.github/workflows/go.yaml

@@ -0,0 +1,23 @@
+name: Go
+
+on:
+  push:
+  pull_request:
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Go
+      uses: actions/setup-go@v3
+      with:
+        go-version: 1.18
+
+    - name: Build
+      run: go build -v ./...
+
+    - name: Test
+      run: go test -v ./...

go.mod

@@ -1,3 +1,3 @@
 module github.com/cenkalti/backoff/v4
 
-go 1.13
+go 1.18

retry.go

@@ -5,10 +5,20 @@ import (
 	"time"
 )
 
+// An OperationWithData is executing by RetryWithData() or RetryNotifyWithData().
+// The operation will be retried using a backoff policy if it returns an error.
+type OperationWithData[T any] func() (T, error)
+
 // An Operation is executing by Retry() or RetryNotify().
 // The operation will be retried using a backoff policy if it returns an error.
 type Operation func() error
 
+func (o Operation) withEmptyData() OperationWithData[struct{}] {
+	return func() (struct{}, error) {
+		return struct{}{}, o()
+	}
+}
+
 // Notify is a notify-on-error function. It receives an operation error and
 // backoff delay if the operation failed (with an error).
 //
@@ -28,18 +38,41 @@ func Retry(o Operation, b BackOff) error {
 	return RetryNotify(o, b, nil)
 }
 
+// RetryWithData is like Retry but returns data in the response too.
+func RetryWithData[T any](o OperationWithData[T], b BackOff) (T, error) {
+	return RetryNotifyWithData(o, b, nil)
+}
+
 // RetryNotify calls notify function with the error and wait duration
 // for each failed attempt before sleep.
 func RetryNotify(operation Operation, b BackOff, notify Notify) error {
 	return RetryNotifyWithTimer(operation, b, notify, nil)
 }
 
+// RetryNotifyWithData is like RetryNotify but returns data in the response too.
+func RetryNotifyWithData[T any](operation OperationWithData[T], b BackOff, notify Notify) (T, error) {
+	return doRetryNotify(operation, b, notify, nil)
+}
+
 // RetryNotifyWithTimer calls notify function with the error and wait duration using the given Timer
 // for each failed attempt before sleep.
 // A default timer that uses system timer is used when nil is passed.
 func RetryNotifyWithTimer(operation Operation, b BackOff, notify Notify, t Timer) error {
-	var err error
-	var next time.Duration
+	_, err := doRetryNotify(operation.withEmptyData(), b, notify, t)
+	return err
+}
+
+// RetryNotifyWithTimerAndData is like RetryNotifyWithTimer but returns data in the response too.
+func RetryNotifyWithTimerAndData[T any](operation OperationWithData[T], b BackOff, notify Notify, t Timer) (T, error) {
+	return doRetryNotify(operation, b, notify, t)
+}
+
+func doRetryNotify[T any](operation OperationWithData[T], b BackOff, notify Notify, t Timer) (T, error) {
+	var (
+		err  error
+		next time.Duration
+		res  T
+	)
 	if t == nil {
 		t = &defaultTimer{}
 	}
@@ -52,21 +85,22 @@ func RetryNotifyWithTimer(operation Operation, b BackOff, notify Notify, t Timer
 
 	b.Reset()
 	for {
-		if err = operation(); err == nil {
-			return nil
+		res, err = operation()
+		if err == nil {
+			return res, nil
 		}
 
 		var permanent *PermanentError
 		if errors.As(err, &permanent) {
-			return permanent.Err
+			return res, permanent.Err
 		}
 
 		if next = b.NextBackOff(); next == Stop {
 			if cerr := ctx.Err(); cerr != nil {
-				return cerr
+				return res, cerr
 			}
 
-			return err
+			return res, err
 		}
 
 		if notify != nil {
@@ -77,7 +111,7 @@ func RetryNotifyWithTimer(operation Operation, b BackOff, notify Notify, t Timer
 
 		select {
 		case <-ctx.Done():
-			return ctx.Err()
+			return res, ctx.Err()
 		case <-t.C():
 		}
 	}

retry_test.go

@@ -55,6 +55,36 @@ func TestRetry(t *testing.T) {
 	}
 }
 
+func TestRetryWithData(t *testing.T) {
+	const successOn = 3
+	var i = 0
+
+	// This function is successful on "successOn" calls.
+	f := func() (int, error) {
+		i++
+		log.Printf("function is called %d. time\n", i)
+
+		if i == successOn {
+			log.Println("OK")
+			return 42, nil
+		}
+
+		log.Println("error")
+		return 1, errors.New("error")
+	}
+
+	res, err := RetryNotifyWithTimerAndData(f, NewExponentialBackOff(), nil, &testTimer{})
+	if err != nil {
+		t.Errorf("unexpected error: %s", err.Error())
+	}
+	if i != successOn {
+		t.Errorf("invalid number of retries: %d", i)
+	}
+	if res != 42 {
+		t.Errorf("invalid data in response: %d, expected 42", res)
+	}
+}
+
 func TestRetryContext(t *testing.T) {
 	var cancelOn = 3
 	var i = 0
@@ -90,15 +120,15 @@ func TestRetryContext(t *testing.T) {
 }
 
 func TestRetryPermanent(t *testing.T) {
-	ensureRetries := func(test string, shouldRetry bool, f func() error) {
+	ensureRetries := func(test string, shouldRetry bool, f func() (int, error), expectRes int) {
 		numRetries := -1
 		maxRetries := 1
 
-		_ = RetryNotifyWithTimer(
-			func() error {
+		res, _ := RetryNotifyWithTimerAndData(
+			func() (int, error) {
 				numRetries++
 				if numRetries >= maxRetries {
-					return Permanent(errors.New("forced"))
+					return -1, Permanent(errors.New("forced"))
 				}
 				return f()
 			},
@@ -114,43 +144,52 @@ func TestRetryPermanent(t *testing.T) {
 		if !shouldRetry && numRetries > 0 {
 			t.Errorf("Test: '%s', backoff should not have retried", test)
 		}
+
+		if res != expectRes {
+			t.Errorf("Test: '%s', got res %d but expected %d", test, res, expectRes)
+		}
 	}
 
 	for _, testCase := range []struct {
 		name        string
-		f           func() error
+		f           func() (int, error)
 		shouldRetry bool
+		res         int
 	}{
 		{
 			"nil test",
-			func() error {
-				return nil
+			func() (int, error) {
+				return 1, nil
 			},
 			false,
+			1,
 		},
 		{
 			"io.EOF",
-			func() error {
-				return io.EOF
+			func() (int, error) {
+				return 2, io.EOF
 			},
 			true,
+			-1,
 		},
 		{
 			"Permanent(io.EOF)",
-			func() error {
-				return Permanent(io.EOF)
+			func() (int, error) {
+				return 3, Permanent(io.EOF)
 			},
 			false,
+			3,
 		},
 		{
 			"Wrapped: Permanent(io.EOF)",
-			func() error {
-				return fmt.Errorf("Wrapped error: %w", Permanent(io.EOF))
+			func() (int, error) {
+				return 4, fmt.Errorf("Wrapped error: %w", Permanent(io.EOF))
 			},
 			false,
+			4,
 		},
 	} {
-		ensureRetries(testCase.name, testCase.shouldRetry, testCase.f)
+		ensureRetries(testCase.name, testCase.shouldRetry, testCase.f, testCase.res)
 	}
 }