go-emlid/reach/discovery/discovery.go

package discovery

import (
	"context"
	"net"

	"github.com/grandcat/zeroconf"
	"github.com/pkg/errors"
)

// Service is a ReachRS service discovered via MDNS-SD
type Service struct {
	Name   string
	AddrV4 *net.IP
	Port   int
}

// Discover tries to discover ReachRS services on the local network via mDNS-SD
func Discover(ctx context.Context) ([]Service, error) {
	services := make([]Service, 0)

	watch, err := Watch(ctx)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	for srv := range watch {
		services = append(services, srv)
	}

	return services, nil
}

// Watch watches ReachRS services on the local network via mDNS-SD
func Watch(ctx context.Context) (chan Service, error) {
	out := make(chan Service, 0)

	resolver, err := zeroconf.NewResolver()
	if err != nil {
		return nil, errors.WithStack(err)
	}

	entries := make(chan *zeroconf.ServiceEntry)

	go func() {
		defer close(out)

		for e := range entries {
			var addr *net.IP
			if len(e.AddrIPv4) > 0 {
				addr = &e.AddrIPv4[0]
			}
			srv := Service{
				Name:   e.Instance,
				AddrV4: addr,
				Port:   e.Port,
			}
			out <- srv
		}

	}()

	if err = resolver.Browse(ctx, "_reach._tcp", ".local", entries); err != nil {
		return nil, err
	}

	return out, nil
}