stats: Add network and http statisics (#3686)

Network: total bytes of incoming and outgoing server's data
by taking advantage of our ConnMux Read/Write wrapping

HTTP: total number of different http verbs passed in http
requests and different status codes passed in http responses.
This is counted in a new http handler.

cmd/stats.go

@@ -0,0 +1,129 @@
+/*
+ * Minio Cloud Storage, (C) 2017 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 cmd
+
+import (
+	"net/http"
+	"sync/atomic"
+)
+
+// counter - simplify atomic counting
+type counter struct {
+	val uint64
+}
+
+// Inc increases counter atomically
+func (c *counter) Inc(n uint64) {
+	atomic.AddUint64(&c.val, n)
+}
+
+// Value fetches counter's value atomically
+func (c *counter) Value() uint64 {
+	return atomic.LoadUint64(&c.val)
+}
+
+// ConnStats - Network statistics
+// Count total input/output transferred bytes during
+// the server's life.
+type ConnStats struct {
+	totalInputBytes  counter
+	totalOutputBytes counter
+}
+
+// Increase total input bytes
+func (s *ConnStats) incInputBytes(n int) {
+	s.totalInputBytes.Inc(uint64(n))
+}
+
+// Increase total output bytes
+func (s *ConnStats) incOutputBytes(n int) {
+	s.totalOutputBytes.Inc(uint64(n))
+}
+
+// Return total input bytes
+func (s *ConnStats) getTotalInputBytes() uint64 {
+	return s.totalInputBytes.Value()
+}
+
+// Return total output bytes
+func (s *ConnStats) getTotalOutputBytes() uint64 {
+	return s.totalOutputBytes.Value()
+}
+
+// Prepare new ConnStats structure
+func newConnStats() *ConnStats {
+	return &ConnStats{}
+}
+
+// httpStats holds statistics information about
+// HTTP requests made by all clients
+type httpStats struct {
+	// HEAD request stats
+	totalHEADs   counter
+	successHEADs counter
+	// GET request stats
+	totalGETs   counter
+	successGETs counter
+	// PUT request
+	totalPUTs   counter
+	successPUTs counter
+	// POST request
+	totalPOSTs   counter
+	successPOSTs counter
+	// DELETE request
+	totalDELETEs   counter
+	successDELETEs counter
+}
+
+// Update statistics from http request and response data
+func (st *httpStats) updateStats(r *http.Request, w *httpResponseRecorder) {
+	// A successful request has a 2xx response code
+	successReq := (w.respStatusCode >= 200 && w.respStatusCode < 300)
+	// Update stats according to method verb
+	switch r.Method {
+	case "HEAD":
+		st.totalHEADs.Inc(1)
+		if successReq {
+			st.successHEADs.Inc(1)
+		}
+	case "GET":
+		st.totalGETs.Inc(1)
+		if successReq {
+			st.successGETs.Inc(1)
+		}
+	case "PUT":
+		st.totalPUTs.Inc(1)
+		if successReq {
+			st.successPUTs.Inc(1)
+		}
+	case "POST":
+		st.totalPOSTs.Inc(1)
+		if successReq {
+			st.successPOSTs.Inc(1)
+		}
+	case "DELETE":
+		st.totalDELETEs.Inc(1)
+		if successReq {
+			st.successDELETEs.Inc(1)
+		}
+	}
+}
+
+// Prepare new HttpStats structure
+func newHTTPStats() *httpStats {
+	return &httpStats{}
+}