From 99cda74f6a4aada0b79950466b30a21077461100 Mon Sep 17 00:00:00 2001
From: Oliver Gugger <gugger@gmail.com>
Date: Wed, 27 Apr 2022 21:05:39 +0200
Subject: [PATCH] input: define new signing method constants

---
 input/signdescriptor.go | 62 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/input/signdescriptor.go b/input/signdescriptor.go
index e3ffc5e24..039523108 100644
--- a/input/signdescriptor.go
+++ b/input/signdescriptor.go
@@ -3,6 +3,7 @@ package input
 import (
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
 
 	"github.com/btcsuite/btcd/btcec/v2"
@@ -89,6 +90,67 @@ type SignDescriptor struct {
 	InputIndex int
 }
 
+// SignMethod defines the different ways a signer can sign, given a specific
+// input.
+type SignMethod uint8
+
+const (
+	// WitnessV0SignMethod denotes that a SegWit v0 (p2wkh, np2wkh, p2wsh)
+	// input script should be signed.
+	WitnessV0SignMethod SignMethod = 0
+
+	// TaprootKeySpendBIP0086SignMethod denotes that a SegWit v1 (p2tr)
+	// input should be signed by using the BIP0086 method (commit to
+	// internal key only).
+	TaprootKeySpendBIP0086SignMethod SignMethod = 1
+
+	// TaprootKeySpendSignMethod denotes that a SegWit v1 (p2tr)
+	// input should be signed by using a given taproot hash to commit to in
+	// addition to the internal key.
+	TaprootKeySpendSignMethod SignMethod = 2
+
+	// TaprootScriptSpendSignMethod denotes that a SegWit v1 (p2tr) input
+	// should be spent using the script path and that a specific leaf script
+	// should be signed for.
+	TaprootScriptSpendSignMethod SignMethod = 3
+)
+
+// String returns a human-readable representation of the signing method.
+func (s SignMethod) String() string {
+	switch s {
+	case WitnessV0SignMethod:
+		return "witness_v0"
+	case TaprootKeySpendBIP0086SignMethod:
+		return "taproot_key_spend_bip86"
+	case TaprootKeySpendSignMethod:
+		return "taproot_key_spend"
+	case TaprootScriptSpendSignMethod:
+		return "taproot_script_spend"
+	default:
+		return fmt.Sprintf("unknown<%d>", s)
+	}
+}
+
+// PkScriptCompatible returns true if the given public key script is compatible
+// with the sign method.
+func (s SignMethod) PkScriptCompatible(pkScript []byte) bool {
+	switch s {
+	// SegWit v0 can be p2wkh, np2wkh, p2wsh.
+	case WitnessV0SignMethod:
+		return txscript.IsPayToWitnessPubKeyHash(pkScript) ||
+			txscript.IsPayToWitnessScriptHash(pkScript) ||
+			txscript.IsPayToScriptHash(pkScript)
+
+	case TaprootKeySpendBIP0086SignMethod, TaprootKeySpendSignMethod,
+		TaprootScriptSpendSignMethod:
+
+		return txscript.IsPayToTaproot(pkScript)
+
+	default:
+		return false
+	}
+}
+
 // WriteSignDescriptor serializes a SignDescriptor struct into the passed
 // io.Writer stream.
 //