 org.bluez.Error.NotSupported
By my Implementaion old dbus-api testing, I found most characteristic will not
changed. So in previous email that I said listen for characteristic notification
such as heartrate. But this also very useful especially control point characteristic
to ensure the value has been written into remote device and send PropertyChanged
signal. I agree with you.
> +		void WriteValue(array{byte} value)
> +
> +			Issues a request to write the value of the
> +			characteristic.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +					 org.bluez.Error.InProgress
> +					 org.bluez.Error.WriteNotPermitted
> +					 org.bluez.Error.NotPaired
> +					 org.bluez.Error.NotSupported
Let characteristic value property be read-only, this make sense.
> +		void StartNotify()
> +
> +			Starts a notification session from this characteristic
> +			if it supports value notifications or indications.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +					 org.bluez.Error.InProgress
> +					 org.bluez.Error.NotSupported
About this method , I think other LE profile offer similar interface to user,
such as in heartrate profile. It will give registerwatcher method, in which 
it will enable notify for heartrate. This will help to trace descriptor
including notification bit changed and send Propertychanged signal.
> +		void StopNotify()
> +
> +			This method will cancel any previous StartNotify
> +			transaction. Note that notifications from a
> +			characteristic are shared between sessions thus
> +			calling StopNotify will release a single session.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +
>  Properties	string UUID [read-only]
>  
>  			128-bit characteristic UUID.
> @@ -57,12 +117,19 @@ Properties	string UUID [read-only]
>  			Object path of the GATT service the characteristc
>  			belongs to.
>  
> -		array{byte} Value [read-write]
> +		array{byte} Value [read-only, optional]
> +
> +			The cached value of the characteristic. This property
> +			gets updated only after a successful read request and
> +			when a notification or indication is received, upon
> +			which a PropertiesChanged signal will be emitted.
>  
> -			Value read from the remote Bluetooth device or from
> -			the external application implementing GATT services.
> +		boolean Notifying [read-only]
>  
> -		array{string} Flags [read-only, optional]
> +			True, if notifications or indications on this
> +			characteristic are currently enabled.
> +
> +		array{string} Flags [read-only]
>  
>  			Defines how the characteristic value can be used. See
>  			Core spec "Table 3.5: Characteristic Properties bit
> @@ -79,6 +146,14 @@ Properties	string UUID [read-only]
>  				"reliable-write"
>  				"writable-auxiliaries"
>  
> +		array{object} Descriptors [read-only]
> +
> +			Array of object paths representing the descriptors
> +			of this service. This property is set only when the
> +			descriptor discovery has been completed, however the
> +			descriptor objects will become available via
> +			ObjectManager as soon as they get discovered.
> +
>  
>  Characteristic Descriptors hierarchy
>  ====================================
> @@ -89,6 +164,29 @@ Service		org.bluez
>  Interface	org.bluez.GattDescriptor1 [Experimental]
>  Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/serviceXX/charYYYY/descriptorZZZ
>  
> +Methods		array{byte} ReadValue()
> +
> +			Issues a request to read the value of the
> +			characteristic and returns the value if the
> +			operation was successful.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +					 org.bluez.Error.InProgress
> +					 org.bluez.Error.ReadNotPermitted
> +					 org.bluez.Error.NotPaired
> +					 org.bluez.Error.NotSupported
> +
> +		void WriteValue(array{byte} value)
> +
> +			Issues a request to write the value of the
> +			characteristic.
> +
> +			Possible Errors: org.bluez.Error.Failed
> +					 org.bluez.Error.InProgress
> +					 org.bluez.Error.WriteNotPermitted
> +					 org.bluez.Error.NotPaired
> +					 org.bluez.Error.NotSupported
> +
>  Properties	string UUID [read-only]
>  
>  			128-bit descriptor UUID.
> @@ -98,16 +196,12 @@ Properties	string UUID [read-only]
>  			Object path of the GATT characteristc the descriptor
>  			belongs to.
>  
> -		array{byte} Value [read-write]
> -
> -			Raw characteristic descriptor value read from the
> -			remote Bluetooth device or from the external
> -			application implementing GATT services.
> +		array{byte} Value [read-only, optional]
>  
> -		string Permissions [read-only]: To be defined
> +			The cached value of the descriptor. This property
> +			gets updated only after a successful read request, upon
> +			which a PropertiesChanged signal will be emitted.
>  
> -			Defines read/write authentication and authorization
> -			requirements.
>  
>  Service Manager hierarchy
>  =============================
> -- 
> 2.0.0.526.g5318336
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Johan Hedberg]

Hi Arman,

On Mon, Jul 21, 2014, Arman Uguray wrote:
>     - Replaced the "Authentication", "Authorization", and "Encryption" errors
>       with a simpler "NotPaired" error, since there's not much the external
>       application can do on these errors other than try to pair. bluetoothd will
>       automatically attempt to raise the security level of the connection on
>       these errors.

"Insufficient Authorization" seems different from the other two in that
it's something that can't be attempted to be "fixed" from the client
side. It effectively means that our request was rejected by the remote
user, doesn't it?

Johan

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Chaojie, Johan,

Please see my responses inline:


>> +             array{object} Characteristics [read-only]
>> +
>> +                     Array of object paths representing the characteristics
>> +                     of this service. This property is set only when the
>> +                     characteristic discovery has been completed, however the
>> +                     characteristic objects will become available via
>> +                     ObjectManager as soon as they get discovered.
> For this new property, I think there is not essential as other property,
> because when characteristic discovery happen , all the object path will setup
> on DBus Hierarchy. And user can get all the characteristic by ObjectManger.

The problem is that ObjectManager has no clear way to tell a client
that "this subset of object paths have been published" and when they
are all available via GetManagedObjects. The most a client can do is
observe the InterfacesAdded signal and that signal is sent on a per
object path basis. For most external applications, it might be enough
but I would like application APIs to have to ability to say "all
objects published, service is ready to use".


> Through this, User can use their own structure to get this array of object.
> That is also why we need object property such as Device, Service and so on.
>
> And another reason , it have to wait for characteristic discovery completed, it
> also can say that it have to wait for characteristic setup DBus Hirarchy is
> ready. There exists asynchronous issues, if user get this property operation
> before all the characteristic DBus setup is ready, it will make a mistake.
>

This is exactly the problem. A simple update of this property lets the
user know that the hierarchy has been set up. For all I care, this
could even be a simple boolean property such as "DiscoveryComplete"
but I kind of like the list of characteristics even though
GetManagedObjects/InterfacesAdded, as you say, can achieve the same
result. We have the similar "Includes" property already, so it's not
entirely inconsistent from an API standpoint.


