Error handling on Android

Kotlin doesn't support checked exceptions. This simplifies and streamlines error handling, because you can choose to handle only those exceptions that are potentially recoverable. And because you don't have to explicitly handle every possible exception, your code is less cluttered and consequently, remains more focused on its primary purpose.

Recoverable failures are issues that a developer can address from their end. For example, if an ID used in a call is not valid, the API throws a HomeException with an invalid data message. The app developer can then choose to either remove that ID from their cache or show the user a message like "Structure not found".

An example of how one might handle a recoverable failure:

val result =
   try {
     homeManager.requestPermissions()
   } catch (e: HomeException) {
     PermissionsResult(
       PermissionsResultStatus.ERROR,
       "Got HomeException with error: ${e.message}",
     )
   }

Any method in the Home APIs can throw a HomeException, so we recommend that you use a try-catch block to catch HomeException on all calls.

When handling HomeException, check its error.code and error.message fields to learn what went wrong. There may be sub-error codes as well, so call the getSubErrorCodes() method and check the result.

Any unhandled exceptions will result in your app crashing.

The following table provides the meanings of HomeException codes that you may encounter:

Table: HomeException codes

Code	Meaning
ABORTED	The operation was aborted, typically due to a concurrency issue such as a sequencer check failure or transaction abort.
ALREADY_EXISTS	The entity that a client attempted to create, for example a file or directory, already exists.
API_NOT_CONNECTED	The client attempted to call a method from an API that failed to connect. This can happen when the device is offline or doesn't support the API that the client attempted to call.
CANCELLED	The operation was cancelled, typically by the caller.
COMMAND_FAILED	The command failed to execute. Check the sub error codes for more details.
CURSOR_WINDOW_NOT_SUPPORTED	A method was called which uses a CursorWindow, but a CursorWindow either isn't enabled or isn't supported in the present context.
DATA_LOSS	Unrecoverable data loss or corruption has occurred.
DEADLINE_EXCEEDED	The deadline expired before the operation could complete. For operations that change the state of the system, this error may be returned even if the operation has completed successfully.
DECOMMISSIONING_INELIGIBLE	The decommissioning failed because the device isn't eligible for decommissioning.
FAILED_PRECONDITION	The operation was rejected because the system is not in a state required for the operation's execution. For example, you might get this message if the stop command of the OvenCavityOperationalStateTrait was called on an oven that's already stopped.
INTERNAL	Internal errors. This means that some invariants expected by the underlying system have been broken. This error code is reserved for serious errors.
INVALID_ARGUMENT	The client provided an argument that is outside the expected range of values.
INVALID_DATA_HOLDER	The data holder is invalid.
NOT_FOUND	A requested entity, such as a file or directory, was not found. If a request is denied for an entire class of users, such as a gradual feature rollout or undocumented allowlist, NOT_FOUND may be used. If a request is denied for some users within a class of users, such as user-based access control, PERMISSION_DENIED must be used.
OUT_OF_RANGE	The operation was attempted past the valid range, such as seeking or reading past end-of-file. Unlike INVALID_ARGUMENT, this error indicates a problem that may be fixed if the system state changes.
PERMISSION_DENIED	The caller does not have permission to execute the specified operation. PERMISSION_DENIED must not be used for rejections caused by exhausting some resource (use RESOURCE_EXHAUSTED for those errors). PERMISSION_DENIED must not be used if the caller cannot be identified (use UNAUTHENTICATED for those errors). This error code does not imply the request is valid or that the requested entity exists or satisfies other preconditions.
RESOURCE_EXHAUSTED	Some resource has been exhausted, perhaps due to a per-user quota being reached or the entire file system running out of space. For example, this error could be thrown if the dispense command of the DispenseTrait is called on a pet-feeder device but there is no more food left in the unit.
SDK_INITIALIZATION_MISSING_INFO	The SDK was initialized without all the required information. For example, this error is thrown if the client attempts to get a TraitFactory for a given trait ID but the trait was not included when initializing the SDK. See Initialize the home on Android.
UNAUTHENTICATED	The caller cannot be identified or the request doesn't have valid authentication credentials.
UNAVAILABLE	The service is unavailable. This is most likely a transient condition, which can be corrected by retrying with a backoff. Note that it's not always safe to retry non-idempotent operations.
UNIMPLEMENTED	The requested operation isn't implemented, supported or enabled in this service.
UNKNOWN	Unknown error. UNKNOWN appears when an error condition occurs that can't be classified using any of the other error codes. For example, this error may be returned when a status value received from an external API lacks sufficient information as to the root cause.
WRITE_FAILED	The write failed to execute. Check the sub error codes for more details.