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From "Christopher Collins (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MYNEWT-291) BLE Host - Split GATT attribute access function into more specific events
Date Mon, 02 May 2016 21:15:12 GMT

     [ https://issues.apache.org/jira/browse/MYNEWT-291?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Christopher Collins updated MYNEWT-291:
---------------------------------------
    Description: 
Nimble notifies the app that a characteristic or descriptor is being accessed via an access
callback.  The access callback takes a context parameter which points to an instance of the
following union:

{noformat}
union ble_gatt_access_ctxt {
    struct {
        const struct ble_gatt_chr_def *chr;
        void *data;
        int len;
    } chr_access;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        void *data;
        int len;
    } dsc_access;
};
{noformat}

This is problematic because the user may wish to point the _data_ fields to read-only data,
requiring them to "cast away const."  This looks questionable in code, and is difficult to
document in the user guide with a straight face.

Instead, we should change the union to the following:

{noformat}
union ble_gatt_access_ctxt {
    struct {
        const struct ble_gatt_chr_def *chr;
        const void *data;
        int len;
    } chr_read;

    struct {
        const struct ble_gatt_chr_def *chr;
        void *data;
        int len;
    } chr_write;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        const void *data;
        int len;
    } dsc_read;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        void *data;
        int len;
    } dsc_write;
};
{noformat}

  was:
Nimble notifies the app that a characteristic or descriptor is being accessed via an access
callback.  The access callback takes a context parameter which points to an instance of the
following union:

{noformat}
union ble_gatt_access_ctxt {
    struct {
        const struct ble_gatt_chr_def *chr;
        void *data;
        int len;
    } chr_access;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        void *data;
        int len;
    } dsc_access;
};
{noformat}

This is problematic because the user may wish to point the _data_ fields to read-only data,
requiring them to "cast away const."  This looks questionable in code, and is difficult to
document in the user guide with a straight face.

Instead, we should change the union to the following:
union ble_gatt_access_ctxt {
    struct {
        const struct ble_gatt_chr_def *chr;
        const void *data;
        int len;
    } chr_read;

    struct {
        const struct ble_gatt_chr_def *chr;
        void *data;
        int len;
    } chr_write;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        const void *data;
        int len;
    } dsc_read;

    struct {
        const struct ble_gatt_dsc_def *dsc;
        void *data;
        int len;
    } dsc_write;
};


> BLE Host - Split GATT attribute access function into more specific events
> -------------------------------------------------------------------------
>
>                 Key: MYNEWT-291
>                 URL: https://issues.apache.org/jira/browse/MYNEWT-291
>             Project: Mynewt
>          Issue Type: Bug
>          Components: Nimble
>            Reporter: Christopher Collins
>            Assignee: Christopher Collins
>             Fix For: 0.9.0
>
>
> Nimble notifies the app that a characteristic or descriptor is being accessed via an
access callback.  The access callback takes a context parameter which points to an instance
of the following union:
> {noformat}
> union ble_gatt_access_ctxt {
>     struct {
>         const struct ble_gatt_chr_def *chr;
>         void *data;
>         int len;
>     } chr_access;
>     struct {
>         const struct ble_gatt_dsc_def *dsc;
>         void *data;
>         int len;
>     } dsc_access;
> };
> {noformat}
> This is problematic because the user may wish to point the _data_ fields to read-only
data, requiring them to "cast away const."  This looks questionable in code, and is difficult
to document in the user guide with a straight face.
> Instead, we should change the union to the following:
> {noformat}
> union ble_gatt_access_ctxt {
>     struct {
>         const struct ble_gatt_chr_def *chr;
>         const void *data;
>         int len;
>     } chr_read;
>     struct {
>         const struct ble_gatt_chr_def *chr;
>         void *data;
>         int len;
>     } chr_write;
>     struct {
>         const struct ble_gatt_dsc_def *dsc;
>         const void *data;
>         int len;
>     } dsc_read;
>     struct {
>         const struct ble_gatt_dsc_def *dsc;
>         void *data;
>         int len;
>     } dsc_write;
> };
> {noformat}



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