>> +             void StartNotify()
>> +
>> +                     Starts a notification session from this characteristic
>> +                     if it supports value notifications or indications.
>> +
>> +                     Possible Errors: org.bluez.Error.Failed
>> +                                      org.bluez.Error.InProgress
>> +                                      org.bluez.Error.NotSupported
> About this method , I think other LE profile offer similar interface to user,
> such as in heartrate profile. It will give registerwatcher method, in which
> it will enable notify for heartrate. This will help to trace descriptor
> including notification bit changed and send Propertychanged signal.

Are you referring to the HeartRateManager1 hierarchy? Since we're now
building a generic API, we need a proper way of reference-counted,
per-connection way to access the Client Characteristic Configuration
descriptor. In this proposal, calling WriteValue on the CCC descriptor
will always fail with WriteNotPermitted.

Do you have any suggestions for the method name or are you OK with
StartNotify for now? We can always change it later.


> "Insufficient Authorization" seems different from the other two in that
> it's something that can't be attempted to be "fixed" from the client
> side. It effectively means that our request was rejected by the remote
> user, doesn't it?

Good point, there is really not much bluetoothd or the external app
can do in this case so we should probably propagate the authentication
error separately from the NotPaired cases. Or do you think that it
would be beneficial to have separate error definitions for Encryption
and Authentication as well? Having Error.NotPaired and
Error.Authentication seems reasonable to me.

Cheers,
Arman

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcin Kraglak]

Hi Arman,

On 22 July 2014 22:40, Arman Uguray <armansito@chromium.org> wrote:
> Hi Chaojie, Johan,
>
> Please see my responses inline:
>
>
>>> +             array{object} Characteristics [read-only]
>>> +
>>> +                     Array of object paths representing the characteristics
>>> +                     of this service. This property is set only when the
>>> +                     characteristic discovery has been completed, however the
>>> +                     characteristic objects will become available via
>>> +                     ObjectManager as soon as they get discovered.
>> For this new property, I think there is not essential as other property,
>> because when characteristic discovery happen , all the object path will setup
>> on DBus Hierarchy. And user can get all the characteristic by ObjectManger.
>
> The problem is that ObjectManager has no clear way to tell a client
> that "this subset of object paths have been published" and when they
> are all available via GetManagedObjects. The most a client can do is
> observe the InterfacesAdded signal and that signal is sent on a per
> object path basis. For most external applications, it might be enough
> but I would like application APIs to have to ability to say "all
> objects published, service is ready to use".
>
>
>> Through this, User can use their own structure to get this array of object.
>> That is also why we need object property such as Device, Service and so on.
>>
>> And another reason , it have to wait for characteristic discovery completed, it
>> also can say that it have to wait for characteristic setup DBus Hirarchy is
>> ready. There exists asynchronous issues, if user get this property operation
>> before all the characteristic DBus setup is ready, it will make a mistake.
>>
>
> This is exactly the problem. A simple update of this property lets the
> user know that the hierarchy has been set up. For all I care, this
> could even be a simple boolean property such as "DiscoveryComplete"
> but I kind of like the list of characteristics even though
> GetManagedObjects/InterfacesAdded, as you say, can achieve the same
> result. We have the similar "Includes" property already, so it's not
> entirely inconsistent from an API standpoint.
>
>
>>> +             void StartNotify()
>>> +
>>> +                     Starts a notification session from this characteristic
>>> +                     if it supports value notifications or indications.
>>> +
>>> +                     Possible Errors: org.bluez.Error.Failed
>>> +                                      org.bluez.Error.InProgress
>>> +                                      org.bluez.Error.NotSupported
>> About this method , I think other LE profile offer similar interface to user,
>> such as in heartrate profile. It will give registerwatcher method, in which
>> it will enable notify for heartrate. This will help to trace descriptor
>> including notification bit changed and send Propertychanged signal.
>
> Are you referring to the HeartRateManager1 hierarchy? Since we're now
> building a generic API, we need a proper way of reference-counted,
> per-connection way to access the Client Characteristic Configuration
> descriptor. In this proposal, calling WriteValue on the CCC descriptor
> will always fail with WriteNotPermitted.
>
> Do you have any suggestions for the method name or are you OK with
> StartNotify for now? We can always change it later.
>
>
>> "Insufficient Authorization" seems different from the other two in that
>> it's something that can't be attempted to be "fixed" from the client
>> side. It effectively means that our request was rejected by the remote
>> user, doesn't it?
>
> Good point, there is really not much bluetoothd or the external app
> can do in this case so we should probably propagate the authentication
> error separately from the NotPaired cases. Or do you think that it
> would be beneficial to have separate error definitions for Encryption
> and Authentication as well? Having Error.NotPaired and
> Error.Authentication seems reasonable to me.

Error.Authorization seems to be higher layer specific:

"The authorization requirements for access
to a given attribute are not defined in this specification. Each
device implemen-
tation will determine how authorization occurs. Authorization procedures are
defined in GAP, and may be further refined in a higher layer specification."

so it seems reasonable to send this error to application.
We could also add Invalid Value Length error.

>
> Cheers,
> Arman
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BR
Marcin

RE: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Gu, Chao Jie]

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Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Chaojie,

> Of course if DBus has these array object of characteristic property, there is more clear and easy for client to get. However, in my opinion, bluez just put out least but enough information in DBus Hierarchy for application to use. Just you said, to add array object property , this could even be a simple boolean property such as "DiscoveryComplete". That would be add more property in DBus, so on the contrary it would not let DBus Hierarchy look simple and clear.
> Through the objectAdded and InterfaceAdded Signal, application can acquire this subset of object in fact.

Explain to me how, using only the InterfacesAdded signal, an
application can know that all characteristic objects under a service
hierarchy have been added? The only way is if the external application
already knows about service it's interacting with, which is not the
case if you're building a generic application API on top of
bluetoothd. Without what I'm proposing, you can't build a generic GATT
application API without requiring cumbersome event handling for each
service, characteristic, and descriptor object as they get added and
have only partial access to these objects in the handlers as the
objects are getting processed. This might be fine for low-level
applications that interact with D-Bus directly, but for higher level
app developers this is a real issue that we want to handle properly
and make their lives easier.


>why adapter did not export array object of devices and device not export array object of services ?

