在golang中的X ms之后以编程方式关闭http连接

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 
", 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
", 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.