feat(snap): add support for environment varariable 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]

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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?)
• 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-device-camera --channel=edge/pr-200

2. Enable config and set a global config value:

$ snap set edgex-device-camera config-enabled=true
$ snap set edgex-device-camera config.service-startupmsg="testing injection"

$ snap start edgex-device-camera
Started.

$ snap logs -n=all edgex-device-camera | grep "testing"
2022-04-26T10:47:09+02:00 edgex-device-camera.device-camera[44710]: level=INFO ts=2022-04-26T08:47:09.92085086Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.StartupMsg' by environment variable: SERVICE_STARTUPMSG=testing injection"
2022-04-26T10:47:10+02:00 edgex-device-camera.device-camera[44710]: level=INFO ts=2022-04-26T08:47:10.260535937Z app=device-camera source=message.go:55 msg="testing injection"

3. Set a app-specific value:

$ snap set edgex-device-camera apps.device-camera.config.service-port=11111

$ snap restart edgex-device-camera
Restarted.

$ snap logs -n=all edgex-device-camera | grep "11111"
2022-04-26T10:47:39+02:00 edgex-device-camera.device-camera[44902]: level=INFO ts=2022-04-26T08:47:39.401816616Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T10:47:39+02:00 edgex-device-camera.device-camera[44902]: level=INFO ts=2022-04-26T08:47:39.414801789Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T10:47:39+02:00 edgex-device-camera.device-camera[44902]: level=INFO ts=2022-04-26T08:47:39.440629755Z app=device-camera source=httpserver.go:123 msg="Web server starting (localhost:11111)"

New Dependency Instructions (If applicable)

[farshidtz]

@MonicaisHer please review. Thanks.

[MonicaisHer]

@farshidtz Thank you. It works as expected.

Validate error handling:

$ snap install edgex-device-camera --channel=edge/pr-200
$ snap set edgex-device-camera config.service-startupmsg="testing injection"
error: cannot perform the following tasks:
- Run configure hook of "edgex-device-camera" snap (run hook "configure": 
-----
edgex-device-camera.configure: could not process options: 'config.' and 'apps.' options are allowed only when config-enabled is true.

WARNING: Setting config-enabled=true will unset existing 'env.' options and ignore future sets!!
-----)

$ snap set edgex-device-camera config-enabled=true
$ snap set edgex-device-camera config.service.startupmsg="testing injection"
error: cannot perform the following tasks:
- Run configure hook of "edgex-device-camera" snap (run hook "configure": edgex-device-camera.configure: could not process options: error converting config key to environment variable key: config key must not contain dots: service.startupmsg)

Test:

$ snap set edgex-device-camera config.service-startupmsg="testing injection"
$ snap start edgex-device-camera
Started.

$ snap logs -n=all edgex-device-camera | grep "testing"
2022-04-26T11:52:45+02:00 edgex-device-camera.device-camera[1764467]: level=INFO ts=2022-04-26T09:52:45.477255393Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.StartupMsg' by environment variable: SERVICE_STARTUPMSG=testing injection"
2022-04-26T11:52:45+02:00 edgex-device-camera.device-camera[1764467]: level=INFO ts=2022-04-26T09:52:45.496986552Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.StartupMsg' by environment variable: SERVICE_STARTUPMSG=testing injection"


$ snap set edgex-device-camera apps.device-camera.config.service-port=11111
$ snap restart edgex-device-camera
Restarted.

$ snap logs -n=all edgex-device-camera | grep "11111"
2022-04-26T11:53:28+02:00 edgex-device-camera.device-camera[1764673]: level=INFO ts=2022-04-26T09:53:28.528545011Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T11:53:28+02:00 edgex-device-camera.device-camera[1764673]: level=INFO ts=2022-04-26T09:53:28.540771503Z app=device-camera source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T11:53:28+02:00 edgex-device-camera.device-camera[1764673]: level=INFO ts=2022-04-26T09:53:28.565197185Z app=device-camera source=httpserver.go:123 msg="Web server starting (localhost:11111)"