Because it doesn't need to. You always deal with individual devices as
they get added. You do NOT have this hierarchy with adapter where
doing anything meaningful with the adapter requires you to have seen a
certain set of multiple device objects.


> I am totally ok with generic notify API to application, but I am afraid that there would be conflict between LE profile and generic notify API. Because application does not know RegisterWatcher method has enable the notification. I do not know org.bluez.Inprogress error code could warn this condition or not.
>

You're right, as we move to the new shared GATT/ATT stack, we will
have to change the way the LE plugins work. We need an internal API
for bluetoothd that will handle discovery and other resource
management (such as the CCC write) among daemon plugins and external
applications. Without that, there will be conflict since the plugins,
as they are today, perform these operations directly.

Eventually what we want is to allow plugins to expose methods such as
RegisterWatcher but have that call an internal API method so that
UnregisterWatcher won't cause a write to the CCC descriptor if an
external app called StartNotify on that characteristic and vice versa.

So yes, there will be conflict unless we fix the whole stack, but
that's what we'll do as we deprecate attrib/*.


> BTW, you saidi that calling WriteValue on the CCC descriptor will always fail with WriteNotPermitted. I think gatt_write_char function can write CCC descriptor , do you mean in WriteValue method to refuse write CCC descriptor on purpose and return WriteNotPermitted ?

Yes, I meant the latter (WriteValue method will refuse on purpose).

Cheers and thanks for the comments,
Arman

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcin,

> We could also add Invalid Value Length error.

Good point, I will add that to the list of errors for WriteValue.

Cheers,
Arman

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Arman,

>> Of course if DBus has these array object of characteristic property, there is more clear and easy for client to get. However, in my opinion, bluez just put out least but enough information in DBus Hierarchy for application to use. Just you said, to add array object property , this could even be a simple boolean property such as "DiscoveryComplete". That would be add more property in DBus, so on the contrary it would not let DBus Hierarchy look simple and clear.
>> Through the objectAdded and InterfaceAdded Signal, application can acquire this subset of object in fact.
> 
> Explain to me how, using only the InterfacesAdded signal, an
> application can know that all characteristic objects under a service
> hierarchy have been added? The only way is if the external application
> already knows about service it's interacting with, which is not the
> case if you're building a generic application API on top of
> bluetoothd. Without what I'm proposing, you can't build a generic GATT
> application API without requiring cumbersome event handling for each
> service, characteristic, and descriptor object as they get added and
> have only partial access to these objects in the handlers as the
> objects are getting processed. This might be fine for low-level
> applications that interact with D-Bus directly, but for higher level
> app developers this is a real issue that we want to handle properly
> and make their lives easier.

since InterfacesAdded is per object path, the extra Characteristics array makes sense. However that really only applies to application passively monitoring the bus objects and properties. The initiator of service discovery should only return from that method call when all other object signals have been send out. Similar to what we are doing with pairing or other potential long run asynchronous method calls.

Regards

Marcel

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcel,

> since InterfacesAdded is per object path, the extra Characteristics array=
 makes sense. However that really only applies to application passively mon=
itoring the bus objects and properties. The initiator of service discovery =
should only return from that method call when all other object signals have=
 been send out. Similar to what we are doing with pairing or other potentia=
l long run asynchronous method calls.
>

That makes sense. Then again we don't really have a clear method for
this yet other than org.bluez.Device1.Connect. We are going to have to
figure out the behavior of that method when plugins and the GATT DBus
API are involved as we build the new stack. I also have in mind a
separate, application-specific method for creating a GATT connection
(something like ConnectGatt), where the system UI would call the old
Connect/Disconnect methods but applications would have to use a
ConnectGatt/DisconnectGatt API that keeps track of the different dbus
connections/sessions, but that's a subject for another discussion and
I haven't fully thought this through yet.

Coming back to your point, yes, the application that called Connect
should receive InterfacesAdded for all objects before the call
returns, as you said. Other applications might be passively observing
these events, so they can also wait for PropertiesChanged on
"Characteristics" to know that object creation for a particular
service is complete.

Cheers,
Arman

RE: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Gu, Chao Jie]

Hi Arman,=20

> Explain to me how, using only the InterfacesAdded signal, an=20
> application can know that all characteristic objects under a service=20
> hierarchy have been added? The only way is if the external application=20
> already knows about service it's interacting with, which is not the=20
> case if you're building a generic application API on top of=20
> bluetoothd. Without what I'm proposing, you can't build a generic GATT=20
> application API without requiring cumbersome event handling for each=20
> service, characteristic, and descriptor object as they get added and=20
> have only partial access to these objects in the handlers as the=20
> objects are getting processed. This might be fine for low-level=20
> applications that interact with D-Bus directly, but for higher level=20
> app developers this is a real issue that we want to handle properly=20
> and make their lives easier.

You are right, we work on Tizen Bluetooth-frwk which is low-level service/a=
pplication in system . Bluetooth-frwk can take a role to handle D-Bus infor=
maiton and give defined API to application such as characteristic discovery=
 method, so we refer to different level application indeed.
>From your aspect, I understood that you consider that high level app develo=
per how to get characteristic array directly from bluetoothd. .=20

Thanks
Chaojie
-----Original Message-----
From: Marcel Holtmann [mailto:marcel@holtmann.org]=20
Sent: Thursday, July 24, 2014 12:33 AM
To: Arman Uguray
Cc: Gu, Chao Jie; BlueZ development; Johan Hedberg
Subject: Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for =
the GATT D-Bus API.

Hi Arman,

>> Of course if DBus has these array object of characteristic property, the=
re is more clear and easy for client to get. However, in my opinion, bluez =
just put out least but enough information in DBus Hierarchy for application=
 to use. Just you said, to add array object property , this could even be a=
 simple boolean property such as "DiscoveryComplete". That would be add mor=
e property in DBus, so on the contrary it would not let DBus Hierarchy look=
 simple and clear.
>> Through the objectAdded and InterfaceAdded Signal, application can acqui=
re this subset of object in fact.
>=20
> Explain to me how, using only the InterfacesAdded signal, an=20
> application can know that all characteristic objects under a service=20
> hierarchy have been added? The only way is if the external application=20
> already knows about service it's interacting with, which is not the=20
> case if you're building a generic application API on top of=20
> bluetoothd. Without what I'm proposing, you can't build a generic GATT=20
> application API without requiring cumbersome event handling for each=20
> service, characteristic, and descriptor object as they get added and=20
> have only partial access to these objects in the handlers as the=20
> objects are getting processed. This might be fine for low-level=20
> applications that interact with D-Bus directly, but for higher level=20
> app developers this is a real issue that we want to handle properly=20
> and make their lives easier.

since InterfacesAdded is per object path, the extra Characteristics array m=
akes sense. However that really only applies to application passively monit=
oring the bus objects and properties. The initiator of service discovery sh=
ould only return from that method call when all other object signals have b=
een send out. Similar to what we are doing with pairing or other potential =
long run asynchronous method calls.

