blocks|key|21620|text|net/http中的相关类型为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|21621|type+Handler+interface+{
++++ServeHTTP(ResponseWriter,+*Request)
}|code-block|syntax|javascript|21622|一种接口类型。实现此接口的任何具体类型都可用于服务HTTP请求。您的处理程序是foo类型的，并且foo实现了bar接口。如果内置HTTP服务器必须处理请求，它将调用bar的ServeHTTP方法。|offset|length|style|CODE|21623|entityMap^0|0|0|13|3|1I|3|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

The relevant type in net/http is

<pre><code>type Handler interface {
 ServeHTTP(ResponseWriter, *Request)
}
</code></pre>

an interface type. Any concrete type implementing this interface can be used to serve HTTP request. Your <code>bar</code> is of type <code>foo</code> and foo implements the Handler interface. If the builtin HTTP server has to handle a request it will call the ServeHTTP method of your bar.

blocks|key|23172|text|Go的HTTP服务器接受一个要侦听的地址和一个处理程序。在内部，它创建一个TCP侦听器来接受给定地址上的连接，并且每当有请求进入时，它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|23173|通过调用http.Request|offset|length|style|CODE|23174|Creates方法并传入response|unordered-list-item|23175|
|23176|Invokes和ResponseWriter|23177|
，|23178|将原始HTTP请求(路径、标头等)解析为http.ResponseWriter，以便向ServeHTTP发送处理程序|ordered-list-item|23179|23180|处理程序可以是满足Handler接口的任何东西，foo类型就是这样做的：|23181|type+Handler+interface+{
++++ServeHTTP(ResponseWriter,+*Request)
}|code-block|syntax|javascript|23182|标准库还包括一些便利功能，比如HandlerFunc+(它允许您传递任何func(ResponseWriter,+*Request)并将其用作Handler)和ServeMux，它允许您注册许多Handler，并根据传入的请求路径选择处理哪个请求。|23183|entityMap^0|0|4|C|0|0|0|8|E|0|0|K|J|17|9|0|0|9|7|O|3|0|0|F|B|10|U|1Z|7|28|8|2P|7|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|16|8|@$D|17|E|18|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|M|3|N|5|J|7|1B|8|@$D|1C|E|1D|F|G]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1E|8|@]|9|@]|A|$]]|$1|Q|3|R|5|S|7|1F|8|@$D|1G|E|1H|F|G]|$D|1I|E|1J|F|G]]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1L|8|@$D|1M|E|1N|F|G]|$D|1O|E|1P|F|G]]|9|@]|A|$]]|$1|W|3|X|5|Y|7|1Q|8|@]|9|@]|A|$Z|10]]|$1|11|3|12|5|6|7|1R|8|@$D|1S|E|1T|F|G]|$D|1U|E|1V|F|G]|$D|1W|E|1X|F|G]|$D|1Y|E|1Z|F|G]|$D|20|E|21|F|G]]|9|@]|A|$]]|$1|13|3|-4|5|6|7|22|8|@]|9|@]|A|$]]]|14|$]]

Go's HTTP server takes in an address to listen on, and a handler. Internally, it creates a TCP listener to accept connections on the given address, and whenever a request comes in, it:

<ol>
<li>Parses the raw HTTP request (path, headers, etc) into a <code>http.Request</code></li>
<li>Creates a <code>http.ResponseWriter</code> for sending the response</li>
<li>Invokes the handler by calling its <code>ServeHTTP</code> method, passing in the <code>Request</code> and <code>ResponseWriter</code></li>
</ol>

The handler can be anything that satisfies the <code>Handler</code> interface, which your <code>foo</code> type does:

<pre><code>type Handler interface {
 ServeHTTP(ResponseWriter, *Request)
}
</code></pre>

The standard library also includes some conveniences, like <code>HandlerFunc</code> (which allows you to pass any <code>func(ResponseWriter, *Request)</code> and use it as a <code>Handler</code>) and <code>ServeMux</code>, which allows you to register many <code>Handler</code>s and choose which one handles which request based on the incoming request path.

