type Context interface {
    Deadline() (deadline time.Time, ok bool)
    Done() <-chan struct{}
    Err() error
    Value(key interface{}) interface{}
}

// 傳遞一個父Context作為參數(shù)，返回子Context，以及一個取消函數(shù)用來取消Context。
func WithCancel(parent Context) (ctx Context, cancel CancelFunc)
// 和WithCancel差不多，它會多傳遞一個截止時間參數(shù)，意味著到了這個時間點，會自動取消Context，
// 當然我們也可以不等到這個時候，可以提前通過取消函數(shù)進行取消。
func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc)

// WithTimeout和WithDeadline基本上一樣，這個表示是超時自動取消，是多少時間后自動取消Context的意思
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)

//WithValue函數(shù)和取消Context無關(guān)，它是為了生成一個綁定了一個鍵值對數(shù)據(jù)的Context，
// 綁定的數(shù)據(jù)可以通過Context.Value方法訪問到，這是我們實際用經(jīng)常要用到的技巧，一般我們想要通過上下文來傳遞數(shù)據(jù)時，可以通過這個方法，
// 如我們需要tarce追蹤系統(tǒng)調(diào)用棧的時候。
func WithValue(parent Context, key, val interface{}) Context

package main

import (
	"context"
	"fmt"
	"net/http"
	"time"
)

func IndexHandler(resp http.ResponseWriter, req *http.Request) {
	ctx := req.Context()
	go func(ctx context.Context) {
		for {
			select {
			case <-ctx.Done():
				fmt.Println("gorountine off,the err is: ", ctx.Err())
				return
			default:
				fmt.Println(333)
			}
		}
	}(ctx)

	time.Sleep(1000)
	resp.Write([]byte{1})
}
func main() {

	http.HandleFunc("/test1", IndexHandler)
	http.ListenAndServe("127.0.0.1:8080", nil)
}

// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
	c.remoteAddr = c.rwc.RemoteAddr().String()
	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
	defer func() {
		if err := recover(); err != nil && err != ErrAbortHandler {
			const size = 64 << 10
			buf := make([]byte, size)
			buf = buf[:runtime.Stack(buf, false)]
			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
		}
		if !c.hijacked() {
			c.close()
			c.setState(c.rwc, StateClosed, runHooks)
		}
	}()

	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
		if d := c.server.ReadTimeout; d != 0 {
			c.rwc.SetReadDeadline(time.Now().Add(d))
		}
		if d := c.server.WriteTimeout; d != 0 {
			c.rwc.SetWriteDeadline(time.Now().Add(d))
		}
		if err := tlsConn.Handshake(); err != nil {
			// If the handshake failed due to the client not speaking
			// TLS, assume they're speaking plaintext HTTP and write a
			// 400 response on the TLS conn's underlying net.Conn.
			if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
				io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
				re.Conn.Close()
				return
			}
			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), err)
			return
		}
		c.tlsState = new(tls.ConnectionState)
		*c.tlsState = tlsConn.ConnectionState()
		if proto := c.tlsState.NegotiatedProtocol; validNextProto(proto) {
			if fn := c.server.TLSNextProto[proto]; fn != nil {
				h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
				// Mark freshly created HTTP/2 as active and prevent any server state hooks
				// from being run on these connections. This prevents closeIdleConns from
				// closing such connections. See issue https://golang.org/issue/39776.
				c.setState(c.rwc, StateActive, skipHooks)
				fn(c.server, tlsConn, h)
			}
			return
		}
	}

	// HTTP/1.x from here on.

	ctx, cancelCtx := context.WithCancel(ctx)
	c.cancelCtx = cancelCtx
	defer cancelCtx()

	c.r = &connReader{conn: c}
	c.bufr = newBufioReader(c.r)
	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)

	for {
		// 從連接中讀取請求
		w, err := c.readRequest(ctx)
		if c.r.remain != c.server.initialReadLimitSize() {
			// If we read any bytes off the wire, we're active.
			c.setState(c.rwc, StateActive, runHooks)
		}
		.....
		.....
		// Expect 100 Continue support
		req := w.req
		if req.expectsContinue() {
			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
				// Wrap the Body reader with one that replies on the connection
				req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
				w.canWriteContinue.setTrue()
			}
		} else if req.Header.get("Expect") != "" {
			w.sendExpectationFailed()
			return
		}

		c.curReq.Store(w)
		
		// 啟動協(xié)程后臺讀取連接
		if requestBodyRemains(req.Body) {
			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
		} else {
			w.conn.r.startBackgroundRead() 
		}

		// HTTP cannot have multiple simultaneous active requests.[*]
		// Until the server replies to this request, it can't read another,
		// so we might as well run the handler in this goroutine.
		// [*] Not strictly true: HTTP pipelining. We could let them all process
		// in parallel even if their responses need to be serialized.
		// But we're not going to implement HTTP pipelining because it
		// was never deployed in the wild and the answer is HTTP/2.
		serverHandler{c.server}.ServeHTTP(w, w.req)
		/**
		* 重點在這兒，處理完請求后將會調(diào)用w.cancelCtx()方法cancel掉context
		**/
		w.cancelCtx()
		if c.hijacked() {
			return
		}
		w.finishRequest()
		if !w.shouldReuseConnection() {
			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
				c.closeWriteAndWait()
			}
			return
		}
		c.setState(c.rwc, StateIdle, runHooks)
		c.curReq.Store((*response)(nil))

		if !w.conn.server.doKeepAlives() {
			// We're in shutdown mode. We might've replied
			// to the user without "Connection: close" and
			// they might think they can send another
			// request, but such is life with HTTP/1.1.
			return
		}

		if d := c.server.idleTimeout(); d != 0 {
			c.rwc.SetReadDeadline(time.Now().Add(d))
			if _, err := c.bufr.Peek(4); err != nil {
				return
			}
		}
		c.rwc.SetReadDeadline(time.Time{})
	}
}