Regards

Marcel

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Luiz Augusto von Dentz]

[-- Attachment #1: Type: text/plain, Size: 1837 bytes --]

Hi Arman,


On Thu, Jul 24, 2014 at 7:11 AM, Gu, Chao Jie <chao.jie.gu@intel.com> wrote:

> Hi Arman,
>
> > Explain to me how, using only the InterfacesAdded signal, an
> > application can know that all characteristic objects under a service
> > hierarchy have been added? The only way is if the external application
> > already knows about service it's interacting with, which is not the
> > case if you're building a generic application API on top of
> > bluetoothd. Without what I'm proposing, you can't build a generic GATT
> > application API without requiring cumbersome event handling for each
> > service, characteristic, and descriptor object as they get added and
> > have only partial access to these objects in the handlers as the
> > objects are getting processed. This might be fine for low-level
> > applications that interact with D-Bus directly, but for higher level
> > app developers this is a real issue that we want to handle properly
> > and make their lives easier.
>

Im just wondering why we did not use variant type instead of array of bytes
for value, imo it seems a better fit since it can be extended with
different types in host byte order.


> You are right, we work on Tizen Bluetooth-frwk which is low-level
> service/application in system . Bluetooth-frwk can take a role to handle
> D-Bus informaiton and give defined API to application such as
> characteristic discovery method, so we refer to different level application
> indeed.
> From your aspect, I understood that you consider that high level app
> developer how to get characteristic array directly from bluetoothd. .
>

>
Tizen has to follow BlueZ design, you can offer a C binding for it exposing
the exact same (or a subset) of the D-Bus API, anything other than that
will cause a maintenance burden in your end.

-- 
Luiz Augusto von Dentz

[-- Attachment #2: Type: text/html, Size: 2808 bytes --]

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Luiz Augusto von Dentz]

Hi,

On Thu, Jul 24, 2014 at 10:58 AM, Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
> Hi Arman,
>
>
> On Thu, Jul 24, 2014 at 7:11 AM, Gu, Chao Jie <chao.jie.gu@intel.com> wrote:
>>
>> Hi Arman,
>>
>> > Explain to me how, using only the InterfacesAdded signal, an
>> > application can know that all characteristic objects under a service
>> > hierarchy have been added? The only way is if the external application
>> > already knows about service it's interacting with, which is not the
>> > case if you're building a generic application API on top of
>> > bluetoothd. Without what I'm proposing, you can't build a generic GATT
>> > application API without requiring cumbersome event handling for each
>> > service, characteristic, and descriptor object as they get added and
>> > have only partial access to these objects in the handlers as the
>> > objects are getting processed. This might be fine for low-level
>> > applications that interact with D-Bus directly, but for higher level
>> > app developers this is a real issue that we want to handle properly
>> > and make their lives easier.
>
>
> Im just wondering why we did not use variant type instead of array of bytes
> for value, imo it seems a better fit since it can be extended with different
> types in host byte order.
>
>>
>> You are right, we work on Tizen Bluetooth-frwk which is low-level
>> service/application in system . Bluetooth-frwk can take a role to handle
>> D-Bus informaiton and give defined API to application such as characteristic
>> discovery method, so we refer to different level application indeed.
>> From your aspect, I understood that you consider that high level app
>> developer how to get characteristic array directly from bluetoothd. .
>>
>>
>
> Tizen has to follow BlueZ design, you can offer a C binding for it exposing
> the exact same (or a subset) of the D-Bus API, anything other than that will
> cause a maintenance burden in your end.

Resending since vger rejected my last email claiming it contained HTML subparts.


-- 
Luiz Augusto von Dentz

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Luiz,

> Im just wondering why we did not use variant type instead of array of bytes
> for value, imo it seems a better fit since it can be extended with different
> types in host byte order.
>

I don't think that is such a good idea. Characteristic/descriptor
values are usually meant to be interpreted as a series of bytes
encoding different kinds of data of various lengths based on the
profile (e.g. the first byte is a bit mask, the following two bytes
are a uint16, etc). I think it's better to just leave it as an array
of bytes in the order that it was received from the wire as this is
what clients will expect and the order in which the bytes should be
interpreted will be explicitly specified by the profile

On occasion you have a characteristic value that encodes, for example,
a complete string. Then again, if we put a variant of string as the
value property there, only those clients that know beforehand that the
value contains a string will be able to work with it. If you're
implementing a high-level generic application API, this won't work.

Cheers,
Arman

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Luiz Augusto von Dentz]

Hi Arman,

On Fri, Jul 25, 2014 at 9:50 PM, Arman Uguray <armansito@google.com> wrote:
> Hi Luiz,
>
>> Im just wondering why we did not use variant type instead of array of bytes
>> for value, imo it seems a better fit since it can be extended with different
>> types in host byte order.
>>
>
> I don't think that is such a good idea. Characteristic/descriptor
> values are usually meant to be interpreted as a series of bytes
> encoding different kinds of data of various lengths based on the
> profile (e.g. the first byte is a bit mask, the following two bytes
> are a uint16, etc). I think it's better to just leave it as an array
> of bytes in the order that it was received from the wire as this is
> what clients will expect and the order in which the bytes should be
> interpreted will be explicitly specified by the profile

In case we know the profile we could go ahead an decode upfront and in
case we don't know how to decode we keep the array of bytes inside the
variant.

> On occasion you have a characteristic value that encodes, for example,
> a complete string. Then again, if we put a variant of string as the
> value property there, only those clients that know beforehand that the
> value contains a string will be able to work with it. If you're
> implementing a high-level generic application API, this won't work.

Well a variant is a container so it can carry any of those values
including string or even an array of strings and I believe it would
make things even more simple to a client generic API because it can
directly be based on D-Bus variant type that most bindings do already
support.


