aboutsummaryrefslogtreecommitdiffstats
path: root/rlp/decode.go
blob: c4e5869cc90727c703bb69281ca9239137936117 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package rlp

import (
    "bufio"
    "bytes"
    "encoding/binary"
    "errors"
    "fmt"
    "io"
    "math/big"
    "reflect"
    "strings"
)

var (
    errNoPointer     = errors.New("rlp: interface given to Decode must be a pointer")
    errDecodeIntoNil = errors.New("rlp: pointer given to Decode must not be nil")
)

// Decoder is implemented by types that require custom RLP
// decoding rules or need to decode into private fields.
//
// The DecodeRLP method should read one value from the given
// Stream. It is not forbidden to read less or more, but it might
// be confusing.
type Decoder interface {
    DecodeRLP(*Stream) error
}

// Decode parses RLP-encoded data from r and stores the result in the
// value pointed to by val. Val must be a non-nil pointer. If r does
// not implement ByteReader, Decode will do its own buffering.
//
// Decode uses the following type-dependent decoding rules:
//
// If the type implements the Decoder interface, decode calls
// DecodeRLP.
//
// To decode into a pointer, Decode will decode into the value pointed
// to. If the pointer is nil, a new value of the pointer's element
// type is allocated. If the pointer is non-nil, the existing value
// will reused.
//
// To decode into a struct, Decode expects the input to be an RLP
// list. The decoded elements of the list are assigned to each public
// field in the order given by the struct's definition. The input list
// must contain an element for each decoded field. Decode returns an
// error if there are too few or too many elements.
//
// The decoding of struct fields honours two struct tags, "tail" and
// "nil". For an explanation of "tail", see the example.
// The "nil" tag applies to pointer-typed fields and changes the
// decoding rules for the field such that input values of size zero
// decode as a nil pointer. This tag can be useful when decoding
// recursive types.
//
//     type StructWithEmptyOK struct {
//         Foo *[20]byte `rlp:"nil"`
//     }
//
// To decode into a slice, the input must be a list and the resulting
// slice will contain the input elements in order. For byte slices,
// the input must be an RLP string. Array types decode similarly, with
// the additional restriction that the number of input elements (or
// bytes) must match the array's length.
//
// To decode into a Go string, the input must be an RLP string. The
// input bytes are taken as-is and will not necessarily be valid UTF-8.
//
// To decode into an unsigned integer type, the input must also be an RLP
// string. The bytes are interpreted as a big endian representation of
// the integer. If the RLP string is larger than the bit size of the
// type, Decode will return an error. Decode also supports *big.Int.
// There is no size limit for big integers.
//
// To decode into an interface value, Decode stores one of these
// in the value:
//
//    []interface{}, for RLP lists
//    []byte, for RLP strings
//
// Non-empty interface types are not supported, nor are booleans,
// signed integers, floating point numbers, maps, channels and
// functions.
//
// Note that Decode does not set an input limit for all readers
// and may be vulnerable to panics cause by huge value sizes. If
// you need an input limit, use
//
//     NewStream(r, limit).Decode(val)
func Decode(r io.Reader, val interface{}) error {
    // TODO: this could use a Stream from a pool.
    return NewStream(r, 0).Decode(val)
}

// DecodeBytes parses RLP data from b into val.
// Please see the documentation of Decode for the decoding rules.
// The input must contain exactly one value and no trailing data.
func DecodeBytes(b []byte, val interface{}) error {
    // TODO: this could use a Stream from a pool.
    r := bytes.NewReader(b)
    if err := NewStream(r, uint64(len(b))).Decode(val); err != nil {
        return err
    }
    if r.Len() > 0 {
        return ErrMoreThanOneValue
    }
    return nil
}

