Go之net/http/server.go中Handler、ServeMux、Server阅读笔记

 

1. Handler是什么？

A Handler responds to an HTTP request. 这是源码中的注释，说的就是：一个Handler响应一个HTTP请求。

 

Handler的定义

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

 

2. Handler的实现者及他们之间的关系

// 实现一：HandlerFunc

// HandlerFunc是对是用户定义的处理函数的包装，实现了ServeHTTP方法，在方法内执行HandlerFunc对象
type HandlerFunc func(ResponseWriter, *Request)
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
    f(w, r)
}


// 实现二：ServeMux

// ServeMux是管理http请求pattern和handler的，实现了ServeHTTP方法，在其内根据请求匹配HandlerFunc，并执行其ServeHTTP方法
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
}
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
    h, _ := mux.Handler(r)
    h.ServeHTTP(w, r) // 调用的是HandlerFunc的ServeHTTP
}


// 实现三：serverHandler

// serverHandler是对Server的封装，实现了ServeHTTP方法，并在其内执行ServeMux的ServeHTTP方法
type serverHandler struct {
    srv *Server
}
func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
    handler := sh.srv.Handler
    if handler == nil {
        handler = DefaultServeMux
    }
    ...
    handler.ServeHTTP(rw, req) // 调用的是ServerMux的ServeHTTP
}


// 其他实现
// ...

3. ServeMux是干什么的

 ServeMux是一个HTTP请求多路复用器。它根据已注册模式（pattern）列表匹配每个传入请求的URL，并调用与URL最匹配的模式的处理程序（handler）。 

// ServeMux 是 server multiplexer 简写
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
}

type muxEntry struct {
    h       Handler
    pattern string
}

// DefaultServeMux是被Serve使用的默认的ServeMux
var DefaultServeMux = &defaultServeMux
var defaultServeMux ServeMux

// 服务HTTP
func (mux *ServeMux) ServeHTTP(W ResponseWriter， r *Request) {
    ...
    h, _ := mux.Handler(r) // 根据请求获取用户定义的handler
    h.ServeHTTP(w, r) // 执行用户定义的handler
}

// ServeMux处理http请求
func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
    ...
    return mux.handler(host, r.URL.Path)
}

// 根据host和path获取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)
    }
    if h == nil {
        h, pattern = mux.match(path)
    }
    if h == nil {
        h, pattern = NotFoundHandler(), ""
    }
    return
}


// 根据path在hanlder map中寻找handler（最长匹配）
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, ""
}


// 为pattern注册对应的Handler，如果handler已存在，则panic
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)
    }

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

// 为pattern注册对应的handler function
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
    if handler == nil {
        panic("http: nil handler")
    }
    mux.Handle(pattern, HandlerFunc(handler))
}

4. 处理函数的注册过程

http.HandleFunc(pattern, handler)

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

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

5. Handle & HandleFunc区别

HandleFunc内部实际调用的是Handle，HandleFunc将func转化为handler

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

6. 从Server到conn再到ServeMux的调用逻辑

 服务启动过程

http.ListenAndServe(addr, handler) // 这里的handler如果为空，在serverHander执行ServeHTTP内使用DefaultServeMux作为默认的handler

func ListenAndServe(addr string, handler Handler) error {
    server := &Server{Addr: addr, Handler: handler}
    server.ListenAndServe() // 这里的server是在函数内部新创建的

    func (srv *Server) ListenAndServe() error {
        ln, err := net.Listen("tcp", addr) // 创建一个监听者
        srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)}) // 启动服务

        func (srv *Server) Serve(l net.Listener) error {
            for { // 死循环处理
                rw, e := l.Accept() // 接收连接
                ...
                c := srv.newConn(rw)
                c.setState(c.rwc, StateNew) // before Serve can return
                go c.serve(ctx) // 处理连接

                // Serve a new connection.
                func (c *conn) serve(ctx context.Context) {
                    for {
                        w, err := c.readRequest(ctx)
                        ...
                        serverHandler{c.server}.ServeHTTP(w, w.req) // Server层服务处理

                        func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
                            handler := sh.srv.Handler
                            if handler == nil {
                                handler = DefaultServeMux
                            }
                            handler.ServeHTTP(rw, req)

                            func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) { // ServeMux层服务处理
                                h, _ := mux.Handler(r)
                                h.ServeHTTP(w, r)

                                func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) { // HandlerFunc层服务处理
                                    f(w, r) // 至此，会执行用户自定义的请求处理函数
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}