feat(snap): add support for environment variable injection

[farshidtz]

For details on the new scheme for setting environment variables, please refer to edgexfoundry/edgex-go#3986.

Signed-off-by: Farshid Tavakolizadeh [email protected]

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/app-rfid-llrp-inventory/blob/main/.github/Contributing.md

PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?): Add tests for snap config options canonical/edgex-snap-testing#53
• I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• I have opened a PR for the related docs change (if not, why?)

Testing Instructions

1. Set up:

snap install edgexfoundry --edge
snap install edgex-app-rfid-llrp-inventory --channel=edge/pr-74

2. Enable config and set a global config value:

$ snap set edgex-app-rfid-llrp-inventory config-enabled=true
$ snap set edgex-app-rfid-llrp-inventory config.service-startupmsg="testing injection"

$ snap start edgex-app-rfid-llrp-inventory
Started.

$ snap logs -n=all edgex-app-rfid-llrp-inventory | grep "testing injection"
2022-04-25T16:28:59+02:00 edgex-app-rfid-llrp-inventory.app-rfid-llrp-inventory[429579]: level=INFO ts=2022-04-25T14:28:59.224445693Z app=app-rfid-llrp-inventory source=variables.go:352 msg="Variables override of 'Service.StartupMsg' by environment variable: SERVICE_STARTUPMSG=testing injection"
2022-04-25T16:28:59+02:00 edgex-app-rfid-llrp-inventory.app-rfid-llrp-inventory[429579]: level=INFO ts=2022-04-25T14:28:59.323556738Z app=app-rfid-llrp-inventory source=service.go:184 msg="testing injection"

3. Set a app-specific value:

$ snap set edgex-app-rfid-llrp-inventory apps.app-rfid-llrp-inventory.config.service-port=11111

$ snap restart edgex-app-rfid-llrp-inventory
Restarted.

$ snap logs -n=all edgex-app-rfid-llrp-inventory | grep "11111"
2022-04-25T16:31:05+02:00 edgex-app-rfid-llrp-inventory.app-rfid-llrp-inventory[430015]: level=INFO ts=2022-04-25T14:31:05.094926172Z app=app-rfid-llrp-inventory source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-25T16:31:05+02:00 edgex-app-rfid-llrp-inventory.app-rfid-llrp-inventory[430015]: level=INFO ts=2022-04-25T14:31:05.198346026Z app=app-rfid-llrp-inventory source=server.go:156 msg="Starting HTTP Web Server on address localhost:11111"

New Dependency Instructions (If applicable)

[farshidtz]

@MonicaisHer please review

[MonicaisHer]

@farshidtz Thank you

[MonicaisHer]

The go.sum needs update for edgex-snap-hooks/v2 v2.2.0-beta.5

[lenny-goodell]

LGTM