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replay.go
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replay.go
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/*
* Copyright (c) 2020, Psiphon Inc.
* All rights reserved.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package server
import (
"fmt"
"sync"
"time"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/errors"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/parameters"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/prng"
lrucache "github.com/cognusion/go-cache-lru"
)
const (
REPLAY_CACHE_MAX_ENTRIES = 100000
REPLAY_CACHE_CLEANUP_INTERVAL = 1 * time.Minute
)
// ReplayCache is a cache of recently used and successful network obfuscation
// parameters that may be replayed -- reused -- for subsequent tunnel
// connections.
//
// Server-side replay is analogous to client-side replay, with one key
// difference: server-side replay can be applied across multiple clients in
// the same GeoIP scope.
//
// Replay is enabled with tactics, and tactics determine the tunnel quality
// targets for establishing and clearing replay parameters.
//
// ReplayCache has a maximum capacity with an LRU strategy to cap memory
// overhead.
type ReplayCache struct {
support *SupportServices
cacheMutex sync.Mutex
cache *lrucache.Cache
metrics *replayCacheMetrics
}
type replayCacheMetrics struct {
MaxCacheEntries int64
SetReplayCount int64
GetReplayHitCount int64
GetReplayMissCount int64
FailedReplayCount int64
DeleteReplayCount int64
}
type replayParameters struct {
replayPacketManipulation bool
packetManipulationSpecName string
replayFragmentor bool
fragmentorSeed *prng.Seed
failedCount int
}
// NewReplayCache creates a new ReplayCache.
func NewReplayCache(support *SupportServices) *ReplayCache {
return &ReplayCache{
support: support,
cache: lrucache.NewWithLRU(
0, REPLAY_CACHE_CLEANUP_INTERVAL, REPLAY_CACHE_MAX_ENTRIES),
metrics: &replayCacheMetrics{},
}
}
// Flush clears all entries in the ReplayCache. Flush should be called when
// tactics hot reload and change to clear any cached replay parameters that
// may be based on stale tactics.
func (r *ReplayCache) Flush() {
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
r.cache.Flush()
}
// GetMetrics returns a snapshop of current ReplayCache event counters and
// resets all counters to zero.
func (r *ReplayCache) GetMetrics() LogFields {
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
logFields := LogFields{
"replay_max_cache_entries": r.metrics.MaxCacheEntries,
"replay_set_replay_count": r.metrics.SetReplayCount,
"replay_get_replay_hit_count": r.metrics.GetReplayHitCount,
"replay_get_replay_miss_count": r.metrics.GetReplayMissCount,
"replay_failed_replay_count": r.metrics.FailedReplayCount,
"replay_delete_replay_count": r.metrics.DeleteReplayCount,
}
r.metrics = &replayCacheMetrics{}
return logFields
}
// GetReplayTargetDuration returns the tactics replay target tunnel duration
// for the specified GeoIP data. Tunnels which are active for the specified
// duration are candidates for setting or extending replay parameters. Wait
// for the returned wait duration before evaluating the tunnel duration. Once
// this target is met, call SetReplayParameters, which will check additional
// targets and conditionally set replay parameters.
func (r *ReplayCache) GetReplayTargetDuration(
geoIPData GeoIPData) (bool, time.Duration, time.Duration) {
p, err := r.support.ServerTacticsParametersCache.Get(geoIPData)
if err != nil {
log.WithTraceFields(LogFields{"error": errors.Trace(err)}).Warning(
"ServerTacticsParametersCache.Get failed")
return false, 0, 0
}
if p.IsNil() {
// No tactics are configured; replay is disabled.
return false, 0, 0
}
if !p.Bool(parameters.ServerReplayUnknownGeoIP) &&
geoIPData.Country == GEOIP_UNKNOWN_VALUE &&
geoIPData.ISP == GEOIP_UNKNOWN_VALUE {
// Unless configured otherwise, skip replay for unknown GeoIP, since clients
// may not have equivilent network conditions.
return false, 0, 0
}
TTL := p.Duration(parameters.ServerReplayTTL)
if TTL == 0 {
// Server replay is disabled when TTL is 0.
return false, 0, 0
}
return true,
p.Duration(parameters.ServerReplayTargetWaitDuration),
p.Duration(parameters.ServerReplayTargetTunnelDuration)
}
// SetReplayParameters sets replay parameters, packetManipulationSpecName and
// fragmentorSeed, for the specified tunnel protocol and GeoIP scope.
// Once set, replay parameters are active for a tactics-configurable TTL.
//
// The specified tunneledBytesUp/Down must meet tactics replay bytes
// transferred targets. SetReplayParameters should be called only after first
// calling ReplayTargetDuration and ensuring the tunnel meets the active
// tunnel duration target. When cached replay parameters exist, their TTL is
// extended and any failure counts are reset to zero.
//
// SetReplayParameters must be called only once per tunnel. Extending replay
// parameters TTL should only be done only immediately after a successful
// tunnel dial and target achievement, as this is the part of a tunnel
// lifecycle at highest risk of blocking.
