difference b/w attribute write/read permission with respect to characteristic properties

RE: difference b/w attribute write/read permission with respect to characteristic properties

Paul — Fri, 06 May 2016 19:26:33 GMT

I got into this question in my mind today. Glad to see this post there. My understanding is the characteristic properties is for telling the GATT client (normally a smart phone) this characteristic could be read, written or sending notifications. But Attribute permission is adding another layer for "security" for how you can read, how you can write. Right?

RE: difference b/w attribute write/read permission with respect to characteristic properties

Petter Myhre — Fri, 31 Jul 2015 10:20:07 GMT

Asking is good :) If you feel I have answered your question, I would appreciate if you could accept my answer.

RE: difference b/w attribute write/read permission with respect to characteristic properties

akhil — Fri, 31 Jul 2015 08:06:30 GMT

@Peter Myhre . yeah. sure. We have to follow the spec strictly. No, I don't have any such use case. Just asked as from a beginner's point of view.:) I surely has to go in depth of the spec to understand such things. :)

RE: difference b/w attribute write/read permission with respect to characteristic properties

Petter Myhre — Fri, 31 Jul 2015 07:34:40 GMT

I'm not sure exactly why there are two such things. It is two different layers of the protocol, but the spec is the spec. We need to follow it. Do you have any use case where this is unfortunate?

RE: difference b/w attribute write/read permission with respect to characteristic properties

akhil — Fri, 31 Jul 2015 04:54:14 GMT

@Petter Myhre regarding table, I have to confirm it once more. One more doubt, but why should be two such things(permission and properties)? why can't the server also follow the characteristic properties? will not that make things little bit more easy?

RE: difference b/w attribute write/read permission with respect to characteristic properties

Petter Myhre — Thu, 30 Jul 2015 15:39:00 GMT

I think you have understood correctly, but is your table incorrect?

RE: difference b/w attribute write/read permission with respect to characteristic properties

akhil — Thu, 30 Jul 2015 13:26:56 GMT

@Petter Myhre I understood it like this. please correct me if I am wrong. attribute permission is for the knowledge of server to give permission to the client requests. whereas characteristic properties is for the knowledge of the client to understand the permissions of the characteristic value. so the final access permission to the characteristic value is based on the value of the attribute permission even though client tries to read/write to the server characteristic value based on the characteristic value. Is it fine?

RE: difference b/w attribute write/read permission with respect to characteristic properties

Petter Myhre — Wed, 29 Jul 2015 13:26:21 GMT

You have attribute permissions and characterisitc properties, not characteristic permissions.

Attribute permissions are described in Vol. 3, Part F, Section 3.2.5, and Characteristic properties are described in Vol. 3, Part G, Section 3.3.1.1 in the Bluetooth Core Specification v4.2.

The characteristic properties determine how the characterisitic value can be used, this information is given to the GATT client as a reference.

The attribute permissions, or the attribute access permissions specifies that it may be read and/or written, this information is not given to the GATT client.

If you try to write to an attribute that only is readable, you would get an Write Not Permitted error.

If you try to write to an attribute that is writeable, you would be able to write to it regardless of what the characteristic properties are.

This is assuming that none of the other type of permissions are set, and that the device with GATT server doesn't check the characteristic permissions first.