Re: Re: Fwd: Fwd: [PATCH 1/1] shared/gatt-client: Fix the "Find Information req" error

Nagaraj D R <nagaraj.dr@xxxxxxxxxxx> · Thu, 11 Jun 2015 10:16:49 +0000 (GMT)

Hello Luiz,
The problem that I was trying to address is for the characteristic attribute at 0Xfffe and characteristic value declaration at oxffff.
This is a valid scenario. Characteristic need to have a characteristic value declaration but need not have characteristic descriptors.

Since present design search the descriptors b/w the characteristic value declaration and service end handle,
if service end handle and characteristic value declaration end handle are same (i.e 0xffff in a particular case)
then descriptor search handle will be initialized to 0X000 (i.e by incrementing characteristic value handle (0xffff) )
0x0000 handle is reserved handle + intention of searching descriptor will not be achieved.

Regards
Nagaraj D R

------- Original Message -------
Sender : Luiz Augusto von Dentz<luiz.dentz@xxxxxxxxx>
Date : Jun 11, 2015 15:24 (GMT+05:30)
Title : Re: Fwd: Fwd: [PATCH 1/1] shared/gatt-client: Fix the "Find Information req" error

Hi Nagaraj,

On Thu, Jun 11, 2015 at 7:09 AM, Nagaraj D R wrote:
> ping
>
> ------- Original Message -------
> Sender : Nagaraj D R Lead Engineer/SRI-Bangalore-System & Connectivity/Samsung Electronics
> Date : May 15, 2015 11:50 (GMT+05:30)
> Title : Fwd: [PATCH 1/1] shared/gatt-client: Fix the "Find Information req" error
>
> ping
>
> ------- Original Message -------
> Sender : Nagaraj D R Lead Engineer/SRI-Bangalore-System & Connectivity/Samsung Electronics
> Date : May 13, 2015 17:05 (GMT+05:30)
> Title : [PATCH 1/1] shared/gatt-client: Fix the "Find Information req" error
>
> From: "nagaraj.dr"
>
> characteristic descriptor is searched b/w the
> characteristic "value_handle + 1" and
> characteristic "end_handle" using "Find Information req"
>
> if remote device had declared the characteristic value_handle
> at 0XFFFF (which also means there is no characteristic descriptors),then
> present code would make start_handle has 0X0000(because of 16 bit
> integer overflow) for "Find Information req"
>
> desc_start = chrc_data->value_handle + 1;
>
> Consequence:  Below request will be sent,
>         ATT: Find Information req (0x04)
>         start 0x0000, end 0xffff
>
>         and below will be the proper response from the remote device
>         ATT: Error (0x01)
>         Error: Invalid handle (1)
>         Find Information req (0x04) on handle 0x0000
> ---
> src/shared/gatt-client.c |    6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/src/shared/gatt-client.c b/src/shared/gatt-client.c
> index 7bc3b71..9b944ee 100644
> --- a/src/shared/gatt-client.c
> +++ b/src/shared/gatt-client.c
> @@ -601,13 +601,13 @@ static bool discover_descs(struct discovery_op *op, bool *discovering)
> chrc_data->value_handle)
> goto failed;

Actually this check should happen in
gatt_db_service_insert_characteristic which is probably creating
something with handle 0 in the database which is wrong, actually
perhaps it should just fail to create a characteristic in 0xffff,
characteristics shall always have a value descriptor:

3.3.2 Characteristic Value Declaration
The Characteristic Value declaration contains the value of the
characteristic. It
is the first Attribute after the characteristic declaration. All characteristic
definitions shall have a Characteristic Value declaration.

So I would suggest something like this:

iff --git a/src/shared/gatt-db.c b/src/shared/gatt-db.c
index 5e1537e..7f863ef 100644

--- a/src/shared/gatt-db.c
+++ b/src/shared/gatt-db.c
@@ -706,6 +706,18 @@ service_insert_characteristic(struct
gatt_db_service *service,
        if (handle && handle <= service->attributes[0]->handle)
                return NULL;

+       /*
+        * It is not possible to allocate last handle for a Characteristic
+        * since it would not have space for its value:
+        * 3.3.2 Characteristic Value Declaration
+        * The Characteristic Value declaration contains the value of the
+        * characteristic. It is the first Attribute after the characteristic
+        * declaration. All characteristic definitions shall have a
+        * Characteristic Value declaration.
+        */
+       if (handle == UINT16_MAX)
+               return NULL;
+
        i = get_attribute_index(service, 1);
        if (!i)
                return NULL;

-- 
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