-- 
Luiz Augusto von Dentz

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Luiz,

>>> Im just wondering why we did not use variant type instead of array of bytes
>>> for value, imo it seems a better fit since it can be extended with different
>>> types in host byte order.
>>> 
>> 
>> I don't think that is such a good idea. Characteristic/descriptor
>> values are usually meant to be interpreted as a series of bytes
>> encoding different kinds of data of various lengths based on the
>> profile (e.g. the first byte is a bit mask, the following two bytes
>> are a uint16, etc). I think it's better to just leave it as an array
>> of bytes in the order that it was received from the wire as this is
>> what clients will expect and the order in which the bytes should be
>> interpreted will be explicitly specified by the profile
> 
> In case we know the profile we could go ahead an decode upfront and in
> case we don't know how to decode we keep the array of bytes inside the
> variant.

I prefer we keep the Value property as array of bytes. We should always expose the real value information for all characteristics. This is especially important for custom services.

The one thing I always wanted is a string representation of the Value property as a second property. That way some clients and tools that only need to display the value can rely on bluetoothd giving it a nice translated string. 

>> On occasion you have a characteristic value that encodes, for example,
>> a complete string. Then again, if we put a variant of string as the
>> value property there, only those clients that know beforehand that the
>> value contains a string will be able to work with it. If you're
>> implementing a high-level generic application API, this won't work.
> 
> Well a variant is a container so it can carry any of those values
> including string or even an array of strings and I believe it would
> make things even more simple to a client generic API because it can
> directly be based on D-Bus variant type that most bindings do already
> support.

The problem is that values are include also types of what their content is. Being it a temperature value, percentage or some other value.

Regards

Marcel

Re: [RFC v1 0/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Luiz & Marcel,


> The one thing I always wanted is a string representation of the Value property as a second property. That way some clients and tools that only need to display the value can rely on bluetoothd giving it a nice translated string.
>

We could do something like this, then again, if a tool wants to
display the value as a string couldn't they just convert it to a
string themselves and simply format it however they like?


>> Well a variant is a container so it can carry any of those values
>> including string or even an array of strings and I believe it would
>> make things even more simple to a client generic API because it can
>> directly be based on D-Bus variant type that most bindings do already
>> support.
>

IMO bluetoothd is not the right place to do this. The high-level API
can allow programmers to do some of these conversions, using features
of the programming language (like in JavaScript or Python) or by
providing additional API functions to perform these conversions (like
on Android). Just returning the raw value also makes the development
of these APIs easier, especially those that have internal bindings for
other platforms such as Windows and Mac that don't necessarily provide
the same variant-based data in their Bluetooth APIs (the new Chrome
bluetooth APIs are such an example).

Cheers,
Arman

RE: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Gu, Chao Jie]

Hi Arman,
	In this weekend, I think about this API again , and there is one question =
for you:
	In your new proposal , bluez offer two ways for application to read charac=
teristic value, one is to get property array of value, the other is to use =
ReadValue method.
	For applications, in which condition they use property array of value and =
in which condition they use ReadValue ? will it cause a confusion for user =
when offer two ways for user at the same time?

> I have to disagree here. I think making the DBus.Properties interface wor=
k for this particular case doesn't make the API particularly simpler, in fa=
ct I think it adds unnecessary complexity and ambiguity to the semantics in=
volved. It's not clear, for instance, if Get should always return the cache=
d value or if it should issue a=20
> Read request to the remote end. You suggest making an initial read reques=
t and storing that value and updating it on notifications. What if the char=
acteristic doesn't support notifications but it's value can change? What if=
 the client is implementing a profile that warrants a read request to the r=
emote end to get the
> freshest value on demand?
You said "What if the characteristic doesn't support notifications but it's=
 value can change?" It means cached array of value cannot be trusted in the=
 condition you said exist if this value changes happen not result from writ=
ing to the remote end device.=20
So in my understanding, there is no worth to read characteristic value by p=
roperty array of value, the property's role is just to emit propertychanged=
 signal when write/read/notification operation changes its value. If so, we=
 just define a signal such as ValueUpdated to tell user value has been chan=
ged is ok.

"What if the characteristic doesn't support notifications but it's value ca=
n change?", if this value change just happen only one condition that client=
 write the value to remote, not in which remote change its value itself spo=
ntaneously and not send notification. In fact, Set/Get property also can ac=
hieve the same result as your new proposal. Because the cache value can be =
trusted in this condition. And the cache value is the freshest value becaus=
e client write value to the remote would let cache value send propertychang=
ed signal to refresh itself to newest value.

So there are two API design can be used:
1. array of value property  Get/Set  (This design just happen only one cond=
ition that client write the value to remote, not in which remote change its=
 value itself spontaneously and not send notification.)
2. ReadValue /WriteValue method and signal ValueUpdated=20

However, in the conclusion, array of value property and ReadValue/WriteValu=
e can not be coexist, otherwise that design will result in ambiguity and no=
t make sense.

Thanks
Chaojie
-----Original Message-----
From: linux-bluetooth-owner@vger.kernel.org [mailto:linux-bluetooth-owner@v=
ger.kernel.org] On Behalf Of Arman Uguray
Sent: Tuesday, July 22, 2014 7:41 AM
To: linux-bluetooth@vger.kernel.org
Cc: Arman Uguray
Subject: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the =
GATT D-Bus API.

This patch proposes changes to the currently unimplemented GATT D-Bus API f=
or desktop bluetoothd. This is the first step in implementing a GATT client=
 layer for bluetoothd that will change the way remote attributes are access=
ed via bluetoothd plugins and external applications.
---
 doc/gatt-api.txt | 118 +++++++++++++++++++++++++++++++++++++++++++++++++--=
----
 1 file changed, 106 insertions(+), 12 deletions(-)

