pkg/xorshift: rebuild to use stack only

middleware/pkg/random/entropy.go

@@ -0,0 +1,17 @@
+package random
+
+import (
+	"encoding/binary"
+
+	"github.com/chihaya/chihaya/bittorrent"
+)
+
+// DeriveEntropyFromRequest generates 2*64 bits of pseudo random state from an
+// AnnounceRequest.
+//
+// Calling DeriveEntropyFromRequest multiple times yields the same values.
+func DeriveEntropyFromRequest(req *bittorrent.AnnounceRequest) (uint64, uint64) {
+	v0 := binary.BigEndian.Uint64([]byte(req.InfoHash[:8])) + binary.BigEndian.Uint64([]byte(req.InfoHash[8:16]))
+	v1 := binary.BigEndian.Uint64([]byte(req.Peer.ID[:8])) + binary.BigEndian.Uint64([]byte(req.Peer.ID[8:16]))
+	return v0, v1
+}

middleware/pkg/random/xorshift.go

@@ -0,0 +1,28 @@
+// Package random implements the XORShift PRNG and a way to derive random state
+// from an AnnounceRequest.
+package random
+
+// GenerateAndAdvance applies XORShift128Plus on s0 and s1, returning
+// the new states newS0, newS1 and a pseudo-random number v.
+func GenerateAndAdvance(s0, s1 uint64) (v, newS0, newS1 uint64) {
+	v = s0 + s1
+	newS0 = s1
+	s0 ^= (s0 << 23)
+	newS1 = s0 ^ s1 ^ (s0 >> 18) ^ (s1 >> 5)
+	return
+}
+
+// Intn generates an int k that satisfies k >= 0 && k < n.
+// n must be > 0.
+// It returns the generated k and the new state of the generator.
+func Intn(s0, s1 uint64, n int) (int, uint64, uint64) {
+	if n <= 0 {
+		panic("invalid n <= 0")
+	}
+	v, newS0, newS1 := GenerateAndAdvance(s0, s1)
+	k := int(v)
+	if k < 0 {
+		k = -k
+	}
+	return k % n, newS0, newS1
+}

middleware/pkg/random/xorshift_test.go

@@ -0,0 +1,38 @@
+package random
+
+import (
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIntn(t *testing.T) {
+	rand.Seed(time.Now().UnixNano())
+	s0, s1 := rand.Uint64(), rand.Uint64()
+	var k int
+	for i := 0; i < 10000; i++ {
+		k, s0, s1 = Intn(s0, s1, 10)
+		require.True(t, k >= 0, "Intn() must be >= 0")
+		require.True(t, k < 10, "Intn(k) must be < k")
+	}
+}
+
+func BenchmarkAdvanceXORShift128Plus(b *testing.B) {
+	s0, s1 := rand.Uint64(), rand.Uint64()
+	var v uint64
+	for i := 0; i < b.N; i++ {
+		v, s0, s1 = GenerateAndAdvance(s0, s1)
+	}
+	_, _, _ = v, s0, s1
+}
+
+func BenchmarkIntn(b *testing.B) {
+	s0, s1 := rand.Uint64(), rand.Uint64()
+	var v int
+	for i := 0; i < b.N; i++ {
+		v, s0, s1 = Intn(s0, s1, 1000)
+	}
+	_, _, _ = v, s0, s1
+}

middleware/varinterval/varinterval.go

@@ -3,13 +3,12 @@ package varinterval
 import (
 	"context"
 	"errors"
-	"math/rand"
 	"sync"
 	"time"
 
 	"github.com/chihaya/chihaya/bittorrent"
 	"github.com/chihaya/chihaya/middleware"
-	"github.com/chihaya/chihaya/pkg/xorshift"
+	"github.com/chihaya/chihaya/middleware/pkg/random"
 )
 
 // ErrInvalidModifyResponseProbability is returned for a config with an invalid
@@ -48,7 +47,6 @@ func checkConfig(cfg Config) error {
 
 type hook struct {
 	cfg Config
-	pr  [1024]*xorshift.LockedXORShift128Plus
 	sync.Mutex
 }
 
@@ -62,23 +60,19 @@ func New(cfg Config) (middleware.Hook, error) {
 
 	h := &hook{
 		cfg: cfg,
-		pr:  [1024]*xorshift.LockedXORShift128Plus{},
-	}
-	for i := range h.pr {
-		h.pr[i] = xorshift.NewLockedXORShift128Plus(rand.Uint64(), rand.Uint64())
 	}
 	return h, nil
 }
 
