From cc8178cdc4096ebf66fc2f467fd8f3be9ff1b99b Mon Sep 17 00:00:00 2001
From: Krishna Srinivas <634494+krishnasrinivas@users.noreply.github.com>
Date: Wed, 9 May 2018 15:59:45 -0700
Subject: [PATCH] Log errors only once for event notification errors (#5905)

---
 cmd/logger/logonce.go | 82 +++++++++++++++++++++++++++++++++++++++++++
 cmd/notification.go   |  2 +-
 2 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 cmd/logger/logonce.go

diff --git a/cmd/logger/logonce.go b/cmd/logger/logonce.go
new file mode 100644
index 000000000..cfa16951b
--- /dev/null
+++ b/cmd/logger/logonce.go
@@ -0,0 +1,82 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * 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 logger
+
+import (
+	"context"
+	"sync"
+
+	"time"
+)
+
+// Holds a map of recently logged errors.
+type logOnceType struct {
+	IDMap map[interface{}]error
+	sync.Mutex
+}
+
+// One log message per error.
+func (l *logOnceType) logOnceIf(ctx context.Context, err error, id interface{}) {
+	if err == nil {
+		return
+	}
+	l.Lock()
+	shouldLog := false
+	prevErr := l.IDMap[id]
+	if prevErr == nil {
+		l.IDMap[id] = err
+		shouldLog = true
+	} else {
+		if prevErr.Error() != err.Error() {
+			l.IDMap[id] = err
+			shouldLog = true
+		}
+	}
+	l.Unlock()
+
+	if shouldLog {
+		LogIf(ctx, err)
+	}
+}
+
+// Cleanup the map every 30 minutes so that the log message is printed again for the user to notice.
+func (l *logOnceType) cleanupRoutine() {
+	for {
+		select {
+		case <-time.After(time.Minute * 30):
+			l.Lock()
+			l.IDMap = make(map[interface{}]error)
+			l.Unlock()
+		}
+	}
+}
+
+// Returns logOnceType
+func newLogOnceType() *logOnceType {
+	l := &logOnceType{IDMap: make(map[interface{}]error)}
+	go l.cleanupRoutine()
+	return l
+}
+
+var logOnce = newLogOnceType()
+
+// LogOnceIf - Logs notification errors - once per error.
+// id is a unique identifier for related log messages, refer to cmd/notification.go
+// on how it is used.
+func LogOnceIf(ctx context.Context, err error, id interface{}) {
+	logOnce.logOnceIf(ctx, err, id)
+}
diff --git a/cmd/notification.go b/cmd/notification.go
index 71d60e64c..e570f414b 100644
--- a/cmd/notification.go
+++ b/cmd/notification.go
@@ -532,7 +532,7 @@ func sendEvent(args eventArgs) {
 		reqInfo.AppendTags("EventName", args.EventName.String())
 		reqInfo.AppendTags("targetID", err.ID.Name)
 		ctx := logger.SetReqInfo(context.Background(), reqInfo)
-		logger.LogIf(ctx, err.Err)
+		logger.LogOnceIf(ctx, err.Err, err.ID)
 	}
 }