http.HandleFunc("/foo", fooHandler)

// HandleFunc registers the handler function for the given pattern
// in the DefaultServeMux.
// The documentation for ServeMux explains how patterns are matched.
func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	DefaultServeMux.HandleFunc(pattern, handler)
}

handler func(ResponseWriter, *Request)

// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
    // ...
	mux.Handle(pattern, HandlerFunc(handler))
}

// Handle registers the handler for the given pattern.
// If a handler already exists for pattern, Handle panics.
func (mux *ServeMux) Handle(pattern string, handler Handler) {
    // ...
	mux.m[pattern] = muxEntry{h: handler, pattern: pattern}
	// ...
}

type muxEntry struct {
	h       Handler
	pattern string
}

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

// A Server defines parameters for running an HTTP server.
// The zero value for Server is a valid configuration.
type Server struct {
	Addr    string  // TCP address to listen on, ":http" if empty
	Handler Handler // handler to invoke, http.DefaultServeMux if nil

	// ...
}

// A Handler responds to an HTTP request.
type Handler interface {
	ServeHTTP(ResponseWriter, *Request)
}

// ListenAndServe listens on the TCP network address srv.Addr and then
// calls Serve to handle requests on incoming connections.
// ...
func (srv *Server) ListenAndServe() error {
	ln, err := net.Listen("tcp", addr)
	// ...
	return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
}

// A Listener is a generic network listener for stream-oriented protocols.
//
// Multiple goroutines may invoke methods on a Listener simultaneously.
type Listener interface {
	// Accept waits for and returns the next connection to the listener.
	Accept() (Conn, error)

	// Close closes the listener.
	// Any blocked Accept operations will be unblocked and return errors.
	Close() error

	// Addr returns the listener's network address.
	Addr() Addr
}

// Serve accepts incoming connections on the Listener l, creating a
// new service goroutine for each. The service goroutines read requests and
// then call srv.Handler to reply to them.
// ...
func (srv *Server) Serve(l net.Listener) error {
	// ...
	for {
		rw, e := l.Accept()
		// ...
		c := srv.newConn(rw)
		c.setState(c.rwc, StateNew) // before Serve can return
		go c.serve(ctx)
	}
}

// Conn is a generic stream-oriented network connection.
type Conn interface {
	Read(b []byte) (n int, err error)
	Write(b []byte) (n int, err error)
	// ...
}

// 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() {
		// 异常panic处理
	}()

	// ... tls相关的处理

	// 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 {
		w, err := c.readRequest(ctx)
		// ...

		// 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)
		// ...
	}
}

func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
	handler := sh.srv.Handler
	if handler == nil {
		handler = DefaultServeMux
	}
	if req.RequestURI == "*" && req.Method == "OPTIONS" {
		handler = globalOptionsHandler{}
	}
	handler.ServeHTTP(rw, req)
}

// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = &defaultServeMux

var defaultServeMux ServeMux

type ServeMux struct {
	mu    sync.RWMutex
	m     map[string]muxEntry
	hosts bool // whether any patterns contain hostnames
}

// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
	// ...
	h, _ := mux.Handler(r)
	h.ServeHTTP(w, r)
}

// Handler returns the handler to use for the given request,
// consulting r.Method, r.Host, and r.URL.Path. It always returns
// a non-nil handler. 
func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
	// ...
	return mux.handler(host, r.URL.Path)
}

// handler is the main implementation of Handler.
// The path is known to be in canonical form, except for CONNECT methods.
func (mux *ServeMux) handler(host, path string) (h Handler, pattern string) {
	mux.mu.RLock()
	defer mux.mu.RUnlock()

	// Host-specific pattern takes precedence over generic ones
	if mux.hosts {
		h, pattern = mux.match(host + path)
	}
	if h == nil {
		h, pattern = mux.match(path)
	}
	if h == nil {
		h, pattern = NotFoundHandler(), ""
	}
	return
}

// NotFound replies to the request with an HTTP 404 not found error.
func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }

// NotFoundHandler returns a simple request handler
// that replies to each request with a ``404 page not found'' reply.
func NotFoundHandler() Handler { return HandlerFunc(NotFound) }

// Find a handler on a handler map given a path string.
// Most-specific (longest) pattern wins.
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
}

// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
	// ...
	h, _ := mux.Handler(r)
	h.ServeHTTP(w, r)
}

type Handler interface {
	ServeHTTP(ResponseWriter, *Request)
}

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

// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	// ...
	mux.Handle(pattern, HandlerFunc(handler))
}

// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
	f(w, r)
}