client-go/rest: backoff with context support

The BackoffManager interface sleeps without considering the caller's context,
i.e. cancellation is not supported. This alone is reason enough to deprecate it
and to replace it with an interface that supports a context parameter.

The other reason is that contextual logging needs that parameter.

Kubernetes-commit: b15a1943d51adfb8c5e0185d58d25e038c3d6ade

rest/request.go

@@ -106,7 +106,7 @@ type Request struct {
 	warningHandler WarningHandlerWithContext
 
 	rateLimiter flowcontrol.RateLimiter
-	backoff     BackoffManager
+	backoff     BackoffManagerWithContext
 	timeout     time.Duration
 	maxRetries  int
 
@@ -136,7 +136,7 @@ type Request struct {
 
 // NewRequest creates a new request helper object for accessing runtime.Objects on a server.
 func NewRequest(c *RESTClient) *Request {
-	var backoff BackoffManager
+	var backoff BackoffManagerWithContext
 	if c.createBackoffMgr != nil {
 		backoff = c.createBackoffMgr()
 	}
@@ -259,13 +259,27 @@ func (r *Request) Resource(resource string) *Request {
 }
 
 // BackOff sets the request's backoff manager to the one specified,
-// or defaults to the stub implementation if nil is provided
+// or defaults to the stub implementation if nil is provided.
+//
+// Deprecated: BackoffManager.Sleep ignores the caller's context. Use BackOffWithContext and BackoffManagerWithContext instead.
 func (r *Request) BackOff(manager BackoffManager) *Request {
 	if manager == nil {
 		r.backoff = &NoBackoff{}
 		return r
 	}
 
+	r.backoff = &backoffManagerNopContext{BackoffManager: manager}
+	return r
+}
+
+// BackOffWithContext sets the request's backoff manager to the one specified,
+// or defaults to the stub implementation if nil is provided.
+func (r *Request) BackOffWithContext(manager BackoffManagerWithContext) *Request {
+	if manager == nil {
+		r.backoff = &NoBackoff{}
+		return r
+	}
+
 	r.backoff = manager
 	return r
 }