Resource poller using goroutines

resource_poller.go

package main

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

const (
	statusInterval = 2 * time.Second
	pollInterval   = 2 * time.Second
)

var urls = []string{
	"http://www.google.com",
	"http://www.facebook.com",
	"http://www.twitter.com",
	"http://www.esimov.com",
}

type Resource struct {
	url         string
	errorsCount int
}

type State struct {
	url    string
	status string
}

func (r *Resource) Poll() string {
	resp, err := http.Head(r.url)

	if err != nil {
		fmt.Println("Error...", r.url, err)
		r.errorsCount++
		return err.Error()
	}

	r.errorsCount = 0
	return resp.Status
}

func Poller(in <-chan *Resource, out chan<- *Resource, status chan<- State) {
	for s := range in {
		state := s.Poll()
		status <- State{s.url, state}
		out <- s
	}
}

func StateMonitor(updateInterval time.Duration) chan<- State {
	ticker := time.NewTicker(updateInterval)
	updates := make(chan State)
	urlStatus := make(map[string]string)

	go func() {
		for {
			select {
			case <-ticker.C:
				logState(urlStatus)
			case s := <-updates:
				urlStatus[s.status] = s.status
			}
		}
	}()

	return updates
}

func (r *Resource) Sleep(done chan<- *Resource) {
	time.Sleep(pollInterval + 2*time.Second*time.Duration(r.errorsCount))
	done <- r
}

func logState(s map[string]string) {
	log.Println("Current State: ")
	for k, v := range s {
		log.Printf("%s %s", k, v)
	}
}

func main() {
	pending, complete := make(chan *Resource), make(chan *Resource)

	// Launch the StateMonitor.
	status := StateMonitor(statusInterval)

	// Launch some Poller goroutines.
	for i := 0; i < 2; i++ {
		go Poller(pending, complete, status)
	}

	// Send some Resources to the pending queue.
	go func() {
		for _, url := range urls {
			pending <- &Resource{url: url}
		}
	}()

	for r := range complete {
		go r.Sleep(pending)
	}

}