[GO]conext的使用

package main

import (
    "context"
    "time"
    "net/http"
    "fmt"
    "io/ioutil"
)

type Result struct {
    r *http.Response
    err error
}

func process() {
    ctx,cancel := context.WithTimeout(context.Background(), 2*time.Second)
    defer cancel()

    tr := &http.Transport{}
    client := &http.Client{Transport:tr}
    c := make(chan Result, 1)
    req, err := http.NewRequest("GET", "http://google.com", nil)
    if err != nil{
        fmt.Println("http request filed, err:", err)
        return
    }
    go func() {
        resp, err := client.Do(req)
        pack := Result{r:resp, err:err}
        c <- pack
    }()

    select {
    case <- ctx.Done()://内部也是一个管道，如果这个管道能够读到数据，说明已经超时了
        tr.CancelRequest(req)//取消正在请求的http请求
        res := <-c
        fmt.Println("timeout!", res.err)
    case res := <-c:
        defer res.r.Body.Close()
        out, _ := ioutil.ReadAll(res.r.Body)
        fmt.Printf("server response:%s", out)
    }
    return
}

func main() {
    process()
}

执行结果 

timeout! Get http://google.com: net/http: request canceled while waiting for connection