Hands-On System Programming with Go

Request cancellation

A good usage of context is for cancellation and timeout when you're executing an HTTP request using http.Client, which handles the interruption automatically from the context. The following example does exactly that:

func main() {    const addr = "localhost:8080"    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {        time.Sleep(time.Second * 5)    })    go func() {        if err := http.ListenAndServe(addr, nil); err != nil {            log.Fatalln(err)        }    }()    req, _ := http.NewRequest(http.MethodGet, "http://"+addr, nil)    ctx, canc := context.WithTimeout(context.Background(), time.Second*2)    defer canc()    time.Sleep(time.Second)    if _, err := http.DefaultClient.Do(req.WithContext(ctx)); err != nil {        log.Fatalln(err)    }}

The context cancellation ...