/
dns.go
201 lines (172 loc) · 3.98 KB
/
dns.go
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package connect
import (
dproto "connect/proto/dns"
"encoding/base32"
"fmt"
"net"
"os"
"packet"
"strings"
)
const BASECHUNK = 340
type dns struct {
*ConnectorStats
*packet.Factory
*packet.Queue
domain string
id uint16
conn *net.UDPConn
connHost *net.UDPAddr
rbuf []byte
}
func NewDnsConnector() Connector {
return &dns{&ConnectorStats{}, nil, nil, "", 0, nil, nil, nil}
}
func splitDomainAddr(address string) (string, string, error) {
domaddr := strings.Split(address, "@")
if len(domaddr) < 2 {
return "", "", fmt.Errorf("missing domain name")
}
if !strings.HasPrefix(domaddr[0], ".") {
domaddr[0] = "." + domaddr[0]
}
return domaddr[0], domaddr[1], nil
}
func (d *dns) Name() string {
return "dns"
}
func (d *dns) Description() string {
return "Read/write from DNS packets"
}
func (d *dns) Stats() *ConnectorStats {
return d.ConnectorStats
}
func (d *dns) Connect(listen, plain bool, address string) (Connector, error) {
var laddr *net.UDPAddr = nil
var raddr *net.UDPAddr = nil
var err error = nil
domain, addr, err := splitDomainAddr(address)
if err != nil {
return nil, err
}
ip, port, err := ParseAddress(addr)
if err != nil {
return nil, err
}
laddr = &net.UDPAddr{IP: ip, Port: port, Zone: ""}
if !listen {
raddr = laddr
laddr = &net.UDPAddr{IP: net.IPv4zero, Port: 0, Zone: ""}
}
conn, err := net.ListenUDP("udp", laddr)
if err != nil {
return nil, err
}
pktFactory, _ := packet.NewPacketFactory(computeChunkSize(domain), uint32(os.Getpid()))
return &dns{
&ConnectorStats{},
pktFactory,
packet.NewQueue(),
domain,
uint16(os.Getpid()),
conn,
raddr,
make([]byte, BASECHUNK)}, nil
}
func (d *dns) Close() {
d.Write(nil, 0)
d.conn.Close()
d.Queue.Clear()
}
func (d *dns) Read() ([]byte, int, error) {
var data []byte = nil
var pkt *packet.Packet = nil
var addr *net.UDPAddr = nil
var err error = nil
var length = 0
var ok = false
for {
if length, addr, err = d.conn.ReadFromUDP(d.rbuf); err != nil {
return nil, 0, err
}
if data, length, err = extractData(d.rbuf[:length], d.domain[1:]); err != nil {
return nil, 0, err
}
if length == 0 || !d.checkPartner(addr) {
continue
}
if pkt, err = d.Deserialize(data, length); err != nil {
return nil, 0, err
}
d.Add(pkt)
if data, ok = d.Buffer(); ok {
d.recv += len(data)
break
}
}
return data, len(data), nil
}
func (d *dns) checkPartner(addr *net.UDPAddr) bool {
if d.connHost == nil {
d.connHost = addr
return true
}
return d.connHost.IP.Equal(addr.IP) && d.connHost.Port == addr.Port
}
func (d *dns) Write(buf []byte, length int) (int, error) {
if d.connHost == nil {
return 0, nil
}
pkts, err := d.Buffer2pkts(buf, length)
if err != nil {
return 0, err
}
for i := range pkts {
dpkt := dproto.NewDnsPacket(d.id)
data := base32.StdEncoding.EncodeToString(pkts[i].Serialize())
ldata := len(data)
wlen := dproto.MAXLBLSIZE
wb := 0
for ; ldata != 0; ldata -= wlen {
if wlen >= ldata {
wlen = ldata
}
dpkt.AddQuestion(dproto.NewQuery(data[wb:wb+wlen]+d.domain, dproto.TYPE_A, dproto.CLASS_IN))
wb += wlen
}
_, err := d.conn.WriteToUDP(dpkt.Serialize(), d.connHost)
if err != nil {
return 0, err
}
d.id += 1
}
d.send += length
return length, nil
}
func computeChunkSize(domain string) (chunk int) {
chunk = BASECHUNK - len(domain) - dproto.DNSHDRSIZE
chunk = (chunk / 8) * 5
chunk -= (dproto.QUERYSIZE + 1) * (((chunk / 5) * 8) / dproto.MAXLBLSIZE)
return
}
func extractData(buf []byte, base string) ([]byte, int, error) {
var data []byte
var pkt *dproto.Dns
var err error
var b32data = ""
if pkt, err = dproto.Deserialize(buf); err == nil {
questions := pkt.GetQuestions()
for i := range questions {
if questions[i].CountLabel() < 2 {
continue
}
if payload, domain := questions[i].SplitLast(); domain == base {
b32data += payload
}
}
if data, err = base32.StdEncoding.DecodeString(b32data); err == nil {
return data, len(data), nil
}
}
return nil, 0, err
}