blocks|key|21699|text|这到底是怎么回事？如何访问ServeHTTP函数？|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|21700|要回答这个问题，我们需要看看http.ListenAndServe是如何工作的：|CODE|21701|func+ListenAndServe(addr+string,+handler+Handler)+error+{
++++server+:=+&Server{Addr:+addr,+Handler:+handler}
++++return+server.ListenAndServe()
}|code-block|syntax|javascript|21702|在这里，我们使用给定的地址和处理程序创建一个服务器，并调用ListenAndServer方法，因此让我们来看看这里：|21703|func+(srv+*Server)+ListenAndServe()+error+{
++++addr+:=+srv.Addr
++++if+addr+==+""+{
++++++++addr+=+":http"
++++}
++++ln,+err+:=+net.Listen("tcp",+addr)
++++if+err+!=+nil+{
++++++++return+err
++++}
++++return+srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
}|21704|此方法只是开始侦听给定的地址，并使用新创建的侦听器调用Server方法，因此让我们跟随下面的步骤：|21705|func+(srv+*Server)+Serve(l+net.Listener)+error+{
++++defer+l.Close()

++++...

++++for+{
++++++++rw,+e+:=+l.Accept()

++++++++...

++++++++c+:=+srv.newConn(rw)
++++++++c.setState(c.rwc,+StateNew)+//+before+Serve+can+return
++++++++go+c.serve(ctx)
++++}
}|21706|从Serve方法我们可以看到，这是我们接受新连接并开始在它自己的goroutine中处理它的地方。|21707|//+Serve+a+new+connection.
func+(c+*conn)+serve(ctx+context.Context)+{
++++...
++++for+{
++++++++w,+err+:=+c.readRequest(ctx)
++++++++...
++++++++serverHandler{c.server}.ServeHTTP(w,+w.req)
++++++++...
++++}
}|21708|在这里，我们最终调用了ServeHTTP方法，但正如我们所看到的，这还不是我们对该函数的实现，而是来自标准库的东西，所以让我们来看看这个serverHandler结构包含了什么：|21709|//+serverHandler+delegates+to+either+the+server's+Handler+or
//+DefaultServeMux+and+also+handles+"OPTIONS+*"+requests.
type+serverHandler+struct+{
++++srv+*Server
}

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)
}|21710|所以它终于出现了。如果我们没有提供任何处理程序，将使用DefaultServeMux，但是因为我们提供了foo处理程序ServeHTTP，所以从foo+get的调用中调用。|21711|就是这样。所有这些都可以在server.go中找到|21712|entityMap|0|LINK|mutability|MUTABLE|url|https://golang.org/src/net/http/server.go^0|0|P|0|E|J|0|0|0|0|0|0|0|0|0|0|0|D|9|0|0^^$0|@$1|2|3|4|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1I|8|@$9|1J|A|1K|B|H]]|D|@]|E|$]]|$1|I|3|J|5|K|7|1L|8|@]|D|@]|E|$L|M]]|$1|N|3|O|5|6|7|1M|8|@]|D|@]|E|$]]|$1|P|3|Q|5|K|7|1N|8|@]|D|@]|E|$L|M]]|$1|R|3|S|5|6|7|1O|8|@]|D|@]|E|$]]|$1|T|3|U|5|K|7|1P|8|@]|D|@]|E|$L|M]]|$1|V|3|W|5|6|7|1Q|8|@]|D|@]|E|$]]|$1|X|3|Y|5|K|7|1R|8|@]|D|@]|E|$L|M]]|$1|Z|3|10|5|6|7|1S|8|@]|D|@]|E|$]]|$1|11|3|12|5|K|7|1T|8|@]|D|@]|E|$L|M]]|$1|13|3|14|5|6|7|1U|8|@]|D|@]|E|$]]|$1|15|3|16|5|6|7|1V|8|@]|D|@$9|1W|A|1X|1|1Y]]|E|$]]|$1|17|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]]|18|$19|$5|1A|1B|1C|E|$1D|1E]]]]

How does this exactly work? How is that ServeHTTP function being accessed?

To answer this question we need to look how <code>http.ListenAndServe</code> works:

<pre><code>func ListenAndServe(addr string, handler Handler) error {
 server := &amp;Server{Addr: addr, Handler: handler}
 return server.ListenAndServe()
}
</code></pre>

Here we create a Server with given address and handler and call the ListenAndServer method so let's take a look there:

<pre><code>func (srv *Server) ListenAndServe() error {
 addr := srv.Addr
 if addr == "" {
 addr = ":http"
 }
 ln, err := net.Listen("tcp", addr)
 if err != nil {
 return err
 }
 return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
}
</code></pre>

This method just starts listening given address and calls the Server method with our freshly created listener so let's follow the trail there:

<pre><code>func (srv *Server) Serve(l net.Listener) error {
 defer l.Close()

 ...

 for {
 rw, e := l.Accept()

 ...

 c := srv.newConn(rw)
 c.setState(c.rwc, StateNew) // before Serve can return
 go c.serve(ctx)
 }
}
</code></pre>

From the Serve method we can see that this is the point where we accept the new connection and start handling it in it's own goroutine.

