State Change Callback in circuit breaker

README.md

@@ -95,6 +95,15 @@ hystrix.ConfigureCommand("my_command", hystrix.CommandConfig{
 
 You can also use ```hystrix.Configure()``` which accepts a ```map[string]CommandConfig```.
 
+
+### Enable State Change Callback
+In your main.go, register the Callback handler for a command which will be called in a goroutine.
+
+```go
+callback.Register("my_command", func(name string, state callback.State) {
+		fmt.Println("Name ", name, " State ", state)
+})
+```
 ### Enable dashboard metrics
 
 In your main.go, register the event stream HTTP handler on a port and launch it in a goroutine.  Once you configure turbine for your [Hystrix Dashboard](https://github.com/Netflix/Hystrix/tree/master/hystrix-dashboard) to start streaming events, your commands will automatically begin appearing.

go.mod

@@ -0,0 +1,13 @@
+module github.com/afex/hystrix-go
+
+go 1.15
+
+require (
+	github.com/DataDog/datadog-go v4.0.1+incompatible
+	github.com/cactus/go-statsd-client/statsd v0.0.0-20200728222731-a2baea3bbfc6
+	github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0
+	github.com/smartystreets/goconvey v1.6.4
+	github.com/stretchr/testify v1.6.1 // indirect
+)
+
+replace github.com/afex/hystrix-go => github.com/ContinuumLLC/hystrix-go v1.0.1

go.sum

@@ -0,0 +1,31 @@
+github.com/DataDog/datadog-go v4.0.1+incompatible h1:6BF/mPNV2f+PJzpw5vxDK91Z3IfOM7fEmz5ptuL+0vo=
+github.com/DataDog/datadog-go v4.0.1+incompatible/go.mod h1:LButxg5PwREeZtORoXG3tL4fMGNddJ+vMq1mwgfaqoQ=
+github.com/cactus/go-statsd-client/statsd v0.0.0-20200728222731-a2baea3bbfc6 h1:arL5CcymFtWyyi5Xk44VpSxUfFfJqxCMbhZQ0lxLkDE=
+github.com/cactus/go-statsd-client/statsd v0.0.0-20200728222731-a2baea3bbfc6/go.mod h1:l/bIBLeOl9eX+wxJAzxS4TveKRtAqlyDpHjhkfO0MEI=
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1 h1:EGx4pi6eqNxGaHF6qqu48+N2wcFQ5qg5FXgOdqsJ5d8=
+github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1/go.mod h1:wJfORRmW1u3UXTncJ5qlYoELFm8eSnnEO6hX4iZ3EWY=
+github.com/jtolds/gls v4.20.0+incompatible h1:xdiiI2gbIgH/gLH7ADydsJ1uDOEzR8yvV7C0MuV77Wo=
+github.com/jtolds/gls v4.20.0+incompatible/go.mod h1:QJZ7F/aHp+rZTRtaJ1ow/lLfFfVYBRgL+9YlvaHOwJU=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0 h1:MkV+77GLUNo5oJ0jf870itWm3D0Sjh7+Za9gazKc5LQ=
+github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
+github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d h1:zE9ykElWQ6/NYmHa3jpm/yHnI4xSofP+UP6SpjHcSeM=
+github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d/go.mod h1:OnSkiWE9lh6wB0YB77sQom3nweQdgAjqCqsofrRNTgc=
+github.com/smartystreets/goconvey v1.6.4 h1:fv0U8FUIMPNf1L9lnHLvLhgicrIVChEkdzIKYqbNC9s=
+github.com/smartystreets/goconvey v1.6.4/go.mod h1:syvi0/a8iFYH4r/RixwvyeAJjdLS9QV7WQ/tjFTllLA=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