diff --git a/doc/gatt-api.txt b/doc/gatt-api.txt index 8c7975c..741bd18 100=
644
--- a/doc/gatt-api.txt
+++ b/doc/gatt-api.txt
@@ -32,6 +32,25 @@ Properties	string UUID [read-only]
=20
 			128-bit service UUID.
=20
+		boolean Primary [read-only]
+
+			Indicates whether or not this GATT service is a
+			primary service. If false, the service is secondary.
+
+		object Device [read-only, optional]
+
+			Object path of the Bluetooth device the service
+			belongs to. Only present on services from remote
+			devices.
+
+		array{object} Characteristics [read-only]
+
+			Array of object paths representing the characteristics
+			of this service. This property is set only when the
+			characteristic discovery has been completed, however the
+			characteristic objects will become available via
+			ObjectManager as soon as they get discovered.
+
 		array{object} Includes [read-only]: Not implemented
=20
 			Array of object paths representing the included
@@ -48,6 +67,47 @@ Service		org.bluez
 Interface	org.bluez.GattCharacteristic1 [Experimental]
 Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/servic=
eXX/charYYYY
=20
+Methods		array{byte} ReadValue()
+
+			Issues a request to read the value of the
+			characteristic and returns the value if the
+			operation was successful.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.ReadNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void WriteValue(array{byte} value)
+
+			Issues a request to write the value of the
+			characteristic.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.WriteNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void StartNotify()
+
+			Starts a notification session from this characteristic
+			if it supports value notifications or indications.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.NotSupported
+
+		void StopNotify()
+
+			This method will cancel any previous StartNotify
+			transaction. Note that notifications from a
+			characteristic are shared between sessions thus
+			calling StopNotify will release a single session.
+
+			Possible Errors: org.bluez.Error.Failed
+
 Properties	string UUID [read-only]
=20
 			128-bit characteristic UUID.
@@ -57,12 +117,19 @@ Properties	string UUID [read-only]
 			Object path of the GATT service the characteristc
 			belongs to.
=20
-		array{byte} Value [read-write]
+		array{byte} Value [read-only, optional]
+
+			The cached value of the characteristic. This property
+			gets updated only after a successful read request and
+			when a notification or indication is received, upon
+			which a PropertiesChanged signal will be emitted.
=20
-			Value read from the remote Bluetooth device or from
-			the external application implementing GATT services.
+		boolean Notifying [read-only]
=20
-		array{string} Flags [read-only, optional]
+			True, if notifications or indications on this
+			characteristic are currently enabled.
+
+		array{string} Flags [read-only]
=20
 			Defines how the characteristic value can be used. See
 			Core spec "Table 3.5: Characteristic Properties bit
@@ -79,6 +146,14 @@ Properties	string UUID [read-only]
 				"reliable-write"
 				"writable-auxiliaries"
=20
+		array{object} Descriptors [read-only]
+
+			Array of object paths representing the descriptors
+			of this service. This property is set only when the
+			descriptor discovery has been completed, however the
+			descriptor objects will become available via
+			ObjectManager as soon as they get discovered.
+
=20
 Characteristic Descriptors hierarchy
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
@@ -89,6 +164,29 @@ Service		org.bluez
 Interface	org.bluez.GattDescriptor1 [Experimental]
 Object path	[variable prefix]/{hci0,hci1,...}/dev_XX_XX_XX_XX_XX_XX/servic=
eXX/charYYYY/descriptorZZZ
=20
+Methods		array{byte} ReadValue()
+
+			Issues a request to read the value of the
+			characteristic and returns the value if the
+			operation was successful.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.ReadNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
+		void WriteValue(array{byte} value)
+
+			Issues a request to write the value of the
+			characteristic.
+
+			Possible Errors: org.bluez.Error.Failed
+					 org.bluez.Error.InProgress
+					 org.bluez.Error.WriteNotPermitted
+					 org.bluez.Error.NotPaired
+					 org.bluez.Error.NotSupported
+
 Properties	string UUID [read-only]
=20
 			128-bit descriptor UUID.
@@ -98,16 +196,12 @@ Properties	string UUID [read-only]
 			Object path of the GATT characteristc the descriptor
 			belongs to.
=20
-		array{byte} Value [read-write]
-
-			Raw characteristic descriptor value read from the
-			remote Bluetooth device or from the external
-			application implementing GATT services.
+		array{byte} Value [read-only, optional]
=20
-		string Permissions [read-only]: To be defined
+			The cached value of the descriptor. This property
+			gets updated only after a successful read request, upon
+			which a PropertiesChanged signal will be emitted.
=20
-			Defines read/write authentication and authorization
-			requirements.
=20
 Service Manager hierarchy
 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
--
2.0.0.526.g5318336

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Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Chaojie,


>         In this weekend, I think about this API again , and there is one =
question for you:
>         In your new proposal , bluez offer two ways for application to re=
ad characteristic value, one is to get property array of value, the other i=
s to use ReadValue method.
>         For applications, in which condition they use property array of v=
alue and in which condition they use ReadValue ? will it cause a confusion =
for user when offer two ways for user at the same time?
>

In this new proposal, the "Value" property simply stores the most
recently cached value after the most recent read procedure or
notification/indication. So, Get will simply return this cached value.
If an application wants to issue a read request to the remote
peripheral, then they will call ReadValue.


> You said "What if the characteristic doesn't support notifications but it=
's value can change?" It means cached array of value cannot be trusted in t=
he condition you said exist if this value changes happen not result from wr=
iting to the remote end device.

This is why the property is optional and wouldn't exist if the value
cannot be read or notified.

> So in my understanding, there is no worth to read characteristic value by=
 property array of value, the property's role is just to emit propertychang=
ed signal when write/read/notification operation changes its value. If so, =
we just define a signal such as ValueUpdated to tell user value has been ch=
anged is ok.
>

I only added this property back after initial feedback, which seemed
to suggest that having this cached property might have some value for
certain profile implementations. In short, if an application is always
interested in the latest, most accurate characteristic value, then
yeah, they would use ReadValue and not bother with the property at
all, as you said. I personally find that caching the value after a
write request is a bad idea, since bluetoothd can only guess what the
new value of the remote characteristic is based on the write value
that it just sent. My proposal is to only set this property and emit a
PropertiesChanged after a successful read request and on
notifications/indications. If we use PropertiesChanged this way, then
there wouldn't be a need for ValueUpdated.

I agree that this might be confusing, especially for applications that
didn't issue a read request. If one application performs a read, all
applications will then receive a PropertiesChanged signal, yet it is
not clear to them if this was due to a notification or because
somebody performed a read.

This is why, in my initial proposal, I removed the "Value" property
entirely, since any caching needed by an application can be performed
directly by them as necessary, since most apps will be interested in
getting the value directly from the remote peripheral via a call to
ReadValue anyway. Then we would just have a ValueUpdated (or
ValueNotified) signal which would only be emitted on
notifications/indications. Marcel, any thoughts on this?


> So there are two API design can be used:
> 1. array of value property  Get/Set  (This design just happen only one co=
ndition that client write the value to remote, not in which remote change i=
ts value itself spontaneously and not send notification.)
> 2. ReadValue /WriteValue method and signal ValueUpdated
>
> However, in the conclusion, array of value property and ReadValue/WriteVa=
lue can not be coexist, otherwise that design will result in ambiguity and =
not make sense.
>


Aside from the ambiguity that I mentioned above, these CAN nicely
coexist. Again, the latest proposal is to add a read-only "Value"
property which represents the cached value and have
ReadValue/WriteValue for the remote procedures on the peripheral. Set
is not allowed in this scenario and no read semantics are bound to
Get/GetAll.


