[fix] Handle negative big ints correctly

pkg/values/big_int.go

@@ -16,7 +16,10 @@ func NewBigInt(b *big.Int) *BigInt {
 }
 
 func (b *BigInt) proto() *pb.Value {
-	return pb.NewBigIntValue(b.Underlying.Bytes())
+	return pb.NewBigIntValue(
+		b.Underlying.Sign(),
+		b.Underlying.Bytes(),
+	)
 }
 
 func (b *BigInt) Unwrap() (any, error) {

pkg/values/big_int_test.go

@@ -31,3 +31,34 @@ func Test_BigIntUnwrapTo(t *testing.T) {
 	err = v.UnwrapTo(&varStr)
 	assert.ErrorContains(t, err, "cannot unwrap to value of type: *string")
 }
+
+func Test_BigInt(t *testing.T) {
+	testCases := []struct {
+		name string
+		bi   *big.Int
+	}{
+		{
+			name: "positive",
+			bi:   big.NewInt(100),
+		},
+		{
+			name: "0",
+			bi:   big.NewInt(0),
+		},
+		{
+			name: "negative",
+			bi:   big.NewInt(-1),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			v := NewBigInt(tc.bi)
+
+			vp := Proto(v)
+			got := FromProto(vp)
+
+			assert.Equal(t, tc.bi, got.(*BigInt).Underlying)
+		})
+	}
+}

pkg/values/pb/values.go

@@ -64,10 +64,13 @@ func NewInt64Value(i int64) *Value {
 	}
 }
 
-func NewBigIntValue(bib []byte) *Value {
+func NewBigIntValue(sign int, bib []byte) *Value {
 	return &Value{
 		Value: &Value_BigintValue{
-			BigintValue: bib,
+			BigintValue: &BigInt{
+				AbsVal: bib,
+				Sign:   int64(sign),
+			},
 		},
 	}
 }

pkg/values/pb/values.proto

@@ -5,6 +5,7 @@ option go_package = "github.com/smartcontractkit/chainlink-common/pkg/values/pb"
 package values;
 
 message Value {
+  reserved 8;
   oneof value {
     string string_value = 1;
     bool bool_value = 2;
@@ -13,10 +14,15 @@ message Value {
     List list_value = 5;
     string decimal_value = 6;
     int64 int64_value = 7;
-    bytes bigint_value = 8;
+    BigInt bigint_value = 9;
   }
 }
 
+message BigInt {
+     bytes abs_val = 1;
+     int64 sign = 2;
+}
+
 message Map {
   map<string, Value> fields = 1;
 }

pkg/values/value.go

@@ -174,10 +174,15 @@ func fromDecimalValueProto(decStr string) *Decimal {
 	return NewDecimal(dec)
 }
 
-func fromBigIntValueProto(b []byte) *BigInt {
-	i := big.Int{}
-	bi := i.SetBytes(b)
-	return NewBigInt(bi)
+func fromBigIntValueProto(biv *pb.BigInt) *BigInt {
+	av := &big.Int{}
+	av = av.SetBytes(biv.AbsVal)
+
+	if biv.Sign < 0 {
+		av.Neg(av)
+	}
+
+	return NewBigInt(av)
 }
 
 func createMapFromStruct(v any) (Value, error) {