type decodeError struct {
    msg string
    typ reflect.Type
    ctx []string
}

func (err *decodeError) Error() string {
    ctx := ""
    if len(err.ctx) > 0 {
        ctx = ", decoding into "
        for i := len(err.ctx) - 1; i >= 0; i-- {
            ctx += err.ctx[i]
        }
    }
    return fmt.Sprintf("rlp: %s for %v%s", err.msg, err.typ, ctx)
}

func wrapStreamError(err error, typ reflect.Type) error {
    switch err {
    case ErrCanonInt:
        return &decodeError{msg: "non-canonical integer (leading zero bytes)", typ: typ}
    case ErrCanonSize:
        return &decodeError{msg: "non-canonical size information", typ: typ}
    case ErrExpectedList:
        return &decodeError{msg: "expected input list", typ: typ}
    case ErrExpectedString:
        return &decodeError{msg: "expected input string or byte", typ: typ}
    case errUintOverflow:
        return &decodeError{msg: "input string too long", typ: typ}
    case errNotAtEOL:
        return &decodeError{msg: "input list has too many elements", typ: typ}
    }
    return err
}

func addErrorContext(err error, ctx string) error {
    if decErr, ok := err.(*decodeError); ok {
        decErr.ctx = append(decErr.ctx, ctx)
    }
    return err
}

var (
    decoderInterface = reflect.TypeOf(new(Decoder)).Elem()
    bigInt           = reflect.TypeOf(big.Int{})
)

func makeDecoder(typ reflect.Type, tags tags) (dec decoder, err error) {
    kind := typ.Kind()
    switch {
    case typ == rawValueType:
        return decodeRawValue, nil
    case typ.Implements(decoderInterface):
        return decodeDecoder, nil
    case kind != reflect.Ptr && reflect.PtrTo(typ).Implements(decoderInterface):
        return decodeDecoderNoPtr, nil
    case typ.AssignableTo(reflect.PtrTo(bigInt)):
        return decodeBigInt, nil
    case typ.AssignableTo(bigInt):
        return decodeBigIntNoPtr, nil
    case isUint(kind):
        return decodeUint, nil
    case kind == reflect.Bool:
        return decodeBool, nil
    case kind == reflect.String:
        return decodeString, nil
    case kind == reflect.Slice || kind == reflect.Array:
        return makeListDecoder(typ, tags)
    case kind == reflect.Struct:
        return makeStructDecoder(typ)
    case kind == reflect.Ptr:
        if tags.nilOK {
            return makeOptionalPtrDecoder(typ)
        }
        return makePtrDecoder(typ)
    case kind == reflect.Interface:
        return decodeInterface, nil
    default:
        return nil, fmt.Errorf("rlp: type %v is not RLP-serializable", typ)
    }
}

func decodeRawValue(s *Stream, val reflect.Value) error {
    r, err := s.Raw()
    if err != nil {
        return err
    }
    val.SetBytes(r)
    return nil
}

func decodeUint(s *Stream, val reflect.Value) error {
    typ := val.Type()
    num, err := s.uint(typ.Bits())
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    val.SetUint(num)
    return nil
}

func decodeBool(s *Stream, val reflect.Value) error {
    b, err := s.Bool()
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    val.SetBool(b)
    return nil
}

func decodeString(s *Stream, val reflect.Value) error {
    b, err := s.Bytes()
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    val.SetString(string(b))
    return nil
}

func decodeBigIntNoPtr(s *Stream, val reflect.Value) error {
    return decodeBigInt(s, val.Addr())
}

func decodeBigInt(s *Stream, val reflect.Value) error {
    b, err := s.Bytes()
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    i := val.Interface().(*big.Int)
    if i == nil {
        i = new(big.Int)
        val.Set(reflect.ValueOf(i))
    }
    // Reject leading zero bytes
    if len(b) > 0 && b[0] == 0 {
        return wrapStreamError(ErrCanonInt, val.Type())
    }
    i.SetBytes(b)
    return nil
}

