bencode: Decode very large integers as big.Int if they overflow int64

bencode/decode.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"errors"
 	"io"
+	"math/big"
 	"reflect"
 	"runtime"
 	"strconv"
@@ -503,7 +504,7 @@ func (d *decoder) parse_value_interface() (interface{}, bool) {
 	}
 }
 
-func (d *decoder) parse_int_interface() interface{} {
+func (d *decoder) parse_int_interface() (ret interface{}) {
 	start := d.offset - 1
 	d.read_until('e')
 	if d.buf.Len() == 0 {
@@ -514,9 +515,23 @@ func (d *decoder) parse_int_interface() interface{} {
 	}
 
 	n, err := strconv.ParseInt(d.buf.String(), 10, 64)
-	check_for_int_parse_error(err, start)
+	if ne, ok := err.(*strconv.NumError); ok && ne.Err == strconv.ErrRange {
+		i := new(big.Int)
+		_, ok := i.SetString(d.buf.String(), 10)
+		if !ok {
+			panic(&SyntaxError{
+				Offset: start,
+				What:   errors.New("failed to parse integer"),
+			})
+		}
+		ret = i
+	} else {
+		check_for_int_parse_error(err, start)
+		ret = n
+	}
+
 	d.buf.Reset()
-	return n
+	return
 }
 
 func (d *decoder) parse_string_interface() interface{} {

bencode/decode_test.go

@@ -3,6 +3,8 @@ package bencode
 import (
 	"bytes"
 	"io"
+	"log"
+	"math/big"
 	"reflect"
 	"testing"
 
@@ -24,6 +26,10 @@ var random_decode_tests = []random_decode_test{
 		[]interface{}{int64(5), int64(10), int64(15), int64(20), "bencode"}},
 	{"ldedee", []interface{}{map[string]interface{}{}, map[string]interface{}{}}},
 	{"le", []interface{}{}},
+	{"i604919719469385652980544193299329427705624352086e", func() *big.Int {
+		ret, _ := big.NewInt(-1).SetString("604919719469385652980544193299329427705624352086", 10)
+		return ret
+	}()},
 }
 
 func TestRandomDecode(t *testing.T) {