package main

import "net/http"

func main() {
	mux := http.NewServeMux()

	mux.HandleFunc("/a", func(writer http.ResponseWriter, request *http.Request) {
		writer.Write([]byte("aaaaaa"))
	})
	mux.HandleFunc("/b", func(writer http.ResponseWriter, request *http.Request) {
		writer.Write([]byte("bbbbbb"))
	})
	http.ListenAndServe(":3000",mux)
}

type ServeMux struct {
	mu    sync.RWMutex
	m     map[string]muxEntry
	es    []muxEntry // slice of entries sorted from longest to shortest.
	hosts bool       // whether any patterns contain hostnames
}

// HandleFunc registers the handler function for the given pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	if handler == nil {
		panic("http: nil handler")
	}
	mux.Handle(pattern, HandlerFunc(handler))
}

// ListenAndServe listens on the TCP network address addr and then calls
// Serve with handler to handle requests on incoming connections.
// Accepted connections are configured to enable TCP keep-alives.
//
// The handler is typically nil, in which case the DefaultServeMux is used.
//
// ListenAndServe always returns a non-nil error.
func ListenAndServe(addr string, handler Handler) error {
	server := &Server{Addr: addr, Handler: handler}
	return server.ListenAndServe()
}

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(tcpKeepAliveListener{ln.(*net.TCPListener)})
}

// 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.
//
// HTTP/2 support is only enabled if the Listener returns *tls.Conn
// connections and they were configured with "h2" in the TLS
// Config.NextProtos.
//
// Serve always returns a non-nil error and closes l.
// After Shutdown or Close, the returned error is ErrServerClosed.
func (srv *Server) Serve(l net.Listener) error {
	if fn := testHookServerServe; fn != nil {
		fn(srv, l) // call hook with unwrapped listener
	}

	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)

	var tempDelay time.Duration     // how long to sleep on accept failure
	baseCtx := context.Background() // base is always background, per Issue 16220
	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
	for {
		rw, e := l.Accept()
		if e != nil {
			select {
			case <-srv.getDoneChan():
				return ErrServerClosed
			default:
			}
			if ne, ok := e.(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", e, tempDelay)
				time.Sleep(tempDelay)
				continue
			}
			return e
		}
		tempDelay = 0
		c := srv.newConn(rw)
		c.setState(c.rwc, StateNew) // before Serve can return
		go c.serve(ctx)
	}
}

func (ln tcpKeepAliveListener) Accept() (net.Conn, error) {
	tc, err := ln.AcceptTCP()
	if err != nil {
		return nil, err
	}
	tc.SetKeepAlive(true)
	tc.SetKeepAlivePeriod(3 * time.Minute)
	return tc, 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)
		}
	}()

	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; validNPN(proto) {
			if fn := c.server.TLSNextProto[proto]; fn != nil {
				h := initNPNRequest{tlsConn, serverHandler{c.server}}
				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 {
		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)
		}
		if err != nil {
			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"

			if err == errTooLarge {
				// Their HTTP client may or may not be
				// able to read this if we're
				// responding to them and hanging up
				// while they're still writing their
				// request. Undefined behavior.
				const publicErr = "431 Request Header Fields Too Large"
				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
				c.closeWriteAndWait()
				return
			}
			if isCommonNetReadError(err) {
				return // don't reply
			}

			publicErr := "400 Bad Request"
			if v, ok := err.(badRequestError); ok {
				publicErr = publicErr + ": " + string(v)
			}

			fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
			return
		}

		// 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}
			}
		} else if req.Header.get("Expect") != "" {
			w.sendExpectationFailed()
			return
		}

		c.curReq.Store(w)

		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)
		w.cancelCtx()
		if c.hijacked() {
			return
		}
		w.finishRequest()
		if !w.shouldReuseConnection() {
			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
				c.closeWriteAndWait()
			}
			return
		}
		c.setState(c.rwc, StateIdle)
		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{})
	}
}

type serverHandler struct {
	srv *Server
}

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)
}

// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
	if r.RequestURI == "*" {
		if r.ProtoAtLeast(1, 1) {
			w.Header().Set("Connection", "close")
		}
		w.WriteHeader(StatusBadRequest)
		return
	}
	h, _ := mux.Handler(r)
	h.ServeHTTP(w, r)
}

func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {

	// CONNECT requests are not canonicalized.
	if r.Method == "CONNECT" {
		// If r.URL.Path is /tree and its handler is not registered,
		// the /tree -> /tree/ redirect applies to CONNECT requests
		// but the path canonicalization does not.
		if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
		}

		return mux.handler(r.Host, r.URL.Path)
	}

	// All other requests have any port stripped and path cleaned
	// before passing to mux.handler.
	host := stripHostPort(r.Host)
	path := cleanPath(r.URL.Path)

	// If the given path is /tree and its handler is not registered,
	// redirect for /tree/.
	if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
	}

	if path != r.URL.Path {
		_, pattern = mux.handler(host, path)
		url := *r.URL
		url.Path = path
		return RedirectHandler(url.String(), StatusMovedPermanently), pattern
	}

	return mux.handler(host, r.URL.Path)
}

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