TUTORIALS DEVICE LIBRARY

Create & Delete device resources

Creating resources

Device with a collection resource allows dynamic creation of resources. The created resource can only be of a well defined type (see call to oc_collections_add_rt_factory in Guide) and all created resources are contained within the collection.

How to create a resource

To develop your own device you can check the example in cloud_server. Lets examine the code to identify the necessary steps that allow a device to dynamically create resources in a collection.

Create a collection resource 

oc_resource_t* col = oc_new_collection(NULL, "/switches", 1, 0);
oc_resource_bind_resource_type(col, "oic.wk.col");

For precise description of the arguments of the given functions please refer to the iotivity-lite documentation.

Determine which resource types can populate the collection 

oc_collection_add_supported_rt(col, "oic.r.switch.binary");

Supported resource types are visible through oic.if.baseline interface in the rts property of the collection.

Enable create operation on the collection resource 

oc_resource_bind_resource_interface(col, OC_IF_CREATE);

Supporting creating of resources is visible through oic.if.baseline interface in the if property of the collection. To support creation of resources the property must contain the oic.if.create interface.

Define constructor and destructor 

oc_collections_add_rt_factory("oic.r.switch.binary", new_switch_instance, free_switch_instance);

typedef struct oc_switch_t
{
  struct oc_switch_t *next;
  oc_resource_t *resource;
  bool state;
} oc_switch_t;
OC_MEMB(switch_s, oc_switch_t, 1);
OC_LIST(switches);

static oc_resource_t*
new_switch_instance(const char* href, oc_string_array_t *types,
                    oc_resource_properties_t bm, oc_interface_mask_t iface_mask,
                    size_t device)
{
  oc_switch_t *cswitch = (oc_switch_t *)oc_memb_alloc(&switch_s);
  if (cswitch) {
    cswitch->resource = oc_new_resource(
      NULL, href, oc_string_array_get_allocated_size(*types), device);
    if (cswitch->resource) {
      size_t i;
      for (i = 0; i < oc_string_array_get_allocated_size(*types); i++) {
        const char *rt = oc_string_array_get_item(*types, i);
        oc_resource_bind_resource_type(cswitch->resource, rt);
      }
      oc_resource_bind_resource_interface(cswitch->resource, iface_mask);
      cswitch->resource->properties = bm;
      oc_resource_set_default_interface(cswitch->resource, OC_IF_A);
      oc_resource_set_request_handler(cswitch->resource, OC_GET, get_cswitch,
                                      cswitch);
      oc_resource_set_request_handler(cswitch->resource, OC_DELETE, delete_cswitch,
                                      cswitch);
      oc_resource_set_request_handler(cswitch->resource, OC_POST, post_cswitch,
                                      cswitch);
      oc_resource_set_properties_cbs(cswitch->resource, get_switch_properties,
                                     cswitch, set_switch_properties, cswitch);
      oc_add_resource(cswitch->resource);
      oc_set_delayed_callback(cswitch->resource, register_to_cloud, 0);

      oc_list_insert(switches, prev, cswitch);
      return cswitch->resource;
    }
    oc_memb_free(&switch_s, cswitch);
  }
  return NULL;
}

static void
free_switch_instance(oc_resource_t *resource)
{
  oc_switch_t *cswitch = (oc_switch_t *)oc_list_head(switches);
  while (cswitch) {
    if (cswitch->resource == resource) {
      oc_delete_resource(resource);
      oc_list_remove(switches, cswitch);
      oc_memb_free(&switch_s, cswitch);
      return;
    }
    cswitch = oc_list_item_next(cswitch);
  }
}

To enable create operation in iotivity-lite library compile with CREATE=1 option.

make cloud_server CLOUD=1 SECURE=0 CREATE=1

Create a resource

When you have a cloud backend and a cloud_server binary running, you can use a cloud client to create a resource.

Create by go grpc client

Go grpc client is a simple tool that supports several useful commands we can combine to create a resource.

  • Use the get command to identify the collection device

The get command retrieves data of all available devices. To correctly call the create command the device id and href properties are necessary. In the output find the item with type oic.wk.col.

// retrieves all resources of all devices
./grpc -get

Output:

...
{
    "content": {
        "content_type": "application/vnd.ocf+cbor",
        "data": "n/8="
    },
    "resource_id": {
        "device_id": "2b9ed3ed-ddf3-4c9c-4d21-9ec1f6ba6b03",
        "href": "/switches"
    },
    "status": 1,
    "types": [
        "oic.wk.col"
    ]
}
...
  • Create a binary switch resource in the collection
./grpc -create -deviceid 2b9ed3ed-ddf3-4c9c-4d21-9ec1f6ba6b03 -href /switches <<EOF
{
    "rt": [
        "oic.r.switch.binary"
    ],
    "if": [
        "oic.if.a",
        "oic.if.baseline"
    ],
    "rep": {
        "value": false
    },
    "p": {
        "bm": 3
    }
}
EOF

The command creates a binary switch (oic.r.switch.binary), which supports actuator interface (oic.if.a) and has two possible states (“value”: true/false). The switch is set to be discoverable and observable (bm: 3; mask value 3 equals OC_DISCOVERABLE | OC_OBSERVABLE).

  • Use the get command again to examine the newly created switch
// retrieves all resources of all devices
./grpc -get

Output:

...
{
    "content": {
        "content_type": "application/vnd.ocf+cbor",
        "data": "v2V2YWx1ZfT/"
    },
    "resource_id": {
        "device_id": "2b9ed3ed-ddf3-4c9c-4d21-9ec1f6ba6b03",
        "href": "/4rLN4BlwJmFmbbMJblChB2kyT2zJEP"
    },
    "status": 1,
    "types": [
        "oic.r.switch.binary"
    ]
},
...

Deleting resources

Device with collection resource allows to delete dynamically created resource. To delete resource you need to set delete handler during creating resource.

How to delete a resource

To develop your own device check the example in cloud_server. Lets examine the code to identify the necessary steps that allow a device to delete a dynamically created resource from a collection.

Set delete handler at constructor 

// delete handler of switch
static void
delete_cswitch(oc_request_t *request, oc_interface_mask_t iface_mask,
            void *user_data)
{
  OC_DBG("%s", __func__);
  (void)request;
  (void)iface_mask;
  oc_switch_t *cswitch = (oc_switch_t *)user_data;

  // cleanup resource data
  ...

  // we cannot delete resource immediately via oc_delete_resource because
  // it is used during invocation delete handler. So we plan deleting via oc_delayed_delete_resource call.
  oc_delayed_delete_resource(cswitch->resource);
}

static oc_resource_t*
new_switch_instance(const char* href, oc_string_array_t *types,
                    oc_resource_properties_t bm, oc_interface_mask_t iface_mask,
                    size_t device)
{
  ...
      oc_resource_set_request_handler(cswitch->resource, OC_GET, get_cswitch,
                                      cswitch);

      // set delete handler to the created resource
      oc_resource_set_request_handler(cswitch->resource, OC_DELETE, delete_cswitch,
                                      cswitch);
      oc_resource_set_request_handler(cswitch->resource, OC_POST, post_cswitch,
                                      cswitch);
  ...
}

Delete by go grpc client

Delete a created binary switch resource from the collection.

./grpc -delete -deviceid 2b9ed3ed-ddf3-4c9c-4d21-9ec1f6ba6b03 -href /4rLN4BlwJmFmbbMJblChB2kyT2zJEP

See Also

“Create & Delete device resources” was last updated: August 17, 2021: content/en: fix markdown linter issues (1c0122f)
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