Hi @WEI_You ,
1. The proxy mapping will be necessary if there is to be any communication with the application from outside of the localhost. If you are making REST API calls from a PC client like you describe in #2, you will need proxy mapping in the package manifest.
2. Absolutely. You can create your own API reference and make custom calls to your application server.
3. You can set this up however you'd like. Usually, if the application is running locally, you can use Unix Sockets. Otherwise, you'd use TCP. Here is an example showing both methods.
Regarding your test code, a front end isn't required. You can do whatever you'd like here to fit your requirements.
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