From 94168c3fe521cabdcaee6d693e872dd40925bf41 Mon Sep 17 00:00:00 2001
From: Slyghtning <hieblmi@protonmail.com>
Date: Thu, 17 Jul 2025 15:08:11 +0200
Subject: [PATCH] utils: function to get dust limit for a pkscript.

---
 utils/dust_limit.go      | 15 +++++++++++++++
 utils/dust_limit_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 utils/dust_limit.go
 create mode 100644 utils/dust_limit_test.go

diff --git a/utils/dust_limit.go b/utils/dust_limit.go
new file mode 100644
index 00000000..ba9b567a
--- /dev/null
+++ b/utils/dust_limit.go
@@ -0,0 +1,15 @@
+package utils
+
+import (
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/mempool"
+	"github.com/btcsuite/btcd/wire"
+)
+
+// DustLimitForPkScript returns the dust limit for a given pkScript. An output
+// must be greater or equal to this value.
+func DustLimitForPkScript(pkscript []byte) btcutil.Amount {
+	return btcutil.Amount(mempool.GetDustThreshold(&wire.TxOut{
+		PkScript: pkscript,
+	}))
+}
diff --git a/utils/dust_limit_test.go b/utils/dust_limit_test.go
new file mode 100644
index 00000000..be6d84bb
--- /dev/null
+++ b/utils/dust_limit_test.go
@@ -0,0 +1,32 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/stretchr/testify/require"
+)
+
+type pkScriptGetter func([]byte) ([]byte, error)
+
+// TestDustLimitForPkScript checks that the dust limit for a given script size
+// matches the calculation in lnwallet.DustLimitForSize.
+func TestDustLimitForPkScript(t *testing.T) {
+	getScripts := map[int]pkScriptGetter{
+		input.P2WPKHSize: input.WitnessPubKeyHash,
+		input.P2WSHSize:  input.WitnessScriptHash,
+		input.P2SHSize:   input.GenerateP2SH,
+		input.P2PKHSize:  input.GenerateP2PKH,
+	}
+
+	for scriptSize, getPkScript := range getScripts {
+		pkScript, err := getPkScript([]byte{})
+		require.NoError(t, err, "failed to generate pkScript")
+
+		require.Equal(
+			t, lnwallet.DustLimitForSize(scriptSize),
+			DustLimitForPkScript(pkScript),
+		)
+	}
+}