Don't pass around a pointer to service.

[jholdstock]

It makes more sense for the functions to be methods of the service, rather than accepting the service as a param.

[davecgh]

Nice update overall. It is cleaner to have the methods on the type and more customary to use a short name for receiver.

[davecgh]

I think it would be better to just take the vsp as a 2nd param. Then you wouldn't have to take the mutex again here. It looks like it's only called from the loop in vspData which already holds the mutex.

func (s *Service) vspStats(url string, vsp Vsp) error {
	infoURL := fmt.Sprintf("https://%s/api/v3/vspinfo", url)
	...
}

func (s *Service) vspData() {
	...
	for url, vsp := range s.Vsps {
		go func(url string, vsp Vsp) {
			defer wg.Done()
			err := s.vspStats(url, vsp)
			...
		}(url, vsp)
	...
}

[davecgh]

By the way, it doesn't really matter, but you could shorten all of these mutex accesses by just embedding the mutex in the service since the mutex is already exported anyway.

e.g.

type Service struct {
	// the http client
	HTTPClient *http.Client
	// the http router
	Router *http.ServeMux

	// Data cached by the service, protected by a mutex.
	sync.RWMutex
	Vsps      vspSet
	...

Then:

s.RLock()
...
s.RUnlock()