Ninja Level 3 Hands on Exercise #4

main.go

package main

import (
	"context"
	"fmt"
	"time"

	profiler "github.com/mannion007/whatever/profiler"
)

func main() {

	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*1005)
	defer cancel()

	endpoints := []string{
		"http://www.google.co.uk",
		"http://www.google.co.in",
		"http://www.ebay.co.uk",
		"http://www.ebay.co.jp",
		"http://www.twitter.com",
		"https://www.facebook.com",
		"http://www.youtube.com",
		"http://www.deliveroo.co.uk",
		"http://www.github.com",
		"http://www.iflscience.com",
	}

	results, errors := profiler.Profile(ctx, endpoints)

	for i := 0; i <= len(endpoints); i++ {
		select {
		case result := <-results:
			fmt.Printf("Success [%s] responded in [%v]\n", result.URL, result.ResponseTime)
		case err := <-errors:
			fmt.Printf("Error [%s]\n", err)
		}
	}
}

profiler.go

package poller

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

// Endpoint is a struct which represents the measured performance of an endpoint
type Endpoint struct {
	URL          string
	ResponseTime time.Duration
}

// Profile sends a GET request to each of the endpoints in the supplied list and times how long it takes to respond
func Profile(ctx context.Context, endpoints []string) (<-chan Endpoint, <-chan error) {

	successChan := make(chan Endpoint)
	errorChan := make(chan error)

	for _, ep := range endpoints {

		go func(ctx context.Context, url string, output chan<- Endpoint, errorChan chan<- error) {

			start := time.Now()

			// Don't bother to even start a request if <1 second remaining. Doesn't make much sense given how quickly Go routines spawn, but demonstrates utilisation of context deadline
			deadline, ok := ctx.Deadline()
			if ok && deadline.Before(time.Now().Add(time.Second)) {
				errorChan <- fmt.Errorf("skipping profiling [%s] as there is less than 1 second to go", url)
				return
			}

			req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)

			if err != nil {
				errorChan <- fmt.Errorf("error building request for [%s]", url)
			}

			resp, err := http.DefaultClient.Do(req)

			if err != nil {
				errorChan <- fmt.Errorf("failed profiling endpoint [%s] [%s]", url, err)
				return
			}

			if resp.StatusCode != http.StatusOK {
				errorChan <- fmt.Errorf("Unexpected response code from [%s] [%d]", url, resp.StatusCode)
			}

			output <- Endpoint{
				URL:          url,
				ResponseTime: time.Since(start),
			}

		}(ctx, ep, successChan, errorChan)
	}

	return successChan, errorChan
}