✨ Surface API Server warnings in client (#1468)

* Surface API Server warnings in client

- Add a wrapper around `logr.Logger` that implements WarnignHandler
- Add options in client.go for settiing up behaviour of warning handler

Signed-off-by: Madhav Jivrajani <madhav.jiv@gmail.com>

* rename logger type

Signed-off-by: Madhav Jivrajani <madhav.jiv@gmail.com>

pkg/client/client.go

@@ -31,15 +31,34 @@ import (
 	"k8s.io/client-go/rest"
 
 	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
+	"sigs.k8s.io/controller-runtime/pkg/log"
 )
 
+// WarningHandlerOptions are options for configuring a
+// warning handler for the client which is responsible
+// for surfacing API Server warnings.
+type WarningHandlerOptions struct {
+	// SuppressWarnings decides if the warnings from the
+	// API server are suppressed or surfaced in the client.
+	SuppressWarnings bool
+	// AllowDuplicateLogs does not deduplicate the to-be
+	// logged surfaced warnings messages. See
+	// log.WarningHandlerOptions for considerations
+	// regarding deuplication
+	AllowDuplicateLogs bool
+}
+
 // Options are creation options for a Client
 type Options struct {
 	// Scheme, if provided, will be used to map go structs to GroupVersionKinds
 	Scheme *runtime.Scheme
 
 	// Mapper, if provided, will be used to map GroupVersionKinds to Resources
 	Mapper meta.RESTMapper
+
+	// Opts is used to configure the warning handler responsible for
+	// surfacing and handling warnings messages sent by the API server.
+	Opts WarningHandlerOptions
 }
 
 // New returns a new Client using the provided config and Options.
@@ -61,6 +80,23 @@ func newClient(config *rest.Config, options Options) (*client, error) {
 		return nil, fmt.Errorf("must provide non-nil rest.Config to client.New")
 	}
 
+	if !options.Opts.SuppressWarnings {
+		// surface warnings
+		logger := log.Log.WithName("KubeAPIWarningLogger")
+		// Set a WarningHandler, the default WarningHandler
+		// is log.KubeAPIWarningLogger with deduplication enabled.
+		// See log.KubeAPIWarningLoggerOptions for considerations
+		// regarding deduplication.
+		rest.SetDefaultWarningHandler(
+			log.NewKubeAPIWarningLogger(
+				logger,
+				log.KubeAPIWarningLoggerOptions{
+					Deduplicate: !options.Opts.AllowDuplicateLogs,
+				},
+			),
+		)
+	}
+
 	// Init a scheme if none provided
 	if options.Scheme == nil {
 		options.Scheme = scheme.Scheme

pkg/log/warning_handler.go

@@ -0,0 +1,76 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+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 log
+
+import (
+	"sync"
+
+	"github.com/go-logr/logr"
+)
+
+// KubeAPIWarningLoggerOptions controls the behavior
+// of a rest.WarningHandler constructed using NewKubeAPIWarningLogger()
+type KubeAPIWarningLoggerOptions struct {
+	// Deduplicate indicates a given warning message should only be written once.
+	// Setting this to true in a long-running process handling many warnings can
+	// result in increased memory use.
+	Deduplicate bool
+}
+
+// KubeAPIWarningLogger is a wrapper around
+// a provided logr.Logger that implements the
+// rest.WarningHandler interface.
+type KubeAPIWarningLogger struct {
+	// logger is used to log responses with the warning header
+	logger logr.Logger
+	// opts contain options controlling warning output
+	opts KubeAPIWarningLoggerOptions
+	// writtenLock gurads written
+	writtenLock sync.Mutex
+	// used to keep track of already logged messages
+	// and help in de-duplication.
+	written map[string]struct{}
+}
+
+// HandleWarningHeader handles logging for responses from API server that are
+// warnings with code being 299 and uses a logr.Logger for it's logging purposes.
+func (l *KubeAPIWarningLogger) HandleWarningHeader(code int, agent string, message string) {
+	if code != 299 || len(message) == 0 {
+		return
+	}
+
+	if l.opts.Deduplicate {
+		l.writtenLock.Lock()
+		defer l.writtenLock.Unlock()
+
+		if _, alreadyLogged := l.written[message]; alreadyLogged {
+			return
+		}
+		l.written[message] = struct{}{}
+	}
+	l.logger.Info(message)
+}
+
+// NewKubeAPIWarningLogger returns an implementation of rest.WarningHandler that logs warnings
+// with code = 299 to the provided logr.Logger.
+func NewKubeAPIWarningLogger(l logr.Logger, opts KubeAPIWarningLoggerOptions) *KubeAPIWarningLogger {
+	h := &KubeAPIWarningLogger{logger: l, opts: opts}
+	if opts.Deduplicate {
+		h.written = map[string]struct{}{}
+	}
+	return h
+}