How to add a judgment before writing the cluster attribute and return the specified result status，

[colddownz]

When I was simulating the matter Thermostat device just now, the test case required the read-write attribute to exceed the limit and return a General error of 0x87 (TRUSTINT-ERROR). I searched for examples in the code but couldn't find a solution。

#1. Test Harness Client attempts to write OccupiedHeatingSetpoint below the MinHeatSetpointLimit and confirms that the device does not accept the value

./chip-tool thermostat write occupied-heating-setpoint 500 1 1

On TH(chip-tool) verify that DUT sends a CONSTRAINT_ERROR (0x87)

[1676029113.651245][19392:19394] CHIP:DMG: WriteClient moving to [AwaitingDe]
[1676029113.651285][19392:19394] CHIP:TOO: Response Failure: IM Error 0x00000587: General error: 0x87 (CONSTRAINT_ERROR)
[1676029113.651397][19392:19394] CHIP:EM: <<< [E:43315i M:59735604 (Ack:107613834)] (S) Msg TX to 1:0000000000000001 [E8D5] --- Type 0000:10

[Apollon77]

This is done by actually throwing a StatusResponseError with the right code. This is then automatically converted into a matching status response.

So i fact in this case you do it like here:
1.) you register a event handler for the "Changeing" event - this is triggered when the value changes on write but before the value is committed internally

matter.js/packages/node/src/behaviors/window-covering/WindowCoveringServer.ts

Line 123 in 06a8040

this.reactTo(this.events.mode$Changing, this.#handleModeChanging);

2.) In the handler you do the needed checks and can access current cluster state and such and throw an error when needed

matter.js/packages/node/src/behaviors/window-covering/WindowCoveringServer.ts

Lines 172 to 174 in 06a8040

	if (mode.maintenanceMode && !this.state.supportsMaintenanceMode) {
	throw new StatusResponseError("Maintenance mode not supported", StatusCode.ConstraintError);
	}

With this the "Changing" process errors which will rollback the state values and respond to the write call with the defined statuscode

[Apollon77]

Seems you implement "Thermostat" cluster? If you like it would be cool if you could do a PR with your implementation or show details so that we can maybe add a default implementation to the library itself.

[colddownz]

Thank you for your reply. I have just learned to use the TypeScirpt language and currently trying to simulate a Thermostat "cluster with matter.js. If I can complete the V1.3 test case requirements, I also look forward to sharing it in the matter.js project.

[Apollon77]

Awesome, thank you. If you have any issues just ask - you can also join the Discord for a more direct exchange if you like.