mux源码分析

http服务

http相关的网络服务，我们需要关注的都是客户端请求和服务端应答。在客户端请求（request）的过程中，重要的是路由。在服务端当接收到路由请求的时候，需要通过处理，再进行应答（response）。在接收request的过程中，路由是很重要的，这相当于是一个Multiplexer，Go中有内置的DefaultServerMux，也可以自定义Multiplexer。这里的Multiplexer的目的就是为了找到一个处理器函数（Handler），这样就可以对客户端进行响应了。
 

路由函数

func main() {
  r := mux.NewRouter()
  r.HandleFunc("/", HomeHandler)
  r.HandleFunc("/products", ProductsHandler)
  r.HandleFunc("/articles", ArticlesHandler)
  http.Handle("/", r)
}

 

匹配部分

r := mux.NewRouter()
r.HandleFunc("/products/{key}", ProductHandler)
r.HandleFunc("/articles/{category}/", ArticlesCategoryHandler)
r.HandleFunc("/articles/{category}/{id:[0-9]+}", ArticleHandler)

读取变量

func ArticlesCategoryHandler(w http.ResponseWriter, r *http.Request) {
  vars := mux.Vars(r)
  w.WriteHeader(http.StatusOK)
  fmt.Fprintf(w, "Category: %v\n", vars["category"])
}

筛选条件

r.Headers("X-Requested-With", "XMLHttpRequest")
r.MatcherFunc(func(r *http.Request, rm *RouteMatch) bool {
  return r.ProtoMajor == 0
})
r.HandleFunc("/products", ProductsHandler).
	Host("www.example.com").
	Methods("GET").
	Schemes("http")

子路由

r := mux.NewRouter()
s := r.Host("www.example.com").Subrouter()
s.HandleFunc("/products/", ProductsHandler)
s.HandleFunc("/products/{key}", ProductHandler)
s.HandleFunc("/articles/{category}/{id:[0-9]+}", ArticleHandler)

中间件

func loggingMiddleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // Do stuff here
    log.Println(r.RequestURI)
    // Call the next handler, which can be another middleware in the chain, or the final handler.
    next.ServeHTTP(w, r)
  })
}

r := mux.NewRouter()
r.HandleFunc("/", handler)
r.Use(loggingMiddleware)

使用 Router 的 HandleFunc 、Host 、 Methods 、 Schemes 、 Headers 等方法会创建一个路由并且为其添加相应类型 matcher，当然你也可以使用 MatcherFunc 来创建自己的 matcher。

gorilla/mux 会查找 Router 下的 Route 列表，找到是否有无匹配的路由，而 Route 会遍历其 matchers 列表来看看是否满足所有的 matchers，只要一个不匹配，则失败。

 

客户端

net/http包在编写golang web应用中有很重要的作用，它主要提供了基于HTTP协议进行工作的client实现和server实现，可用于编写HTTP服务端和客户端。

首先来看一下客户端代码：

// 用http包中默认的Client进行请求（因为没有指定Client）
resp, err := http.Get("http://example.com/")
...
resp, err := http.Post("http://example.com/upload", "image/jpeg", &buf)
...
resp, err := http.PostForm("http://example.com/form",
	url.Values{"key": {"Value"}, "id": {"123"}})


// 用自定义的Client进行请求
client := &http.Client{
	CheckRedirect: redirectPolicyFunc,
}

resp, err := client.Get("http://example.com")
// ...

req, err := http.NewRequest("GET", "http://example.com", nil)
// ...
req.Header.Add("If-None-Match", `W/"wyzzy"`)
resp, err := client.Do(req)
// ...

可以有两种方式，第一种比较直接，用默认即可；第二种比较复杂一点，是分布来完成的。

客户端的定义：

type Client struct {
	// Transport specifies the mechanism by which individual
	// HTTP requests are made.
	// If nil, DefaultTransport is used.
	Transport RoundTripper

	// CheckRedirect specifies the policy for handling redirects.
	// If CheckRedirect is not nil, the client calls it before
	// following an HTTP redirect. The arguments req and via are
	// the upcoming request and the requests made already, oldest
	// first. If CheckRedirect returns an error, the Client's Get
	// method returns both the previous Response (with its Body
	// closed) and CheckRedirect's error (wrapped in a url.Error)
	// instead of issuing the Request req.
	// As a special case, if CheckRedirect returns ErrUseLastResponse,
	// then the most recent response is returned with its body
	// unclosed, along with a nil error.
	//
	// If CheckRedirect is nil, the Client uses its default policy,
	// which is to stop after 10 consecutive requests.
	CheckRedirect func(req *Request, via []*Request) error

	// Jar specifies the cookie jar.
	//
	// The Jar is used to insert relevant cookies into every
	// outbound Request and is updated with the cookie values
	// of every inbound Response. The Jar is consulted for every
	// redirect that the Client follows.
	//
	// If Jar is nil, cookies are only sent if they are explicitly
	// set on the Request.
	Jar CookieJar

