fix:When reading's value is string type, it will be released prematurely

[ych988]

When reading's value is string type, it will be released prematurely.

ae_runner → edgex_data_process_event → devsdk_commandresult_free
string of IOT_DATA_REF will be release prematurely by devsdk_commandresult_free

[ych988]

Issue #493

[FelixTing]

@ych988 Please add "fix: " at the beginning of the commit message to pass Semantic PR checks.

In addition, EdgeXFoundry currently requires signed commit. For instructions on setting up a GPG key for signing commits, see https://wiki.edgexfoundry.org/display/FA/Secrets+of+GitHub+Signing%2C+Keys+and+Commits+Setup.

[FelixTing]

String values with ownership IOT_DATA_REF will not be freed by devsdk_commandresult_free. @iain-anderson Please correct me if I am wrong.

@ych988 Could you please provide steps to reproduce the issue and describe the scenario in which the problem occurred?

[ych988]

This problem is not easy to reproduce. Because if the released memory data area is not overwritten when data is uploaded, the problem will not occur.
Steps:
1 Prepare a resource which attributes are R/W.
2 Events triggered by ae_runner are reported regularly.
3 Send write events on the web page.
Scenario:
The reading will be garbled character if the released memory data area is overwrittren.

[FelixTing]

@ych988 May I ask which EdgeX device service you are using?

[ych988]

Sorry, My service depends on the device environment. This might be useful. [
HikPlatFaceAcsCtrProfile.json
](url)

"name": "doorStatusCtr",

[FelixTing]

Thanks for the information. I will test this with an existing edgex device service.

[FelixTing]

Verified this fix with device-bacnet. This fix also applies to GET commands for string type resources.

[FelixTing]

LGTM