Adding Exp and Const backoff for good measure.

Signed-off-by: Scott Nichols <snichols@vmware.com>

v2/alias.go

@@ -96,10 +96,15 @@ var (
 	WithTimeNow          = client.WithTimeNow
 	WithTracePropagation = client.WithTracePropagation()
 
+	// Event Creation
+
+	NewEvent = event.New
+
 	// Results
 
-	ResultIs = protocol.ResultIs
-	ResultAs = protocol.ResultAs
+	NewResult = protocol.NewResult
+	ResultIs  = protocol.ResultIs
+	ResultAs  = protocol.ResultAs
 
 	// Receipt helpers
 
@@ -111,13 +116,8 @@ var (
 	IsACK  = protocol.IsACK
 	IsNACK = protocol.IsNACK
 
-	// Event Creation
-
-	NewEvent = event.New
+	// HTTP Results
 
-	// Results
-
-	NewResult            = protocol.NewResult
 	NewHTTPResult        = http.NewResult
 	NewHTTPRetriesResult = http.NewRetriesResult
 
@@ -135,11 +135,14 @@ var (
 
 	// Context
 
-	ContextWithTarget               = context.WithTarget
-	TargetFromContext               = context.TargetFrom
-	ContextWithRetriesLinearBackoff = context.WithRetriesLinearBackoff
-	WithEncodingBinary              = binding.WithForceBinary
-	WithEncodingStructured          = binding.WithForceStructured
+	ContextWithTarget                    = context.WithTarget
+	TargetFromContext                    = context.TargetFrom
+	ContextWithRetriesConstantBackoff    = context.WithRetriesConstantBackoff
+	ContextWithRetriesLinearBackoff      = context.WithRetriesLinearBackoff
+	ContextWithRetriesExponentialBackoff = context.WithRetriesExponentialBackoff
+
+	WithEncodingBinary     = binding.WithForceBinary
+	WithEncodingStructured = binding.WithForceStructured
 
 	// Custom Types
 

v2/cmd/samples/http/sender_retry/main.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"context"
+	"log"
+	"time"
+
+	cloudevents "github.com/cloudevents/sdk-go/v2"
+)
+
+func main() {
+	ctx := cloudevents.ContextWithTarget(context.Background(), "http://localhost:8080/")
+
+	p, err := cloudevents.NewHTTP()
+	if err != nil {
+		log.Fatalf("failed to create protocol: %s", err.Error())
+	}
+
+	c, err := cloudevents.NewClient(p, cloudevents.WithTimeNow(), cloudevents.WithUUIDs())
+	if err != nil {
+		log.Fatalf("failed to create client, %v", err)
+	}
+
+	// must send each event within 5 seconds for sleepy demo.
+
+	log.Println("--- Constant ---")
+	send10(cloudevents.ContextWithRetriesConstantBackoff(ctx, 10*time.Millisecond, 10), c)
+	log.Println("--- Linear ---")
+	send10(cloudevents.ContextWithRetriesLinearBackoff(ctx, 10*time.Millisecond, 10), c)
+	log.Println("--- Exponential ---")
+	send10(cloudevents.ContextWithRetriesExponentialBackoff(ctx, 10*time.Millisecond, 10), c)
+}
+
+func send10(ctx context.Context, c cloudevents.Client) {
+	for i := 0; i < 100; i++ {
+		e := cloudevents.NewEvent()
+		e.SetType("com.cloudevents.sample.sent")
+		e.SetSource("https://github.com/cloudevents/sdk-go/v2/cmd/samples/httpb/sender")
+		_ = e.SetData(cloudevents.ApplicationJSON, map[string]interface{}{
+			"id":      i,
+			"message": "Hello, World!",
+		})
+
+		if result := c.Send(ctx, e); !cloudevents.IsACK(result) {
+			log.Printf("failed to send: %s", result.Error())
+		} else {
+			log.Printf("sent: %d", i)
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+}

v2/cmd/samples/http/sleepy/main.go

@@ -43,19 +43,19 @@ func gotEvent(event cloudevents.Event) error {
 }
 
 func _main(args []string, env envConfig) int {
-	p, err := cloudevents.NewHTTP(cloudevents.WithPort(env.Port), cloudevents.WithPath(env.Path))
-	if err != nil {
-		log.Fatalf("failed to create protocol: %s", err.Error())
-	}
-	c, err := cloudevents.NewClient(p)
-	if err != nil {
-		log.Printf("failed to create client, %v", err)
-		return 1
-	}
+	for {
+		p, err := cloudevents.NewHTTP(cloudevents.WithPort(env.Port), cloudevents.WithPath(env.Path))
+		if err != nil {
+			log.Fatalf("failed to create protocol: %s", err.Error())
+		}
+		c, err := cloudevents.NewClient(p)
+		if err != nil {
+			log.Printf("failed to create client, %v", err)
+			return 1
+		}
 