-func (h *hook) getXORShiftByInfohash(ih *bittorrent.InfoHash) *xorshift.LockedXORShift128Plus {
-	return h.pr[(int(ih[1])|int(ih[0])<<8)%len(h.pr)]
-}
-
 func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) (context.Context, error) {
-	r := h.getXORShiftByInfohash(&req.InfoHash)
+	s0, s1 := random.DeriveEntropyFromRequest(req)
-
+	// Generate a probability p < 1.0.
-	if h.cfg.ModifyResponseProbability == 1 || float32(xorshift.Intn(r, 1<<24))/(1<<24) < h.cfg.ModifyResponseProbability {
+	v, s0, s1 := random.Intn(s0, s1, 1<<24)
-		addSeconds := time.Duration(xorshift.Intn(r, h.cfg.MaxIncreaseDelta)+1) * time.Second
+	p := float32(v) / (1 << 24)
+	if h.cfg.ModifyResponseProbability == 1 || p < h.cfg.ModifyResponseProbability {
+		// Generate the increase delta.
+		v, _, _ = random.Intn(s0, s1, h.cfg.MaxIncreaseDelta)
+		addSeconds := time.Duration(v+1) * time.Second
 
 		resp.Interval += addSeconds
 

pkg/xorshift/xorshift.go

@@ -1,71 +0,0 @@
-// Package xorshift implements the XORShift PRNG.
-package xorshift
-
-import "sync"
-
-// XORShift describes the functionality of an XORShift PRNG.
-type XORShift interface {
-	Next() uint64
-}
-
-// XORShift128Plus holds the state of an XORShift128Plus PRNG.
-type XORShift128Plus struct {
-	state [2]uint64
-}
-
-// Next generates a pseudorandom number and advances the state of s.
-func (s *XORShift128Plus) Next() uint64 {
-	s1 := s.state[0]
-	s0 := s.state[1]
-	s1Tmp := s1 // need this for result computation
-	s.state[0] = s0
-	s1 ^= (s1 << 23)                              // a
-	s.state[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5) // b, c
-	return s0 + s1Tmp
-}
-
-// NewXORShift128Plus creates a new XORShift PRNG.
-func NewXORShift128Plus(s0, s1 uint64) *XORShift128Plus {
-	return &XORShift128Plus{
-		state: [2]uint64{s0, s1},
-	}
-}
-
-// LockedXORShift128Plus is a thread-safe XORShift128Plus.
-type LockedXORShift128Plus struct {
-	sync.Mutex
-	state [2]uint64
-}
-
-// NewLockedXORShift128Plus creates a new LockedXORShift128Plus.
-func NewLockedXORShift128Plus(s0, s1 uint64) *LockedXORShift128Plus {
-	return &LockedXORShift128Plus{
-		state: [2]uint64{s0, s1},
-	}
-}
-
-// Next generates a pseudorandom number and advances the state of s.
-func (s *LockedXORShift128Plus) Next() uint64 {
-	s.Lock()
-	s1 := s.state[0]
-	s0 := s.state[1]
-	s1Tmp := s1 // need this for result computation
-	s.state[0] = s0
-	s1 ^= (s1 << 23)                              // a
-	s.state[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5) // b, c
-	s.Unlock()
-	return s0 + s1Tmp
-}
-
-// Intn generates an int k that satisfies k >= 0 && k < n.
-// n must be > 0.
-func Intn(s XORShift, n int) int {
-	if n <= 0 {
-		panic("invalid n <= 0")
-	}
-	v := int(s.Next())
-	if v < 0 {
-		v = -v
-	}
-	return v % n
-}

pkg/xorshift/xorshift_test.go

@@ -1,46 +0,0 @@
-package xorshift
-
-import (
-	"math/rand"
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestIntn(t *testing.T) {
-	rand.Seed(time.Now().UnixNano())
-	s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
-	for i := 0; i < 10000; i++ {
-		k := Intn(s, 10)
-		require.True(t, k >= 0, "Intn() must be >= 0")
-		require.True(t, k < 10, "Intn(k) must be < k")
-	}
-}
-
-func BenchmarkXORShift128Plus_Next(b *testing.B) {
-	s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
-	var k uint64
-	for i := 0; i < b.N; i++ {
-		k = s.Next()
-	}
-	_ = k
-}
-
-func BenchmarkIntnXORShift128Plus(b *testing.B) {
-	s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
-	var k int
-	for i := 0; i < b.N; i++ {
-		k = Intn(s, 1000)
-	}
-	_ = k
-}
-
-func BenchmarkLockedXORShift128Plus_Next(b *testing.B) {
-	s := NewLockedXORShift128Plus(rand.Uint64(), rand.Uint64())
-	var k uint64
-	for i := 0; i < b.N; i++ {
-		k = s.Next()
-	}
-	_ = k
-}