一文详解Golang中net/http包的实现原理

前言

Gonet/httphttpHTTPHTTPnet/httpwebnet/http HTTP Server 

http包执行流程

net/http

具体流程如下：

Listen SocketListenAndServer(...)Listen SocketClient SocketListen Socket srv.Server(...)Client SocketHttpHandlerHandlerClient Socketc.server(...)

http包源码分析

http.ListenAndServe

端口监听

http.ListenAndServer()

func ListenAndServe(addr string, handler Handler) error {
	server := &Server{Addr: addr, Handler: handler}
	return server.ListenAndServe()
}

ServerListenAndServer

func (srv *Server) ListenAndServe() error {
	if srv.shuttingDown() {
		return ErrServerClosed
	}
	addr := srv.Addr
	if addr == "" {
		addr = ":http"
	}
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}
	return srv.Serve(ln)
}

net.Listenlistenerserver.Server()

func (srv *Server) Serve(l net.Listener) error {
	if fn := testHookServerServe; fn != nil {
		fn(srv, l) // call hook with unwrapped listener
	}

	origListener := l
	l = &onceCloseListener{Listener: l}
	defer l.Close()

	if err := srv.setupHTTP2_Serve(); err != nil {
		return err
	}

	if !srv.trackListener(&l, true) {
		return ErrServerClosed
	}
	defer srv.trackListener(&l, false)

	baseCtx := context.Background()
	if srv.BaseContext != nil {
		baseCtx = srv.BaseContext(origListener)
		if baseCtx == nil {
			panic("BaseContext returned a nil context")
		}
	}

	var tempDelay time.Duration // how long to sleep on accept failure

	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
	for { //循环逻辑，接收请求处理
          //有新的连接
		rw, err := l.Accept()
		if err != nil {
			select {
			case <-srv.getDoneChan():
				return ErrServerClosed
			default:
			}
			if ne, ok := err.(net.Error); ok && ne.Temporary() {
				if tempDelay == 0 {
					tempDelay = 5 * time.Millisecond
				} else {
					tempDelay *= 2
				}
				if max := 1 * time.Second; tempDelay > max {
					tempDelay = max
				}
				srv.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
				time.Sleep(tempDelay)
				continue
			}
			return err
		}
		connCtx := ctx
		if cc := srv.ConnContext; cc != nil {
			connCtx = cc(connCtx, rw)
			if connCtx == nil {
				panic("ConnContext returned nil")
			}
		}
		tempDelay = 0
        //创建新的连接
		c := srv.newConn(rw)
		c.setState(c.rwc, StateNew) // before Serve can return
        //启动新的goroutine进行处理
		go c.serve(connCtx)
	}
}

forl.Accept()Conngoroutineconn.serve(ctx)contextgoroutinecontext

请求解析

// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
    // ...
}

/net/http/server.godefer func() {...}()

readRequestHeaderBodyserverHandlerrequestserverHandler{c.server}.ServeHTTP(w, w.req)serverHandlerServeHTTP

路由分配

使用者注册一个HandlerFunc，被转为Handler

func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	DefaultServeMux.HandleFunc(pattern, handler)
}

ServeMux的Handle方法，将会对pattern和Handler做map映射。

handler会创建一个锁，同时调用match方法返回一个Handler和pattern。

func (mux *ServeMux) Handle(pattern string, handler Handler) {
	mux.mu.Lock()
	defer mux.mu.Unlock()

	if pattern == "" {
		panic("http: invalid pattern")
	}
	if handler == nil {
		panic("http: nil handler")
	}
	if _, exist := mux.m[pattern]; exist {
		panic("http: multiple registrations for " + pattern)
	}

	if mux.m == nil {
		mux.m = make(map[string]muxEntry)
	}
	e := muxEntry{h: handler, pattern: pattern}
	mux.m[pattern] = e
	if pattern[len(pattern)-1] == '/' {
		mux.es = appendSorted(mux.es, e)
	}

	if pattern[0] != '/' {
		mux.hosts = true
	}
}

响应处理

其实就是如何根据路由，找到对应的handler。

在match方法中，对于handler，优先查找m表，若不能找到结果，则在es表中进行匹配，路径长的优先匹配。

func (mux *ServeMux) match(path string) (h Handler, pattern string) {
	// Check for exact match first.
	v, ok := mux.m[path]
	if ok {
		return v.h, v.pattern
	}

	// Check for longest valid match.
	var n = 0
	for k, v := range mux.m {
		if !pathMatch(k, path) {
			continue
		}
		if h == nil || len(k) > n {
			n = len(k)
			h = v.h
			pattern = v.pattern
		}
	}
	return
}

服务端处理完请求后，处理器可以通过ResponseWriter接口创建HTTP响应，ResponseWriter接口具有如下三个方法：

type ResponseWriter interface {
	Header() Header
	Write([]byte) (int, error)
	WriteHeader(statusCode int)
}