-	log.Printf("listening on :%d%s\n", env.Port, env.Path)
+		log.Printf("listening on :%d%s\n", env.Port, env.Path)
 
-	for {
 		ctx, cancel := context.WithCancel(context.TODO())
 
 		go func() {

v2/context/context.go

@@ -57,16 +57,41 @@ type retriesKeyType struct{}
 
 var retriesKey = retriesKeyType{}
 
-// WithRetriesLinearBackoff returns back a new context with retries parameters using linear backoff strategy.
+// WithRetriesConstantBackoff returns back a new context with retries parameters using constant backoff strategy.
 // MaxTries is the maximum number for retries and delay is the time interval between retries
+func WithRetriesConstantBackoff(ctx context.Context, delay time.Duration, maxTries int) context.Context {
+	return WithRetryParams(ctx, &RetryParams{
+		Strategy: BackoffStrategyConstant,
+		Period:   delay,
+		MaxTries: maxTries,
+	})
+}
+
+// WithRetriesLinearBackoff returns back a new context with retries parameters using linear backoff strategy.
+// MaxTries is the maximum number for retries and delay*tries is the time interval between retries
 func WithRetriesLinearBackoff(ctx context.Context, delay time.Duration, maxTries int) context.Context {
-	return context.WithValue(ctx, retriesKey, &RetryParams{
+	return WithRetryParams(ctx, &RetryParams{
 		Strategy: BackoffStrategyLinear,
 		Period:   delay,
 		MaxTries: maxTries,
 	})
 }
 
+// WithRetriesExponentialBackoff returns back a new context with retries parameters using exponential backoff strategy.
+// MaxTries is the maximum number for retries and period is the amount of time to wait, used as `period * 2^retries`.
+func WithRetriesExponentialBackoff(ctx context.Context, period time.Duration, maxTries int) context.Context {
+	return WithRetryParams(ctx, &RetryParams{
+		Strategy: BackoffStrategyExponential,
+		Period:   period,
+		MaxTries: maxTries,
+	})
+}
+
+// WithRetryParams returns back a new context with retries parameters.
+func WithRetryParams(ctx context.Context, rp *RetryParams) context.Context {
+	return context.WithValue(ctx, retriesKey, rp)
+}
+
 // RetriesFrom looks in the given context and returns the retries parameters if found.
 // Otherwise returns the default retries configuration (ie. no retries).
 func RetriesFrom(ctx context.Context) *RetryParams {

v2/context/retry.go

@@ -1,15 +1,19 @@
 package context
 
-import "time"
+import (
+	"context"
+	"errors"
+	"math"
+	"time"
+)
 
 type BackoffStrategy string
 
 const (
-	BackoffStrategyNone   = "none"
-	BackoffStrategyLinear = "linear"
-
-	// TODO
-	// BackoffStrategyExponential = "exponential"
+	BackoffStrategyNone        = "none"
+	BackoffStrategyConstant    = "constant"
+	BackoffStrategyLinear      = "linear"
+	BackoffStrategyExponential = "exponential"
 )
 
 var DefaultRetryParams = RetryParams{Strategy: BackoffStrategyNone}
@@ -23,7 +27,45 @@ type RetryParams struct {
 	MaxTries int
 
 	// Period is
-	// - for linear strategy: the delay interval between retries
-	// - for exponential strategy: the factor applied after each retry
+	// - for none strategy: no delay
+	// - for constant strategy: the delay interval between retries
+	// - for linear strategy: interval between retries = Period * retries
+	// - for exponential strategy: interval between retries = Period * retries^2
 	Period time.Duration
 }
+
+// BackoffFor tries will return the time duration that should be used for this
+// current try count.
+// `tries` is assumed to be the number of times the caller has already retried.
+func (r *RetryParams) BackoffFor(tries int) time.Duration {
+	switch r.Strategy {
+	case BackoffStrategyConstant:
+		return r.Period
+	case BackoffStrategyLinear:
+		return r.Period * time.Duration(tries)
+	case BackoffStrategyExponential:
+		exp := math.Exp2(float64(tries))
+		return r.Period * time.Duration(exp)
+	case BackoffStrategyNone:
+		fallthrough // default
+	default:
+		return r.Period
+	}
+}
+
+// Backoff is a blocking call to wait for the correct amount of time for the retry.
+// `tries` is assumed to be the number of times the caller has already retried.
+func (r *RetryParams) Backoff(ctx context.Context, tries int) error {
+	if tries > r.MaxTries {
+		return errors.New("too many retries")
+	}
+	ticker := time.NewTicker(r.BackoffFor(tries))
+	select {
+	case <-ctx.Done():
+		ticker.Stop()
+		return errors.New("context has been cancelled")
+	case <-ticker.C:
+		ticker.Stop()
+	}
+	return nil
+}

