Close http connection programmatically after X ms in golang - http

Question

I'm doing X parallel http requests and when one of them does not respond in X ms (imagine is 100ms) or less I want to cut this connection. The code I wrote does not seem to work so, how can I cut the connection and get the response as nil?
This is my sample code:
cx, cancel := context.WithCancel(context.Background())
ch := make(chan *HttpResponse)
var responses []*HttpResponse
timeout := 1.000 //1ms for testing purposes
var client = &http.Client{
Timeout: 1 * time.Second,
}
startTime := time.Now()
for _, url := range urls {
go func(url string) {
fmt.Printf("Fetching %s \n", url)
req, _ := http.NewRequest("POST", url, bytes.NewReader(request)) //request is json string
req.WithContext(cx)
resp, err := client.Do(req)
ch <- &HttpResponse{url, resp, err}
var timeElapsed = time.Since(startTime)
msec := timeElapsed.Seconds() * float64(time.Second/time.Millisecond)
if msec >= timeout {
cancel()
}
if err != nil && resp != nil && resp.StatusCode == http.StatusOK {
resp.Body.Close()
}
}(url)
}
for {
select {
case r := <-ch:
fmt.Printf("%s was fetched\n", r.Url)
if r.Err != nil {
fmt.Println("with an error", r.Err)
}
responses = append(responses, r)
if len(responses) == len(*feeds) {
return responses
}
case <-time.After(100):
//Do something
}
}

Answer 1

Your code waits until a requests finishes (and get a resposne or an error), and then calculate the time passed, and if it was longer than the time expect, your code would cancel all the requests.
req, _ := http.NewRequest("POST", url, bytes.NewReader(request)) //request is json string
req.WithContext(cx) //Here you use a common cx, which all requests share.
resp, err := client.Do(req) //Here the request is being sent and you wait it until done.
ch <- &HttpResponse{url, resp, err}
var timeElapsed = time.Since(startTime)
msec := timeElapsed.Seconds() * float64(time.Second/time.Millisecond)
if msec >= timeout {
cancel() //here you cancel all the requests.
}
The fix is to utilize the context package right.
req, _ := http.NewRequest("POST", url, bytes.NewReader(request)) //request is json string
ctx,cancel := context.WithTimeout(request.Context(),time.Duration(timeout)*time.Millisecond)
resp,err:=client.Do(req.WithContext(ctx))
defer cancel()
With that, you will get a nil resp (and an error) and get the connection cut when time out.