136 lines
4.4 KiB
Markdown
136 lines
4.4 KiB
Markdown
# 3.4 Get into http package
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In previous sections, we learned the work flow of web, and talked about a little about `http` package. In this section, we are going to learn two core functions in `http` package: Conn, ServeMux.
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## goroutine in Conn
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Unlike normal HTTP servers, Go uses goroutine for every affair that created by Conn in order to achieve high concurrency and performance, so every affair is independent.
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Go uses following code to wait for new connections from clients.
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c, err := srv.newConn(rw)
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if err != nil {
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continue
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}
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go c.serve()
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As you can see, it creates goroutine for every connection, and passes handler that is able to read data from request to the goroutine.
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## Customized ServeMux
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We used default router in previous section when talked about conn.server, the router passed request data to back-end handler.
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The struct of default router:
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type ServeMux struct {
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mu sync.RWMutex // because of concurrency, we have to use mutex here
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m map[string]muxEntry // router rules, every string mapping to a handler
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}
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The struct of muxEntry:
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type muxEntry struct {
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explicit bool // exact match or not
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h Handler
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}
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The interface of Handler:
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type Handler interface {
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ServeHTTP(ResponseWriter, *Request) // routing implementer
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}
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`Handler` is a interface, but the function `sayhelloName` didn't implement this interface, why could we add it as handler? Because there is another type `HandlerFunc` in `http` package. We called `HandlerFunc` to define our `sayhelloName`, so `sayhelloName` implemented `Handler` at the same time. it's like we call `HandlerFunc(f)`, and function `f` is forced converted to type `HandlerFunc`.
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type HandlerFunc func(ResponseWriter, *Request)
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// ServeHTTP calls f(w, r).
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func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
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f(w, r)
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}
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How the router calls handlers after we set router rules?
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The router calls `mux.handler.ServeHTTP(w, r)` when it receives requests. In other words, it calls `ServeHTTP` interface of handlers.
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Now, let's see how `mux.handler` works.
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func (mux *ServeMux) handler(r *Request) Handler {
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mux.mu.RLock()
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defer mux.mu.RUnlock()
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// Host-specific pattern takes precedence over generic ones
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h := mux.match(r.Host + r.URL.Path)
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if h == nil {
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h = mux.match(r.URL.Path)
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}
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if h == nil {
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h = NotFoundHandler()
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}
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return h
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}
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The router uses URL as a key to find corresponding handler that saved in map, and calls handler.ServeHTTP to execute functions to handle data.
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You should understand the router work flow now, and Go actually supports customized routers. The second argument of `ListenAndServe` is for configuring customized router, it's a interface of `Handler`. Therefore, any router implements interface `Handler` that can be used.
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The following example shows how to implement a simple router.
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package main
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import (
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"fmt"
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"net/http"
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)
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type MyMux struct {
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}
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func (p *MyMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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if r.URL.Path == "/" {
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sayhelloName(w, r)
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return
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}
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http.NotFound(w, r)
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return
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}
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func sayhelloName(w http.ResponseWriter, r *http.Request) {
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fmt.Fprintf(w, "Hello myroute!")
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}
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func main() {
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mux := &MyMux{}
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http.ListenAndServe(":9090", mux)
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}
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## Go code execution flow
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Let's take a look at the list of whole execution flow.
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- Call `http.HandleFunc`
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1. Call HandleFunc of DefaultServeMux
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2. Call Handle of DefaultServeMux
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3. Add router rules to map[string]muxEntry of DefaultServeMux
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- Call `http.ListenAndServe(":9090", nil)`
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1. Instantiated Server
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2. Call ListenAndServe of Server
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3. Call net.Listen("tcp", addr) to listen to port.
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4. Start a loop, and accept requests in loop body.
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5. Instantiated a Conn and start a goroutine for every request: `go c.serve()`.
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6. Read request data: `w, err := c.readRequest()`.
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7. Check handler is empty or not, if it's empty then use DefaultServeMux.
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8. Call ServeHTTP of handler.
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9. Execute code in DefaultServeMux in this case.
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10. Choose handler by URL and execute code in that handler function: `mux.handler.ServeHTTP(w, r)`
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11. How to choose handler:
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A. Check router rules for this URL.
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B. Call ServeHTTP in that handler if there is one.
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C. Call ServeHTTP of NotFoundHandler otherwise.
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## Links
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- [Directory](preface.md)
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- Previous section: [How Go works with web](03.3.md)
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- Next section: [Summary](03.5.md)
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