16 // The default bencode string length limit. This is a poor attempt to prevent excessive memory
17 // allocation when parsing, but also leaves the window open to implement a better solution.
18 const DefaultDecodeMaxStrLen = 1<<27 - 1 // ~128MiB
20 type MaxStrLen = int64
23 // Maximum parsed bencode string length. Defaults to DefaultMaxStrLen if zero.
30 // Sum of bytes used to Decode values.
35 func (d *Decoder) Decode(v interface{}) (err error) {
44 _, ok := r.(runtime.Error)
48 if err, ok = r.(error); !ok {
51 // Errors thrown from deeper in parsing are unexpected. At value boundaries, errors should
52 // be returned directly (at least until all the panic nonsense is removed entirely).
54 err = io.ErrUnexpectedEOF
58 pv := reflect.ValueOf(v)
59 if pv.Kind() != reflect.Ptr || pv.IsNil() {
60 return &UnmarshalInvalidArgError{reflect.TypeOf(v)}
63 ok, err := d.parseValue(pv.Elem())
68 d.throwSyntaxError(d.Offset-1, errors.New("unexpected 'e'"))
73 func checkForUnexpectedEOF(err error, offset int64) {
77 What: io.ErrUnexpectedEOF,
82 func (d *Decoder) readByte() byte {
83 b, err := d.r.ReadByte()
85 checkForUnexpectedEOF(err, d.Offset)
93 // reads data writing it to 'd.buf' until 'sep' byte is encountered, 'sep' byte
94 // is consumed, but not included into the 'd.buf'
95 func (d *Decoder) readUntil(sep byte) {
105 func checkForIntParseError(err error, offset int64) {
114 func (d *Decoder) throwSyntaxError(offset int64, err error) {
121 // Assume the 'i' is already consumed. Read and validate the rest of an int into the buffer.
122 func (d *Decoder) readInt() error {
123 // start := d.Offset - 1
125 if err := d.checkBufferedInt(); err != nil {
128 // if d.buf.Len() == 0 {
129 // panic(&SyntaxError{
131 // What: errors.New("empty integer value"),
137 // called when 'i' was consumed, for the integer type in v.
138 func (d *Decoder) parseInt(v reflect.Value) error {
139 start := d.Offset - 1
141 if err := d.readInt(); err != nil {
144 s := bytesAsString(d.buf.Bytes())
147 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
148 n, err := strconv.ParseInt(s, 10, 64)
149 checkForIntParseError(err, start)
151 if v.OverflowInt(n) {
152 return &UnmarshalTypeError{
153 BencodeTypeName: "int",
154 UnmarshalTargetType: v.Type(),
158 case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
159 n, err := strconv.ParseUint(s, 10, 64)
160 checkForIntParseError(err, start)
162 if v.OverflowUint(n) {
163 return &UnmarshalTypeError{
164 BencodeTypeName: "int",
165 UnmarshalTargetType: v.Type(),
172 return &UnmarshalTypeError{
173 BencodeTypeName: "int",
174 UnmarshalTargetType: v.Type(),
181 func (d *Decoder) checkBufferedInt() error {
189 if b[0] < '1' || b[0] > '9' {
190 return errors.New("invalid leading digit")
195 func (d *Decoder) parseStringLength() (int, error) {
196 // We should have already consumed the first byte of the length into the Decoder buf.
197 start := d.Offset - 1
199 if err := d.checkBufferedInt(); err != nil {
202 // Really the limit should be the uint size for the platform. But we can't pass in an allocator,
203 // or limit total memory use in Go, the best we might hope to do is limit the size of a single
204 // decoded value (by reading it in in-place and then operating on a view).
205 length, err := strconv.ParseInt(bytesAsString(d.buf.Bytes()), 10, 0)
206 checkForIntParseError(err, start)
207 if int64(length) > d.getMaxStrLen() {
208 err = fmt.Errorf("parsed string length %v exceeds limit (%v)", length, DefaultDecodeMaxStrLen)
211 return int(length), err
214 func (d *Decoder) parseString(v reflect.Value) error {
215 length, err := d.parseStringLength()
220 read := func(b []byte) {
221 n, err := io.ReadFull(d.r, b)
224 checkForUnexpectedEOF(err, d.Offset)
227 What: errors.New("unexpected I/O error: " + err.Error()),
234 b := make([]byte, length)
236 v.SetString(bytesAsString(b))
239 if v.Type().Elem().Kind() != reflect.Uint8 {
242 b := make([]byte, length)
247 if v.Type().Elem().Kind() != reflect.Uint8 {
251 b := d.buf.Bytes()[:length]
253 reflect.Copy(v, reflect.ValueOf(b))
257 b := d.buf.Bytes()[:length]
259 x, err := strconv.ParseBool(unsafe.String(unsafe.SliceData(b), len(b)))
266 // Can't move this into default clause because some cases above fail through to here after
267 // additional checks.
269 read(d.buf.Bytes()[:length])
270 // I believe we return here to support "ignore_unmarshal_type_error".
