Encode: add bound check for uint64 > math.Int64

marshaler.go

@@ -107,6 +107,13 @@ func (enc *Encoder) SetIndentTables(indent bool) *Encoder {
 // a newline character or a single quote. In that case they are emitted as
 // quoted strings.
 //
+// Unsigned integers larger than math.MaxInt64 cannot be encoded. Doing so
+// results in an error. This rule exists because the TOML specification only
+// requires parsers to support at least the 64 bits integer range. Allowing
+// larger numbers would create non-standard TOML documents, which may not be
+// readable (at best) by other implementations. To encode such numbers, a
+// solution is a custom type that implements encoding.TextMarshaler.
+//
 // When encoding structs, fields are encoded in order of definition, with their
 // exact name.
 //
@@ -303,7 +310,11 @@ func (enc *Encoder) encode(b []byte, ctx encoderCtx, v reflect.Value) ([]byte, e
 			b = append(b, "false"...)
 		}
 	case reflect.Uint64, reflect.Uint32, reflect.Uint16, reflect.Uint8, reflect.Uint:
-		b = strconv.AppendUint(b, v.Uint(), 10)
+		x := v.Uint()
+		if x > uint64(math.MaxInt64) {
+			return nil, fmt.Errorf("toml: not encoding uint (%d) greater than max int64 (%d)", x, math.MaxInt64)
+		}
+		b = strconv.AppendUint(b, x, 10)
 	case reflect.Int64, reflect.Int32, reflect.Int16, reflect.Int8, reflect.Int:
 		b = strconv.AppendInt(b, v.Int(), 10)
 	default:

marshaler_test.go

@@ -1102,6 +1102,19 @@ func TestLocalTime(t *testing.T) {
 	require.Equal(t, expected, string(out))
 }
 
+func TestMarshalUint64Overflow(t *testing.T) {
+	// The TOML spec only requires implementation to provide support for the
+	// int64 range. To avoid generating TOML documents that would not be
+	// supported by standard-compliant parsers, uint64 > max int64 cannot be
+	// marshaled.
+	x := map[string]interface{}{
+		"foo": uint64(math.MaxInt64) + 1,
+	}
+
+	_, err := toml.Marshal(x)
+	require.Error(t, err)
+}
+
 func ExampleMarshal() {
 	type MyConfig struct {
 		Version int