Refactor HTTP server to address bugs (#4636)

* Refactor HTTP server to address bugs
* Remove unnecessary goroutine to start multiple TCP listeners.
* HTTP server waits for shutdown to maximum of Server.ShutdownTimeout
  than per serverShutdownPoll.
* Handles new connection errors properly.
* Handles read and write timeout properly.
* Handles error on start of HTTP server properly by exiting minio
  process.

Fixes #4494 #4476 & fixed review comments

pkg/http/server.go

@@ -0,0 +1,173 @@
+/*
+ * 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 http
+
+import (
+	"crypto/tls"
+	"errors"
+	"net/http"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	humanize "github.com/dustin/go-humanize"
+)
+
+const (
+	serverShutdownPoll = 500 * time.Millisecond
+
+	// DefaultShutdownTimeout - default shutdown timeout used for graceful http server shutdown.
+	DefaultShutdownTimeout = 5 * time.Second
+
+	// DefaultTCPKeepAliveTimeout - default TCP keep alive timeout for accepted connection.
+	DefaultTCPKeepAliveTimeout = 10 * time.Second
+
+	// DefaultReadTimeout - default timout to read data from accepted connection.
+	DefaultReadTimeout = 30 * time.Second
+
+	// DefaultWriteTimeout - default timout to write data to accepted connection.
+	DefaultWriteTimeout = 30 * time.Second
+
+	// DefaultMaxHeaderBytes - default maximum HTTP header size in bytes.
+	DefaultMaxHeaderBytes = 1 * humanize.MiByte
+)
+
+// Server - extended http.Server supports multiple addresses to serve and enhanced connection handling.
+type Server struct {
+	http.Server
+	Addrs                  []string                            // addresses on which the server listens for new connection.
+	ShutdownTimeout        time.Duration                       // timeout used for graceful server shutdown.
+	TCPKeepAliveTimeout    time.Duration                       // timeout used for underneath TCP connection.
+	UpdateBytesReadFunc    func(int)                           // function to be called to update bytes read in bufConn.
+	UpdateBytesWrittenFunc func(int)                           // function to be called to update bytes written in bufConn.
+	ErrorLogFunc           func(error, string, ...interface{}) // function to be called on errors.
+	listenerMutex          *sync.Mutex                         // to guard 'listener' field.
+	listener               *httpListener                       // HTTP listener for all 'Addrs' field.
+	inShutdown             uint32                              // indicates whether the server is in shutdown or not
+	requestCount           int32                               // counter holds no. of request in process.
+}
+
+// Start - start HTTP server
+func (srv *Server) Start() (err error) {
+	// Take a copy of server fields.
+	tlsConfig := srv.TLSConfig
+	readTimeout := srv.ReadTimeout
+	writeTimeout := srv.WriteTimeout
+	handler := srv.Handler
+
+	addrs := srv.Addrs
+	tcpKeepAliveTimeout := srv.TCPKeepAliveTimeout
+	updateBytesReadFunc := srv.UpdateBytesReadFunc
+	updateBytesWrittenFunc := srv.UpdateBytesWrittenFunc
+	errorLogFunc := srv.ErrorLogFunc
+
+	// Create new HTTP listener.
+	var listener *httpListener
+	listener, err = newHTTPListener(
+		addrs,
+		tlsConfig,
+		tcpKeepAliveTimeout,
+		readTimeout,
+		writeTimeout,
+		updateBytesReadFunc,
+		updateBytesWrittenFunc,
+		errorLogFunc,
+	)
+	if err != nil {
+		return err
+	}
+
+	// Wrap given handler to do additional
+	// * return 503 (service unavailable) if the server in shutdown.
+	wrappedHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		atomic.AddInt32(&srv.requestCount, 1)
+		defer atomic.AddInt32(&srv.requestCount, -1)
+
+		// If server is in shutdown, return 503 (service unavailable)
+		if atomic.LoadUint32(&srv.inShutdown) != 0 {
+			w.WriteHeader(http.StatusServiceUnavailable)
+			return
+		}
+
+		// Handle request using passed handler.
+		handler.ServeHTTP(w, r)
+	})
+
+	srv.listenerMutex.Lock()
+	srv.Handler = wrappedHandler
+	srv.listener = listener
+	srv.listenerMutex.Unlock()
+
+	// Start servicing with listener.
+	return srv.Server.Serve(listener)
+}
+
+// Shutdown - shuts down HTTP server.
+func (srv *Server) Shutdown() error {
+	if atomic.AddUint32(&srv.inShutdown, 1) > 1 {
+		// shutdown in progress
+		return errors.New("http server already in shutdown")
+	}
+
+	// Close underneath HTTP listener.
+	srv.listenerMutex.Lock()
+	err := srv.listener.Close()
+	srv.listenerMutex.Unlock()
+
+	// Wait for opened connection to be closed up to Shutdown timeout.
+	shutdownTimeout := srv.ShutdownTimeout
+	shutdownTimer := time.NewTimer(shutdownTimeout)
+	ticker := time.NewTicker(serverShutdownPoll)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-shutdownTimer.C:
+			return errors.New("timed out. some connections are still active. doing abnormal shutdown")
+		case <-ticker.C:
+			if atomic.LoadInt32(&srv.requestCount) <= 0 {
+				return err
+			}
+		}
+	}
+}
+
+// NewServer - creates new HTTP server using given arguments.
+func NewServer(addrs []string, handler http.Handler, certificate *tls.Certificate) *Server {
+	var tlsConfig *tls.Config
+	if certificate != nil {
+		tlsConfig = &tls.Config{
+			PreferServerCipherSuites: true,
+			MinVersion:               tls.VersionTLS12,
+			NextProtos:               []string{"http/1.1", "h2"},
+		}
+		tlsConfig.Certificates = append(tlsConfig.Certificates, *certificate)
+	}
+
+	httpServer := &Server{
+		Addrs:               addrs,
+		ShutdownTimeout:     DefaultShutdownTimeout,
+		TCPKeepAliveTimeout: DefaultTCPKeepAliveTimeout,
+		listenerMutex:       &sync.Mutex{},
+	}
+	httpServer.Handler = handler
+	httpServer.TLSConfig = tlsConfig
+	httpServer.ReadTimeout = DefaultReadTimeout
+	httpServer.WriteTimeout = DefaultWriteTimeout
+	httpServer.MaxHeaderBytes = DefaultMaxHeaderBytes
+
+	return httpServer
+}