271 return &UnmarshalTypeError{
272 BencodeTypeName: "string",
273 UnmarshalTargetType: v.Type(),
277 // Info for parsing a dict value.
278 type dictField struct {
280 Get func(value reflect.Value) func(reflect.Value)
284 // Returns specifics for parsing a dict field value.
285 func getDictField(dict reflect.Type, key string) (_ dictField, err error) {
286 // get valuev as a map value or as a struct field
287 switch k := dict.Kind(); k {
291 Get: func(mapValue reflect.Value) func(reflect.Value) {
292 return func(value reflect.Value) {
293 if mapValue.IsNil() {
294 mapValue.Set(reflect.MakeMap(dict))
296 // Assigns the value into the map.
297 // log.Printf("map type: %v", mapValue.Type())
298 mapValue.SetMapIndex(reflect.ValueOf(key).Convert(dict.Key()), value)
303 return getStructFieldForKey(dict, key), nil
304 // if sf.r.PkgPath != "" {
305 // panic(&UnmarshalFieldError{
307 // Type: dict.Type(),
312 err = fmt.Errorf("can't assign bencode dict items into a %v", k)
318 structFieldsMu sync.Mutex
319 structFields = map[reflect.Type]map[string]dictField{}
322 func parseStructFields(struct_ reflect.Type, each func(key string, df dictField)) {
323 for _i, n := 0, struct_.NumField(); _i < n; _i++ {
325 f := struct_.Field(i)
328 if t.Kind() == reflect.Ptr {
331 parseStructFields(t, func(key string, df dictField) {
333 df.Get = func(value reflect.Value) func(reflect.Value) {
334 anonPtr := value.Field(i)
335 if anonPtr.Kind() == reflect.Ptr && anonPtr.IsNil() {
336 anonPtr.Set(reflect.New(f.Type.Elem()))
337 anonPtr = anonPtr.Elem()
339 return innerGet(anonPtr)
345 tagStr := f.Tag.Get("bencode")
349 tag := parseTag(tagStr)
354 each(key, dictField{f.Type, func(value reflect.Value) func(reflect.Value) {
355 return value.Field(i).Set
360 func saveStructFields(struct_ reflect.Type) {
361 m := make(map[string]dictField)
362 parseStructFields(struct_, func(key string, sf dictField) {
365 structFields[struct_] = m
368 func getStructFieldForKey(struct_ reflect.Type, key string) (f dictField) {
369 structFieldsMu.Lock()
370 if _, ok := structFields[struct_]; !ok {
371 saveStructFields(struct_)
373 f, ok := structFields[struct_][key]
374 structFieldsMu.Unlock()
376 var discard interface{}
378 Type: reflect.TypeOf(discard),
379 Get: func(reflect.Value) func(reflect.Value) { return func(reflect.Value) {} },
386 func (d *Decoder) parseDict(v reflect.Value) error {
387 // At this point 'd' byte was consumed, now read key/value pairs
390 keyValue := reflect.ValueOf(&keyStr).Elem()
391 ok, err := d.parseValue(keyValue)
393 return fmt.Errorf("error parsing dict key: %w", err)
399 df, err := getDictField(v.Type(), keyStr)
401 return fmt.Errorf("parsing bencode dict into %v: %w", v.Type(), err)
404 // now we need to actually parse it
406 // Discard the value, there's nowhere to put it.
408 if_, ok = d.parseValueInterface()
410 return fmt.Errorf("error parsing value for key %q", keyStr)
413 return fmt.Errorf("missing value for key %q", keyStr)
417 setValue := reflect.New(df.Type).Elem()
418 // log.Printf("parsing into %v", setValue.Type())
419 ok, err = d.parseValue(setValue)
421 var target *UnmarshalTypeError
422 if !(errors.As(err, &target) && df.Tags.IgnoreUnmarshalTypeError()) {
423 return fmt.Errorf("parsing value for key %q: %w", keyStr, err)
427 return fmt.Errorf("missing value for key %q", keyStr)
433 func (d *Decoder) parseList(v reflect.Value) error {
436 // If the list is a singleton of the expected type, use that value. See
437 // https://github.com/anacrolix/torrent/issues/297.
438 l := reflect.New(reflect.SliceOf(v.Type()))
439 if err := d.parseList(l.Elem()); err != nil {
442 if l.Elem().Len() != 1 {
443 return &UnmarshalTypeError{
444 BencodeTypeName: "list",
445 UnmarshalTargetType: v.Type(),
448 v.Set(l.Elem().Index(0))
450 case reflect.Array, reflect.Slice:
451 // We can work with this. Normal case, fallthrough.
