From 781bc3b39d7f885f3b97f9e184a064fc05302e20 Mon Sep 17 00:00:00 2001
From: Jack Lindamood <cep221@gmail.com>
Date: Tue, 27 Aug 2019 10:20:05 -0700
Subject: [PATCH 1/2] Error: add Error type.

Clarify how to check for internal circuit errors

Resolves #77
---
 v3/circuit.go                           | 2 ++
 v3/errors.go                            | 9 +++++++++
 v3/example_test.go                      | 8 ++++++++
 v3/metrics/statsdmetrics/statsd.go      | 2 +-
 v3/metrics/statsdmetrics/statsd_test.go | 5 +++--
 5 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/v3/circuit.go b/v3/circuit.go
index 40d1bb8..79607e5 100644
--- a/v3/circuit.go
+++ b/v3/circuit.go
@@ -218,6 +218,8 @@ func (c *Circuit) Run(ctx context.Context, runFunc func(context.Context) error)
 }
 
 // Execute the circuit.  Prefer this over Go.  Similar to http://netflix.github.io/Hystrix/javadoc/com/netflix/hystrix/HystrixCommand.html#execute--
+// The returned error will either be the result of runFunc, the result of fallbackFunc, or an internal library error.
+// Internal library errors will match the interface Error and you can use type casting to check this.
 func (c *Circuit) Execute(ctx context.Context, runFunc func(context.Context) error, fallbackFunc func(context.Context, error) error) error {
 	if c.isEmptyOrNil() || c.threadSafeConfig.CircuitBreaker.Disabled.Get() {
 		return runFunc(ctx)
diff --git a/v3/errors.go b/v3/errors.go
index cad9b8b..dfa95ce 100644
--- a/v3/errors.go
+++ b/v3/errors.go
@@ -12,6 +12,15 @@ type circuitError struct {
 	msg                     string
 }
 
+// Error is the type of error returned by internal errors using the circuit library.
+type Error interface {
+	error
+	// ConcurrencyLimitReached returns true if this error is because the concurrency limit has been reached.
+	ConcurrencyLimitReached() bool
+	// CircuitOpen returns true if this error is because the circuit is open.
+	CircuitOpen() bool
+}
+
 func (m *circuitError) Error() string {
 	return fmt.Sprintf("%s: concurrencyReached=%t circuitOpen=%t", m.msg, m.ConcurrencyLimitReached(), m.CircuitOpen())
 }
diff --git a/v3/example_test.go b/v3/example_test.go
index 9f7834b..8cf7858 100644
--- a/v3/example_test.go
+++ b/v3/example_test.go
@@ -293,3 +293,11 @@ func ExampleConfig_custommetrics() {
 	circuit.NewCircuitFromConfig("custom-metrics", config)
 	// Output:
 }
+
+// Shows how to check if an error is part of the circuit library.
+func ExampleError_checking() {
+	x := errors.New("an error")
+	if _, ok := x.(circuit.Error); ok {
+		// this error is a circuit library error, not the result of runFunc or fallbackFunc
+	}
+}
diff --git a/v3/metrics/statsdmetrics/statsd.go b/v3/metrics/statsdmetrics/statsd.go
index cf8d9c1..b3fdb20 100644
--- a/v3/metrics/statsdmetrics/statsd.go
+++ b/v3/metrics/statsdmetrics/statsd.go
@@ -90,9 +90,9 @@ type ConcurrencyCollector struct {
 	Delay                  faststats.AtomicInt64
 	onClose                chan struct{}
 	Manager                *circuit.Manager
-	SampleRate             float32
 	timeAfter              func(time.Duration) <-chan time.Time
 	once                   sync.Once
+	SampleRate             float32
 }
 
 func (c *ConcurrencyCollector) delay() time.Duration {
diff --git a/v3/metrics/statsdmetrics/statsd_test.go b/v3/metrics/statsdmetrics/statsd_test.go
index 94e24ec..d656f43 100644
--- a/v3/metrics/statsdmetrics/statsd_test.go
+++ b/v3/metrics/statsdmetrics/statsd_test.go
@@ -147,6 +147,7 @@ func Test_sanitizeStatsd(t *testing.T) {
 		},
 	}
 	for _, tt := range tests {
+		tt := tt
 		t.Run(tt.name, func(t *testing.T) {
 			if got := sanitizeStatsd(tt.args.s); got != tt.want {
 				t.Errorf("sanitizeStatsd() = %v, want %v", got, tt.want)
@@ -162,7 +163,7 @@ func TestConcurrencyCollector_delay(t *testing.T) {
 	require.Equal(t, x.delay(), time.Second*3)
 }
 
-func waitForGauge(name string, ss *rememberStats, clk *clock.MockClock) {
+func waitForGauge(name string, ss *rememberStats, _ *clock.MockClock) {
 	hasGauge := false
 	for !hasGauge {
 		time.Sleep(time.Millisecond)
@@ -174,7 +175,7 @@ func waitForGauge(name string, ss *rememberStats, clk *clock.MockClock) {
 	}
 }
 
-func waitForCounter(name string, ss *rememberStats, clk *clock.MockClock) {
+func waitForCounter(name string, ss *rememberStats, _ *clock.MockClock) {
 	hasCounter := false
 	for !hasCounter {
 		time.Sleep(time.Millisecond)

From 4d3f8440d1e32987329b3bca4f528a788b74d477 Mon Sep 17 00:00:00 2001
From: Jack Lindamood <cep221@gmail.com>
Date: Tue, 27 Aug 2019 10:23:08 -0700
Subject: [PATCH 2/2] errors: type check circuitError

---
 v3/errors.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/v3/errors.go b/v3/errors.go
index dfa95ce..712d5ce 100644
--- a/v3/errors.go
+++ b/v3/errors.go
@@ -11,6 +11,7 @@ type circuitError struct {
 	circuitOpen             bool
 	msg                     string
 }
+var _ Error = &circuitError{}
 
 // Error is the type of error returned by internal errors using the circuit library.
 type Error interface {