From e3c060b7392618c814ed9c338cd72f993fbc02ed Mon Sep 17 00:00:00 2001
From: Alex Vanin <alexey@nspcc.ru>
Date: Wed, 28 Oct 2020 15:59:40 +0300
Subject: [PATCH] [#122] Add BigIntFromStackItem

Neo-go can return big.Int values on stack after contract execution.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>
---
 pkg/morph/client/util.go      |  6 ++++++
 pkg/morph/client/util_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/pkg/morph/client/util.go b/pkg/morph/client/util.go
index 59f60830..4066472e 100644
--- a/pkg/morph/client/util.go
+++ b/pkg/morph/client/util.go
@@ -2,6 +2,7 @@ package client
 
 import (
 	"encoding/binary"
+	"math/big"
 
 	sc "github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
@@ -157,6 +158,11 @@ func IntFromStackItem(param stackitem.Item) (int64, error) {
 	}
 }
 
+// BigIntFromStackItem receives numerical value from the value of a smart contract parameter.
+func BigIntFromStackItem(param stackitem.Item) (*big.Int, error) {
+	return param.TryInteger()
+}
+
 // BytesFromStackItem receives binary value from the value of a smart contract parameter.
 func BytesFromStackItem(param stackitem.Item) ([]byte, error) {
 	switch param.Type() {
diff --git a/pkg/morph/client/util_test.go b/pkg/morph/client/util_test.go
index 8b0eff8f..9d73376a 100644
--- a/pkg/morph/client/util_test.go
+++ b/pkg/morph/client/util_test.go
@@ -1,9 +1,11 @@
 package client
 
 import (
+	"math"
 	"math/big"
 	"testing"
 
+	"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
 	sc "github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 	"github.com/stretchr/testify/require"
@@ -50,9 +52,13 @@ var (
 		Value: []sc.Parameter{intParam, byteArrayParam},
 	}
 
+	bigIntValue = new(big.Int).Mul(big.NewInt(math.MaxInt64), big.NewInt(10))
+
 	stringByteItem     = stackitem.NewByteArray([]byte("Hello World"))
 	intItem            = stackitem.NewBigInteger(new(big.Int).SetInt64(1))
+	bigIntItem         = stackitem.NewBigInteger(bigIntValue)
 	byteWithIntItem    = stackitem.NewByteArray([]byte{0x0a})
+	byteWithBigIntItem = stackitem.NewByteArray(bigint.ToBytes(bigIntValue))
 	emptyByteArrayItem = stackitem.NewByteArray([]byte{})
 	trueBoolItem       = stackitem.NewBool(true)
 	falseBoolItem      = stackitem.NewBool(false)
@@ -233,6 +239,27 @@ func TestIntFromStackItem(t *testing.T) {
 	})
 }
 
+func TestBigIntFromStackItem(t *testing.T) {
+	t.Run("correct assert", func(t *testing.T) {
+		val, err := BigIntFromStackItem(bigIntItem)
+		require.NoError(t, err)
+		require.Equal(t, bigIntValue, val)
+
+		val, err = BigIntFromStackItem(byteWithBigIntItem)
+		require.NoError(t, err)
+		require.Equal(t, bigIntValue, val)
+
+		val, err = BigIntFromStackItem(emptyByteArrayItem)
+		require.NoError(t, err)
+		require.Equal(t, big.NewInt(0), val)
+	})
+
+	t.Run("incorrect assert", func(t *testing.T) {
+		_, err := BigIntFromStackItem(arrayItem)
+		require.Error(t, err)
+	})
+}
+
 func TestStringFromStackItem(t *testing.T) {
 	t.Run("correct assert", func(t *testing.T) {
 		val, err := StringFromStackItem(stringByteItem)