	// Timeout specifies a time limit for requests made by this
	// Client. The timeout includes connection time, any
	// redirects, and reading the response body. The timer remains
	// running after Get, Head, Post, or Do return and will
	// interrupt reading of the Response.Body.
	//
	// A Timeout of zero means no timeout.
	//
	// The Client cancels requests to the underlying Transport
	// as if the Request's Context ended.
	//
	// For compatibility, the Client will also use the deprecated
	// CancelRequest method on Transport if found. New
	// RoundTripper implementations should use the Request's Context
	// for cancelation instead of implementing CancelRequest.
	Timeout time.Duration
}

// DefaultClient is the default Client and is used by Get, Head, and Post.
var DefaultClient = &Client{}

从Client对象定义上方的注释我们可以知道Client是一个HTTP客户端，且它是个可用的缺省客户端，该缺省客户端使用的是DefaultTransport。DefaultTransport对象是一个Transport类型的对象，它维持了内部的状态（缓存TCP连接）。而且Client对象是线程安全的，即支持被多个线程安全地同时使用。
 

Transport：

type Client struct {
	Transport RoundTripper
	CheckRedirect func(req *Request, via []*Request) error
	Jar CookieJar
	Timeout time.Duration
}

Transport字段是RoundTripper类型的对象，它决定了发出每个HTTP请求所使用的机制。

 

RoundTripper：

type RoundTripper interface {
	// RoundTrip executes a single HTTP transaction, returning
	// a Response for the provided Request.
	//
	// RoundTrip should not attempt to interpret the response. In
	// particular, RoundTrip must return err == nil if it obtained
	// a response, regardless of the response's HTTP status code.
	// A non-nil err should be reserved for failure to obtain a
	// response. Similarly, RoundTrip should not attempt to
	// handle higher-level protocol details such as redirects,
	// authentication, or cookies.
	//
	// RoundTrip should not modify the request, except for
	// consuming and closing the Request's Body. RoundTrip may
	// read fields of the request in a separate goroutine. Callers
	// should not mutate or reuse the request until the Response's
	// Body has been closed.
	//
	// RoundTrip must always close the body, including on errors,
	// but depending on the implementation may do so in a separate
	// goroutine even after RoundTrip returns. This means that
	// callers wanting to reuse the body for subsequent requests
	// must arrange to wait for the Close call before doing so.
	//
	// The Request's URL and Header fields must be initialized.
	RoundTrip(*Request) (*Response, error)
}

RoundTripper同样是个接口，包含了RoundTrip方法，接受Request对象然后返回Response对象。

 

客户端对象的实现：

func (c *Client) Get(url string) (resp *Response, err error) {
	req, err := NewRequest("GET", url, nil)
	if err != nil {
		return nil, err
	}
	return c.Do(req)
}


func (c *Client) Post(url, contentType string, body io.Reader) (resp *Response, err error) {
	req, err := NewRequest("POST", url, body)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", contentType)
	return c.Do(req)
}

构造包含请求方法和url，请求体(body)的Request对象，然后再通过Client.Do方法执行该请求。

 

客户端Do方法：

func (c *Client) Do(req *Request) (*Response, error) {
	return c.do(req)
}

var testHookClientDoResult func(retres *Response, reterr error)

func (c *Client) do(req *Request) (retres *Response, reterr error) {
	// 进行一些检查
	if testHookClientDoResult != nil {
		defer func() { testHookClientDoResult(retres, reterr) }()
	}
	if req.URL == nil {
		req.closeBody()
		return nil, &url.Error{
			Op:  urlErrorOp(req.Method),
			Err: errors.New("http: nil Request.URL"),
		}
	}
	// 定义相关变量（重点关注reqs及参数req）
	var (
		deadline      = c.deadline()
		reqs          []*Request
		resp          *Response
		copyHeaders   = c.makeHeadersCopier(req)
		reqBodyClosed = false // have we closed the current req.Body?

		// Redirect behavior:
		redirectMethod string
		includeBody    bool
	)
	uerr := func(err error) error {
		// the body may have been closed already by c.send()
		if !reqBodyClosed {
			req.closeBody()
		}
		var urlStr string
		if resp != nil && resp.Request != nil {
			urlStr = stripPassword(resp.Request.URL)
		} else {
			urlStr = stripPassword(req.URL)
		}
		return &url.Error{
			Op:  urlErrorOp(reqs[0].Method),
			URL: urlStr,
			Err: err,
		}
	}
	// 通过循环，从原始请求req开始执行，得到响应后判断是否应该重定向，若需要
	// 则更新req对象发送新的请求，直至不需要再重定向或出现错误为止
	for {
		// For all but the first request, create the next
		// request hop and replace req.
		if len(reqs) > 0 {
			loc := resp.Header.Get("Location")
			if loc == "" {
				resp.closeBody()
				return nil, uerr(fmt.Errorf("%d response missing Location header", resp.StatusCode))
			}
			u, err := req.URL.Parse(loc)
			if err != nil {
				resp.closeBody()
				return nil, uerr(fmt.Errorf("failed to parse Location header %q: %v", loc, err))
			}
			host := ""
			if req.Host != "" && req.Host != req.URL.Host {
				// If the caller specified a custom Host header and the
				// redirect location is relative, preserve the Host header
				// through the redirect. See issue #22233.
				if u, _ := url.Parse(loc); u != nil && !u.IsAbs() {
					host = req.Host
				}
			}
			ireq := reqs[0]
			req = &Request{
				Method:   redirectMethod,
				Response: resp,
				URL:      u,
				Header:   make(Header),
				Host:     host,
				Cancel:   ireq.Cancel,
				ctx:      ireq.ctx,
			}
			if includeBody && ireq.GetBody != nil {
				req.Body, err = ireq.GetBody()
				if err != nil {
					resp.closeBody()
					return nil, uerr(err)
				}
				req.ContentLength = ireq.ContentLength
			}

