// Runs DNS-SD discover of a service by a given type, calls given handler
// on the first result, stops discovery afterwards
func DiscoverAndExecute(serviceType string, handler DiscoverHandler) {
log.Println("Discovering catalog via DNS-SD...")
services := make(chan *bonjour.ServiceEntry)
resolver, err := bonjour.NewResolver(nil)
if err != nil {
log.Println("Failed to create DNS-SD resolver:", err.Error())
return
}
go func(services chan *bonjour.ServiceEntry, exitCh chan<- bool) {
for service := range services {
log.Println("Catalog discovered:", service.ServiceInstanceName())
// stop resolver
exitCh <- true
// executing the handler
handler(service)
// exit the loop
break
}
}(services, resolver.Exit)
if err := resolver.Browse(serviceType, "", services); err != nil {
log.Printf("Failed to browse services using type %s", serviceType)
}
}
// Discovers a catalog endpoint given the serviceType
func DiscoverCatalogEndpoint(serviceType string) (endpoint string, err error) {
sysSig := make(chan os.Signal, 1)
signal.Notify(sysSig,
syscall.SIGHUP,
syscall.SIGINT,
syscall.SIGTERM,
syscall.SIGQUIT)
for {
// create resolver
resolver, err := bonjour.NewResolver(nil)
if err != nil {
logger.Println("Failed to initialize DNS-SD resolver:", err.Error())
break
}
// init the channel for results
results := make(chan *bonjour.ServiceEntry)
// send query and listen for answers
logger.Println("Browsing...")
err = resolver.Browse(serviceType, "", results)
if err != nil {
logger.Println("Unable to browse DNS-SD services: ", err)
break
}
// if not found - block with timeout
var foundService *bonjour.ServiceEntry
select {
case foundService = <-results:
logger.Printf("[DiscoverCatalogEndpoint] Discovered service: %v\n", foundService.ServiceInstanceName())
case <-time.After(time.Duration(discoveryTimeoutSec) * time.Second):
logger.Println("[DiscoverCatalogEndpoint] Timeout looking for a service")
case <-sysSig:
logger.Println("[DiscoverCatalogEndpoint] System interrupt signal received. Aborting the discovery")
return endpoint, fmt.Errorf("Aborted by system interrupt")
}
// check if something found
if foundService == nil {
logger.Printf("[DiscoverCatalogEndpoint] Could not discover a service %v withing the timeout. Starting from scratch...", serviceType)
// stop resolver
resolver.Exit <- true
// start the new iteration
continue
}
// stop the resolver and close the channel
resolver.Exit <- true
close(results)
uri := ""
for _, s := range foundService.Text {
if strings.HasPrefix(s, "uri=") {
tmp := strings.Split(s, "=")
if len(tmp) == 2 {
uri = tmp[1]
break
}
}
}
endpoint = fmt.Sprintf("http://%s:%v%s", foundService.HostName, foundService.Port, uri)
break
}
return endpoint, err
}