//
// The value pointed to by fragmentorSeed must not be mutated after calling
// SetReplayParameters.
func (r *ReplayCache) SetReplayParameters(
tunnelProtocol string,
geoIPData GeoIPData,
packetManipulationSpecName string,
fragmentorSeed *prng.Seed,
tunneledBytesUp int64,
tunneledBytesDown int64) {
p, err := r.support.ServerTacticsParametersCache.Get(geoIPData)
if err != nil {
log.WithTraceFields(LogFields{"error": errors.Trace(err)}).Warning(
"ServerTacticsParametersCache.Get failed")
return
}
if p.IsNil() {
// No tactics are configured; replay is disabled.
return
}
TTL := p.Duration(parameters.ServerReplayTTL)
if TTL == 0 {
return
}
targetUpstreamBytes := p.Int(parameters.ServerReplayTargetUpstreamBytes)
targetDownstreamBytes := p.Int(parameters.ServerReplayTargetDownstreamBytes)
if tunneledBytesUp < int64(targetUpstreamBytes) {
return
}
if tunneledBytesDown < int64(targetDownstreamBytes) {
return
}
key := r.makeKey(tunnelProtocol, geoIPData)
value := &replayParameters{}
if p.Bool(parameters.ServerReplayPacketManipulation) {
value.replayPacketManipulation = true
value.packetManipulationSpecName = packetManipulationSpecName
}
if p.Bool(parameters.ServerReplayFragmentor) {
value.replayFragmentor = (fragmentorSeed != nil)
value.fragmentorSeed = fragmentorSeed
}
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
r.cache.Add(key, value, TTL)
// go-cache-lru is typically safe for concurrent access but explicit
// synchronization is required when accessing Items. Items may include
// entries that are expired but not yet purged.
cacheSize := int64(len(r.cache.Items()))
if cacheSize > r.metrics.MaxCacheEntries {
r.metrics.MaxCacheEntries = cacheSize
}
r.metrics.SetReplayCount += 1
}
// GetReplayPacketManipulation returns an active replay packet manipulation
// spec for the specified tunnel protocol and GeoIP scope.
//
// While Flush should be called to clear parameters based on stale tactics,
// it's still possible for GetReplayPacketManipulation to return a spec name
// that's no longer in the current list of known specs.
func (r *ReplayCache) GetReplayPacketManipulation(
tunnelProtocol string,
geoIPData GeoIPData) (string, bool) {
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
parameters, ok := r.getReplayParameters(
tunnelProtocol, geoIPData)
if !ok {
return "", false
}
if !parameters.replayPacketManipulation {
return "", false
}
return parameters.packetManipulationSpecName, true
}
// GetReplayFragmentor returns an active replay fragmentor seed for the
// specified tunnel protocol and GeoIP scope.
func (r *ReplayCache) GetReplayFragmentor(
tunnelProtocol string,
geoIPData GeoIPData) (*prng.Seed, bool) {
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
parameters, ok := r.getReplayParameters(
tunnelProtocol, geoIPData)
if !ok {
return nil, false
}
if !parameters.replayFragmentor {
return nil, false
}
return parameters.fragmentorSeed, true
}
func (r *ReplayCache) getReplayParameters(
tunnelProtocol string,
geoIPData GeoIPData) (*replayParameters, bool) {
key := r.makeKey(tunnelProtocol, geoIPData)
value, ok := r.cache.Get(key)
if !ok {
r.metrics.GetReplayMissCount += 1
return nil, false
}
r.metrics.GetReplayHitCount += 1
parameters, ok := value.(*replayParameters)
return parameters, ok
}
// FailedReplayParameters increments the count of tunnels which failed to
// complete any liveness test and API handshake after using replay parameters.
// Once a failure threshold is reached, cached replay parameters are cleared.
// Call this function for tunnels which meet the failure criteria.
func (r *ReplayCache) FailedReplayParameters(
tunnelProtocol string,
geoIPData GeoIPData,
packetManipulationSpecName string,
fragmentorSeed *prng.Seed) {
p, err := r.support.ServerTacticsParametersCache.Get(geoIPData)
if err != nil {
log.WithTraceFields(LogFields{"error": errors.Trace(err)}).Warning(
"ServerTacticsParametersCache.Get failed")
return
}
thresholdFailedCount := p.Int(parameters.ServerReplayFailedCountThreshold)
key := r.makeKey(tunnelProtocol, geoIPData)
r.cacheMutex.Lock()
defer r.cacheMutex.Unlock()
parameters, ok := r.getReplayParameters(tunnelProtocol, geoIPData)
if !ok {
return
}
// Do not count the failure if the replay values for the tunnel protocol and
// GeoIP scope are now different; these parameters now reflect a newer,
// successful tunnel.
if (parameters.replayPacketManipulation &&
parameters.packetManipulationSpecName != packetManipulationSpecName) ||
(parameters.replayFragmentor &&
(fragmentorSeed == nil ||
*parameters.fragmentorSeed != *fragmentorSeed)) {
return
}
parameters.failedCount += 1
r.metrics.FailedReplayCount += 1
if thresholdFailedCount == 0 {
// No failure limit; the entry will not be deleted.
return
}
if parameters.failedCount >= thresholdFailedCount {
r.cache.Delete(key)
r.metrics.DeleteReplayCount += 1
}
}
func (r *ReplayCache) makeKey(
tunnelProtocol string, geoIPData GeoIPData) string {
return fmt.Sprintf(
"%s-%s-%s",
tunnelProtocol, geoIPData.Country, geoIPData.ISP)
}