Where's the option for fallback function?

[cyantarek]

No description provided.

[YoshiyukiMineo]

Which fallback function are you referring to? Do you mean callback functions?

https://github.com/sony/gobreaker/blob/master/gobreaker.go#L106-L107

[wjh000123]

Hi, @YoshiyukiMineo ,
in hystrix pattern, an optional fallback function is used when the original func failed. Here's the wiki.

[timjonesdev]

I didn't see fallback specifically in the example, but cb.Execute returns a specific error immediately if the request is not going to be allowed (this is documented). It looks like you can check for gobreaker.ErrOpenState to trigger fallback logic. Something like:

mySuccessReturn, err := cb.Execute(func() (interface{}, error) {
    // do stuff
})
if err != nil {
    if errors.Is(err, gobreaker.ErrOpenState) {
        // circuit is open
        // this is where a fallback option happens
    } else { // this will be the returned error from "do stuff"
    }
}

[ahmedashraff]

@timjonesdev what you suggested to implement the circuit breaker default fallback is good as it's true. However, if there's a default function passed with the setting struct it will be more easy to point, simple to change without touch the actual implementation, and descriptive for each service.

Its an opinion at the end.

[1500mh]

@ahmedashraff hello, i think we can customize trigger conditions by replacing cb.afterRequest(generation, err != nil) with cb.afterRequest(generation, cb.shouldChangeState(err)) like this:

type CircuitBreaker struct {
    ...
   shouldChangeState func(err error) bool
}

func defaultShouldChange(err error) bool {
    return err != nil
}

func (cb *CircuitBreaker) Execute(req func() (interface{}, error)) (interface{}, error) {
        ...
	result, err := req()
	cb.afterRequest(generation, cb.shouldChangeState(err))
	return result, err
}