Add admin API to send trace notifications to registered (#7128)

Remove current functionality to log trace to file
using MINIO_HTTP_TRACE env, and replace it with
mc admin trace command on mc client.

pkg/pubsub/pubsub_test.go

@@ -0,0 +1,66 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 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 pubsub
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestSubscribe(t *testing.T) {
+	ps := New()
+	ps.Subscribe()
+	ps.Subscribe()
+	if len(ps.subs) != 2 {
+		t.Errorf("expected 2 subscribers")
+	}
+}
+
+func TestUnsubscribe(t *testing.T) {
+	ps := New()
+	c1 := ps.Subscribe()
+	ps.Subscribe()
+	ps.Unsubscribe(c1)
+	if len(ps.subs) != 1 {
+		t.Errorf("expected 1 subscriber")
+	}
+}
+
+func TestPubSub(t *testing.T) {
+	ps := New()
+	c1 := ps.Subscribe()
+	val := "hello"
+	ps.Publish(val)
+	msg := <-c1
+	if msg != "hello" {
+		t.Errorf(fmt.Sprintf("expected %s , found %s", val, msg))
+	}
+}
+
+func TestMultiPubSub(t *testing.T) {
+	ps := New()
+	c1 := ps.Subscribe()
+	c2 := ps.Subscribe()
+	val := "hello"
+	ps.Publish(val)
+
+	msg1 := <-c1
+	msg2 := <-c2
+	if msg1 != "hello" && msg2 != "hello" {
+		t.Errorf(fmt.Sprintf("expected both subscribers to have%s , found %s and  %s", val, msg1, msg2))
+	}
+}