			// Copy original headers before setting the Referer,
			// in case the user set Referer on their first request.
			// If they really want to override, they can do it in
			// their CheckRedirect func.
			copyHeaders(req)

			// Add the Referer header from the most recent
			// request URL to the new one, if it's not https->http:
			if ref := refererForURL(reqs[len(reqs)-1].URL, req.URL); ref != "" {
				req.Header.Set("Referer", ref)
			}
			err = c.checkRedirect(req, reqs)

			// Sentinel error to let users select the
			// previous response, without closing its
			// body. See Issue 10069.
			if err == ErrUseLastResponse {
				return resp, nil
			}

			// Close the previous response's body. But
			// read at least some of the body so if it's
			// small the underlying TCP connection will be
			// re-used. No need to check for errors: if it
			// fails, the Transport won't reuse it anyway.
			const maxBodySlurpSize = 2 << 10
			if resp.ContentLength == -1 || resp.ContentLength <= maxBodySlurpSize {
				io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
			}
			resp.Body.Close()

			if err != nil {
				// Special case for Go 1 compatibility: return both the response
				// and an error if the CheckRedirect function failed.
				// See https://golang.org/issue/3795
				// The resp.Body has already been closed.
				ue := uerr(err)
				ue.(*url.Error).URL = loc
				return resp, ue
			}
		}
		
		// 通过send方法将req请求发送出去，并通过响应内容判断是否需要重定向。
		// 若需要重定向，则进入下一个循环将req替换为一个新的req对象用于发生新的请求到重定向所指向的地址
		// 若不需要重定向，则返回响应结果
		reqs = append(reqs, req)
		var err error
		var didTimeout func() bool
		if resp, didTimeout, err = c.send(req, deadline); err != nil {
			// c.send() always closes req.Body
			reqBodyClosed = true
			if !deadline.IsZero() && didTimeout() {
				err = &httpError{
					// TODO: early in cycle: s/Client.Timeout exceeded/timeout or context cancelation/
					err:     err.Error() + " (Client.Timeout exceeded while awaiting headers)",
					timeout: true,
				}
			}
			return nil, uerr(err)
		}

		var shouldRedirect bool
		redirectMethod, shouldRedirect, includeBody = redirectBehavior(req.Method, resp, reqs[0])
		if !shouldRedirect {
			return resp, nil
		}

		req.closeBody()
	}
}

方法中主要包含一些检查，一些相关变量的定义，还有是一个for循环，负责处理传递给该方法的req参数的一系列请求。

 

服务端

服务端代码：

// 这里没有指定server，所以是用http包中默认的server来处理客户端请求
http.Handle("/foo", fooHandler)

http.HandleFunc("/bar", func(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello, %q", html.EscapeString(r.URL.Path))
})

log.Fatal(http.ListenAndServe(":8080", nil))



// 自定义server
s := &http.Server{
	Addr:           ":8080",
	Handler:        myHandler,
	ReadTimeout:    10 * time.Second,
	WriteTimeout:   10 * time.Second,
	MaxHeaderBytes: 1 << 20,
}
log.Fatal(s.ListenAndServe())

同样是两种，一种为直接用默认server，第二种为自定义。

 

服务端定义：

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.
	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, ReadHeaderTimeout is used.
	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

	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:

// ListenAndServe always returns a non-nil error.
func ListenAndServe(addr string, handler Handler) error {
	server := &Server{Addr: addr, Handler: handler}
	return server.ListenAndServe()
}

ListenAndServe方法根据Addr和Handler参数构建了一个Server对象，并调用该对象的ListenAndServe方法进行监听和响应。

 

ServeMux:

type ServeMux struct {
	mu    sync.RWMutex
	m     map[string]muxEntry
	hosts bool // whether any patterns contain hostnames
}

ServeMux对象是一个HTTP请求的分发器，将匹配了相应URL的请求分发给相应的处理函数进行处理。

 

Handler:

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

Handler是一个接口类型，包含了ServerHTTP方法，该方法对客户端的请求（Request对象）进行处理，并通过ResponseWriter将响应信息传送回客户端。