func makeListDecoder(typ reflect.Type, tag tags) (decoder, error) {
    etype := typ.Elem()
    if etype.Kind() == reflect.Uint8 && !reflect.PtrTo(etype).Implements(decoderInterface) {
        if typ.Kind() == reflect.Array {
            return decodeByteArray, nil
        } else {
            return decodeByteSlice, nil
        }
    }
    etypeinfo, err := cachedTypeInfo1(etype, tags{})
    if err != nil {
        return nil, err
    }
    var dec decoder
    switch {
    case typ.Kind() == reflect.Array:
        dec = func(s *Stream, val reflect.Value) error {
            return decodeListArray(s, val, etypeinfo.decoder)
        }
    case tag.tail:
        // A slice with "tail" tag can occur as the last field
        // of a struct and is upposed to swallow all remaining
        // list elements. The struct decoder already called s.List,
        // proceed directly to decoding the elements.
        dec = func(s *Stream, val reflect.Value) error {
            return decodeSliceElems(s, val, etypeinfo.decoder)
        }
    default:
        dec = func(s *Stream, val reflect.Value) error {
            return decodeListSlice(s, val, etypeinfo.decoder)
        }
    }
    return dec, nil
}

func decodeListSlice(s *Stream, val reflect.Value, elemdec decoder) error {
    size, err := s.List()
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    if size == 0 {
        val.Set(reflect.MakeSlice(val.Type(), 0, 0))
        return s.ListEnd()
    }
    if err := decodeSliceElems(s, val, elemdec); err != nil {
        return err
    }
    return s.ListEnd()
}

func decodeSliceElems(s *Stream, val reflect.Value, elemdec decoder) error {
    i := 0
    for ; ; i++ {
        // grow slice if necessary
        if i >= val.Cap() {
            newcap := val.Cap() + val.Cap()/2
            if newcap < 4 {
                newcap = 4
            }
            newv := reflect.MakeSlice(val.Type(), val.Len(), newcap)
            reflect.Copy(newv, val)
            val.Set(newv)
        }
        if i >= val.Len() {
            val.SetLen(i + 1)
        }
        // decode into element
        if err := elemdec(s, val.Index(i)); err == EOL {
            break
        } else if err != nil {
            return addErrorContext(err, fmt.Sprint("[", i, "]"))
        }
    }
    if i < val.Len() {
        val.SetLen(i)
    }
    return nil
}

func decodeListArray(s *Stream, val reflect.Value, elemdec decoder) error {
    if _, err := s.List(); err != nil {
        return wrapStreamError(err, val.Type())
    }
    vlen := val.Len()
    i := 0
    for ; i < vlen; i++ {
        if err := elemdec(s, val.Index(i)); err == EOL {
            break
        } else if err != nil {
            return addErrorContext(err, fmt.Sprint("[", i, "]"))
        }
    }
    if i < vlen {
        return &decodeError{msg: "input list has too few elements", typ: val.Type()}
    }
    return wrapStreamError(s.ListEnd(), val.Type())
}

func decodeByteSlice(s *Stream, val reflect.Value) error {
    b, err := s.Bytes()
    if err != nil {
        return wrapStreamError(err, val.Type())
    }
    val.SetBytes(b)
    return nil
}

func decodeByteArray(s *Stream, val reflect.Value) error {
    kind, size, err := s.Kind()
    if err != nil {
        return err
    }
    vlen := val.Len()
    switch kind {
    case Byte:
        if vlen == 0 {
            return &decodeError{msg: "input string too long", typ: val.Type()}
        }
        if vlen > 1 {
            return &decodeError{msg: "input string too short", typ: val.Type()}
        }
        bv, _ := s.Uint()
        val.Index(0).SetUint(bv)
    case String:
        if uint64(vlen) < size {
            return &decodeError{msg: "input string too long", typ: val.Type()}
        }
        if uint64(vlen) > size {
            return &decodeError{msg: "input string too short", typ: val.Type()}
        }
        slice := val.Slice(0, vlen).Interface().([]byte)
        if err := s.readFull(slice); err != nil {
            return err
        }
        // Reject cases where single byte encoding should have been used.
        if size == 1 && slice[0] < 128 {
            return wrapStreamError(ErrCanonSize, val.Type())
        }
    case List:
        return wrapStreamError(ErrExpectedString, val.Type())
    }
    return nil
}

