From c0d13d3fa9fded78d539beab23c4bdc3c235c15c Mon Sep 17 00:00:00 2001
From: Wilmer Paulino <wilmer.paulino@gmail.com>
Date: Wed, 11 Nov 2020 14:09:36 -0800
Subject: [PATCH] account: check dust outputs on account spending transactions

---
 account/manager.go      | 11 +++++++++--
 account/manager_test.go | 24 ++++++++++++++++++------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/account/manager.go b/account/manager.go
index 070b49bf0..59afa85fe 100644
--- a/account/manager.go
+++ b/account/manager.go
@@ -972,7 +972,7 @@ func (m *Manager) DepositAccount(ctx context.Context,
 		return nil, nil, err
 	}
 	if account.State != StateOpen {
-		return nil, nil, fmt.Errorf("account must be in %v to be"+
+		return nil, nil, fmt.Errorf("account must be in %v to be "+
 			"modified", StateOpen)
 	}
 
@@ -1044,7 +1044,7 @@ func (m *Manager) WithdrawAccount(ctx context.Context,
 		return nil, nil, err
 	}
 	if account.State != StateOpen {
-		return nil, nil, fmt.Errorf("account must be in %v to be"+
+		return nil, nil, fmt.Errorf("account must be in %v to be "+
 			"modified", StateOpen)
 	}
 
@@ -1700,6 +1700,13 @@ func sanityCheckAccountSpendTx(tx *wire.MsgTx, account *Account,
 		return err
 	}
 
+	// None of the outputs should be dust.
+	for _, output := range tx.TxOut {
+		if txrules.IsDustOutput(output, txrules.DefaultRelayFeePerKb) {
+			return fmt.Errorf("dust output %x", output.PkScript)
+		}
+	}
+
 	// CheckTransactionSanity doesn't have enough context to attempt fee
 	// calculation, but we do.
 	//
diff --git a/account/manager_test.go b/account/manager_test.go
index e14cfec83..8cf062a02 100644
--- a/account/manager_test.go
+++ b/account/manager_test.go
@@ -857,14 +857,27 @@ func TestAccountWithdrawal(t *testing.T) {
 	defer h.stop()
 
 	const bestHeight = 100
+	const feeRate = chainfee.FeePerKwFloor
+
 	account := h.openAccount(
 		maxAccountValue, bestHeight+maxAccountExpiry, bestHeight,
 	)
 
-	// With our account created, we'll start our withdrawal by creating the
-	// outputs we'll withdraw our funds to. We'll create three outputs, one
-	// of each supported output type. Each output will have 1/4 of the
-	// account's value.
+	// With our account created, we'll start with an invalid withdrawal to a
+	// dust output, which should fail.
+	dustOutput := &wire.TxOut{Value: 0, PkScript: p2wsh}
+	_, _, err := h.manager.WithdrawAccount(
+		context.Background(), account.TraderKey.PubKey,
+		[]*wire.TxOut{dustOutput}, feeRate, bestHeight,
+	)
+	if err == nil || !strings.Contains(err.Error(), "dust output") {
+		t.Fatalf("expected dust output error, got: %v", err)
+	}
+
+	// We'll now attempt a withdrawal that should succeed. We'll start by
+	// creating the outputs we'll withdraw our funds to. We'll create three
+	// outputs, one of each supported output type. Each output will have 1/4
+	// of the account's value.
 	valuePerOutput := account.Value / 4
 	outputs := []*wire.TxOut{
 		{
@@ -884,14 +897,13 @@ func TestAccountWithdrawal(t *testing.T) {
 	// We'll use the lowest fee rate possible, which should yield a
 	// transaction fee of 260 satoshis when taking into account the outputs
 	// we'll be withdrawing to.
-	const feeRate = chainfee.FeePerKwFloor
 	const expectedFee btcutil.Amount = 260
 
 	// Attempt the withdrawal.
 	//
 	// If successful, we'll follow with a series of assertions to ensure it
 	// was performed correctly.
-	_, _, err := h.manager.WithdrawAccount(
+	_, _, err = h.manager.WithdrawAccount(
 		context.Background(), account.TraderKey.PubKey, outputs,
 		feeRate, bestHeight,
 	)