Merge pull request #1908 from livepeer/nv/low-tickets

pm: low ticket facevalue safeguard

CHANGELOG_PENDING.md

@@ -12,6 +12,7 @@
 - \#1879 Add mp4 download of recorded stream (@darkdarkdragon)
 - \#1899 Record million pixels processed metric (@yondonfu)
 - \#1888 Should not save (when recording) segments with zero video frames (@darkdarkdragon)
+- \#1908 Prevent Broadcaster from sending low face value PM tickets (@kyriediculous)
 
 #### Orchestrator
 

core/orch_test.go

@@ -1251,7 +1251,7 @@ func TestSufficientBalance_IsSufficient_ReturnsTrue(t *testing.T) {
 
 	err := orch.ProcessPayment(payment, manifestID)
 	assert.Nil(err)
-	recipient.On("EV").Return(big.NewRat(100, 1))
+	recipient.On("EV").Return(big.NewRat(100, 100))
 	assert.True(orch.SufficientBalance(ethcommon.BytesToAddress(payment.Sender), manifestID))
 }
 

pm/recipient.go

@@ -24,6 +24,8 @@ var maxWinProb = new(big.Int).Sub(new(big.Int).Lsh(big.NewInt(1), 256), big.NewI
 var paramsExpirationBlock = big.NewInt(10)
 var paramsExpiryBuffer = int64(1)
 
+var evMultiplier = big.NewInt(100)
+
 // Recipient is an interface which describes an object capable
 // of receiving tickets
 type Recipient interface {
@@ -229,14 +231,8 @@ func (r *recipient) faceValue(sender ethcommon.Address) (*big.Int, error) {
 	// faceValue = txCost * txCostMultiplier
 	faceValue := new(big.Int).Mul(r.txCost(), big.NewInt(int64(r.cfg.TxCostMultiplier)))
 
-	// TODO: Consider setting faceValue to some value higher than
-	// EV in this case where the default faceValue < the desired EV.
-	// At the moment, for simplicity we just adjust faceValue to the
-	// desired EV in this case (which would result in winProb = 100%).
-	// In practice, EV should be smaller than the default faceValue
-	// so this shouldn't be a problem in most cases
 	if faceValue.Cmp(r.cfg.EV) < 0 {
-		faceValue = r.cfg.EV
+		faceValue = new(big.Int).Mul(r.cfg.EV, evMultiplier)
 	}
 
 	// Fetch current max float for sender

pm/recipient_test.go

@@ -528,9 +528,9 @@ func TestTicketParams(t *testing.T) {
 	params5, err := r.TicketParams(sender, big.NewRat(1, 1))
 	require.Nil(err)
 
-	assert.Equal(cfg.EV, params5.FaceValue)
-	assert.Equal(maxWinProb, params5.WinProb)
-
+	assert.Equal(new(big.Int).Mul(cfg.EV, evMultiplier), params5.FaceValue)
+	expWinProb := calcWinProb(params5.FaceValue, cfg.EV)
+	assert.Equal(expWinProb, params5.WinProb)
 	// Test default faceValue < EV and maxFloat < EV
 	sm.maxFloat = big.NewInt(0) // Set maxFloat to some value less than EV
 
@@ -675,3 +675,22 @@ func TestSenderNoncesCleanupLoop(t *testing.T) {
 	time.Sleep(20 * time.Millisecond)
 	assert.True(tm.blockNumSub.(*stubSubscription).unsubscribed)
 }
+
+func calcWinProb(faceValue, EV *big.Int) *big.Int {
+	// Return 0 if faceValue happens to be 0
+	if faceValue.Cmp(big.NewInt(0)) == 0 {
+		return big.NewInt(0)
+	}
+	// Return maxWinProb if faceValue = EV
+	if faceValue.Cmp(EV) == 0 {
+		return maxWinProb
+	}
+
+	m := new(big.Int)
+	x, m := new(big.Int).DivMod(maxWinProb, faceValue, m)
+	if m.Int64() != 0 {
+		return new(big.Int).Mul(EV, x.Add(x, big.NewInt(1)))
+	}
+	// Compute winProb as the numerator of a fraction over maxWinProb
+	return new(big.Int).Mul(EV, x)
+}

pm/sender.go

@@ -166,6 +166,10 @@ func (s *sender) validateTicketParams(ticketParams *TicketParams, numTickets int
 		return nil
 	}
 
+	if ev.Cmp(new(big.Rat).SetInt(ticketParams.FaceValue)) >= 0 {
+		return fmt.Errorf("ticket faceValue too low faceValue=%v", ticketParams.FaceValue)
+	}
+
 	info, err := s.senderManager.GetSenderInfo(s.signer.Account().Address)
 	if err != nil {
 		return err

pm/sender_test.go

@@ -187,7 +187,7 @@ func TestCreateTicketBatch_GetSenderInfoError_ReturnsError(t *testing.T) {
 func TestCreateTicketBatch_EVTooHigh_ReturnsError(t *testing.T) {
 	// Test single ticket EV too high
 	sender := defaultSender(t)
-	sender.maxEV = big.NewRat(100, 1)
+	sender.maxEV = big.NewRat(1, 1)
 
 	ticketParams := defaultTicketParams(t, RandAddress())
 	ticketParams.FaceValue = big.NewInt(202)
@@ -199,7 +199,7 @@ func TestCreateTicketBatch_EVTooHigh_ReturnsError(t *testing.T) {
 	assert.EqualError(t, err, expErrStr)
 
 	// Test multiple tickets EV too high
-	sender.maxEV = big.NewRat(102, 1)
+	sender.maxEV = big.NewRat(200, 1)
 
 	expErrStr = maxEVErrStr(ev.Mul(ev, new(big.Rat).SetInt64(2)), 2, sender.maxEV)
 	_, err = sender.CreateTicketBatch(sessionID, 2)
@@ -449,7 +449,7 @@ func TestValidateParams_ValidateSender(t *testing.T) {
 
 func TestValidateTicketParams_EVTooHigh_ReturnsError(t *testing.T) {
 	sender := defaultSender(t)
-	sender.maxEV = big.NewRat(100, 1)
+	sender.maxEV = big.NewRat(1, 1)
 
 	ticketParams := &TicketParams{
 		FaceValue:       big.NewInt(202),
@@ -490,6 +490,22 @@ func TestValidateTicketParams_FaceValueTooHigh_ReturnsError(t *testing.T) {
 	assert.EqualError(err, expErrStr)
 }
 
+func TestValidateTicketParams_FaceValueTooLow_ReturnsErr(t *testing.T) {
+	oldEVMul := evMultiplier
+	evMultiplier = big.NewInt(1)
+	sender := defaultSender(t)
+	sender.maxEV = big.NewRat(1000, 1)
+
+	ticketParams := &TicketParams{
+		FaceValue:       big.NewInt(1000),
+		WinProb:         maxWinProb,
+		ExpirationBlock: big.NewInt(100),
+	}
+	err := sender.ValidateTicketParams(ticketParams)
+	assert.EqualError(t, err, fmt.Sprintf("ticket faceValue too low faceValue=%v", ticketParams.FaceValue))
+	evMultiplier = oldEVMul
+}
+
 func TestValidateTicketParams_ExpiredParams_ReturnsError(t *testing.T) {
 	sender := defaultSender(t)
 	senderAddr := sender.signer.Account().Address