v2/context/retry_test.go

@@ -0,0 +1,110 @@
+package context
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestRetryParams_Backoff(t *testing.T) {
+	tests := map[string]struct {
+		rp      *RetryParams
+		ctx     context.Context
+		tries   int
+		wantErr bool
+	}{
+		"none 1": {
+			ctx:     context.Background(),
+			rp:      &RetryParams{Strategy: BackoffStrategyNone},
+			tries:   1,
+			wantErr: true,
+		},
+		"const 1": {
+			ctx:   context.Background(),
+			rp:    &RetryParams{Strategy: BackoffStrategyConstant, MaxTries: 10, Period: 1 * time.Nanosecond},
+			tries: 5,
+		},
+		"linear 1": {
+			ctx:   context.Background(),
+			rp:    &RetryParams{Strategy: BackoffStrategyLinear, MaxTries: 10, Period: 1 * time.Nanosecond},
+			tries: 1,
+		},
+		"exponential 1": {
+			ctx:   context.Background(),
+			rp:    &RetryParams{Strategy: BackoffStrategyExponential, MaxTries: 10, Period: 1 * time.Nanosecond},
+			tries: 1,
+		},
+		"const timeout": {
+			ctx: func() context.Context {
+				ctx, _ := context.WithTimeout(context.Background(), 10*time.Millisecond)
+				return ctx
+			}(),
+			rp:      &RetryParams{Strategy: BackoffStrategyConstant, MaxTries: 10, Period: 1 * time.Second},
+			tries:   5,
+			wantErr: true,
+		},
+	}
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			if err := tc.rp.Backoff(tc.ctx, tc.tries); (err != nil) != tc.wantErr {
+				t.Errorf("Backoff() error = %v, wantErr %v", err, tc.wantErr)
+			}
+		})
+	}
+}
+
+func TestRetryParams_BackoffFor(t *testing.T) {
+	tests := map[string]struct {
+		rp    *RetryParams
+		tries int
+		want  time.Duration
+	}{
+		"none 1": {
+			rp:    &RetryParams{Strategy: BackoffStrategyNone},
+			tries: 1,
+			want:  time.Duration(0),
+		},
+		"const 1": {
+			rp:    &RetryParams{Strategy: BackoffStrategyConstant, MaxTries: 10, Period: 1 * time.Second},
+			tries: 1,
+			want:  1 * time.Second,
+		},
+		"linear 1": {
+			rp:    &RetryParams{Strategy: BackoffStrategyLinear, MaxTries: 10, Period: 1 * time.Second},
+			tries: 1,
+			want:  1 * time.Second,
+		},
+		"exponential 1": {
+			rp:    &RetryParams{Strategy: BackoffStrategyExponential, MaxTries: 10, Period: 1 * time.Second},
+			tries: 1,
+			want:  2 * time.Second, // 1 == 2^1
+		},
+		"none 5": {
+			rp:    &RetryParams{Strategy: BackoffStrategyNone},
+			tries: 5,
+			want:  time.Duration(0),
+		},
+		"const 5": {
+			rp:    &RetryParams{Strategy: BackoffStrategyConstant, MaxTries: 10, Period: 1 * time.Second},
+			tries: 5,
+			want:  1 * time.Second,
+		},
+		"linear 5": {
+			rp:    &RetryParams{Strategy: BackoffStrategyLinear, MaxTries: 10, Period: 1 * time.Second},
+			tries: 5,
+			want:  5 * time.Second,
+		},
+		"exponential 5": {
+			rp:    &RetryParams{Strategy: BackoffStrategyExponential, MaxTries: 10, Period: 1 * time.Second},
+			tries: 5,
+			want:  32 * time.Second, // 32 == 2^5
+		},
+	}
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			if got := tc.rp.BackoffFor(tc.tries); got != tc.want {
+				t.Errorf("BackoffFor() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}