go语言做urlencode go语言http包

go提供了详细且完整的标准库，同样我们使用go语言中的http包也非常方便，只需要几行代码便可以开启一个服务。现在，我们尽量使用代码理解下http包中的工作原理。

package main

import (
	"fmt"
	"log"
	"net/http"
)

func helloWeb(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello GoWeb!") //这个写入到w的是输出到客户端的
}
func main() {
	http.HandleFunc("/", helloWeb) // 设置访问的路由

	err := http.ListenAndServe(":8085", nil) //设置监听的端口
	if err != nil {
		log.Fatal("ListenAndServe: ", err)
	}
}

当我们在浏览器输入http://localhost:8085/时，页面上会呈现Hello GoWeb!的文字，也就是我们通过这几行代码实现的。上述代码里，我们通过HandleFunc设置了路由和对应的路由处理方法，再通过ListenAndServe方法将我们设置的端口或服务地址开启一个服务，实现服务端的开启。接下来我们来看ListenAndServe方法的实现。

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

上述代码根据服务地址和handler创建了server变量，最终还是调用了server的ListenAndServe方法，那我们继续来看ListenAndServe做了什么事。

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)
}

这里的核心代码是调用net包的Listen方法来创建一个tcp连接，接着又调用了Serve方法。

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)
	}
}

虽然serve代码较长，但我们只需要关注for循环里代码逻辑即可。在for循环中，我们调用刚创建的tcp连接变量l的Accept方法，这个方法会进行网络监听，当有请求进来时会调用newConn方法来生成 连接，最终通过go关键字来调用serve方法，这也就让go能并发的处理请求，我们接着看serve的实现。

func (c *conn) serve(ctx context.Context) {
	c.remoteAddr = c.rwc.RemoteAddr().String()
	...

	// 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{})
	}
}

这里代码依然很多，但我们去除了一些边界逻辑，这里核心逻辑是通过生成的conn实例c来调用readRequest方法。readRequest主要生成req请求信息和响应信息，响应信息的格式如下

// A response represents the server side of an HTTP response.
type response struct {
	conn             *conn
	req              *Request // request for this response
	reqBody          io.ReadCloser
	cancelCtx        context.CancelFunc // when ServeHTTP exits
	wroteHeader      bool 
	wroteContinue    bool  
	wants10KeepAlive bool  
	wantsClose       bool        
	w  *bufio.Writer // buffers output in chunks to chunkWriter
	cw chunkWriter
	handlerHeader Header
	calledHeader  bool
	written       int64 // number of bytes written in body
	contentLength int64
	status        int   // status code passed to WriteHeader
	closeAfterReply bool
	requestBodyLimitHit bool
	trailers []string
	handlerDone atomicBool // set true when the handler exits
	dateBuf   [len(TimeFormat)]byte
	clenBuf   [10]byte
	statusBuf [3]byte
	closeNotifyCh  chan bool
	didCloseNotify int32 // atomic (only 0->1 winner should send)
}

通过readRequest生成完这个响应实体后，再根据最初传入的server实例整合成serverHandler，再将请求信息和响应信息作为参数并调用它的ServeHTTP方法。

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)
}

那在这个方法里，有两种handler，一种是我们在最初ListenAndServe方法中写的handler，例子中我们写了nil，另一种是默认的handler就是DefaultServeMux，我们先来看Handler的定义

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

可以看到Handler是一个拥有ServeHTTP方法的接口，那在handler实例为DefaultServeMux时，我们先来看DefaultServeMux类型的定义。

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
}

这时我们要去看DefaultServeMux的ServeHTTP方法实现。

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)
}

我们先来看Handler方法

func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
	...
	// All other requests have any port stripped and path cleaned
	// before passing to mux.handler.
	host := stripHostPort(r.Host)
	path := cleanPath(r.URL.Path)
	
	return mux.handler(host, r.URL.Path)
}

省去了一些分支代码，其实这个方法还是在调用handler方法，

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
}

这里的path是我们在Url里请求的路径，它调用了match方法来匹配对应path的回调函数。有了最终的handler，就调用了handler的ServeHTTP方法，那handler是从哪里来的呢？其实我们在写http.HandleFunc("/", helloWeb) // 设置访问的路由时就将路径和回调函数注册进了路由注册表中，所以在mux.match(path)中可以匹配到对应路径的回调方法。那我们继续看HandleFunc的实现。

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

实际上还是调用了HandleFunc方法。

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

最后调用了Hanlder方法。

func (mux *ServeMux) Handle(pattern string, handler Handler) {
	mux.mu.Lock()
	defer mux.mu.Unlock()
	...
	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
	}
}

这里省去了部分边界判断代码，还记得之前的ServeMux的定义吗，这里其实就是将我们写的路径和回调函数保存在mux.m中。再在mux.match(path)中匹配将回调函数取出来执行。当然除了最初使用默认的ServeMux，我们还可以自定义ServeMux。

import (
    "net/http"
    "io"
)

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/hanru", func(w http.ResponseWriter, r *http.Request) {
        io.WriteString(w, "hello")
    })
    
    mux.HandleFunc("/hello", sayhello)
    http.ListenAndServe(":8085", mux)
}

func sayhello(w http.ResponseWriter, r *http.Request) {
    io.WriteString(w, "hello world")
}

通过NewServeMux方法创建ServeMux，并将ServeMux当做ListenAndServe第二个参数传入，这里内部执行的逻辑和之前差不多，只是之前用的是默认的ServeMux，现在我们自定义了ServeMux，其中的源码大家可以自己分析。