<pre><code>// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
 ...
 for {
 w, err := c.readRequest(ctx)
 ...
 serverHandler{c.server}.ServeHTTP(w, w.req)
 ...
 }
}
</code></pre>

Here we finally call the ServeHTTP method but as we can see this is not yet our implementation of that function but something from the standard library so let's take a look what that serverHandler struct contains:

<pre><code>// serverHandler delegates to either the server's Handler or
// DefaultServeMux and also handles "OPTIONS *" requests.
type serverHandler struct {
 srv *Server
}

func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
 handler := sh.srv.Handler
 if handler == nil {
 handler = DefaultServeMux
 }
 if req.RequestURI == "*" &amp;&amp; req.Method == "OPTIONS" {
 handler = globalOptionsHandler{}
 }
 handler.ServeHTTP(rw, req)
}
</code></pre>

So here it is finally. If we didn't provide any Handler the DefaultServeMux will be used but since we provided our foo handler ServeHTTP from foo get's called.

And that's it. All of this can be found from <a href="https://golang.org/src/net/http/server.go" rel="noreferrer">server.go</a>

blocks|key|21829|text|对于任何想要了解http.Handler的人来说，我推荐阅读这些博客文章|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|21830|A+Recap+of+Request+Handling+in+Go|21831|Making+and+Using+HTTP+Middleware|21832|entityMap|0|LINK|mutability|MUTABLE|url|https://www.alexedwards.net/blog/a-recap-of-request-handling|1|https://www.alexedwards.net/blog/making-and-using-middleware^0|8|C|0|0|X|0|0|0|W|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|H|3|I|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]]|E|$]]|$1|J|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]|R|$5|M|N|O|E|$P|S]]]]

I recommend going through these blog posts for anyone trying to understand about <code>http.Handler</code> 
<a href="https://www.alexedwards.net/blog/a-recap-of-request-handling" rel="nofollow noreferrer">A Recap of Request Handling in Go</a> 
<a href="https://www.alexedwards.net/blog/making-and-using-middleware" rel="nofollow noreferrer">Making and Using HTTP Middleware</a>

I am studying web development in Golang (Beginner) I came across some code I played around with and I'm not too sure why it works, I looked through the library source code and docs but I only have a vague idea it still isn't clicking. Note the code below:

<pre><code>package main

import (
 "fmt"
 "net/http"
)

type foo int

func (m foo) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 fmt.Fprintln(w, "Some text")
}

func main() {
 var bar foo
 http.ListenAndServe(":8080", bar)
}
</code></pre>

From what I understand adding ServeHTTP(w http.ResponseWriter, r *http.Request) as a function method, invokes the handler interface (if I'm saying that correctly) and now foo is of type handler as well. I also understand that http.ListenAndServe takes an input of type handler so that is where my variable bar comes into play. When I run the code and go to localhost:8080 on my browser I get "Some Text" appearing. 

EDIT: Implements the interface is the proper term NOT invoke.

Question:

How does this exactly work? How is that ServeHTTP function being accessed?

I tried looking at the source code of the libraries but couldn't pinpoint exactly how ServeHTTP worked. I found these two pieces of code (not sure if this is applicable) that sort of gave me the idea it was implementing a function but need clarification:

<pre><code>// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
 f(w, r)
}
</code></pre>

I have never seen a type declaration as the one above with HandlerFunc that has a function after the name of the type. I have also seen how methods are declared but not sure what is happening in the code above.

How does ServeHTTP work?

服务器

我正在学习Golang (初学者)的web开发，我遇到了一些我尝试过的代码，我不太确定它为什么会工作，我看了库的源代码和文档，但我只有一个模糊的想法，它仍然没有点击。请注意以下代码：package mainimport (    "fmt"    "net/http")type foo intfunc (m foo) ...

问ServeHTTP是如何工作的？
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