Try catch

Error handler: runs the components behind Try; if they fail with an error, the record is sent to Catch with the error details in the metadata property Error.

Pins

Pin	Kind	Types	Description
Input	start	any	Record to process. If left unconnected, the system calls it once at flow start (with Viaducta.TypeSystem.Metadata.NoInputData).
Try	output	same as input	The protected branch.
Catch	error output	same as input	Called with the original input record when the Try branch failed.

Configuration

Field	Type	Default	Description
RethrowError	boolean	false	true: after Catch has run, the same error is thrown again to the caller (an outer Try catch, Retry, HTTP listener, ...).
LogError	boolean	true	true: every handled error is written to the flow log ("The try catch plugin handled exception ...").

Behaviour

• Before calling Try, the metadata property Error (Viaducta.Plugins.TryCatch.TryCatchPluginMetadata) is reset (Exception = null, FlowId / FlowName = current flow) and the component registers itself as error handler on the metadata.
• If an exception comes back from the Try branch (synchronously, e.g. from an Error component, a failing Http client or script), the component:
  1. unwraps a single inner exception of an AggregateException;
  2. logs it if LogError is true;
  3. sets Error: Exception (the exception, Message etc.), ComponentId, ComponentName, FlowId, FlowName (component and flow where it occurred, when known);
  4. calls Catch with the original input record and the metadata;
  5. rethrows the original error if RethrowError is true, otherwise the request continues as handled (the caller sees success).
• Components that report errors asynchronously (on their own threads) call the error handler registered on the metadata; then Catch is called the same way.
• An exception thrown inside the Catch branch is passed back to the caller.

Notes

• UnRecoverableFlowException (failed expression evaluation, no matching connection for a type, explicit unrecoverable errors) is not caught: the system logs it, pauses and stops the flow.
• When the flow runs in debug mode, component errors are reported to the debugger and are not passed back to the Try catch, so Catch is not called.
• Errors handled downstream (e.g. by an inner Try catch or a component's own error pin) do not reach this component.
• RethrowError always rethrows, even if Error was changed or reset in the Catch branch.
• Nested Try catch components share the one Error metadata property; an inner Try catch overwrites it. For asynchronous errors the first Try catch registered on the request (the outermost) handles the error.
• The Error metadata stays on the request after Catch; check Error.Exception for null to see whether an error occurred.

Example

{ "RethrowError": false, "LogError": true }

Http listener → Try catch → (Try) Http client → Http response ; (Catch) → Http response (status 500, Error.Exception.Message)