REBASE!v0.1

1 files changed, 121 insertions, 0 deletions

diff --git a/discover/discover.go b/discover/discover.go
new file mode 100644
index 0000000000..e8e335e5e2
--- /dev/null
+++ b/discover/discover.go
@@ -0,0 +1,121 @@
+/*
+This is the local node discovery protocol. In principle we might be better
+served by something more standardized, such as mDNS / DNS-SD. In practice, this
+was much easier and quicker to get up and running.
+
+The mode of operation is to periodically (currently once every 30 seconds)
+transmit a broadcast UDP packet to the well known port number 21025. The packet
+has the following format:
+
+     0                   1                   2                   3
+     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |                         Magic Number                          |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |          Port Number          |        Length of NodeID       |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    /                                                               /
+    \                   NodeID (variable length)                    \
+    /                                                               /
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+The sending node's address is not encoded -- it is taken to be the source
+address of the announcement. Every time such a packet is received, a local
+table that maps NodeID to Address is updated. When the local node wants to
+connect to another node with the address specification 'dynamic', this table is
+consulted.
+*/
+package discover
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"sync"
+	"time"
+)
+
+type Discoverer struct {
+	MyID          string
+	ListenPort    int
+	BroadcastIntv time.Duration
+
+	conn         *net.UDPConn
+	registry     map[string]string
+	registryLock sync.RWMutex
+}
+
+func NewDiscoverer(id string, port int) (*Discoverer, error) {
+	local4 := &net.UDPAddr{IP: net.IP{0, 0, 0, 0}, Port: 21025}
+	conn, err := net.ListenUDP("udp4", local4)
+	if err != nil {
+		return nil, err
+	}
+
+	disc := &Discoverer{
+		MyID:          id,
+		ListenPort:    port,
+		BroadcastIntv: 30 * time.Second,
+		conn:          conn,
+		registry:      make(map[string]string),
+	}
+
+	go disc.sendAnnouncements()
+	go disc.recvAnnouncements()
+
+	return disc, nil
+}
+
+func (d *Discoverer) sendAnnouncements() {
+	remote4 := &net.UDPAddr{IP: net.IP{255, 255, 255, 255}, Port: 21025}
+
+	idbs := []byte(d.MyID)
+	buf := make([]byte, 4+4+4+len(idbs))
+
+	binary.BigEndian.PutUint32(buf, uint32(0x121025))
+	binary.BigEndian.PutUint16(buf[4:], uint16(d.ListenPort))
+	binary.BigEndian.PutUint16(buf[6:], uint16(len(idbs)))
+	copy(buf[8:], idbs)
+
+	for {
+		_, _, err := d.conn.WriteMsgUDP(buf, nil, remote4)
+		if err != nil {
+			panic(err)
+		}
+		time.Sleep(d.BroadcastIntv)
+	}
+}
+
+func (d *Discoverer) recvAnnouncements() {
+	var buf = make([]byte, 1024)
+	for {
+		_, addr, err := d.conn.ReadFromUDP(buf)
+		if err != nil {
+			panic(err)
+		}
+		magic := binary.BigEndian.Uint32(buf)
+		if magic != 0x121025 {
+			continue
+		}
+		port := binary.BigEndian.Uint16(buf[4:])
+		l := binary.BigEndian.Uint16(buf[6:])
+		idbs := buf[8 : l+8]
+		id := string(idbs)
+
+		if id != d.MyID {
+			nodeAddr := fmt.Sprintf("%s:%d", addr.IP.String(), port)
+			d.registryLock.Lock()
+			if d.registry[id] != nodeAddr {
+				d.registry[id] = nodeAddr
+			}
+			d.registryLock.Unlock()
+		}
+	}
+}
+
+func (d *Discoverer) Lookup(node string) (string, bool) {
+	d.registryLock.Lock()
+	defer d.registryLock.Unlock()
+	addr, ok := d.registry[node]
+	return addr, ok
+}