func makeStructDecoder(typ reflect.Type) (decoder, error) {
    fields, err := structFields(typ)
    if err != nil {
        return nil, err
    }
    dec := func(s *Stream, val reflect.Value) (err error) {
        if _, err := s.List(); err != nil {
            return wrapStreamError(err, typ)
        }
        for _, f := range fields {
            err := f.info.decoder(s, val.Field(f.index))
            if err == EOL {
                return &decodeError{msg: "too few elements", typ: typ}
            } else if err != nil {
                return addErrorContext(err, "."+typ.Field(f.index).Name)
            }
        }
        return wrapStreamError(s.ListEnd(), typ)
    }
    return dec, nil
}

// makePtrDecoder creates a decoder that decodes into
// the pointer's element type.
func makePtrDecoder(typ reflect.Type) (decoder, error) {
    etype := typ.Elem()
    etypeinfo, err := cachedTypeInfo1(etype, tags{})
    if err != nil {
        return nil, err
    }
    dec := func(s *Stream, val reflect.Value) (err error) {
        newval := val
        if val.IsNil() {
            newval = reflect.New(etype)
        }
        if err = etypeinfo.decoder(s, newval.Elem()); err == nil {
            val.Set(newval)
        }
        return err
    }
    return dec, nil
}

// makeOptionalPtrDecoder creates a decoder that decodes empty values
// as nil. Non-empty values are decoded into a value of the element type,
// just like makePtrDecoder does.
//
// This decoder is used for pointer-typed struct fields with struct tag "nil".
func makeOptionalPtrDecoder(typ reflect.Type) (decoder, error) {
    etype := typ.Elem()
    etypeinfo, err := cachedTypeInfo1(etype, tags{})
    if err != nil {
        return nil, err
    }
    dec := func(s *Stream, val reflect.Value) (err error) {
        kind, size, err := s.Kind()
        if err != nil || size == 0 && kind != Byte {
            // rearm s.Kind. This is important because the input
            // position must advance to the next value even though
            // we don't read anything.
            s.kind = -1
            // set the pointer to nil.
            val.Set(reflect.Zero(typ))
            return err
        }
        newval := val
        if val.IsNil() {
            newval = reflect.New(etype)
        }
        if err = etypeinfo.decoder(s, newval.Elem()); err == nil {
            val.Set(newval)
        }
        return err
    }
    return dec, nil
}

var ifsliceType = reflect.TypeOf([]interface{}{})

func decodeInterface(s *Stream, val reflect.Value) error {
    if val.Type().NumMethod() != 0 {
        return fmt.Errorf("rlp: type %v is not RLP-serializable", val.Type())
    }
    kind, _, err := s.Kind()
    if err != nil {
        return err
    }
    if kind == List {
        slice := reflect.New(ifsliceType).Elem()
        if err := decodeListSlice(s, slice, decodeInterface); err != nil {
            return err
        }
        val.Set(slice)
    } else {
        b, err := s.Bytes()
        if err != nil {
            return err
        }
        val.Set(reflect.ValueOf(b))
    }
    return nil
}

// This decoder is used for non-pointer values of types
// that implement the Decoder interface using a pointer receiver.
func decodeDecoderNoPtr(s *Stream, val reflect.Value) error {
    return val.Addr().Interface().(Decoder).DecodeRLP(s)
}

func decodeDecoder(s *Stream, val reflect.Value) error {
    // Decoder instances are not handled using the pointer rule if the type
    // implements Decoder with pointer receiver (i.e. always)
    // because it might handle empty values specially.
    // We need to allocate one here in this case, like makePtrDecoder does.
    if val.Kind() == reflect.Ptr && val.IsNil() {
        val.Set(reflect.New(val.Type().Elem()))
    }
    return val.Interface().(Decoder).DecodeRLP(s)
}

