Custom checker for half-open state like ReadyToTrip

README.md

@@ -29,7 +29,7 @@ You can configure `CircuitBreaker` by the struct `Settings`:
 ```go
 type Settings struct {
 	Name          string
-	MaxRequests   uint32
+	ReadyToClose  func(counts Counts) (bool, bool)
 	Interval      time.Duration
 	Timeout       time.Duration
 	ReadyToTrip   func(counts Counts) bool
@@ -39,9 +39,11 @@ type Settings struct {
 
 - `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.
+- `ReadyToClose` is called with a copy of `Counts` for each request in the half-open state.
+  If `ReadyToClose` returns true, the `CircuitBreaker` will be placed into the close state.
+  If `ReadyToClose` returns false, the `CircuitBreaker` will be placed into the open state if second returned value is true.
+  If `ReadyToClose` is nil, default `ReadyToClose` is used.
+  Default `ReadyToClose` returns true when the number of consecutive successes is more than 1.
 
 - `Interval` is the cyclic period of the closed state
   for `CircuitBreaker` to clear the internal `Counts`, described later in this section.

gobreaker.go

@@ -20,8 +20,6 @@ const (
 )
 
 var (
-	// ErrTooManyRequests is returned when the CB state is half open and the requests count is over the cb maxRequests
-	ErrTooManyRequests = errors.New("too many requests")
 	// ErrOpenState is returned when the CB state is open
 	ErrOpenState = errors.New("circuit breaker is open")
 )
@@ -80,9 +78,11 @@ func (c *Counts) clear() {
 //
 // 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, the CircuitBreaker allows only 1 request.
+// ReadyToClose is called with a copy of Counts for each request in the half-open state.
+// If ReadyToClose returns true, the CircuitBreaker will be placed into the close state.
+// If ReadyToClose returns false, the CircuitBreaker will be placed into the open state if second returned value is true.
+// If ReadyToClose is nil, default ReadyToClose is used.
+// Default ReadyToClose returns true when the number of consecutive successes is more than 1.
 //
 // Interval is the cyclic period of the closed state
 // for the CircuitBreaker to clear the internal Counts.
@@ -100,7 +100,7 @@ func (c *Counts) clear() {
 // OnStateChange is called whenever the state of the CircuitBreaker changes.
 type Settings struct {
 	Name          string
-	MaxRequests   uint32
+	ReadyToClose  func(counts Counts) (bool, bool)
 	Interval      time.Duration
 	Timeout       time.Duration
 	ReadyToTrip   func(counts Counts) bool
@@ -110,7 +110,7 @@ type Settings struct {
 // CircuitBreaker is a state machine to prevent sending requests that are likely to fail.
 type CircuitBreaker struct {
 	name          string
-	maxRequests   uint32
+	readyToClose  func(counts Counts) (bool, bool)
 	interval      time.Duration
 	timeout       time.Duration
 	readyToTrip   func(counts Counts) bool
@@ -137,10 +137,10 @@ func NewCircuitBreaker(st Settings) *CircuitBreaker {
 	cb.name = st.Name
 	cb.onStateChange = st.OnStateChange
 
-	if st.MaxRequests == 0 {
-		cb.maxRequests = 1
+	if st.ReadyToClose == nil {
+		cb.readyToClose = defaultReadyToClose
 	} else {
-		cb.maxRequests = st.MaxRequests
+		cb.readyToClose = st.ReadyToClose
 	}
 
 	if st.Interval <= 0 {
@@ -180,6 +180,10 @@ func defaultReadyToTrip(counts Counts) bool {
 	return counts.ConsecutiveFailures > 5
 }
 
+func defaultReadyToClose(counts Counts) (bool, bool) {
+	return counts.ConsecutiveSuccesses >= 1, true
+}
+
 // Name returns the name of the CircuitBreaker.
