CHORUS/vendor/github.com/sony/gobreaker/README.md

gobreaker

gobreaker implements the Circuit Breaker pattern in Go.

Installation

go get github.com/sony/gobreaker

Usage

The struct CircuitBreaker is a state machine to prevent sending requests that are likely to fail. The function NewCircuitBreaker creates a new CircuitBreaker.

func NewCircuitBreaker(st Settings) *CircuitBreaker

You can configure CircuitBreaker by the struct Settings:

type Settings struct {
	Name          string
	MaxRequests   uint32
	Interval      time.Duration
	Timeout       time.Duration
	ReadyToTrip   func(counts Counts) bool
	OnStateChange func(name string, from State, to State)
	IsSuccessful  func(err error) bool
}

• Name is the name of the CircuitBreaker.

• MaxRequests is the maximum number of requests allowed to pass through when the CircuitBreaker is half-open. If MaxRequests is 0, CircuitBreaker allows only 1 request.

• Interval is the cyclic period of the closed state for CircuitBreaker to clear the internal Counts, described later in this section. If Interval is 0, CircuitBreaker doesn't clear the internal Counts during the closed state.

• Timeout is the period of the open state, after which the state of CircuitBreaker becomes half-open. If Timeout is 0, the timeout value of CircuitBreaker is set to 60 seconds.

• ReadyToTrip is called with a copy of Counts whenever a request fails in the closed state. If ReadyToTrip returns true, CircuitBreaker will be placed into the open state. If ReadyToTrip is nil, default ReadyToTrip is used. Default ReadyToTrip returns true when the number of consecutive failures is more than 5.

• OnStateChange is called whenever the state of CircuitBreaker changes.

• IsSuccessful is called with the error returned from a request. If IsSuccessful returns true, the error is counted as a success. Otherwise the error is counted as a failure. If IsSuccessful is nil, default IsSuccessful is used, which returns false for all non-nil errors.

The struct Counts holds the numbers of requests and their successes/failures:

type Counts struct {
	Requests             uint32
	TotalSuccesses       uint32
	TotalFailures        uint32
	ConsecutiveSuccesses uint32
	ConsecutiveFailures  uint32
}

CircuitBreaker clears the internal Counts either on the change of the state or at the closed-state intervals. Counts ignores the results of the requests sent before clearing.

CircuitBreaker can wrap any function to send a request:

func (cb *CircuitBreaker) Execute(req func() (interface{}, error)) (interface{}, error)

The method Execute runs the given request if CircuitBreaker accepts it. Execute returns an error instantly if CircuitBreaker rejects the request. Otherwise, Execute returns the result of the request. If a panic occurs in the request, CircuitBreaker handles it as an error and causes the same panic again.

Example

var cb *breaker.CircuitBreaker

func Get(url string) ([]byte, error) {
	body, err := cb.Execute(func() (interface{}, error) {
		resp, err := http.Get(url)
		if err != nil {
			return nil, err
		}

		defer resp.Body.Close()
		body, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			return nil, err
		}

		return body, nil
	})
	if err != nil {
		return nil, err
	}

	return body.([]byte), nil
}

See example for details.

License

The MIT License (MIT)

See LICENSE for details.