// Kind represents the kind of value contained in an RLP stream.
type Kind int

const (
    Byte Kind = iota
    String
    List
)

func (k Kind) String() string {
    switch k {
    case Byte:
        return "Byte"
    case String:
        return "String"
    case List:
        return "List"
    default:
        return fmt.Sprintf("Unknown(%d)", k)
    }
}

var (
    // EOL is returned when the end of the current list
    // has been reached during streaming.
    EOL = errors.New("rlp: end of list")

    // Actual Errors
    ErrExpectedString = errors.New("rlp: expected String or Byte")
    ErrExpectedList   = errors.New("rlp: expected List")
    ErrCanonInt       = errors.New("rlp: non-canonical integer format")
    ErrCanonSize      = errors.New("rlp: non-canonical size information")
    ErrElemTooLarge   = errors.New("rlp: element is larger than containing list")
    ErrValueTooLarge  = errors.New("rlp: value size exceeds available input length")

    // This error is reported by DecodeBytes if the slice contains
    // additional data after the first RLP value.
    ErrMoreThanOneValue = errors.New("rlp: input contains more than one value")

    // internal errors
    errNotInList    = errors.New("rlp: call of ListEnd outside of any list")
    errNotAtEOL     = errors.New("rlp: call of ListEnd not positioned at EOL")
    errUintOverflow = errors.New("rlp: uint overflow")
)

// ByteReader must be implemented by any input reader for a Stream. It
// is implemented by e.g. bufio.Reader and bytes.Reader.
type ByteReader interface {
    io.Reader
    io.ByteReader
}

// Stream can be used for piecemeal decoding of an input stream. This
// is useful if the input is very large or if the decoding rules for a
// type depend on the input structure. Stream does not keep an
// internal buffer. After decoding a value, the input reader will be
// positioned just before the type information for the next value.
//
// When decoding a list and the input position reaches the declared
// length of the list, all operations will return error EOL.
// The end of the list must be acknowledged using ListEnd to continue
// reading the enclosing list.
//
// Stream is not safe for concurrent use.
type Stream struct {
    r ByteReader

    // number of bytes remaining to be read from r.
    remaining uint64
    limited   bool

    // auxiliary buffer for integer decoding
    uintbuf []byte

    kind    Kind   // kind of value ahead
    size    uint64 // size of value ahead
    byteval byte   // value of single byte in type tag
    kinderr error  // error from last readKind
    stack   []listpos
}

type listpos struct{ pos, size uint64 }

// NewStream creates a new decoding stream reading from r.
//
// If r implements the ByteReader interface, Stream will
// not introduce any buffering.
//
// For non-toplevel values, Stream returns ErrElemTooLarge
// for values that do not fit into the enclosing list.
//
// Stream supports an optional input limit. If a limit is set, the
// size of any toplevel value will be checked against the remaining
// input length. Stream operations that encounter a value exceeding
// the remaining input length will return ErrValueTooLarge. The limit
// can be set by passing a non-zero value for inputLimit.
//
// If r is a bytes.Reader or strings.Reader, the input limit is set to
// the length of r's underlying data unless an explicit limit is
// provided.
func NewStream(r io.Reader, inputLimit uint64) *Stream {
    s := new(Stream)
    s.Reset(r, inputLimit)
    return s
}

// NewListStream creates a new stream that pretends to be positioned
// at an encoded list of the given length.
func NewListStream(r io.Reader, len uint64) *Stream {
    s := new(Stream)
    s.Reset(r, len)
    s.kind = List
    s.size = len
    return s
}