-Arman

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Arman,

>>        In this weekend, I think about this API again , and there is one question for you:
>>        In your new proposal , bluez offer two ways for application to read characteristic value, one is to get property array of value, the other is to use ReadValue method.
>>        For applications, in which condition they use property array of value and in which condition they use ReadValue ? will it cause a confusion for user when offer two ways for user at the same time?
>> 
> 
> In this new proposal, the "Value" property simply stores the most
> recently cached value after the most recent read procedure or
> notification/indication. So, Get will simply return this cached value.
> If an application wants to issue a read request to the remote
> peripheral, then they will call ReadValue.

I think one detail that has to be clear os that most likely nobody is calling Get directly. I will be available, but mostly all applications will get the value from calling GetManagedObjects.

So lets say we talk about standard service like Device Information or Battery Status etc., every application gets these information in one go. This is comparing to x number of application calling ReadValue for each value individually. For values that do not change at all or change only every x days this is something that makes sense and I really want. It means that applications do not have to do anything extra for these values. They are just available and they are most likely recent or recent enough.

>> You said "What if the characteristic doesn't support notifications but it's value can change?" It means cached array of value cannot be trusted in the condition you said exist if this value changes happen not result from writing to the remote end device.
> 
> This is why the property is optional and wouldn't exist if the value
> cannot be read or notified.

Your proposal also had the Notifying property in there. Which means an application can know if it is cached value where the up-to-date status is either valid or it is unknown.

And of course if the value can not be read, then as you said, the property just does not exist at all.

>> So in my understanding, there is no worth to read characteristic value by property array of value, the property's role is just to emit propertychanged signal when write/read/notification operation changes its value. If so, we just define a signal such as ValueUpdated to tell user value has been changed is ok.
>> 
> 
> I only added this property back after initial feedback, which seemed
> to suggest that having this cached property might have some value for
> certain profile implementations. In short, if an application is always
> interested in the latest, most accurate characteristic value, then
> yeah, they would use ReadValue and not bother with the property at
> all, as you said. I personally find that caching the value after a
> write request is a bad idea, since bluetoothd can only guess what the
> new value of the remote characteristic is based on the write value
> that it just sent. My proposal is to only set this property and emit a
> PropertiesChanged after a successful read request and on
> notifications/indications. If we use PropertiesChanged this way, then
> there wouldn't be a need for ValueUpdated.

I think this depends a little bit. Most values will be return the exact same value that you write into it. That is what they are suppose to do anyway. The only exception here are control endpoints. So I would agree that for control endpoints we do not expose the Value property at all.

> I agree that this might be confusing, especially for applications that
> didn't issue a read request. If one application performs a read, all
> applications will then receive a PropertiesChanged signal, yet it is
> not clear to them if this was due to a notification or because
> somebody performed a read.

Does this really matter for an application that is not actively interested in interacting with that remote service. Why would it care what triggered the update.

Lets say you just want to monitor your temperature sensor and its battery status. So even if you are a single application and only your application is using that sensor. You just enable notifications for the values you care about and then sit back. Meaning a GetManagedObjects gets you started and PropertiesChanged notification will keep you updated. That sounds like a really nice and simple application interface to me.

> This is why, in my initial proposal, I removed the "Value" property
> entirely, since any caching needed by an application can be performed
> directly by them as necessary, since most apps will be interested in
> getting the value directly from the remote peripheral via a call to
> ReadValue anyway. Then we would just have a ValueUpdated (or
> ValueNotified) signal which would only be emitted on
> notifications/indications. Marcel, any thoughts on this?

I do not like having extra signals that you need to monitor and that do not fit into the standard model of the Object Manager. There is really no point in that we keep playing ping-pong with the remote device to all values some application is interested in. Some stuff should just come with a single call or should be notified once the device connects.

This is especially important when you think about the latency to connect to a sensor and get all information back to the application. The user interface should be able to show all information right away and then just update the ones that changed a few seconds later. However if another application or some system service has already updated these, why would the application need to request them again. It does not make sense to me. Especially once we have sensors that can provide valuable information to more than just one application.

>> So there are two API design can be used:
>> 1. array of value property  Get/Set  (This design just happen only one condition that client write the value to remote, not in which remote change its value itself spontaneously and not send notification.)
>> 2. ReadValue /WriteValue method and signal ValueUpdated
>> 
>> However, in the conclusion, array of value property and ReadValue/WriteValue can not be coexist, otherwise that design will result in ambiguity and not make sense.
>> 
> 
> Aside from the ambiguity that I mentioned above, these CAN nicely
> coexist. Again, the latest proposal is to add a read-only "Value"
> property which represents the cached value and have
> ReadValue/WriteValue for the remote procedures on the peripheral. Set
> is not allowed in this scenario and no read semantics are bound to
> Get/GetAll.

I think this is how we should start right now. If we figure out later that this makes no sense, then we correct it. However only after we get some testing applications talking to some sensors or devices, we will see how this works out.

Please keep in mind that I want to make applications simpler. The less they have to do to get things right, the better. And D-Bus is not a low-level API for me. It is high-level API that an application can use directly without having to pull in a binding or framework to make us of it.

Regards

Marcel

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcel,


> I think one detail that has to be clear os that most likely nobody is cal=
ling Get directly. I will be available, but mostly all applications will ge=
t the value from calling GetManagedObjects.
>
> So lets say we talk about standard service like Device Information or Bat=
tery Status etc., every application gets these information in one go. This =
is comparing to x number of application calling ReadValue for each value in=
dividually. For values that do not change at all or change only every x day=
s this is something that makes sense and I really want. It means that appli=
cations do not have to do anything extra for these values. They are just av=
ailable and they are most likely recent or recent enough.
>

Fair enough, this was enough to sell this to me :)

> I think this depends a little bit. Most values will be return the exact s=
ame value that you write into it. That is what they are suppose to do anywa=
y. The only exception here are control endpoints. So I would agree that for=
 control endpoints we do not expose the Value property at all.
>

Yes, we shouldn't expose the Value property if the characteristic
properties field doesn't contain "read", "notify", or "indicate". With
respect to caching the value before a write operation, I'm still
hesitant towards making any assumptions about the value. I wouldn't
want to cache the value until after the write operation has completed
successfully (which is only possible to determine with the "write
request" and "reliable long write" procedure) and there may be some
race conditions where a characteristic might immediately change it's
value and send a notification before we had a chance to store the
write value. In this case the latest cached value would be incorrect.
I understand that this is an edge case but it's enough to raise some
concern.

