golang中接收者初探

今天使用net/http库做了一个简单的server. 遇到一个之前自己忽略的问题，觉得挺有意思，简单做一个笔记。

server通过调用

func ListenAndServe(addr string, handler Handler) error

1	func ListenAndServe(addr string, handler Handler) error

实现。需要传递一个Handler类型的接口进行request/response的处理。Handler接口定义如下：

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

type Handler interface {

ServeHTTP(ResponseWriter, *Request)

}

一切都非常简单，于是花了一分钟，写了一个server：

package main

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

type MyServer struct {
    i int
}

func (myServer *MyServer) ServeHTTP(w http.ResponseWriter, request *http.Request) {
    io.WriteString(w, "Hello")
    fmt.Println(request.UserAgent())
}

func main() {
    myServer := MyServer{1}
    err := http.ListenAndServe(":8080", myServer)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

package main

import (

"fmt"

"io"

"log"

"net/http"

)

type MyServer struct {

i int

}

func (myServer *MyServer) ServeHTTP(w http.ResponseWriter, request *http.Request) {

io.WriteString(w, "Hello")

fmt.Println(request.UserAgent())

}

func main() {

myServer := MyServer{1}

err := http.ListenAndServe(":8080", myServer)

if err != nil {

log.Fatal("ListenAndServe: ", err)

}

看似一切都没有问题的样子……但是却编译错误：

cannot use myServer (type MyServer) as type http.Handler in function argument:
    MyServer does not implement http.Handler (ServeHTTP method has pointer receiver)

1 2	cannot use myServer (type MyServer) as type http.Handler in function argument: MyServer does not implement http.Handler (ServeHTTP method has pointer receiver)

原来是类型不匹配的问题。具体来说，接收者的类型才是真正实现接口的类型。在本例中，接收者类型是*Myserver，myServer也必须是一个指针。fix后的代码如下：

package main

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

type MyServer struct {
    i int
}

func (myServer *MyServer) ServeHTTP(w http.ResponseWriter, request *http.Request) {
    io.WriteString(w, "Hello")
    fmt.Println(request.UserAgent())
}

func main() {
    myServer := &MyServer{1}
    err := http.ListenAndServe(":8080", myServer)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}