Perform external queries
This commit is contained in:
Jakob Borg
@@ -20,6 +20,12 @@ following format:
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\ NodeID (variable length) \
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/ /
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Length of IP |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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/ /
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\ IP (variable length) \
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/ /
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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This is the XDR encoding of:
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@@ -31,11 +37,15 @@ struct Announcement {
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(Hence NodeID is padded to a multiple of 32 bits)
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The sending node's address is not encoded -- it is taken to be the source
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address of the announcement. Every time such a packet is received, a local
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table that maps NodeID to Address is updated. When the local node wants to
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connect to another node with the address specification 'dynamic', this table is
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consulted.
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The sending node's address is not encoded in local announcement -- the Length
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of IP field is set to zero and the address is taken to be the source address of
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the announcement. In announcement packets sent by a discovery server in
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response to a query, the IP is present and the length is either 4 (IPv4) or 16
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(IPv6).
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Every time such a packet is received, a local table that maps NodeID to Address
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is updated. When the local node wants to connect to another node with the
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address specification 'dynamic', this table is consulted.
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For external discovery, an identical packet is sent every 30 minutes to the
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external discovery server. The server keeps information for up to 60 minutes.
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@@ -71,8 +81,6 @@ server from being used as an amplifier in a DDoS attack.)
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package discover
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"log"
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"net"
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@@ -86,11 +94,6 @@ const (
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QueryMagic = 0x19760309
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)
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var (
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errBadMagic = errors.New("bad magic")
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errFormat = errors.New("incorrect packet format")
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)
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type Discoverer struct {
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MyID string
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ListenPort int
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@@ -104,13 +107,7 @@ type Discoverer struct {
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extServer string
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}
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type packet struct {
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magic uint32 // AnnouncementMagic or QueryMagic
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port uint16 // unset if magic == QueryMagic
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id string
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}
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// We tolerate a certain amount of errors because we might be running in
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// We tolerate a certain amount of errors because we might be running on
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// laptops that sleep and wake, have intermittent network connectivity, etc.
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// When we hit this many errors in succession, we stop.
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const maxErrors = 30
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@@ -149,7 +146,7 @@ func NewDiscoverer(id string, port int, extPort int, extServer string) (*Discove
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func (d *Discoverer) sendAnnouncements() {
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remote4 := &net.UDPAddr{IP: net.IP{255, 255, 255, 255}, Port: AnnouncementPort}
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buf := encodePacket(packet{AnnouncementMagic, uint16(d.ListenPort), d.MyID})
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buf := encodePacket(packet{AnnouncementMagic, uint16(d.ListenPort), d.MyID, nil})
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go d.writeAnnouncements(buf, remote4, d.BroadcastIntv)
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}
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@@ -160,7 +157,7 @@ func (d *Discoverer) sendExtAnnouncements() {
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return
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}
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buf := encodePacket(packet{AnnouncementMagic, uint16(d.ExtListenPort), d.MyID})
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buf := encodePacket(packet{AnnouncementMagic, uint16(d.ExtListenPort), d.MyID, nil})
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for _, extIP := range extIPs {
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remote4 := &net.UDPAddr{IP: extIP, Port: AnnouncementPort}
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go d.writeAnnouncements(buf, remote4, d.ExtBroadcastIntv)
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@@ -215,93 +212,77 @@ func (d *Discoverer) recvAnnouncements() {
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log.Println("discover/read: stopping due to too many errors:", err)
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}
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func (d *Discoverer) externalLookup(node string) (string, bool) {
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extIPs, err := net.LookupIP(d.extServer)
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if err != nil {
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log.Printf("discover/external: %v; no external lookup", err)
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return "", false
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}
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var res = make(chan string, len(extIPs))
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var failed = 0
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for _, extIP := range extIPs {
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remote := &net.UDPAddr{IP: extIP, Port: AnnouncementPort}
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conn, err := net.DialUDP("udp", nil, remote)
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if err != nil {
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log.Printf("discover/external: %v; no external lookup", err)
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failed++
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continue
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}
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_, err = conn.Write(encodePacket(packet{QueryMagic, 0, node, nil}))
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if err != nil {
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log.Printf("discover/external: %v; no external lookup", err)
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failed++
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continue
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}
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go func() {
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var buf = make([]byte, 1024)
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_, err = conn.Read(buf)
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if err != nil {
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log.Printf("discover/external/read: %v; no external lookup", err)
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return
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}
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pkt, err := decodePacket(buf)
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if err != nil {
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log.Printf("discover/external/read: %v; no external lookup", err)
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return
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}
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if pkt.magic != AnnouncementMagic {
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log.Printf("discover/external/read: bad magic; no external lookup", err)
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return
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}
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res <- fmt.Sprintf("%s:%d", ipStr(pkt.ip), pkt.port)
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}()
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}
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if failed == len(extIPs) {
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// no point in waiting
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return "", false
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}
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select {
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case r := <-res:
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return r, true
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case <-time.After(5 * time.Second):
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return "", false
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}
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}
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func (d *Discoverer) Lookup(node string) (string, bool) {
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d.registryLock.Lock()
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defer d.registryLock.Unlock()
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addr, ok := d.registry[node]
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return addr, ok
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}
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func encodePacket(pkt packet) []byte {
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var idbs = []byte(pkt.id)
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var l = len(idbs) + pad(len(idbs)) + 4 + 4
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if pkt.magic == AnnouncementMagic {
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l += 4
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}
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var buf = make([]byte, l)
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var offset = 0
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binary.BigEndian.PutUint32(buf[offset:], pkt.magic)
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offset += 4
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if pkt.magic == AnnouncementMagic {
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binary.BigEndian.PutUint16(buf[offset:], uint16(pkt.port))
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offset += 4
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}
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binary.BigEndian.PutUint32(buf[offset:], uint32(len(idbs)))
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offset += 4
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copy(buf[offset:], idbs)
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return buf
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}
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func decodePacket(buf []byte) (*packet, error) {
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var p packet
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var offset int
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if len(buf) < 4 {
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// short packet
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return nil, errFormat
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}
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p.magic = binary.BigEndian.Uint32(buf[offset:])
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offset += 4
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if p.magic != AnnouncementMagic && p.magic != QueryMagic {
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return nil, errBadMagic
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}
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if p.magic == AnnouncementMagic {
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if len(buf) < offset+4 {
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// short packet
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return nil, errFormat
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}
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p.port = binary.BigEndian.Uint16(buf[offset:])
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offset += 2
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reserved := binary.BigEndian.Uint16(buf[offset:])
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if reserved != 0 {
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return nil, errFormat
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}
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offset += 2
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}
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if len(buf) < offset+4 {
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// short packet
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return nil, errFormat
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}
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l := binary.BigEndian.Uint32(buf[offset:])
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offset += 4
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if len(buf) < offset+int(l)+pad(int(l)) {
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// short packet
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return nil, errFormat
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}
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idbs := buf[offset : offset+int(l)]
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p.id = string(idbs)
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offset += int(l) + pad(int(l))
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if len(buf[offset:]) > 0 {
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// extra data
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return nil, errFormat
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}
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return &p, nil
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}
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func pad(l int) int {
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d := l % 4
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if d == 0 {
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return 0
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}
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return 4 - d
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d.registryLock.Unlock()
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if ok {
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return addr, true
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} else if len(d.extServer) != 0 {
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// We might want to cache this, but not permanently so it needs some intelligence
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return d.externalLookup(node)
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}
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return "", false
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}
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