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udp.go
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udp.go
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package tracker
import (
"bytes"
"context"
"encoding"
"encoding/binary"
"fmt"
"io"
"math/rand"
"net"
"net/url"
"time"
"github.com/anacrolix/dht/v2/krpc"
"github.com/anacrolix/missinggo"
"github.com/anacrolix/missinggo/pproffd"
"github.com/pkg/errors"
)
type Action int32
const (
ActionConnect Action = iota
ActionAnnounce
ActionScrape
ActionError
connectRequestConnectionId = 0x41727101980
// BEP 41
optionTypeEndOfOptions = 0
optionTypeNOP = 1
optionTypeURLData = 2
)
type ConnectionRequest struct {
ConnectionId int64
Action int32
TransctionId int32
}
type ConnectionResponse struct {
ConnectionId int64
}
type ResponseHeader struct {
Action Action
TransactionId int32
}
type RequestHeader struct {
ConnectionId int64
Action Action
TransactionId int32
} // 16 bytes
type AnnounceResponseHeader struct {
Interval int32
Leechers int32
Seeders int32
}
func newTransactionId() int32 {
return int32(rand.Uint32())
}
func timeout(contiguousTimeouts int) (d time.Duration) {
if contiguousTimeouts > 8 {
contiguousTimeouts = 8
}
d = 15 * time.Second
for ; contiguousTimeouts > 0; contiguousTimeouts-- {
d *= 2
}
return
}
type udpAnnounce struct {
contiguousTimeouts int
connectionIdReceived time.Time
connectionId int64
socket net.Conn
url url.URL
a *Announce
}
func (c *udpAnnounce) Close() error {
if c.socket != nil {
return c.socket.Close()
}
return nil
}
func (c *udpAnnounce) ipv6() bool {
if c.a.UdpNetwork == "udp6" {
return true
}
rip := missinggo.AddrIP(c.socket.RemoteAddr())
return rip.To16() != nil && rip.To4() == nil
}
func (c *udpAnnounce) Do(req AnnounceRequest) (res AnnounceResponse, err error) {
err = c.connect()
if err != nil {
return
}
reqURI := c.url.RequestURI()
if c.ipv6() {
// BEP 15
req.IPAddress = 0
} else if req.IPAddress == 0 && c.a.ClientIp4.IP != nil {
req.IPAddress = binary.BigEndian.Uint32(c.a.ClientIp4.IP.To4())
}
// Clearly this limits the request URI to 255 bytes. BEP 41 supports
// longer but I'm not fussed.
options := append([]byte{optionTypeURLData, byte(len(reqURI))}, []byte(reqURI)...)
b, err := c.request(ActionAnnounce, req, options)
if err != nil {
return
}
var h AnnounceResponseHeader
err = readBody(b, &h)
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
err = fmt.Errorf("error parsing announce response: %s", err)
return
}
res.Interval = h.Interval
res.Leechers = h.Leechers
res.Seeders = h.Seeders
nas := func() interface {
encoding.BinaryUnmarshaler
NodeAddrs() []krpc.NodeAddr
} {
if c.ipv6() {
return &krpc.CompactIPv6NodeAddrs{}
} else {
return &krpc.CompactIPv4NodeAddrs{}
}
}()
err = nas.UnmarshalBinary(b.Bytes())
if err != nil {
return
}
for _, cp := range nas.NodeAddrs() {
res.Peers = append(res.Peers, Peer{}.FromNodeAddr(cp))
}
return
}
// body is the binary serializable request body. trailer is optional data
// following it, such as for BEP 41.
func (c *udpAnnounce) write(h *RequestHeader, body interface{}, trailer []byte) (err error) {
var buf bytes.Buffer
err = binary.Write(&buf, binary.BigEndian, h)
if err != nil {
panic(err)
}
if body != nil {
err = binary.Write(&buf, binary.BigEndian, body)
if err != nil {
panic(err)
}
}
_, err = buf.Write(trailer)
if err != nil {
return
}
n, err := c.socket.Write(buf.Bytes())
if err != nil {
return
}
if n != buf.Len() {
panic("write should send all or error")
}
return
}
func read(r io.Reader, data interface{}) error {
return binary.Read(r, binary.BigEndian, data)
}
func write(w io.Writer, data interface{}) error {
return binary.Write(w, binary.BigEndian, data)
}
// args is the binary serializable request body. trailer is optional data
// following it, such as for BEP 41.
func (c *udpAnnounce) request(action Action, args interface{}, options []byte) (*bytes.Buffer, error) {
tid := newTransactionId()
if err := errors.Wrap(
c.write(
&RequestHeader{
ConnectionId: c.connectionId,
Action: action,
TransactionId: tid,
}, args, options),
"writing request",
); err != nil {
return nil, err
}
c.socket.SetReadDeadline(time.Now().Add(timeout(c.contiguousTimeouts)))
b := make([]byte, 0x800) // 2KiB
for {
var (
n int
readErr error
readDone = make(chan struct{})
)
go func() {
defer close(readDone)
n, readErr = c.socket.Read(b)
}()
ctx := c.a.Context
if ctx == nil {
ctx = context.Background()
}
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-readDone:
}
if opE, ok := readErr.(*net.OpError); ok && opE.Timeout() {
c.contiguousTimeouts++
}
if readErr != nil {
return nil, errors.Wrap(readErr, "reading from socket")
}
buf := bytes.NewBuffer(b[:n])
var h ResponseHeader
err := binary.Read(buf, binary.BigEndian, &h)
switch err {
default:
panic(err)
case io.ErrUnexpectedEOF, io.EOF:
continue
case nil:
}
if h.TransactionId != tid {
continue
}
c.contiguousTimeouts = 0
if h.Action == ActionError {
err = errors.New(buf.String())
}
return buf, err
}
}
func readBody(r io.Reader, data ...interface{}) (err error) {
for _, datum := range data {
err = binary.Read(r, binary.BigEndian, datum)
if err != nil {
break
}
}
return
}
func (c *udpAnnounce) connected() bool {
return !c.connectionIdReceived.IsZero() && time.Now().Before(c.connectionIdReceived.Add(time.Minute))
}
func (c *udpAnnounce) dialNetwork() string {
if c.a.UdpNetwork != "" {
return c.a.UdpNetwork
}
return "udp"
}
func (c *udpAnnounce) connect() (err error) {
if c.connected() {
return nil
}
c.connectionId = connectRequestConnectionId
if c.socket == nil {
hmp := missinggo.SplitHostMaybePort(c.url.Host)
if hmp.NoPort {
hmp.NoPort = false
hmp.Port = 80
}
c.socket, err = net.Dial(c.dialNetwork(), hmp.String())
if err != nil {
return
}
c.socket = pproffd.WrapNetConn(c.socket)
}
b, err := c.request(ActionConnect, nil, nil)
if err != nil {
return
}
var res ConnectionResponse
err = readBody(b, &res)
if err != nil {
return
}
c.connectionId = res.ConnectionId
c.connectionIdReceived = time.Now()
return
}
// TODO: Split on IPv6, as BEP 15 says response peer decoding depends on
// network in use.
func announceUDP(opt Announce, _url *url.URL) (AnnounceResponse, error) {
ua := udpAnnounce{
url: *_url,
a: &opt,
}
defer ua.Close()
return ua.Do(opt.Request)
}