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// 创建httpserver
func main() {
  // 注册路由 /demo1
	http.Handle("/demo1", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("demo1"))
	}))
  // 注册路由 /demo2
	http.HandleFunc("/demo2", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("demo2"))
	})
  // 开启服务，监听 7777端口
	http.ListenAndServe(":7777", nil)
}

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// A Handler responds to an HTTP request.
//
// ServeHTTP should write reply headers and data to the ResponseWriter
// and then return. Returning signals that the request is finished; it
// is not valid to use the ResponseWriter or read from the
// Request.Body after or concurrently with the completion of the
// ServeHTTP call.
//
// Depending on the HTTP client software, HTTP protocol version, and
// any intermediaries between the client and the Go server, it may not
// be possible to read from the Request.Body after writing to the
// ResponseWriter. Cautious handlers should read the Request.Body
// first, and then reply.
//
// Except for reading the body, handlers should not modify the
// provided Request.
//
// If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
// that the effect of the panic was isolated to the active request.
// It recovers the panic, logs a stack trace to the server error log,
// and either closes the network connection or sends an HTTP/2
// RST_STREAM, depending on the HTTP protocol. To abort a handler so
// the client sees an interrupted response but the server doesn't log
// an error, panic with the value ErrAbortHandler.
type Handler interface {
	ServeHTTP(ResponseWriter, *Request)
}

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// net/http server.go
// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = &defaultServeMux

var defaultServeMux ServeMux
// Handle registers the handler for the given pattern
// in the DefaultServeMux.
// The documentation for ServeMux explains how patterns are matched.
func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }

// 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)
}

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// net/http server.go

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
}

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// 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.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)//按路由的长度排序后添加到es中
	}

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

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// 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)
}

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// 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)
}
// 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. If the path is not in its canonical form, the
// handler will be an internally-generated handler that redirects
// to the canonical path. If the host contains a port, it is ignored
// when matching handlers.
//
// The path and host are used unchanged for CONNECT requests.
//
// Handler also returns the registered pattern that matches the
// request or, in the case of internally-generated redirects,
// the pattern that will match after following the redirect.
//
// If there is no registered handler that applies to the request,
// Handler returns a ``page not found'' handler and an empty pattern.
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)
}

// 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
}

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// 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.  mux.es contains all patterns
	// that end in / sorted from longest to shortest.
	for _, e := range mux.es {
		if strings.HasPrefix(path, e.pattern) {
			return e.h, e.pattern
		}
	}
	return nil, ""
}

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// 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()
}

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// 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

	// TLSConfig optionally provides a TLS configuration for use
	// by ServeTLS and ListenAndServeTLS. Note that this value is
	// cloned by ServeTLS and ListenAndServeTLS, so it's not
	// possible to modify the configuration with methods like
	// tls.Config.SetSessionTicketKeys. To use
	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
	// instead.
	TLSConfig *tls.Config

	// ReadTimeout is the maximum duration for reading the entire
	// request, including the body.
	//
	// Because ReadTimeout does not let Handlers make per-request
	// decisions on each request body's acceptable deadline or
	// upload rate, most users will prefer to use
	// ReadHeaderTimeout. It is valid to use them both.
	ReadTimeout time.Duration

	// ReadHeaderTimeout is the amount of time allowed to read
	// request headers. The connection's read deadline is reset
	// after reading the headers and the Handler can decide what
	// is considered too slow for the body. If ReadHeaderTimeout
	// is zero, the value of ReadTimeout is used. If both are
	// zero, there is no timeout.
	ReadHeaderTimeout time.Duration

	// WriteTimeout is the maximum duration before timing out
	// writes of the response. It is reset whenever a new
	// request's header is read. Like ReadTimeout, it does not
	// let Handlers make decisions on a per-request basis.
	WriteTimeout time.Duration

	// IdleTimeout is the maximum amount of time to wait for the
	// next request when keep-alives are enabled. If IdleTimeout
	// is zero, the value of ReadTimeout is used. If both are
	// zero, there is no timeout.
	IdleTimeout time.Duration

	// MaxHeaderBytes controls the maximum number of bytes the
	// server will read parsing the request header's keys and
	// values, including the request line. It does not limit the
	// size of the request body.
	// If zero, DefaultMaxHeaderBytes is used.
	MaxHeaderBytes int

	// TLSNextProto optionally specifies a function to take over
	// ownership of the provided TLS connection when an NPN/ALPN
	// protocol upgrade has occurred. The map key is the protocol
	// name negotiated. The Handler argument should be used to
	// handle HTTP requests and will initialize the Request's TLS
	// and RemoteAddr if not already set. The connection is
	// automatically closed when the function returns.
	// If TLSNextProto is not nil, HTTP/2 support is not enabled
	// automatically.
	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)

