golang标准库http服务器处理流程

http标准库

golang本身就提供了http的标志库，在golang中可以轻松的编写http服务，本文主要是因为在编写http服务的过程中，对整个处理流程不是很了解故想了解一下。

示例代码

package main

import (
"fmt"
"net/http"
)

func hello(w http.ResponseWriter, req *http.Request) {

	fmt.Fprintf(w, "hello\n")
}

func headers(w http.ResponseWriter, req *http.Request) {

	for name, headers := range req.Header {
		for _, h := range headers {
			fmt.Fprintf(w, "%v: %v\n", name, h)
		}
	}
}

func main() {
	http.HandleFunc("/hello", hello)
	http.HandleFunc("/headers", headers)
	http.ListenAndServe(":7777", nil)
}

这是官网上面提供的一个简单的http服务的例子，从结构上看处理逻辑相对比较简单清晰，定义一个路由然后定义一个处理函数，许多go的web框架基本上都是在这个标准库的基础上封装而来，如果访问http://127.0.0.1:7777/hello就可以看见输出的内容为hello。

http.ListenAndServe

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

从代码上来看，该函数很简单，直接通过初始化了一个Server，然后调用了ListenAndServe方法，从而开始处理请求。

func (srv *Server) ListenAndServe() error {
	if srv.shuttingDown() {  	// 检查是否关闭
		return ErrServerClosed
	}
	addr := srv.Addr
	if addr == "" {
		addr = ":http"
	}
	ln, err := net.Listen("tcp", addr) 				// 使用tcp协议处理地址与端口的请求
	if err != nil {
		return err
	}
	return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})  // 开始循环处理
}

主要传入了tcpKeepAliveListener这个类型的监听对象；

type tcpKeepAliveListener struct {
	*net.TCPListener
}

func (ln tcpKeepAliveListener) Accept() (net.Conn, error) {
	tc, err := ln.AcceptTCP() 								// 接受请求
	if err != nil {
		return nil, err
	}
	tc.SetKeepAlive(true) 										// 设置keepAlive
	tc.SetKeepAlivePeriod(3 * time.Minute)    // 设置保存的时间
	return tc, nil
}

Server函数处理；

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} 				// 当关闭时 只关闭一次该Listen
	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() 											// 处理接受的请求
		if e != nil {
			select {
			case <-srv.getDoneChan(): 						// 检查是否处理完成，如果关闭则退出
				return ErrServerClosed
			default:
			}
			if ne, ok := e.(net.Error); ok && ne.Temporary() {   // 检查是否有错误 如果有错误则继续等待几首
				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)                  	// 初始化一个新的连接
		c.setState(c.rwc, StateNew) // before Serve can return  
		go c.serve(ctx) 												// 开启协程来处理该请求
	}
}

conn.server

// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
	c.remoteAddr = c.rwc.RemoteAddr().String() 								// 获取远端地址
	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)
		}
	}() 																											// 处理错误

	if tlsConn, ok := c.rwc.(*tls.Conn); ok { 								// 检查是否是https连接
		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} 															// 初始化一个读连接
	c.bufr = newBufioReader(c.r) 														//生成一个读buf
	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)  // 生成一个写buf，该bufw底层写入就是链接c

	for {
		w, err := c.readRequest(ctx) 														// 初始化一个response
		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 																				// 获取解析后的request
		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) {  					// 解析头部信息
			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
		} else {
			w.conn.r.startBackgroundRead() 						// 如果没有读出到则后台读客户端传入的数据
		}

		// 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)      // 通过server设置的handle来处理该请求
		w.cancelCtx()
		if c.hijacked() {
			return
		}
		w.finishRequest() 															// 将处理的请求写入输出缓冲区将处理完成数据返回给客户端
		if !w.shouldReuseConnection() { 								// 检查是否处理完该请求后关闭该链接
			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
				c.closeWriteAndWait()
			}
			return
		}
		c.setState(c.rwc, StateIdle) 										// 设置为空闲
		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{})
	}
}

conn.readRequest

// Read next request from connection.
func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
	if c.hijacked() {
		return nil, ErrHijacked
	}

