From 75a106bf6c8902bd2707218549213cbefdb89ec1 Mon Sep 17 00:00:00 2001
From: charliec <charliec@zetachain.com>
Date: Mon, 9 Oct 2023 15:24:26 -0500
Subject: [PATCH 1/2] special handling to avoid duplicate payment on bitcoin
 outbound nonce 0

---
 zetaclient/bitcoin_client.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/zetaclient/bitcoin_client.go b/zetaclient/bitcoin_client.go
index 2e8c2fd766..33687a688a 100644
--- a/zetaclient/bitcoin_client.go
+++ b/zetaclient/bitcoin_client.go
@@ -348,6 +348,15 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 		if !broadcasted {
 			return false, false, nil
 		}
+		// If the broadcasted outTx is nonce 0, just wait for inclusion and don't schedule more keysign
+		// Schedule more than one keysign for nonce 0 can lead to duplicate payments.
+		// One purpose of nonce mark UTXO is to avoid duplicate payment based on the fact that Bitcoin
+		// prevents double spending of same UTXO. However, for nonce 0, we don't have a prior nonce (e.g., -1)
+		// for the signer to check against when making the payment. Signer treats nonce 0 as a special case in downstream code.
+		if nonce == 0 {
+			return true, false, nil
+		}
+
 		// Get original cctx parameters
 		params, err := ob.GetPendingCctxParams(nonce)
 		if err != nil {

From 62a367e14f69278c8b13acb922556cba31c85985 Mon Sep 17 00:00:00 2001
From: charliec <charliec@zetachain.com>
Date: Mon, 9 Oct 2023 18:15:38 -0500
Subject: [PATCH 2/2] use cctx amount instead of txResult's amount because it's
 not available in bitcoin mainnet

---
 zetaclient/bitcoin_client.go | 30 ++++++++++--------------------
 1 file changed, 10 insertions(+), 20 deletions(-)

diff --git a/zetaclient/bitcoin_client.go b/zetaclient/bitcoin_client.go
index 33687a688a..166c968c8b 100644
--- a/zetaclient/bitcoin_client.go
+++ b/zetaclient/bitcoin_client.go
@@ -344,6 +344,13 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 	res, included := ob.includedTxResults[outTxID]
 	ob.mu.Unlock()
 
+	// Get original cctx parameters
+	params, err := ob.GetPendingCctxParams(nonce)
+	if err != nil {
+		ob.logger.ObserveOutTx.Info().Msgf("IsSendOutTxProcessed: can't find pending cctx for nonce %d", nonce)
+		return false, false, err
+	}
+
 	if !included {
 		if !broadcasted {
 			return false, false, nil
@@ -357,13 +364,6 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 			return true, false, nil
 		}
 
-		// Get original cctx parameters
-		params, err := ob.GetPendingCctxParams(nonce)
-		if err != nil {
-			ob.logger.ObserveOutTx.Info().Msgf("IsSendOutTxProcessed: can't find pending cctx for nonce %d", nonce)
-			return false, false, nil
-		}
-
 		// Try including this outTx broadcasted by myself
 		inMempool, err := ob.checkNSaveIncludedTx(txnHash, params)
 		if err != nil {
@@ -385,23 +385,13 @@ func (ob *BitcoinChainClient) IsSendOutTxProcessed(sendHash string, nonce uint64
 		ob.logger.ObserveOutTx.Info().Msgf("IsSendOutTxProcessed: checkNSaveIncludedTx succeeded for outTx %s", outTxID)
 	}
 
-	var amount float64
-	if res.Amount > 0 {
-		ob.logger.ObserveOutTx.Warn().Msg("IsSendOutTxProcessed: res.Amount > 0")
-		amount = res.Amount
-	} else if res.Amount == 0 {
-		ob.logger.ObserveOutTx.Error().Msg("IsSendOutTxProcessed: res.Amount == 0")
-		return false, false, nil
-	} else {
-		amount = -res.Amount
-	}
-
-	amountInSat, _ := big.NewFloat(amount * 1e8).Int(nil)
+	// It's safe to use cctx's amount to post confirmation because it has already been verified in observeOutTx()
+	amountInSat := params.Amount.BigInt()
 	if res.Confirmations < ob.ConfirmationsThreshold(amountInSat) {
 		return true, false, nil
 	}
 
-	logger.Debug().Msgf("Bitcoin outTx confirmed: txid %s, amount %f\n", res.TxID, res.Amount)
+	logger.Debug().Msgf("Bitcoin outTx confirmed: txid %s, amount %s\n", res.TxID, amountInSat.String())
 	zetaHash, err := ob.zetaClient.PostReceiveConfirmation(
 		sendHash,
 		res.TxID,