1 files changed, 94 insertions, 0 deletions
diff --git a/internal/retry/retry.go b/internal/retry/retry.go
new file mode 100644
index 0000000..c9e3564
--- /dev/null
+++ b/internal/retry/retry.go
@@ -0,0 +1,94 @@
+// Copyright 2019 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package retry provides methods for retrying operations. It is a thin wrapper
+// around k8s.io/apimachinery/pkg/util/wait to make certain operations easier.
+package retry
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/google/go-containerregistry/internal/retry/wait"
+)
+
+// Backoff is an alias of our own wait.Backoff to avoid name conflicts with
+// the kubernetes wait package. Typing retry.Backoff is aesier than fixing
+// the wrong import every time you use wait.Backoff.
+type Backoff = wait.Backoff
+
+// This is implemented by several errors in the net package as well as our
+// transport.Error.
+type temporary interface {
+	Temporary() bool
+}
+
+// IsTemporary returns true if err implements Temporary() and it returns true.
+func IsTemporary(err error) bool {
+	if errors.Is(err, context.DeadlineExceeded) {
+		return false
+	}
+	if te, ok := err.(temporary); ok && te.Temporary() {
+		return true
+	}
+	return false
+}
+
+// IsNotNil returns true if err is not nil.
+func IsNotNil(err error) bool {
+	return err != nil
+}
+
+// Predicate determines whether an error should be retried.
+type Predicate func(error) (retry bool)
+
+// Retry retries a given function, f, until a predicate is satisfied, using
+// exponential backoff. If the predicate is never satisfied, it will return the
+// last error returned by f.
+func Retry(f func() error, p Predicate, backoff wait.Backoff) (err error) {
+	if f == nil {
+		return fmt.Errorf("nil f passed to retry")
+	}
+	if p == nil {
+		return fmt.Errorf("nil p passed to retry")
+	}
+
+	condition := func() (bool, error) {
+		err = f()
+		if p(err) {
+			return false, nil
+		}
+		return true, err
+	}
+
+	wait.ExponentialBackoff(backoff, condition)
+	return
+}
+
+type contextKey string
+
+var key = contextKey("never")
+
+// Never returns a context that signals something should not be retried.
+// This is a hack and can be used to communicate across package boundaries
+// to avoid retry amplification.
+func Never(ctx context.Context) context.Context {
+	return context.WithValue(ctx, key, true)
+}
+
+// Ever returns true if the context was wrapped by Never.
+func Ever(ctx context.Context) bool {
+	return ctx.Value(key) == nil
+}