	var (
		wholeReqDeadline time.Time // or zero if none
		hdrDeadline      time.Time // or zero if none
	)
	t0 := time.Now() 										// 获取当前时间
	if d := c.server.readHeaderTimeout(); d != 0 { 		// 是否设置读头部信息超时
		hdrDeadline = t0.Add(d)
	}
	if d := c.server.ReadTimeout; d != 0 {     // 是否设置读超时
		wholeReqDeadline = t0.Add(d)
	}
	c.rwc.SetReadDeadline(hdrDeadline)
	if d := c.server.WriteTimeout; d != 0 { 		// 是否设置写超时
		defer func() {
			c.rwc.SetWriteDeadline(time.Now().Add(d))
		}()
	}

	c.r.setReadLimit(c.server.initialReadLimitSize())   // 设置读时间限制
	if c.lastMethod == "POST" {
		// RFC 7230 section 3 tolerance for old buggy clients.
		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
		c.bufr.Discard(numLeadingCRorLF(peek))
	}
	req, err := readRequest(c.bufr, keepHostHeader) 		// 读头部信息并解析头部协议
	if err != nil {
		if c.r.hitReadLimit() {
			return nil, errTooLarge
		}
		return nil, err
	}

	if !http1ServerSupportsRequest(req) {             	// 检查是否支持
		return nil, badRequestError("unsupported protocol version")
	}

	c.lastMethod = req.Method
	c.r.setInfiniteReadLimit()

	hosts, haveHost := req.Header["Host"] 							// 获取host信息
	isH2Upgrade := req.isH2Upgrade()
	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
		return nil, badRequestError("missing required Host header")
	}
	if len(hosts) > 1 {
		return nil, badRequestError("too many Host headers")
	}
	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
		return nil, badRequestError("malformed Host header")
	}
	for k, vv := range req.Header {
		if !httpguts.ValidHeaderFieldName(k) {
			return nil, badRequestError("invalid header name")
		}
		for _, v := range vv {
			if !httpguts.ValidHeaderFieldValue(v) {
				return nil, badRequestError("invalid header value")
			}
		}
	}
	delete(req.Header, "Host")

	ctx, cancelCtx := context.WithCancel(ctx)
	req.ctx = ctx
	req.RemoteAddr = c.remoteAddr
	req.TLS = c.tlsState
	if body, ok := req.Body.(*body); ok { 				// 获取请求body
		body.doEarlyClose = true
	}

	// Adjust the read deadline if necessary.
	if !hdrDeadline.Equal(wholeReqDeadline) {
		c.rwc.SetReadDeadline(wholeReqDeadline)
	}

	w = &response{
		conn:          c,
		cancelCtx:     cancelCtx,
		req:           req,
		reqBody:       req.Body,
		handlerHeader: make(Header),
		contentLength: -1,
		closeNotifyCh: make(chan bool, 1),

		// We populate these ahead of time so we're not
		// reading from req.Header after their Handler starts
		// and maybe mutates it (Issue 14940)
		wants10KeepAlive: req.wantsHttp10KeepAlive(),
		wantsClose:       req.wantsClose(),
	} 																			// 生成一个response 将连接信息都传入
	if isH2Upgrade {
		w.closeAfterReply = true
	}
	w.cw.res = w
	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)   // 生成一个写缓冲区
	return w, nil
}

从readRequest执行流程来看，主要就是先检查是否设置超时时间，然后通过readRequest函数来读取并解析http头部内容，最后生成一个response，提供给Handle来处理，提供给serverHandler的ServerHttp函数来处理，ServeHTTP函数就是我们再示例代码中注册的两个func

serverHandler.ServeHTTP

在处理逻辑serverHandler{c.server}.ServeHTTP(w, w.req)这行代码中

type serverHandler struct {
	srv *Server
}

func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
	handler := sh.srv.Handler
	if handler == nil {
		handler = DefaultServeMux 		// 默认的handle 本示例代码中就是该默认的
	}
	if req.RequestURI == "*" && req.Method == "OPTIONS" {
		handler = globalOptionsHandler{}
	}
	handler.ServeHTTP(rw, req)      // 调用该handle来处理请求
}

