287 lines
7.2 KiB
Go
287 lines
7.2 KiB
Go
// Package udp implements a BitTorrent tracker via the UDP protocol as
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// described in BEP 15.
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package udp
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import (
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"bytes"
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"context"
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"encoding/binary"
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"math/rand"
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"net"
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"sync"
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"time"
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log "github.com/Sirupsen/logrus"
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"github.com/prometheus/client_golang/prometheus"
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"github.com/chihaya/chihaya/bittorrent"
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"github.com/chihaya/chihaya/frontend"
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"github.com/chihaya/chihaya/frontend/udp/bytepool"
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)
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var allowedGeneratedPrivateKeyRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890")
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func init() {
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prometheus.MustRegister(promResponseDurationMilliseconds)
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}
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// ErrInvalidIP indicates an invalid IP.
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var ErrInvalidIP = bittorrent.ClientError("invalid IP")
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var promResponseDurationMilliseconds = prometheus.NewHistogramVec(
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prometheus.HistogramOpts{
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Name: "chihaya_udp_response_duration_milliseconds",
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Help: "The duration of time it takes to receive and write a response to an API request",
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Buckets: prometheus.ExponentialBuckets(9.375, 2, 10),
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},
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[]string{"action", "address_family", "error"},
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)
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// recordResponseDuration records the duration of time to respond to a UDP
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// Request in milliseconds .
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func recordResponseDuration(action string, af *bittorrent.AddressFamily, err error, duration time.Duration) {
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var errString string
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if err != nil {
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errString = err.Error()
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}
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var afString string
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if af == nil {
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afString = "Unknown"
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} else if *af == bittorrent.IPv4 {
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afString = "IPv4"
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} else if *af == bittorrent.IPv6 {
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afString = "IPv6"
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}
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promResponseDurationMilliseconds.
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WithLabelValues(action, afString, errString).
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Observe(float64(duration.Nanoseconds()) / float64(time.Millisecond))
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}
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// Config represents all of the configurable options for a UDP BitTorrent
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// Tracker.
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type Config struct {
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Addr string `yaml:"addr"`
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PrivateKey string `yaml:"private_key"`
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MaxClockSkew time.Duration `yaml:"max_clock_skew"`
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AllowIPSpoofing bool `yaml:"allow_ip_spoofing"`
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}
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// Frontend holds the state of a UDP BitTorrent Frontend.
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type Frontend struct {
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socket *net.UDPConn
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closing chan struct{}
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wg sync.WaitGroup
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logic frontend.TrackerLogic
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Config
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}
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// NewFrontend allocates a new instance of a Frontend.
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func NewFrontend(logic frontend.TrackerLogic, cfg Config) *Frontend {
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// Generate a private key if one isn't provided by the user.
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if cfg.PrivateKey == "" {
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rand.Seed(time.Now().UnixNano())
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pkeyRunes := make([]rune, 64)
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for i := range pkeyRunes {
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pkeyRunes[i] = allowedGeneratedPrivateKeyRunes[rand.Intn(len(allowedGeneratedPrivateKeyRunes))]
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}
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cfg.PrivateKey = string(pkeyRunes)
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log.Warn("UDP private key was not provided, using generated key: ", cfg.PrivateKey)
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}
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return &Frontend{
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closing: make(chan struct{}),
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logic: logic,
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Config: cfg,
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}
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}
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// Stop provides a thread-safe way to shutdown a currently running Frontend.
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func (t *Frontend) Stop() {
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close(t.closing)
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t.socket.SetReadDeadline(time.Now())
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t.wg.Wait()
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}
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// ListenAndServe listens on the UDP network address t.Addr and blocks serving
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// BitTorrent requests until t.Stop() is called or an error is returned.
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func (t *Frontend) ListenAndServe() error {
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udpAddr, err := net.ResolveUDPAddr("udp", t.Addr)
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if err != nil {
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return err
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}
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t.socket, err = net.ListenUDP("udp", udpAddr)
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if err != nil {
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return err
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}
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defer t.socket.Close()
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pool := bytepool.New(2048)
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for {
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// Check to see if we need to shutdown.
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select {
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case <-t.closing:
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return nil
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default:
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}
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// Read a UDP packet into a reusable buffer.
