code: func NewHost(id string, addr string, h *http.Client, tags map[string]string) *Host {
  	if h == nil {
  		h = http.DefaultClient
  	}
  	if !strings.HasPrefix(addr, "http") {
  		addr = "http://" + addr
  	}
  	return &Host{
  		id:   id,
  		tags: tags,
  		c: &httpclient.Client{
  			ErrNotFound: ErrNotFound,
  			URL:         addr,
  			HTTP:        h,
  		},
  	}
  }
docs: // NewHost creates a new Host that uses client to communicate with it.
  // addr is used by Attach.