http源码
ServeHTTP函数调用在三个地方,它们三个都实现了Handler接口,
一是serverHandler{c.server}.ServeHTTP(w, w.req),它是serverHandler调用的,里面有ListenAndServe初始化时生成的Server对象,因为Server中有注册的路由。
二是handler.ServeHTTP(rw, req),handler是个接口对象,它绑定了注册的路由,在http中它是DefaultServeMux,在gin中它是Engine。
三是h.ServeHTTP(w, r),h是个接口,这里绑定的是注册的路由函数,但注册的路由函数没有实现这个接口,所以在注册的时候进行了类型强转mux.Handle(pattern, HandlerFunc(handler)),在gin中没有调用这个,估计是不需要,
1 分析以下代码
package main import ( "fmt" "log" "net/http" ) func handleRequest(w http.ResponseWriter, r *http.Request) { fmt.Println("aaaaa") } func main() { // set route http.HandleFunc("/a/", handleRequest) fmt.Println("Listening at port 9090...") // listen at port 9090 and serve requests err := http.ListenAndServe(":9090", nil) if err != nil { log.Fatal("ListenAndServe: ", err) } }
2 http.HandleFunc路由的注册
注册前会先把输入的路由函数做类型转换,转为HandlerFunc类型,而该类型实现了handler接口,之后通过注册的路由找到对应的路由函数时,会直接调用handler接口的ServeHTTP方法,来实现该利用函数,ServeHTTP里只有一个f(w, r)
var DefaultServeMux = &defaultServeMux var defaultServeMux ServeMux // 传入的pattern是URL,handler是路由函数 func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) { DefaultServeMux.HandleFunc(pattern, handler) } // 调用ServerMux的Handle方法注册路由, func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) { if handler == nil { panic("http: nil handler") } // 注意这里的进行了类型的强制转换,handler是传入的函数类型,HandlerFunc是自定义的类型它实现了ServeHTTP方法,所以实现了Handler接口 mux.Handle(pattern, HandlerFunc(handler)) } // 特别注意这里虽然传入的handler函数和这里定义的类型形式上一样,但它不是HandlerFunc类型,因为它没有实现ServeHTTP接口, type HandlerFunc func(ResponseWriter, *Request) func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) { f(w, r) } 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} // 注册的路由实际上就是个map,从这里也可以看出http的路由注册非常简单,所以有了后来的httprouter, mux.m[pattern] = e if pattern[len(pattern)-1] == '/' { mux.es = appendSorted(mux.es, e) } if pattern[0] != '/' { mux.hosts = true } } // m用于存储路由的url和其对应的处理函数, 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 }
3 http.ListenAndServe,监听端口,收到请求,处理请求,返回结果
// 启动监听,Handler是个接口,它里面只有一个ServeHttp方法,直接用http包时,这个置为nil, func ListenAndServe(addr string, handler Handler) error { server := &Server{Addr: addr, Handler: handler} return server.ListenAndServe() } // 调用Server的Serve方法, 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) } // 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 { 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 c := srv.newConn(rw) c.setState(c.rwc, StateNew) // before Serve can return go c.serve(connCtx) } } // 上述for循环可简化为, for { rw, e := l.Accept() // 这里就是监听端口收到的请求,当收到请求后,建立新连接, ... c, err := srv.newConn(rw) ... go c.serve() // 对新建的连接开启一个协程进行处理 } // 注意在新连接生成的时候,将之前ListenAndServe中初始化的Server也保存在了里面, func (srv *Server) newConn(rwc net.Conn) *conn { c := &conn{ server: srv, rwc: rwc, } if debugServerConnections { c.rwc = newLoggingConn("server", c.rwc) } return c } // 调用serve处理收到的Request, 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; validNextProto(proto) { if fn := c.server.TLSNextProto[proto]; fn != nil { h := initALPNRequest{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: const publicErr = "431 Request Header Fields Too Large" fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr) c.closeWriteAndWait() return case isUnsupportedTEError(err): code := StatusNotImplemented 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 } } 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} w.canWriteContinue.setTrue() } } 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() } 