此时调用的就是DefaultServeMux

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)    // 查找匹配的handle
	h.ServeHTTP(w, r)         // 调用该handle的处理方式
}
...
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)     // 获取host
	path := cleanPath(r.URL.Path)     // 获取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)     // 通过host,path来比对
		url := *r.URL
		url.Path = path
		return RedirectHandler(url.String(), StatusMovedPermanently), pattern
	}

	return mux.handler(host, r.URL.Path)     // 调用handler来匹配handler
}

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)   	// 匹配host加path
	}
	if h == nil {
		h, pattern = mux.match(path)            // 如果只有path则匹配path
	}
	if h == nil {
		h, pattern = NotFoundHandler(), ""     //返回没有找到
	}
	return
}

func (mux *ServeMux) match(path string) (h Handler, pattern string) {
	// Check for exact match first.
	v, ok := mux.m[path] 										// 检查该path是否在路径中
	if ok {
		return v.h, v.pattern                 // 如果在则返回handle和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) {  	// 进行字符匹配
			return e.h, e.pattern
		}
	}
	return nil, ""
}

通过ServerHTTP的处理流程可以看出，先通过全路径匹配，然后找到对应自己编写的handle，通过编写的handle处理的流程。

handle注册的流程如下，在本文示例中http.HandleFunc函数就是注册了处理对应url的handle

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)) {
	if handler == nil {
		panic("http: nil handler")
	}
	mux.Handle(pattern, HandlerFunc(handler))
}
...
func (mux *ServeMux) Handle(pattern string, handler Handler) {
	mux.mu.Lock()
	defer mux.mu.Unlock()

	if pattern == "" {
		panic("http: invalid pattern")
	} 
	if handler == nil { 												// 检查注册函数是否为空
		panic("http: nil handler")
	}
	if _, exist := mux.m[pattern]; exist {       // 检查是否已经注册
		panic("http: multiple registrations for " + pattern)
	}

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

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

此时完成了handle的匹配，并调用了该handle来处理具体的业务逻辑。

response.finishRequest

func (w *response) finishRequest() {
	w.handlerDone.setTrue()    // 设置该handle被处理完成

	if !w.wroteHeader {        // 如果没有头部则写入ok头部信息
		w.WriteHeader(StatusOK)
	}

	w.w.Flush() 							// 刷新
	putBufioWriter(w.w)       // 将处理的w刷入
	w.cw.close()  						// 关闭
	w.conn.bufw.Flush()       // 将业务处理所有的buff都发送给客户端

	w.conn.r.abortPendingRead()

	// Close the body (regardless of w.closeAfterReply) so we can
	// re-use its bufio.Reader later safely.
	w.reqBody.Close()

	if w.req.MultipartForm != nil {
		w.req.MultipartForm.RemoveAll()
	}
}

w.conn.bufw就是c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)

通过注册该c，来控制写出的数据发送给客户端；

func (b *Writer) Flush() error {
	if b.err != nil {
		return b.err
	}
	if b.n == 0 {
		return nil
	}
	n, err := b.wr.Write(b.buf[0:b.n])  // 写入处理完成的数据，该wr就是前面初始化传入的c
	if n < b.n && err == nil {
		err = io.ErrShortWrite
	}
	if err != nil {
		if n > 0 && n < b.n {
			copy(b.buf[0:b.n-n], b.buf[n:b.n])
		}
		b.n -= n
		b.err = err
		return err
	}
	b.n = 0
	return nil
}

至此一个业务逻辑的处理流程就基本完成。

整个业务流程

注册对应的url与handle

添加到列表中

添加完成之后启动Server

监听端口

启动服务端

监听新接入的请求

循环等待请求

请求进来

读客户端的数据

处理请求

如果处理完成或者异常

http.HandleFunc

DefaultServeMux.HandleFunc

mux.Handle

http.ListenAndServe

net.Listen

srv.Serve

l.Accept

c.serve

readRequest

serverHandler

退出

总结

本文主要是简单的梳理了一下go标准库里面http服务器的一个基本的处理流程，大致处理流程清楚之后对go相关的web的框架的处理过程也都大致了解，方便开发过程中灵活运用。由于本人才疏学浅，如有错误请批评指正。