From ded6a70335e79533265b2e5a7c3b8d0541070c0b Mon Sep 17 00:00:00 2001
From: Evgeniy Stratonikov <evgeniy@nspcc.ru>
Date: Fri, 5 Mar 2021 12:22:48 +0300
Subject: [PATCH] vm: add `ParseSignatureContract()`

---
 pkg/vm/contract_checks.go      | 18 +++++++++++++-----
 pkg/vm/contract_checks_test.go |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/pkg/vm/contract_checks.go b/pkg/vm/contract_checks.go
index 00b425032..7a721aa3a 100644
--- a/pkg/vm/contract_checks.go
+++ b/pkg/vm/contract_checks.go
@@ -105,24 +105,32 @@ func ParseMultiSigContract(script []byte) (int, [][]byte, bool) {
 // IsSignatureContract checks whether the passed script is a signature check
 // contract.
 func IsSignatureContract(script []byte) bool {
+	_, ok := ParseSignatureContract(script)
+	return ok
+}
+
+// ParseSignatureContract parses simple signature contract and returns
+// public key.
+func ParseSignatureContract(script []byte) ([]byte, bool) {
 	if len(script) != 41 {
-		return false
+		return nil, false
 	}
 
 	ctx := NewContext(script)
 	instr, param, err := ctx.Next()
 	if err != nil || instr != opcode.PUSHDATA1 || len(param) != 33 {
-		return false
+		return nil, false
 	}
+	pub := param
 	instr, _, err = ctx.Next()
 	if err != nil || instr != opcode.PUSHNULL {
-		return false
+		return nil, false
 	}
 	instr, param, err = ctx.Next()
 	if err != nil || instr != opcode.SYSCALL || binary.LittleEndian.Uint32(param) != verifyInteropID {
-		return false
+		return nil, false
 	}
-	return true
+	return pub, true
 }
 
 // IsStandardContract checks whether the passed script is a signature or
diff --git a/pkg/vm/contract_checks_test.go b/pkg/vm/contract_checks_test.go
index 88eb1aeab..29146c4f4 100644
--- a/pkg/vm/contract_checks_test.go
+++ b/pkg/vm/contract_checks_test.go
@@ -25,6 +25,15 @@ func testSignatureContract() []byte {
 	return prog
 }
 
+func TestParseSignatureContract(t *testing.T) {
+	prog := testSignatureContract()
+	pub := randomBytes(33)
+	copy(prog[2:], pub)
+	actual, ok := ParseSignatureContract(prog)
+	require.True(t, ok)
+	require.Equal(t, pub, actual)
+}
+
 func TestIsSignatureContract(t *testing.T) {
 	t.Run("valid contract", func(t *testing.T) {
 		prog := testSignatureContract()