fix: edgex_device_read does not read labels

[FelixTing]

fix: #482

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PR Checklist

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• [x] I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
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Testing Instructions

1. Run the random generator example in debug mode and set a breakpoint at https://github.com/edgexfoundry/device-sdk-c/blob/6bdae90b977cdeecb957260a94da902cfcf10c29/src/c/callback3.c#L80
2. Update device

   curl -X 'PATCH' \
   'http://localhost:59881/api/v3/device' \
   -d '[
   {
   "apiVersion": "v2",
   "device": {
     "name": "RandomDevice1",
     "labels": [
       "label1", "label2"
     ]
   }
   }
   ]'

3. Check the device read by edgex_device_read in step 1

[ych988]

I think use [devsdk_strings_new] directly will cause the order of the label array to be reversed from the original order. This way may not be perfect.

devsdk_strings *edgex_labels_read(const iot_data_t *obj)
{
  devsdk_strings *labels = NULL;
  const iot_data_t *ldata = iot_data_string_map_get (obj, "labels");
  if (ldata)
  {
    iot_data_vector_iter_t iter;
    iot_data_vector_iter (ldata, &iter);
    while (iot_data_vector_iter_next (&iter))
    {
      labels = devsdk_strings_new (iot_data_vector_iter_string (&iter), labels);    <--------- here
    }
  }
  return labels;
}

Reference: devman.c → devsdk_add_discovered_devices → devsdk_strings_new

[FelixTing]

@ych988 I see your point. Code is updated.

[iain-anderson]

You could iterate the vector backward something like

uint32_t i = iot_data_vector_size (ldata);
while (i)
{
   labels = devsdk_strings_new (iot_data_string (iot_data_vector_get (ldata, --i)));
}

[SteveOss]

There is a reverse iteration function: iot_data_vector_iter_prev