In Qntrl Circuit, you can configure error handling while building a circuit. In most cases, state definition errors are detected even before saving the circuit, i.e. when you save the circuit, it runs a compilation check and lists out errors related to its state configurations, logic flow, and design. This will help you to verify and fix errors in your circuit design and configuration even before execution.

Only Functional states, such as Function, Webhook, and Circuit, are bound to have runtime errors, so the error handling feature is only supported for functional states. When you add a Functional state (Function, Webhook, or Circuit), the Error Handling option appears under Configuration on the right panel.

1. On Timeout
2. On Authorization Failure
3. On Execution Failure
4. Custom Error

On Timeout

When a functional state runs longer than the expected time, a timeout error occurs. This option is available for Function and Webhook. For handling timeout errors in Code View, the field value "errorType": "Error.TimeOut"  will be added.

On Authorization Failure

If a state fails because of insufficient privileges to access the specified code, the error is handled as an authorization failure. This option is available only for the Webhook state. In Code View, the name value "errorType": "Error.AuthorizationFailure" is added.

On Execution Failure

When a state execution fails due to some exception that cannot be processed, it can be handled using execution failure. In code view, the name value "errorType": "Error.ExecutionFailure" is appended.

Retry 

You can retry the failed state for a specific number of attempts within predefined intervals using this option.

1. Delay - Set the time in seconds after which the state must be retried after failure.
2. Attempt - Set the number of times the state has to be retried.
3. Step Delay - Increase the delay time for each attempt by multiplying the Delay time with the Step Delay number set.

For example, suppose the Delay is set to 5 seconds, Attempt is set to 3, and Step Delay is set to 2 seconds for a retry.                         

  1st attempt       -->       5s * (2 ^ 0) = 5s  

             2nd attempt      -->       5s * (2 ^ 1) = 10s

             3rd attempt       -->       5s * (2 ^ 2) = 20s

Fallback 

1. Next: Set the state name to which the inputs of the failed state and error output have to be passed.
2. Result: Set the field name from which the error details can be retrieved.
   
3. Error Path: Maps error responses in case of failure, specifying the input for the next state.
4. Error Selector: Configures error responses which can be merged with the previous state input and transitioned to the fallback state.

Custom Error 

1. Click the +Add Custom Error option under Error Handling. A pop-up appears.
   
2. Under Exception, select Error Code/Error Message from the dropdown using which the error handling must take place.
   
3. In the next field, enter the path/value where the error code or error message will be received in the state output.
   

• By default, the Custom Error name is set to Error 1, Error 2, or Error 3 based on the number of custom errors configured. To change the default name, click the 'edit' icon and specify a name.
  
• For custom errors in code view, the name value "errorType": "Error.Custom" is appended.

{
    "Function for stock status": {
      "type": "function",
      "next": "End",
      "start": true,
      "function_id": "updatestockstatus_71",
      "on_error": [
      {
          "error_type": "timeout_error",
          "retry": {
               "delay": 3,
               "attempt": 3,
               "step_delay": 1
          },
          "fallback": {
               "next": "End",
               "error_path": "$.error3"
         }
      },
      {
         "error_type": "custom_error",
         "error_name": "Error 1",
         "error_code": "101",
         "retry": {
            "delay": 3,
            "attempt": 3,
            "step_delay": 1
         },
         "fallback": {
            "next": "End",
            "error_path": "$.Error"
         }
      }
     ]
    }
}