 func (cb *CircuitBreaker) Name() string {
 	return cb.name
@@ -252,8 +256,6 @@ func (cb *CircuitBreaker) beforeRequest() (uint64, error) {
 
 	if state == StateOpen {
 		return generation, ErrOpenState
-	} else if state == StateHalfOpen && cb.counts.Requests >= cb.maxRequests {
-		return generation, ErrTooManyRequests
 	}
 
 	cb.counts.onRequest()
@@ -283,7 +285,7 @@ func (cb *CircuitBreaker) onSuccess(state State, now time.Time) {
 		cb.counts.onSuccess()
 	case StateHalfOpen:
 		cb.counts.onSuccess()
-		if cb.counts.ConsecutiveSuccesses >= cb.maxRequests {
+		if ok, _ := cb.readyToClose(cb.counts); ok {
 			cb.setState(StateClosed, now)
 		}
 	}
@@ -296,8 +298,13 @@ func (cb *CircuitBreaker) onFailure(state State, now time.Time) {
 		if cb.readyToTrip(cb.counts) {
 			cb.setState(StateOpen, now)
 		}
+
 	case StateHalfOpen:
-		cb.setState(StateOpen, now)
+		cb.counts.onFailure()
+		ok, nowOpen := cb.readyToClose(cb.counts)
+		if !ok && nowOpen {
+			cb.setState(StateOpen, now)
+		}
 	}
 }
 
@@ -307,11 +314,13 @@ func (cb *CircuitBreaker) currentState(now time.Time) (State, uint64) {
 		if !cb.expiry.IsZero() && cb.expiry.Before(now) {
 			cb.toNewGeneration(now)
 		}
+
 	case StateOpen:
 		if cb.expiry.Before(now) {
 			cb.setState(StateHalfOpen, now)
 		}
 	}
+
 	return cb.state, cb.generation
 }
 
@@ -342,8 +351,10 @@ func (cb *CircuitBreaker) toNewGeneration(now time.Time) {
 		} else {
 			cb.expiry = now.Add(cb.interval)
 		}
+
 	case StateOpen:
 		cb.expiry = now.Add(cb.timeout)
+
 	default: // StateHalfOpen
 		cb.expiry = zero
 	}

gobreaker_test.go

@@ -81,7 +81,21 @@ func causePanic(cb *CircuitBreaker) error {
 func newCustom() *CircuitBreaker {
 	var customSt Settings
 	customSt.Name = "cb"
-	customSt.MaxRequests = 3
+	customSt.ReadyToClose = func(counts Counts) (bool, bool) {
+		if counts.ConsecutiveSuccesses >= 3 {
+			return true, true
+		}
+
+		numReqs := counts.Requests
+		failureRatio := float64(counts.TotalFailures) / float64(numReqs)
+
+		var nowOpen bool
+		if numReqs >= 3 && failureRatio >= 0.6 {
+			nowOpen = true
+		}
+
+		return false, nowOpen
+	}
 	customSt.Interval = time.Duration(30) * time.Second
 	customSt.Timeout = time.Duration(90) * time.Second
 	customSt.ReadyToTrip = func(counts Counts) bool {
@@ -128,7 +142,7 @@ func TestStateConstants(t *testing.T) {
 func TestNewCircuitBreaker(t *testing.T) {
 	defaultCB := NewCircuitBreaker(Settings{})
 	assert.Equal(t, "", defaultCB.name)
-	assert.Equal(t, uint32(1), defaultCB.maxRequests)
+	assert.NotNil(t, defaultCB.readyToClose)
 	assert.Equal(t, time.Duration(0), defaultCB.interval)
 	assert.Equal(t, time.Duration(60)*time.Second, defaultCB.timeout)
 	assert.NotNil(t, defaultCB.readyToTrip)
@@ -139,7 +153,7 @@ func TestNewCircuitBreaker(t *testing.T) {
 
 	customCB := newCustom()
 	assert.Equal(t, "cb", customCB.name)
-	assert.Equal(t, uint32(3), customCB.maxRequests)
+	assert.NotNil(t, customCB.readyToClose)
 	assert.Equal(t, time.Duration(30)*time.Second, customCB.interval)
 	assert.Equal(t, time.Duration(90)*time.Second, customCB.timeout)
 	assert.NotNil(t, customCB.readyToTrip)
@@ -150,7 +164,7 @@ func TestNewCircuitBreaker(t *testing.T) {
 
 	negativeDurationCB := newNegativeDurationCB()
 	assert.Equal(t, "ncb", negativeDurationCB.name)
-	assert.Equal(t, uint32(1), negativeDurationCB.maxRequests)
+	assert.NotNil(t, negativeDurationCB.readyToClose)
 	assert.Equal(t, time.Duration(0)*time.Second, negativeDurationCB.interval)
 	assert.Equal(t, time.Duration(60)*time.Second, negativeDurationCB.timeout)
 	assert.NotNil(t, negativeDurationCB.readyToTrip)
@@ -258,7 +272,7 @@ func TestCustomCircuitBreaker(t *testing.T) {
 	ch := succeedLater(customCB, time.Duration(100)*time.Millisecond) // 3 consecutive successes
 	time.Sleep(time.Duration(50) * time.Millisecond)
 	assert.Equal(t, Counts{3, 2, 0, 2, 0}, customCB.counts)
-	assert.Error(t, succeed(customCB)) // over MaxRequests
+	assert.Nil(t, succeed(customCB))
 	assert.Nil(t, <-ch)
 	assert.Equal(t, StateClosed, customCB.State())
 	assert.Equal(t, Counts{0, 0, 0, 0, 0}, customCB.counts)