Add sync.Pool to cache *bufio.Reader in tunnel server (openyurtio#381)

* add sync.Pool to cache *bufio.Reader in tunnel server

* Docs: update supported kubernetes version to 1.18

* add comments

README.md

@@ -77,7 +77,7 @@ The major OpenYurt components consist of:
 
 ## Getting started
 
-OpenYurt supports Kubernetes versions up to 1.16. Using higher Kubernetes versions may cause
+OpenYurt supports Kubernetes versions up to 1.18. Using higher Kubernetes versions may cause
 compatibility issues.
 
 You can setup the OpenYurt cluster [manually](docs/tutorial/manually-setup.md), but we recommend to start

README.zh.md

@@ -53,7 +53,7 @@ OpenYurt 的主要组件包括：
 [资源和系统要求](./docs/resource-and-system-requirements-cn.md)
 
 ## 开始使用
-OpenYurt 支持最高版本为1.16的 Kubernetes 。使用更高版本的 Kubernetes 可能会导致兼容性问题。
+OpenYurt 支持最高版本为1.18的 Kubernetes 。使用更高版本的 Kubernetes 可能会导致兼容性问题。
 您可以[手动](docs/tutorial/manually-setup.md)设置 OpenYurt 集群，但是我们建议使用 `yurtctl` 命令行工具启动 OpenYurt 。要快速构建和安装设置 `yurtctl` ，在编译系统已安装了 golang 1.13+ 和 bash 的前提下你可以执行以下命令来完成安装：
 
 ```bash

pkg/yurttunnel/server/interceptor.go

@@ -25,6 +25,7 @@ import (
 	"net"
 	"net/http"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/openyurtio/openyurt/pkg/yurttunnel/constants"
@@ -39,8 +40,26 @@ var (
 	supportedHeaders       = []string{constants.ProxyHostHeaderKey, "User-Agent"}
 	HeaderTransferEncoding = "Transfer-Encoding"
 	HeaderChunked          = "chunked"
+	bufioReaderPool        sync.Pool
 )
 
+// newBufioReader retrieves a cached Reader from the pool if the pool is not empty,
+// otherwise creates a new one
+func newBufioReader(r io.Reader) *bufio.Reader {
+	if v := bufioReaderPool.Get(); v != nil {
+		br := v.(*bufio.Reader)
+		br.Reset(r)
+		return br
+	}
+	return bufio.NewReader(r)
+}
+
+// putBufioReader puts the Reader to the pool.
+func putBufioReader(br *bufio.Reader) {
+	br.Reset(nil)
+	bufioReaderPool.Put(br)
+}
+
 // ReqRequestInterceptor intercepts http/https requests sent from the master,
 // prometheus and metric server, setup proxy tunnel to kubelet, sends requests
 // through the tunnel and sends responses back to the master
@@ -70,7 +89,8 @@ func NewRequestInterceptor(udsSockFile string, cfg *tls.Config) *RequestIntercep
 		}
 
 		fmt.Fprintf(proxyConn, "CONNECT %s HTTP/1.1\r\nHost: %s%s\r\n\r\n", addr, "127.0.0.1", connectHeaders)
-		br := bufio.NewReader(proxyConn)
+		br := newBufioReader(proxyConn)
+		defer putBufioReader(br)
 		res, err := http.ReadResponse(br, nil)
 		if err != nil {
 			proxyConn.Close()
@@ -151,7 +171,9 @@ func (ri *RequestInterceptor) ServeHTTP(w http.ResponseWriter, r *http.Request)
 func getResponse(r io.Reader) (*http.Response, []byte, error) {
 	rawResponse := bytes.NewBuffer(make([]byte, 0, 256))
 	// Save the bytes read while reading the response headers into the rawResponse buffer
-	resp, err := http.ReadResponse(bufio.NewReader(io.TeeReader(r, rawResponse)), nil)
+	br := newBufioReader(io.TeeReader(r, rawResponse))
+	defer putBufioReader(br)
+	resp, err := http.ReadResponse(br, nil)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -250,7 +272,9 @@ func isChunked(response *http.Response) bool {
 
 // serverRequest serves the normal requests, e.g., kubectl logs
 func serveRequest(tunnelConn net.Conn, w http.ResponseWriter, r *http.Request) {
-	tunnelHTTPResp, err := http.ReadResponse(bufio.NewReader(tunnelConn), r)
+	br := newBufioReader(tunnelConn)
+	defer putBufioReader(br)
+	tunnelHTTPResp, err := http.ReadResponse(br, r)
 	if err != nil {
 		klogAndHTTPError(w, http.StatusServiceUnavailable, "fail to read response from the tunnel: %v", err)
 		return