// Bytes reads an RLP string and returns its contents as a byte slice.
// If the input does not contain an RLP string, the returned
// error will be ErrExpectedString.
func (s *Stream) Bytes() ([]byte, error) {
    kind, size, err := s.Kind()
    if err != nil {
        return nil, err
    }
    switch kind {
    case Byte:
        s.kind = -1 // rearm Kind
        return []byte{s.byteval}, nil
    case String:
        b := make([]byte, size)
        if err = s.readFull(b); err != nil {
            return nil, err
        }
        if size == 1 && b[0] < 128 {
            return nil, ErrCanonSize
        }
        return b, nil
    default:
        return nil, ErrExpectedString
    }
}

// Raw reads a raw encoded value including RLP type information.
func (s *Stream) Raw() ([]byte, error) {
    kind, size, err := s.Kind()
    if err != nil {
        return nil, err
    }
    if kind == Byte {
        s.kind = -1 // rearm Kind
        return []byte{s.byteval}, nil
    }
    // the original header has already been read and is no longer
    // available. read content and put a new header in front of it.
    start := headsize(size)
    buf := make([]byte, uint64(start)+size)
    if err := s.readFull(buf[start:]); err != nil {
        return nil, err
    }
    if kind == String {
        puthead(buf, 0x80, 0xB8, size)
    } else {
        puthead(buf, 0xC0, 0xF7, size)
    }
    return buf, nil
}

// Uint reads an RLP string of up to 8 bytes and returns its contents
// as an unsigned integer. If the input does not contain an RLP string, the
// returned error will be ErrExpectedString.
func (s *Stream) Uint() (uint64, error) {
    return s.uint(64)
}

func (s *Stream) uint(maxbits int) (uint64, error) {
    kind, size, err := s.Kind()
    if err != nil {
        return 0, err
    }
    switch kind {
    case Byte:
        if s.byteval == 0 {
            return 0, ErrCanonInt
        }
        s.kind = -1 // rearm Kind
        return uint64(s.byteval), nil
    case String:
        if size > uint64(maxbits/8) {
            return 0, errUintOverflow
        }
        v, err := s.readUint(byte(size))
        switch {
        case err == ErrCanonSize:
            // Adjust error because we're not reading a size right now.
            return 0, ErrCanonInt
        case err != nil:
            return 0, err
        case size > 0 && v < 128:
            return 0, ErrCanonSize
        default:
            return v, nil
        }
    default:
        return 0, ErrExpectedString
    }
}

// Bool reads an RLP string of up to 1 byte and returns its contents
// as an boolean. If the input does not contain an RLP string, the
// returned error will be ErrExpectedString.
func (s *Stream) Bool() (bool, error) {
    num, err := s.uint(8)
    if err != nil {
        return false, err
    }
    switch num {
    case 0:
        return false, nil
    case 1:
        return true, nil
    default:
        return false, fmt.Errorf("rlp: invalid boolean value: %d", num)
    }
}

// List starts decoding an RLP list. If the input does not contain a
// list, the returned error will be ErrExpectedList. When the list's
// end has been reached, any Stream operation will return EOL.
func (s *Stream) List() (size uint64, err error) {
    kind, size, err := s.Kind()
    if err != nil {
        return 0, err
    }
    if kind != List {
        return 0, ErrExpectedList
    }
    s.stack = append(s.stack, listpos{0, size})
    s.kind = -1
    s.size = 0
    return size, nil
}

// ListEnd returns to the enclosing list.
// The input reader must be positioned at the end of a list.
func (s *Stream) ListEnd() error {
    if len(s.stack) == 0 {
        return errNotInList
    }
    tos := s.stack[len(s.stack)-1]
    if tos.pos != tos.size {
        return errNotAtEOL
    }
    s.stack = s.stack[:len(s.stack)-1] // pop
    if len(s.stack) > 0 {
        s.stack[len(s.stack)-1].pos += tos.size
    }
    s.kind = -1
    s.size = 0
    return nil
}

