From 9ebb7930091647e8f331b15c26cf1535a991d160 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Wed, 6 Nov 2019 12:15:55 +0300
Subject: [PATCH] vm: revert SUBSTR offset behavior to NEO 2.x

---
 pkg/vm/vm.go      | 5 ++++-
 pkg/vm/vm_test.go | 7 ++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 8f7db244b..cd9716a53 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -519,7 +519,10 @@ func (v *VM) execute(ctx *Context, op Instruction, parameter []byte) (err error)
 		}
 		s := v.estack.Pop().Bytes()
 		if o > len(s) {
-			panic("invalid offset")
+			// panic("invalid offset")
+			// FIXME revert when NEO 3.0 https://github.com/nspcc-dev/neo-go/issues/477
+			v.estack.PushVal("")
+			break
 		}
 		last := l + o
 		if last > len(s) {
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index 059bc0afd..2819d37df 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -1674,7 +1674,12 @@ func TestSUBSTRBadOffset(t *testing.T) {
 	vm.estack.PushVal([]byte("abcdef"))
 	vm.estack.PushVal(7)
 	vm.estack.PushVal(1)
-	checkVMFailed(t, vm)
+
+	// checkVMFailed(t, vm)
+	// FIXME revert when NEO 3.0 https://github.com/nspcc-dev/neo-go/issues/477
+	runVM(t, vm)
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, []byte{}, vm.estack.Peek(0).Bytes())
 }
 
 func TestSUBSTRBigLen(t *testing.T) {