context.go

package main

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

func main() {
	success := make(chan bool)

	timeout := 300 * time.Millisecond

	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(timeout))
	defer cancel()

	go consulta(ctx, success)

	select {
	case <-ctx.Done():
		fmt.Println("cancelado: ", ctx.Err())
	case status := <-success:
		if status {
			fmt.Println("sucesso na chamada")
		} else {
			fmt.Println("erro na chamada")
		}
	}
}

func consulta(ctx context.Context, success chan bool) {
	defer close(success)
	req, err := http.NewRequest("GET", "http://www.google.com.br", nil)
	if err != nil {
		success <- false
		return
	}

	req = req.WithContext(ctx)

	client := http.DefaultClient
	_, err = client.Do(req)
	if err != nil {
		fmt.Println("erro client.Do()", err)
		success <- false
		return
	}
	success <- true
}