	// ConnState specifies an optional callback function that is
	// called when a client connection changes state. See the
	// ConnState type and associated constants for details.
	ConnState func(net.Conn, ConnState)

	// ErrorLog specifies an optional logger for errors accepting
	// connections, unexpected behavior from handlers, and
	// underlying FileSystem errors.
	// If nil, logging is done via the log package's standard logger.
	ErrorLog *log.Logger

	// BaseContext optionally specifies a function that returns
	// the base context for incoming requests on this server.
	// The provided Listener is the specific Listener that's
	// about to start accepting requests.
	// If BaseContext is nil, the default is context.Background().
	// If non-nil, it must return a non-nil context.
	BaseContext func(net.Listener) context.Context

	// ConnContext optionally specifies a function that modifies
	// the context used for a new connection c. The provided ctx
	// is derived from the base context and has a ServerContextKey
	// value.
	ConnContext func(ctx context.Context, c net.Conn) context.Context

	disableKeepAlives int32     // accessed atomically.
	inShutdown        int32     // accessed atomically (non-zero means we're in Shutdown)
	nextProtoOnce     sync.Once // guards setupHTTP2_* init
	nextProtoErr      error     // result of http2.ConfigureServer if used

	mu         sync.Mutex
	listeners  map[*net.Listener]struct{}
	activeConn map[*conn]struct{}
	doneChan   chan struct{}
	onShutdown []func()
}
// ListenAndServe listens on the TCP network address srv.Addr and then
// calls Serve to handle requests on incoming connections.
// Accepted connections are configured to enable TCP keep-alives.
//
// If srv.Addr is blank, ":http" is used.
//
// ListenAndServe always returns a non-nil error. After Shutdown or Close,
// the returned error is ErrServerClosed.
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)
}

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// 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
	}

	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)

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

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

	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
		}
		if cc := srv.ConnContext; cc != nil {
			ctx = cc(ctx, rw)
			if ctx == nil {
				panic("ConnContext returned nil")
			}
		}
		tempDelay = 0
		c := srv.newConn(rw)
		c.setState(c.rwc, StateNew) // before Serve can return
		go c.serve(ctx)
	}
}

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// A conn represents the server side of an HTTP connection.
type conn struct {
	// server is the server on which the connection arrived.
	// Immutable; never nil.
	server *Server

	// cancelCtx cancels the connection-level context.
	cancelCtx context.CancelFunc

	// rwc is the underlying network connection.
	// This is never wrapped by other types and is the value given out
	// to CloseNotifier callers. It is usually of type *net.TCPConn or
	// *tls.Conn.
	rwc net.Conn

	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
	// inside the Listener's Accept goroutine, as some implementations block.
	// It is populated immediately inside the (*conn).serve goroutine.
	// This is the value of a Handler's (*Request).RemoteAddr.
	remoteAddr string

	// tlsState is the TLS connection state when using TLS.
	// nil means not TLS.
	tlsState *tls.ConnectionState

	// werr is set to the first write error to rwc.
	// It is set via checkConnErrorWriter{w}, where bufw writes.
	werr error

	// r is bufr's read source. It's a wrapper around rwc that provides
	// io.LimitedReader-style limiting (while reading request headers)
	// and functionality to support CloseNotifier. See *connReader docs.
	r *connReader

	// bufr reads from r.
	bufr *bufio.Reader

	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
	bufw *bufio.Writer

	// lastMethod is the method of the most recent request
	// on this connection, if any.
	lastMethod string

	curReq atomic.Value // of *response (which has a Request in it)

	curState struct{ atomic uint64 } // packed (unixtime<<8|uint8(ConnState))

	// mu guards hijackedv
	mu sync.Mutex

	// hijackedv is whether this connection has been hijacked
	// by a Handler with the Hijacker interface.
	// It is guarded by mu.
	hijackedv bool
}

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// 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{ctx, 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"

			switch {
			case 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

			case isUnsupportedTEError(err):
				// Respond as per RFC 7230 Section 3.3.1 which says,
				//      A server that receives a request message with a
				//      transfer coding it does not understand SHOULD
				//      respond with 501 (Unimplemented).
				code := StatusNotImplemented

				// We purposefully aren't echoing back the transfer-encoding's value,
				// so as to mitigate the risk of cross side scripting by an attacker.
				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
				return

			case isCommonNetReadError(err):
				return // don't reply

			default:
				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{})
	}
}

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func main() {
	r, err := http.Get("http://www.baidu.com")
	if err != nil {
		log.Fatalln(err)
	}
	fmt.Println(r)
}