hystrix/callback/callback.go

@@ -0,0 +1,34 @@
+package callback
+
+var circuitCallback map[string]stateFunc
+
+//State is a type to hold Circuit-state this will be used while calling stateFunc on State change
+type State string
+
+const (
+	//Open is a state to indicate that Circuit state is Open
+	Open = "Open"
+	//Close is a state to indicate that Circuit state is Close
+	Close = "Close"
+	//AllowSingle is a state to indicate that Circuit state is AllowSingle or trying to Open Circuit
+	AllowSingle = "Allow Single"
+)
+
+type stateFunc func(name string, state State)
+
+func init() {
+	circuitCallback = make(map[string]stateFunc)
+}
+
+//Register adds callback for a circuit
+func Register(name string, callbackFunc stateFunc) {
+	circuitCallback[name] = callbackFunc
+}
+
+//Invoke is a function to invoke Callback function in a goroutine on State change
+func Invoke(name string, state State) {
+	callbackFunc, _ := circuitCallback[name]
+	if callbackFunc != nil {
+		go callbackFunc(name, state)
+	}
+}

hystrix/callback/callback_test.go

@@ -0,0 +1,57 @@
+package callback
+
+import (
+	"testing"
+	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestRegister(t *testing.T) {
+	Convey("Register a command", t, func() {
+		Register("Test-Command", func(name string, state State) {})
+
+		Convey("Read Callback function for Registered Command", func() {
+			callbackFunc, _ := circuitCallback["Test-Command"]
+			So(callbackFunc, ShouldNotBeNil)
+		})
+		Convey("Read Callback function for unknown Command", func() {
+			callbackFunc, _ := circuitCallback["Command"]
+			So(callbackFunc, ShouldBeNil)
+		})
+	})
+}
+
+func TestInvoke(t *testing.T) {
+	Convey("Register a command", t, func() {
+		var callbackInvoked bool
+		var callbackState State = Close
+		Register("TestInvokeCommand", func(name string, state State) {
+			callbackInvoked = true
+			callbackState = state
+		})
+
+		Invoke("TestInvokeCommand", Open)
+		time.Sleep(2 * time.Second)
+		Convey("Invoke Callback for Registered Command", func() {
+			So(callbackInvoked, ShouldBeTrue)
+			So(callbackState, ShouldEqual, Open)
+		})
+	})
+
+	Convey("Register a Invoke command", t, func() {
+		var callbackInvoked = false
+		var callbackState State = Close
+		Register("TestInvokeCommand", func(name string, state State) {
+			callbackInvoked = true
+			callbackState = state
+		})
+
+		Invoke("Command", Open)
+
+		Convey("Read Callback function for unknown Command", func() {
+			So(callbackInvoked, ShouldBeFalse)
+			So(callbackState, ShouldEqual, Close)
+		})
+	})
+}

hystrix/circuit.go

@@ -5,6 +5,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"github.com/afex/hystrix-go/hystrix/callback"
 )
 
 // CircuitBreaker is created for each ExecutorPool to track whether requests
@@ -128,6 +130,8 @@ func (circuit *CircuitBreaker) allowSingleTest() bool {
 		swapped := atomic.CompareAndSwapInt64(&circuit.openedOrLastTestedTime, openedOrLastTestedTime, now)
 		if swapped {
 			log.Printf("hystrix-go: allowing single test to possibly close circuit %v", circuit.Name)
+
+			callback.Invoke(circuit.Name, callback.AllowSingle)
 		}
 		return swapped
 	}
@@ -144,9 +148,11 @@ func (circuit *CircuitBreaker) setOpen() {
 	}
 
 	log.Printf("hystrix-go: opening circuit %v", circuit.Name)
-
 	circuit.openedOrLastTestedTime = time.Now().UnixNano()
 	circuit.open = true
+
+	callback.Invoke(circuit.Name, callback.Open)
+
 }
 
 func (circuit *CircuitBreaker) setClose() {
@@ -161,6 +167,9 @@ func (circuit *CircuitBreaker) setClose() {
 
 	circuit.open = false
 	circuit.metrics.Reset()
+
+	callback.Invoke(circuit.Name, callback.Close)
+
 }
 
 // ReportEvent records command metrics for tracking recent error rates and exposing data to the dashboard.

hystrix/settings.go

@@ -20,6 +20,7 @@ var (
 	DefaultLogger = NoopLogger{}
 )
 
+//Settings is used to tune circuit settings
 type Settings struct {
 	Timeout                time.Duration
 	MaxConcurrentRequests  int
@@ -106,6 +107,7 @@ func getSettings(name string) *Settings {
 	return s
 }
 
+//GetCircuitSettings returns Circuit Settings for each command
 func GetCircuitSettings() map[string]*Settings {
 	copy := make(map[string]*Settings)