+++ /dev/null
-// Copyright (c) 2016 The btcsuite developers
-// Use of this source code is governed by an ISC
-// license that can be found in the LICENSE file.
-
-package connmgr
-
-import (
- "fmt"
- "math"
- "sync"
- "time"
-)
-
-const (
- // Halflife defines the time (in seconds) by which the transient part
- // of the ban score decays to one half of it's original value.
- Halflife = 60
-
- // lambda is the decaying constant.
- lambda = math.Ln2 / Halflife
-
- // Lifetime defines the maximum age of the transient part of the ban
- // score to be considered a non-zero score (in seconds).
- Lifetime = 1800
-
- // precomputedLen defines the amount of decay factors (one per second) that
- // should be precomputed at initialization.
- precomputedLen = 64
-)
-
-// precomputedFactor stores precomputed exponential decay factors for the first
-// 'precomputedLen' seconds starting from t == 0.
-var precomputedFactor [precomputedLen]float64
-
-// init precomputes decay factors.
-func init() {
- for i := range precomputedFactor {
- precomputedFactor[i] = math.Exp(-1.0 * float64(i) * lambda)
- }
-}
-
-// decayFactor returns the decay factor at t seconds, using precalculated values
-// if available, or calculating the factor if needed.
-func decayFactor(t int64) float64 {
- if t < precomputedLen {
- return precomputedFactor[t]
- }
- return math.Exp(-1.0 * float64(t) * lambda)
-}
-
-// DynamicBanScore provides dynamic ban scores consisting of a persistent and a
-// decaying component. The persistent score could be utilized to create simple
-// additive banning policies similar to those found in other bitcoin node
-// implementations.
-//
-// The decaying score enables the creation of evasive logic which handles
-// misbehaving peers (especially application layer DoS attacks) gracefully
-// by disconnecting and banning peers attempting various kinds of flooding.
-// DynamicBanScore allows these two approaches to be used in tandem.
-//
-// Zero value: Values of type DynamicBanScore are immediately ready for use upon
-// declaration.
-type DynamicBanScore struct {
- lastUnix int64
- transient float64
- persistent uint32
- mtx sync.Mutex
-}
-
-// String returns the ban score as a human-readable string.
-func (s *DynamicBanScore) String() string {
- s.mtx.Lock()
- r := fmt.Sprintf("persistent %v + transient %v at %v = %v as of now",
- s.persistent, s.transient, s.lastUnix, s.Int())
- s.mtx.Unlock()
- return r
-}
-
-// Int returns the current ban score, the sum of the persistent and decaying
-// scores.
-//
-// This function is safe for concurrent access.
-func (s *DynamicBanScore) Int() uint32 {
- s.mtx.Lock()
- r := s.int(time.Now())
- s.mtx.Unlock()
- return r
-}
-
-// Increase increases both the persistent and decaying scores by the values
-// passed as parameters. The resulting score is returned.
-//
-// This function is safe for concurrent access.
-func (s *DynamicBanScore) Increase(persistent, transient uint32) uint32 {
- s.mtx.Lock()
- r := s.increase(persistent, transient, time.Now())
- s.mtx.Unlock()
- return r
-}
-
-// Reset set both persistent and decaying scores to zero.
-//
-// This function is safe for concurrent access.
-func (s *DynamicBanScore) Reset() {
- s.mtx.Lock()
- s.persistent = 0
- s.transient = 0
- s.lastUnix = 0
- s.mtx.Unlock()
-}
-
-// int returns the ban score, the sum of the persistent and decaying scores at a
-// given point in time.
-//
-// This function is not safe for concurrent access. It is intended to be used
-// internally and during testing.
-func (s *DynamicBanScore) int(t time.Time) uint32 {
- dt := t.Unix() - s.lastUnix
- if s.transient < 1 || dt < 0 || Lifetime < dt {
- return s.persistent
- }
- return s.persistent + uint32(s.transient*decayFactor(dt))
-}
-
-// increase increases the persistent, the decaying or both scores by the values
-// passed as parameters. The resulting score is calculated as if the action was
-// carried out at the point time represented by the third parameter. The
-// resulting score is returned.
-//
-// This function is not safe for concurrent access.
-func (s *DynamicBanScore) increase(persistent, transient uint32, t time.Time) uint32 {
- s.persistent += persistent
- tu := t.Unix()
- dt := tu - s.lastUnix
-
- if transient > 0 {
- if Lifetime < dt {
- s.transient = 0
- } else if s.transient > 1 && dt > 0 {
- s.transient *= decayFactor(dt)
- }
- s.transient += float64(transient)
- s.lastUnix = tu
- }
- return s.persistent + uint32(s.transient)
-}
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