Merge pull request #100 from whyrusleeping/steb/reject-negative-big-int

fix: reject negative big integers

gen.go

@@ -440,6 +440,9 @@ func (g Gen) emitCborMarshalStructField(w io.Writer, f Field) error {
 	case bigIntType:
 		return g.doTemplate(w, f, `
 	{
+		if {{ .Name }} != nil && {{ .Name }}.Sign() < 0 {
+			return xerrors.Errorf("Value in field {{ .Name | js }} was a negative big-integer (not supported)")
+		}
 		if err := cw.CborWriteHeader(cbg.MajTag, 2); err != nil {
 			return err
 		}

testgen/main.go

@@ -21,6 +21,7 @@ func main() {
 		types.IntArrayNewType{},
 		types.IntArrayAliasNewType{},
 		types.MapTransparentType{},
+		types.BigIntContainer{},
 	); err != nil {
 		panic(err)
 	}

testing/roundtrip_test.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math/big"
 	"math/rand"
 	"reflect"
 	"testing"
@@ -58,6 +59,38 @@ func TestLongStrings(t *testing.T) {
 	testTypeRoundtrips(t, reflect.TypeOf(LongString{}))
 }
 
+func TestBigInt(t *testing.T) {
+	for _, v := range []BigIntContainer{
+		{Int: big.NewInt(100)},
+		{Int: big.NewInt(0)},
+		{Int: nil},
+	} {
+
+		var buf bytes.Buffer
+		if err := v.MarshalCBOR(&buf); err != nil {
+			t.Fatal(err)
+		}
+
+		var o BigIntContainer
+		if err := o.UnmarshalCBOR(&buf); err != nil {
+			t.Fatal(err)
+		}
+		if v.Int == nil {
+			if o.Int.Sign() != 0 {
+				t.Fatal("expected nil to serialize to 0")
+			}
+		} else if v.Int.Cmp(o.Int) != 0 {
+			t.Fatal("did not round-trip")
+		}
+	}
+	var buf bytes.Buffer
+	v := BigIntContainer{Int: big.NewInt(-1)}
+	err := v.MarshalCBOR(&buf)
+	if err == nil {
+		t.Fatal("marshalling a negative int should have failed")
+	}
+}
+
 type RoundTripOptions struct {
 	Golden []byte
 }

testing/types.go

@@ -1,6 +1,7 @@
 package testing
 
 import (
+	"math/big"
 	"math/rand"
 	"reflect"
 
@@ -194,3 +195,7 @@ func (ls LongString) Generate(rand *rand.Rand, size int) reflect.Value {
 	ols.Val = string(s)
 	return reflect.ValueOf(ols).Elem()
 }
+
+type BigIntContainer struct {
+	Int *big.Int
+}