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buffer := pool.Get()
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t.socket.SetReadDeadline(time.Now().Add(time.Second))
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n, addr, err := t.socket.ReadFromUDP(buffer)
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if err != nil {
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pool.Put(buffer)
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if netErr, ok := err.(net.Error); ok && netErr.Temporary() {
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// A temporary failure is not fatal; just pretend it never happened.
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continue
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}
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return err
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}
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// We got nothin'
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if n == 0 {
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pool.Put(buffer)
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continue
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}
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t.wg.Add(1)
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go func() {
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defer t.wg.Done()
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defer pool.Put(buffer)
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if ip := addr.IP.To4(); ip != nil {
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addr.IP = ip
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}
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// Handle the request.
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start := time.Now()
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action, af, err := t.handleRequest(
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// Make sure the IP is copied, not referenced.
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Request{buffer[:n], append([]byte{}, addr.IP...)},
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ResponseWriter{t.socket, addr},
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)
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recordResponseDuration(action, af, err, time.Since(start))
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}()
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}
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}
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// Request represents a UDP payload received by a Tracker.
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type Request struct {
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Packet []byte
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IP net.IP
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}
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// ResponseWriter implements the ability to respond to a Request via the
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// io.Writer interface.
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type ResponseWriter struct {
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socket *net.UDPConn
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addr *net.UDPAddr
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}
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// Write implements the io.Writer interface for a ResponseWriter.
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func (w ResponseWriter) Write(b []byte) (int, error) {
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w.socket.WriteToUDP(b, w.addr)
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return len(b), nil
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}
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// handleRequest parses and responds to a UDP Request.
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func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string, af *bittorrent.AddressFamily, err error) {
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if len(r.Packet) < 16 {
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// Malformed, no client packets are less than 16 bytes.
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// We explicitly return nothing in case this is a DoS attempt.
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err = errMalformedPacket
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return
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}
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// Parse the headers of the UDP packet.
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connID := r.Packet[0:8]
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actionID := binary.BigEndian.Uint32(r.Packet[8:12])
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txID := r.Packet[12:16]
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// If this isn't requesting a new connection ID and the connection ID is
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// invalid, then fail.
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if actionID != connectActionID && !ValidConnectionID(connID, r.IP, time.Now(), t.MaxClockSkew, t.PrivateKey) {
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err = errBadConnectionID
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WriteError(w, txID, err)
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return
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}
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// Handle the requested action.
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switch actionID {
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case connectActionID:
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actionName = "connect"
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if !bytes.Equal(connID, initialConnectionID) {
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err = errMalformedPacket
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return
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}
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WriteConnectionID(w, txID, NewConnectionID(r.IP, time.Now(), t.PrivateKey))
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case announceActionID, announceV6ActionID:
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actionName = "announce"
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var req *bittorrent.AnnounceRequest
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req, err = ParseAnnounce(r, t.AllowIPSpoofing, actionID == announceV6ActionID)
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if err != nil {
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WriteError(w, txID, err)
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return
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}
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*af = req.IP.AddressFamily
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var resp *bittorrent.AnnounceResponse
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resp, err = t.logic.HandleAnnounce(context.Background(), req)
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if err != nil {
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WriteError(w, txID, err)
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return
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}
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WriteAnnounce(w, txID, resp, actionID == announceV6ActionID)
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go t.logic.AfterAnnounce(context.Background(), req, resp)
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case scrapeActionID:
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actionName = "scrape"
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var req *bittorrent.ScrapeRequest
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req, err = ParseScrape(r)
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if err != nil {
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WriteError(w, txID, err)
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return
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}
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if r.IP.To4() != nil {
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req.AddressFamily = bittorrent.IPv4
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} else if len(r.IP) == net.IPv6len { // implies r.IP.To4() == nil
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req.AddressFamily = bittorrent.IPv6
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} else {
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log.Errorln("udp: invalid IP: neither v4 nor v6, IP was", r.IP)
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WriteError(w, txID, ErrInvalidIP)
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return
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}
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*af = req.AddressFamily
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var resp *bittorrent.ScrapeResponse
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resp, err = t.logic.HandleScrape(context.Background(), req)
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if err != nil {
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WriteError(w, txID, err)
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return
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}
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WriteScrape(w, txID, resp)
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go t.logic.AfterScrape(context.Background(), req, resp)
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default:
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err = errUnknownAction
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WriteError(w, txID, err)
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}
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return
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}
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