mconnect/discovery/listener.go

//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
//
//        http://www.apache.org/licenses/LICENSE-2.0
//
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
package discovery

import (
	"context"
	"net"

	"github.com/pkg/errors"

	"github.com/bboozzoo/mconnect/logger"
	"github.com/bboozzoo/mconnect/protocol"
	"github.com/bboozzoo/mconnect/protocol/packet"
)

type Listener struct {
	conn *net.UDPConn
}

func NewListener() (*Listener, error) {
	conn, err := net.ListenUDP("udp", protocol.UDPDiscoveryAddr)
	if err != nil {
		return nil, err
	}

	listener := &Listener{
		conn: conn,
	}

	return listener, nil
}

// Discovery conveys the received discovery information
type Discovery struct {
	// Packet is the original packet received
	Packet *packet.Packet
	// Identity is the parsed identity data
	Identity *packet.Identity
	// From is the address the packet was received from
	From *net.UDPAddr
}

// Receive blocks waiting to receive a discovery packet. Once received, it will
// parse the packet and return a result.
func (l *Listener) Receive(ctx context.Context) (*Discovery, error) {
	log := logger.FromContext(ctx)
	buf := make([]byte, 4096)
	count, addr, err := l.conn.ReadFromUDP(buf)
	if err != nil {
		return nil, errors.Wrap(err, "failed to receive a packet")
	}

	log.Debugf("got %v bytes from %v", count, addr)
	log.Debugf("data:\n%s", string(buf))
	var p packet.Packet
	if err := packet.Unmarshal(buf, &p); err != nil {
		return nil, errors.Wrap(err, "failed to parse packet")
	}
	identity, err := p.AsIdentity()
	if err != nil {
		return nil, errors.Wrap(err, "failed to parse as identity packet")
	}
	discovery := &Discovery{
		Packet:   &p,
		Identity: identity,
		From:     addr,
	}
	return discovery, nil
}