121 lines
3.3 KiB
Go
121 lines
3.3 KiB
Go
// Copyright 2016 The Chihaya Authors. All rights reserved.
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// Use of this source code is governed by the BSD 2-Clause license,
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// which can be found in the LICENSE file.
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package deniability
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import (
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"errors"
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"math/rand"
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"time"
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"github.com/chihaya/chihaya"
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"github.com/chihaya/chihaya/pkg/random"
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"github.com/chihaya/chihaya/tracker"
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)
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func init() {
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tracker.RegisterAnnounceMiddlewareConstructor("deniability", constructor)
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}
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type deniabilityMiddleware struct {
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cfg *Config
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r *rand.Rand
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}
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// constructor provides a middleware constructor that returns a middleware to
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// insert peers into the peer lists returned as a response to an announce.
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//
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// It returns an error if the config provided is either syntactically or
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// semantically incorrect.
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func constructor(c chihaya.MiddlewareConfig) (tracker.AnnounceMiddleware, error) {
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cfg, err := newConfig(c)
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if err != nil {
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return nil, err
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}
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if cfg.ModifyResponseProbability <= 0 || cfg.ModifyResponseProbability > 1 {
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return nil, errors.New("modify_response_probability must be in [0,1)")
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}
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if cfg.MaxRandomPeers <= 0 {
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return nil, errors.New("max_random_peers must be > 0")
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}
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if cfg.MinPort <= 0 {
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return nil, errors.New("min_port must not be <= 0")
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}
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if cfg.MaxPort > 65536 {
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return nil, errors.New("max_port must not be > 65536")
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}
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if cfg.MinPort >= cfg.MaxPort {
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return nil, errors.New("max_port must not be <= min_port")
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}
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if len(cfg.Prefix) > 20 {
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return nil, errors.New("prefix must not be longer than 20 bytes")
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}
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mw := deniabilityMiddleware{
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cfg: cfg,
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r: rand.New(rand.NewSource(time.Now().UnixNano())),
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}
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return mw.modifyResponse, nil
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}
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func (mw *deniabilityMiddleware) modifyResponse(next tracker.AnnounceHandler) tracker.AnnounceHandler {
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return func(cfg *chihaya.TrackerConfig, req *chihaya.AnnounceRequest, resp *chihaya.AnnounceResponse) error {
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err := next(cfg, req, resp)
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if err != nil {
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return err
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}
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if mw.cfg.ModifyResponseProbability == 1 || mw.r.Float32() < mw.cfg.ModifyResponseProbability {
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numNewPeers := mw.r.Intn(mw.cfg.MaxRandomPeers) + 1
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for i := 0; i < numNewPeers; i++ {
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if len(resp.IPv6Peers) > 0 {
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if len(resp.IPv6Peers) >= int(req.NumWant) {
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mw.replacePeer(resp.IPv6Peers, true)
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} else {
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resp.IPv6Peers = mw.insertPeer(resp.IPv6Peers, true)
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}
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}
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if len(resp.IPv4Peers) > 0 {
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if len(resp.IPv4Peers) >= int(req.NumWant) {
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mw.replacePeer(resp.IPv4Peers, false)
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} else {
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resp.IPv4Peers = mw.insertPeer(resp.IPv4Peers, false)
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}
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}
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}
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}
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return nil
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}
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}
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// replacePeer replaces a peer from a random position within the given slice
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// of peers with a randomly generated one.
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//
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// replacePeer panics if len(peers) == 0.
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func (mw *deniabilityMiddleware) replacePeer(peers []chihaya.Peer, v6 bool) {
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peers[mw.r.Intn(len(peers))] = random.Peer(mw.r, mw.cfg.Prefix, v6, mw.cfg.MinPort, mw.cfg.MaxPort)
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}
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// insertPeer inserts a randomly generated peer at a random position into the
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// given slice and returns the new slice.
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func (mw *deniabilityMiddleware) insertPeer(peers []chihaya.Peer, v6 bool) []chihaya.Peer {
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pos := 0
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if len(peers) > 0 {
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pos = mw.r.Intn(len(peers))
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}
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peers = append(peers, chihaya.Peer{})
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copy(peers[pos+1:], peers[pos:])
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peers[pos] = random.Peer(mw.r, mw.cfg.Prefix, v6, mw.cfg.MinPort, mw.cfg.MaxPort)
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return peers
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}
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