From 793f27084b7383f5de460d6698d89399153d8b44 Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Wed, 31 Mar 2021 13:52:53 +0300
Subject: [PATCH 1/3] vm: specify syscall ID when panicing on syscall
 invocation

It's convinient to know the failing syscall without dumping
smartcontract instructions.
---
 pkg/vm/vm.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 2c887cb86..dc8198ed8 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -1304,7 +1304,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		interopID := GetInteropID(parameter)
 		err := v.SyscallHandler(v, interopID)
 		if err != nil {
-			panic(fmt.Sprintf("failed to invoke syscall: %s", err))
+			panic(fmt.Sprintf("failed to invoke syscall %d: %s", interopID, err))
 		}
 
 	case opcode.RET:

From 93530fa8fae4393ae4947bc256d79d071a3442cd Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Wed, 31 Mar 2021 13:54:53 +0300
Subject: [PATCH 2/3] core: pop all args from stack before validation checks in
 Notify

We should match the C# behaviour.
---
 pkg/core/interop/runtime/engine.go      | 4 ++--
 pkg/core/interop/runtime/engine_test.go | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pkg/core/interop/runtime/engine.go b/pkg/core/interop/runtime/engine.go
index 95eadc05e..4735a3056 100644
--- a/pkg/core/interop/runtime/engine.go
+++ b/pkg/core/interop/runtime/engine.go
@@ -52,11 +52,11 @@ func GetTrigger(ic *interop.Context) error {
 // in neo-go the only meaningful thing to do here is to log.
 func Notify(ic *interop.Context) error {
 	name := ic.VM.Estack().Pop().String()
+	elem := ic.VM.Estack().Pop()
+	args := elem.Array()
 	if len(name) > MaxEventNameLen {
 		return fmt.Errorf("event name must be less than %d", MaxEventNameLen)
 	}
-	elem := ic.VM.Estack().Pop()
-	args := elem.Array()
 	// But it has to be serializable, otherwise we either have some broken
 	// (recursive) structure inside or an interop item that can't be used
 	// outside of the interop subsystem anyway.
diff --git a/pkg/core/interop/runtime/engine_test.go b/pkg/core/interop/runtime/engine_test.go
index 87618e00d..27a2e98f9 100644
--- a/pkg/core/interop/runtime/engine_test.go
+++ b/pkg/core/interop/runtime/engine_test.go
@@ -142,7 +142,7 @@ func TestNotify(t *testing.T) {
 		return ic
 	}
 	t.Run("big name", func(t *testing.T) {
-		ic := newIC(string(make([]byte, MaxEventNameLen+1)), []byte{42})
+		ic := newIC(string(make([]byte, MaxEventNameLen+1)), stackitem.NewArray([]stackitem.Item{stackitem.Null{}}))
 		require.Error(t, Notify(ic))
 	})
 	t.Run("recursive struct", func(t *testing.T) {

From f57187e611b34f5dd68ea1602149cb98b21d6a63 Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Wed, 31 Mar 2021 17:17:54 +0300
Subject: [PATCH 3/3] vm: throw unhandled exception with message instead of
 panic

The result is the same HALT state, but the exception message is the real
one got from user. Changes ported from C#:

1. Throw exception: https://github.com/neo-project/neo-vm/blob/59b8ac73d285aa9d607aee53eeadde82fcba9324/src/neo-vm/ExecutionEngine.cs#L1448
2. Prettify message: https://github.com/neo-project/neo-vm/blob/master/src/neo-vm/VMUnhandledException.cs#L28

The result is that instead of
```
2021-03-31T17:02:54.508+0300	WARN	contract invocation failed	{"tx": "2aefeb705f3a609df8767d9b45e036b9dd1eb77407e5732375981915668889b8", "block": 30640, "error": "error encountered at instruction 970 (THROW): runtime error: invalid memory address or nil pointer dereference"}
```

we'll get
```
2021-03-31T17:33:56.299+0300	WARN	contract invocation failed	{"tx": "2aefeb705f3a609df8767d9b45e036b9dd1eb77407e5732375981915668889b8", "block": 30640, "error": "error encountered at instruction 970 (THROW): unhandled exception: No authorization."}
```
in the node logs.
---
 pkg/vm/vm.go | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index dc8198ed8..6391167ca 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -1602,8 +1602,32 @@ func (v *VM) handleException() {
 		}
 		pop++
 		ictxv = ictxv.Next()
+		if ictxv == nil {
+			break
+		}
 		ictx = ictxv.Value().(*Context)
 	}
+	throwUnhandledException(v.uncaughtException)
+}
+
+// throwUnhandledException gets exception message from the provided stackitem and panics.
+func throwUnhandledException(item stackitem.Item) {
+	msg := "unhandled exception"
+	switch item.Type() {
+	case stackitem.ArrayT:
+		if arr := item.Value().([]stackitem.Item); len(arr) > 0 {
+			data, err := arr[0].TryBytes()
+			if err == nil {
+				msg = fmt.Sprintf("%s: %q", msg, string(data))
+			}
+		}
+	default:
+		data, err := item.TryBytes()
+		if err == nil {
+			msg = fmt.Sprintf("%s: %q", msg, string(data))
+		}
+	}
+	panic(msg)
 }
 
 // CheckMultisigPar checks if sigs contains sufficient valid signatures.