Anyway, we can start out by caching the write value and if people run
into any issues in the field, we can then change the behavior in the
future.


Cheers,
Arman

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Arman,

>> I think this depends a little bit. Most values will be return the exact same value that you write into it. That is what they are suppose to do anyway. The only exception here are control endpoints. So I would agree that for control endpoints we do not expose the Value property at all.
>> 
> 
> Yes, we shouldn't expose the Value property if the characteristic
> properties field doesn't contain "read", "notify", or "indicate". With
> respect to caching the value before a write operation, I'm still
> hesitant towards making any assumptions about the value. I wouldn't
> want to cache the value until after the write operation has completed
> successfully (which is only possible to determine with the "write
> request" and "reliable long write" procedure) and there may be some
> race conditions where a characteristic might immediately change it's
> value and send a notification before we had a chance to store the
> write value. In this case the latest cached value would be incorrect.
> I understand that this is an edge case but it's enough to raise some
> concern.

without thinking too much about the details, I think when notification is enabled, then we just wait for the update from the remote device. If notification is not enabled, then we update the value on write. Since everything is central in bluetoothd, we should be able to make smart decisions.

Regards

Marcel

RE: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Gu, Chao Jie]

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amllIA0KDQo=

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Chaojie,


> If we encounter one condition that the value is determine with the "Write=
 Command" procedure which no response for client, should we expose this kin=
d of property ? If we expose it, we have to write command to the remote and=
 read value back immediately, then emit propertychanged signal if read valu=
e equals to write value(different from old one).
>

I don't think we should expose this value until we have done an
initial read (either internally before we construct the D-Bus
hierarchy or after a call to ReadValue) or via notification. I think
we should just keep the property hidden until we know what the value
is, even in the case of a write.


> In your proposal , I think we also should read initial value from remote =
at the beginning of DBus Hierachy setup. Whatever "read", "notify", or "ind=
icate" even write request to remote, only different value compared with exi=
st cache value such as initial value, then bluez emit propertychanged signa=
l. This would be good, right?
>

I'm not opposed to this, though we can only read the initial value if
the characteristic supports reads. If the characteristic only supports
notify or indicate, then we should wait until we receive the first
notification/indication to expose the property and we keep it hidden
until then.


Cheers,
Arman

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Arman,

>> If we encounter one condition that the value is determine with the "Write Command" procedure which no response for client, should we expose this kind of property ? If we expose it, we have to write command to the remote and read value back immediately, then emit propertychanged signal if read value equals to write value(different from old one).
>> 
> 
> I don't think we should expose this value until we have done an
> initial read (either internally before we construct the D-Bus
> hierarchy or after a call to ReadValue) or via notification. I think
> we should just keep the property hidden until we know what the value
> is, even in the case of a write.

that is the beauty of properties with D-Bus Object Manager, we can actually also invalidate a property and tell the applications that it went away. So yes, initially the value should not be present. If we never read it, then there is no cached value. If we are connecting to a know device, then we only provide the value once we verified that the services have not changed.

>> In your proposal , I think we also should read initial value from remote at the beginning of DBus Hierachy setup. Whatever "read", "notify", or "indicate" even write request to remote, only different value compared with exist cache value such as initial value, then bluez emit propertychanged signal. This would be good, right?
>> 
> 
> I'm not opposed to this, though we can only read the initial value if
> the characteristic supports reads. If the characteristic only supports
> notify or indicate, then we should wait until we receive the first
> notification/indication to expose the property and we keep it hidden
> until then.

Exactly. And with that it is nice for the application since it still does not have to learn any new tricks to get the value. It just sits there and waits until it shows up.

Regards

Marcel

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcel,

I think this all makes sense and the API is in a reasonable shape now.
All of the properties/methods can integrate nicely with client and
server implementations (with one or two properties being optional for
server). I think we can revisit GattManager1 once we start thinking
about the server code but for now I think this is good for client.
And, of course, we can always add new properties/methods later.

RE: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Gu, Chao Jie]

SGkgbWFyY2VsLA0KCUZvciB0aGUgTmV3IEdhdHQgREJ1cyBBUEkgZGVmaW5pdGlvbiBpcyBpbXBv
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b21vLWluZm8uaHRtbA0K

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Chaojie,

the mailing list policy is to NOT top post. So please keep that in mind and do proper inline quoting.

> 	For the New Gatt DBus API definition is important for user to use, so through the discussion, arman's proposal make much sense.
> 	Will this proposal be accepted and when wiil bluez announces new Gatt API ?

I have no major objections to the API, but just an API description is not enough. What is important to also deliver an implementation of this API.

Regards

Marcel

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcel,

> I have no major objections to the API, but just an API description is not enough. What is important to also deliver an implementation of this API.
>

The implementation will come in the next few months as the shared
stack takes shape. The thing is, the existing proposal is not
accompanied by an implementation (it's not even included in the
release bundles) either and it looks like there are several parties
that are implementing their own version of the API based on the
unimplemented proposal. I think it makes sense to update it with the
changes that we discussed so that people can plan their code for
future compatibility.

Either that or remove doc/gatt-api.txt entirely for the time being.

-Arman

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Marcel Holtmann]

Hi Arman,

>> I have no major objections to the API, but just an API description is not enough. What is important to also deliver an implementation of this API.
>> 
> 
> The implementation will come in the next few months as the shared
> stack takes shape. The thing is, the existing proposal is not
> accompanied by an implementation (it's not even included in the
> release bundles) either and it looks like there are several parties
> that are implementing their own version of the API based on the
> unimplemented proposal. I think it makes sense to update it with the
> changes that we discussed so that people can plan their code for
> future compatibility.
> 
> Either that or remove doc/gatt-api.txt entirely for the time being.

then send me a patch that updates the API documentation for what it is suppose to be and deletes pieces are obsolete now.

Regards

Marcel

Re: [RFC v1 1/1] doc/gatt-api: New API properties and methods for the GATT D-Bus API.

[Arman Uguray]

Hi Marcel,

> then send me a patch that updates the API documentation for what it is suppose to be and deletes pieces are obsolete now.
>

Sent v2 with the most recent feedback addressed.

-Arman