// Decode decodes a value and stores the result in the value pointed
// to by val. Please see the documentation for the Decode function
// to learn about the decoding rules.
func (s *Stream) Decode(val interface{}) error {
    if val == nil {
        return errDecodeIntoNil
    }
    rval := reflect.ValueOf(val)
    rtyp := rval.Type()
    if rtyp.Kind() != reflect.Ptr {
        return errNoPointer
    }
    if rval.IsNil() {
        return errDecodeIntoNil
    }
    info, err := cachedTypeInfo(rtyp.Elem(), tags{})
    if err != nil {
        return err
    }

    err = info.decoder(s, rval.Elem())
    if decErr, ok := err.(*decodeError); ok && len(decErr.ctx) > 0 {
        // add decode target type to error so context has more meaning
        decErr.ctx = append(decErr.ctx, fmt.Sprint("(", rtyp.Elem(), ")"))
    }
    return err
}

// Reset discards any information about the current decoding context
// and starts reading from r. This method is meant to facilitate reuse
// of a preallocated Stream across many decoding operations.
//
// If r does not also implement ByteReader, Stream will do its own
// buffering.
func (s *Stream) Reset(r io.Reader, inputLimit uint64) {
    if inputLimit > 0 {
        s.remaining = inputLimit
        s.limited = true
    } else {
        // Attempt to automatically discover
        // the limit when reading from a byte slice.
        switch br := r.(type) {
        case *bytes.Reader:
            s.remaining = uint64(br.Len())
            s.limited = true
        case *strings.Reader:
            s.remaining = uint64(br.Len())
            s.limited = true
        default:
            s.limited = false
        }
    }
    // Wrap r with a buffer if it doesn't have one.
    bufr, ok := r.(ByteReader)
    if !ok {
        bufr = bufio.NewReader(r)
    }
    s.r = bufr
    // Reset the decoding context.
    s.stack = s.stack[:0]
    s.size = 0
    s.kind = -1
    s.kinderr = nil
    if s.uintbuf == nil {
        s.uintbuf = make([]byte, 8)
    }
}

// Kind returns the kind and size of the next value in the
// input stream.
//
// The returned size is the number of bytes that make up the value.
// For kind == Byte, the size is zero because the value is
// contained in the type tag.
//
// The first call to Kind will read size information from the input
// reader and leave it positioned at the start of the actual bytes of
// the value. Subsequent calls to Kind (until the value is decoded)
// will not advance the input reader and return cached information.
func (s *Stream) Kind() (kind Kind, size uint64, err error) {
    var tos *listpos
    if len(s.stack) > 0 {
        tos = &s.stack[len(s.stack)-1]
    }
    if s.kind < 0 {
        s.kinderr = nil
        // Don't read further if we're at the end of the
        // innermost list.
        if tos != nil && tos.pos == tos.size {
            return 0, 0, EOL
        }
        s.kind, s.size, s.kinderr = s.readKind()
        if s.kinderr == nil {
            if tos == nil {
                // At toplevel, check that the value is smaller
                // than the remaining input length.
                if s.limited && s.size > s.remaining {
                    s.kinderr = ErrValueTooLarge
                }
            } else {
                // Inside a list, check that the value doesn't overflow the list.
                if s.size > tos.size-tos.pos {
                    s.kinderr = ErrElemTooLarge
                }
            }
        }
    }
    // Note: this might return a sticky error generated
    // by an earlier call to readKind.
    return s.kind, s.size, s.kinderr
}