456 if v.Kind() == reflect.Slice && i >= v.Len() {
457 v.Set(reflect.Append(v, reflect.Zero(v.Type().Elem())))
461 ok, err := d.parseValue(v.Index(i))
469 _, ok := d.parseValueInterface()
477 if v.Kind() == reflect.Array {
478 z := reflect.Zero(v.Type().Elem())
479 for n := v.Len(); i < n; i++ {
487 if i == 0 && v.Kind() == reflect.Slice {
488 v.Set(reflect.MakeSlice(v.Type(), 0, 0))
493 func (d *Decoder) readOneValue() bool {
494 b, err := d.r.ReadByte()
508 // read until there is nothing to read
509 for d.readOneValue() {
511 // consume 'e' as well
516 d.buf.WriteString("e")
518 if b >= '0' && b <= '9' {
519 start := d.buf.Len() - 1
521 length, err := strconv.ParseInt(bytesAsString(d.buf.Bytes()[start:]), 10, 64)
522 checkForIntParseError(err, d.Offset-1)
524 d.buf.WriteString(":")
525 n, err := io.CopyN(&d.buf, d.r, length)
528 checkForUnexpectedEOF(err, d.Offset)
531 What: errors.New("unexpected I/O error: " + err.Error()),
537 d.raiseUnknownValueType(b, d.Offset-1)
543 func (d *Decoder) parseUnmarshaler(v reflect.Value) bool {
544 if !v.Type().Implements(unmarshalerType) {
545 if v.Addr().Type().Implements(unmarshalerType) {
552 if !d.readOneValue() {
555 m := v.Interface().(Unmarshaler)
556 err := m.UnmarshalBencode(d.buf.Bytes())
558 panic(&UnmarshalerError{v.Type(), err})
563 // Returns true if there was a value and it's now stored in 'v', otherwise
564 // there was an end symbol ("e") and no value was stored.
565 func (d *Decoder) parseValue(v reflect.Value) (bool, error) {
566 // we support one level of indirection at the moment
567 if v.Kind() == reflect.Ptr {
568 // if the pointer is nil, allocate a new element of the type it
571 v.Set(reflect.New(v.Type().Elem()))
576 if d.parseUnmarshaler(v) {
580 // common case: interface{}
581 if v.Kind() == reflect.Interface && v.NumMethod() == 0 {
582 iface, _ := d.parseValueInterface()
583 v.Set(reflect.ValueOf(iface))
587 b, err := d.r.ReadByte()
597 return true, d.parseDict(v)
599 return true, d.parseList(v)
601 return true, d.parseInt(v)
603 if b >= '0' && b <= '9' {
606 // Write the first digit of the length to the buffer.
608 return true, d.parseString(v)
611 d.raiseUnknownValueType(b, d.Offset-1)
616 // An unknown bencode type character was encountered.
617 func (d *Decoder) raiseUnknownValueType(b byte, offset int64) {
620 What: fmt.Errorf("unknown value type %+q", b),
624 func (d *Decoder) parseValueInterface() (interface{}, bool) {
625 b, err := d.r.ReadByte()
635 return d.parseDictInterface(), true
637 return d.parseListInterface(), true
639 return d.parseIntInterface(), true
641 if b >= '0' && b <= '9' {
643 // append first digit of the length to the buffer
645 return d.parseStringInterface(), true
648 d.raiseUnknownValueType(b, d.Offset-1)
653 // Called after 'i', for an arbitrary integer size.
654 func (d *Decoder) parseIntInterface() (ret interface{}) {
655 start := d.Offset - 1
657 if err := d.readInt(); err != nil {
660 n, err := strconv.ParseInt(d.buf.String(), 10, 64)
661 if ne, ok := err.(*strconv.NumError); ok && ne.Err == strconv.ErrRange {
663 _, ok := i.SetString(d.buf.String(), 10)
667 What: errors.New("failed to parse integer"),
672 checkForIntParseError(err, start)
680 func (d *Decoder) readBytes(length int) []byte {
681 b, err := io.ReadAll(io.LimitReader(d.r, int64(length)))
685 if len(b) != length {
686 panic(fmt.Errorf("read %v bytes expected %v", len(b), length))
691 func (d *Decoder) parseStringInterface() string {
692 length, err := d.parseStringLength()
696 b := d.readBytes(int(length))
697 d.Offset += int64(len(b))
699 panic(&SyntaxError{Offset: d.Offset, What: err})
701 return bytesAsString(b)
704 func (d *Decoder) parseDictInterface() interface{} {
705 dict := make(map[string]interface{})
710 keyi, ok := d.parseValueInterface()
715 key, ok := keyi.(string)
719 What: errors.New("non-string key in a dict"),
722 if lastKeyOk && key <= lastKey {
723 d.throwSyntaxError(start, fmt.Errorf("dict keys unsorted: %q <= %q", key, lastKey))
726 valuei, ok := d.parseValueInterface()
728 d.throwSyntaxError(start, fmt.Errorf("dict elem missing value [key=%v]", key))
738 func (d *Decoder) parseListInterface() (list []interface{}) {
739 list = []interface{}{}
740 valuei, ok := d.parseValueInterface()
742 list = append(list, valuei)
743 valuei, ok = d.parseValueInterface()
748 func (d *Decoder) getMaxStrLen() int64 {
749 if d.MaxStrLen == 0 {
750 return DefaultDecodeMaxStrLen