handleError method
Creates a wrapper Stream that intercepts some errors from this stream.
If this stream sends an error that matches test, then it is intercepted
by the onError function.
The onError callback must be of type void onError(error) or
void onError(error, StackTrace stackTrace). Depending on the function
type the stream either invokes onError with or without a stack
trace. The stack trace argument might be null if the stream itself
received an error without stack trace.
An asynchronous error error is matched by a test function if
test(error) returns true. If test is omitted, every error is considered
matching.
If the error is intercepted, the onError function can decide what to do
with it. It can throw if it wants to raise a new (or the same) error,
or simply return to make the stream forget the error.
If the received error value is thrown again by the onError function,
it acts like a rethrow and it is emitted along with its original
stack trace, not the stack trace of the throw inside onError.
If you need to transform an error into a data event, use the more generic Stream.transform to handle the event by writing a data event to the output sink.
The returned stream is a broadcast stream if this stream is.
If a broadcast stream is listened to more than once, each subscription
will individually perform the test and handle the error.
Implementation
Stream<T> handleError(Function onError, {bool test(error)}) {
return new _HandleErrorStream<T>(this, onError, test);
}