func (s *Stream) readKind() (kind Kind, size uint64, err error) {
    b, err := s.readByte()
    if err != nil {
        if len(s.stack) == 0 {
            // At toplevel, Adjust the error to actual EOF. io.EOF is
            // used by callers to determine when to stop decoding.
            switch err {
            case io.ErrUnexpectedEOF:
                err = io.EOF
            case ErrValueTooLarge:
                err = io.EOF
            }
        }
        return 0, 0, err
    }
    s.byteval = 0
    switch {
    case b < 0x80:
        // For a single byte whose value is in the [0x00, 0x7F] range, that byte
        // is its own RLP encoding.
        s.byteval = b
        return Byte, 0, nil
    case b < 0xB8:
        // Otherwise, if a string is 0-55 bytes long,
        // the RLP encoding consists of a single byte with value 0x80 plus the
        // length of the string followed by the string. The range of the first
        // byte is thus [0x80, 0xB7].
        return String, uint64(b - 0x80), nil
    case b < 0xC0:
        // If a string is more than 55 bytes long, the
        // RLP encoding consists of a single byte with value 0xB7 plus the length
        // of the length of the string in binary form, followed by the length of
        // the string, followed by the string. For example, a length-1024 string
        // would be encoded as 0xB90400 followed by the string. The range of
        // the first byte is thus [0xB8, 0xBF].
        size, err = s.readUint(b - 0xB7)
        if err == nil && size < 56 {
            err = ErrCanonSize
        }
        return String, size, err
    case b < 0xF8:
        // If the total payload of a list
        // (i.e. the combined length of all its items) is 0-55 bytes long, the
        // RLP encoding consists of a single byte with value 0xC0 plus the length
        // of the list followed by the concatenation of the RLP encodings of the
        // items. The range of the first byte is thus [0xC0, 0xF7].
        return List, uint64(b - 0xC0), nil
    default:
        // If the total payload of a list is more than 55 bytes long,
        // the RLP encoding consists of a single byte with value 0xF7
        // plus the length of the length of the payload in binary
        // form, followed by the length of the payload, followed by
        // the concatenation of the RLP encodings of the items. The
        // range of the first byte is thus [0xF8, 0xFF].
        size, err = s.readUint(b - 0xF7)
        if err == nil && size < 56 {
            err = ErrCanonSize
        }
        return List, size, err
    }
}

func (s *Stream) readUint(size byte) (uint64, error) {
    switch size {
    case 0:
        s.kind = -1 // rearm Kind
        return 0, nil
    case 1:
        b, err := s.readByte()
        return uint64(b), err
    default:
        start := int(8 - size)
        for i := 0; i < start; i++ {
            s.uintbuf[i] = 0
        }
        if err := s.readFull(s.uintbuf[start:]); err != nil {
            return 0, err
        }
        if s.uintbuf[start] == 0 {
            // Note: readUint is also used to decode integer
            // values. The error needs to be adjusted to become
            // ErrCanonInt in this case.
            return 0, ErrCanonSize
        }
        return binary.BigEndian.Uint64(s.uintbuf), nil
    }
}

func (s *Stream) readFull(buf []byte) (err error) {
    if err := s.willRead(uint64(len(buf))); err != nil {
        return err
    }
    var nn, n int
    for n < len(buf) && err == nil {
        nn, err = s.r.Read(buf[n:])
        n += nn
    }
    if err == io.EOF {
        err = io.ErrUnexpectedEOF
    }
    return err
}

func (s *Stream) readByte() (byte, error) {
    if err := s.willRead(1); err != nil {
        return 0, err
    }
    b, err := s.r.ReadByte()
    if err == io.EOF {
        err = io.ErrUnexpectedEOF
    }
    return b, err
}

func (s *Stream) willRead(n uint64) error {
    s.kind = -1 // rearm Kind

    if len(s.stack) > 0 {
        // check list overflow
        tos := s.stack[len(s.stack)-1]
        if n > tos.size-tos.pos {
            return ErrElemTooLarge
        }
        s.stack[len(s.stack)-1].pos += n
    }
    if s.limited {
        if n > s.remaining {
            return ErrValueTooLarge
        }
        s.remaining -= n
    }
    return nil
}