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() { 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{}) } } //对于同一个连接, 循环地执行读取请求, 处理请求, 完成请求三个操作 for{ w, err := c.readRequest() ... serverHandler{c.server}.ServeHTTP(w, w.req) // 这里直接初始化了一个serverHandler对象, ... w.finishRequest() ... } // rw req都是之前在readRequest中读取的, func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) { // serverHandler只有一个属性*Server,Server的属性Handler即之前http.ListenAndServer中传入的handler, // Server的属性Handler是接口Handler,它只有一个方法ServeHTTP,只要实现了ServeHTTP方法,就实现了Handler接口, if handler == nil { handler = DefaultServeMux } if req.RequestURI == "*" && req.Method == "OPTIONS" { handler = globalOptionsHandler{} } // 若handler接口绑定的类型为Engine,则ServeHTTP在gin中实现, handler.ServeHTTP(rw, req) } // 在gin中,上面的ServeHTTP会调用这个, func (engine *Engine) ServeHTTP(w http.ResponseWriter, req *http.Request) { c := engine.pool.Get().(*Context) c.writermem.reset(w) c.Request = req c.reset() engine.handleHTTPRequest(c) engine.pool.Put(c) } // 在直接调用http包时,上面的handler接口绑定的类型是之前初始化的ServeMux对象 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 } // 在之前注册的ServeMux中找到URL对应的路由函数, h, _ := mux.Handler(r) h.ServeHTTP(w, r) } // 在Handler中调用了handler func (mux *ServeMux) handler(host, path string) (h Handler, pattern string) { mux.mu.RLock() defer mux.mu.RUnlock() if mux.hosts { h, pattern = mux.match(host + path) } if h == nil { h, pattern = mux.match(path) } if h == nil { h, pattern = NotFoundHandler(), "" } return } // match就是直接在map中寻找对应URL的路由函数, func (mux *ServeMux) match(path string) (h Handler, pattern string) { v, ok := mux.m[path] if ok { return v.h, v.pattern } for _, e := range mux.es { if strings.HasPrefix(path, e.pattern) { return e.h, e.pattern } } return nil, "" } // 上面返回的h类型是HandlerFunc,即type HandlerFunc func(ResponseWriter, *Request), // 因为之前在路由注册前进行类型强制转换,HanderFunc类型实现了Handler接口,所以这里可以直接调用, func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) { f(w, r) }
总体流程
一 调用http.HandleFunc("/a/", handleRequest)按如下顺序执行: 1 首先调用Http.HandleFunc, 2 调用了DefaultServerMux的HandleFunc 3 调用了DefaultServerMux的Handle,这里进行了类型的强转,因为传入的函数并没有实现ServeHTTP方法, 往DefaultServerMux的map[string] muxEntry中增加对应的handler和路由规则。 二 调用http.ListenAndServe(":9090",nil),按如下顺序执行: 1 实例化Server。 server := &Server{Addr: addr, Handler: handler} Handler为实现了ServeHTTP的接口, 2 调用Server的ListenAndServe()。 server.ListenAndServe() 3 调用net.Listen("tcp",addr)监听端口。 ln, err := net.Listen("tcp", addr) 4 启动一个for死循环,在循环体中监听请求。 rw, err := l.Accept() 5 一旦收到请求,对该请求实例化一个Conn,并且开启一个goroutine为这个请求进行服务go c.serve()。 c := srv.newConn(rw) go c.serve(connCtx) 6 在c.serve()中仍是启动一个for死循环,读取请求的内容。readRequest是读取数据,解析请求的地方,包括解析请求的header、body,和一些基本的校验, 比如header头信息,请求method等 w, err := c.readRequest(ctx) 7 调用业务层定义的路由,调用最开始在http.ListenAndServe中实例化的Server,它也实现了Handler接口,并将处理好的Request、Response对象作为参数传入 serverHandler{c.server}.ServeHTTP(w, w.req) 8 在Server的ServeHTTP中,将handler设置为1中的handler,若为nil设置为DefaultServeMux handler := sh.srv.Handler if handler == nil {handler = DefaultServeMux} 9 调用handler的ServeHttp。 handler.ServeHTTP(rw, req) 10在之前注册的路由中找到处理请求的路由函数, h, _ := mux.Handler(r) 11如果找到了路由函数,调用这个路由handler的ServeHttp。 h.ServeHTTP(w, r) 否则返回"404 page not found", return HandlerFunc(NotFound)
参考:https://james-yip.github.io/2017/11/16/go-http-src-analysis/
https://www.huweihuang.com/golang-notes/web/golang-http-execution-flow.html
https://www.shipengqi.top/2019/11/12/go-http-resouce-code-analysis/
https://zhuanlan.zhihu.com/p/101995755