path: root/rlp/decode.go

package rlp

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

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.
//
// 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 set the pointer to nil if the
// input has size zero or the input is a single byte with value zero.
// If the input has nonzero size, Decode will allocate a new value of
// the type being pointed to.
//
// 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. If the input
// list has too few elements, no error is returned and the remaining
// fields will have the zero value.
// Recursive struct types are supported.
//
// To decode into a slice, the input must be a list and the resulting
// slice will contain the input elements in order.
// As a special case, if the slice has a byte-size element type, the input
// can also be an RLP string.
//
// To decode into a Go string, the input must be an RLP string. The
// bytes are taken as-is and will not necessarily be valid UTF-8.
//
// To decode into an 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 bool, float32,
// float64, maps, channel types and functions.
func Decode(r ByteReader, val interface{}) error {
    return NewStream(r).Decode(val)
}

func makeNumDecoder(typ reflect.Type) decoder {
    kind := typ.Kind()
    switch {
    case kind <= reflect.Int64:
        return decodeInt
    case kind <= reflect.Uint64:
        return decodeUint
    default:
        panic("fallthrough")
    }
}

func decodeInt(s *Stream, val reflect.Value) error {
    num, err := s.uint(val.Type().Bits())
    if err != nil {
        return err
    }
    val.SetInt(int64(num))
    return nil
}

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

func decodeString(s *Stream, val reflect.Value) error {
    b, err := s.Bytes()
    if err != nil {
        return err
    }
    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 err
    }
    i := val.Interface().(*big.Int)
    if i == nil {
        i = new(big.Int)
        val.Set(reflect.ValueOf(i))
    }
    i.SetBytes(b)
    return nil
}

const maxInt = int(^uint(0) >> 1)

func makeListDecoder(typ reflect.Type) (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)
    if err != nil {
        return nil, err
    }
    var maxLen = maxInt
    if typ.Kind() == reflect.Array {
        maxLen = typ.Len()
    }
    dec := func(s *Stream, val reflect.Value) error {
        return decodeList(s, val, etypeinfo.decoder, maxLen)
    }
    return dec, nil
}

// decodeList decodes RLP list elements into slices and arrays.
//
// The approach here is stolen from package json, although we differ
// in the semantics for arrays. package json discards remaining
// elements that would not fit into the array. We generate an error in
// this case because we'd be losing information.
func decodeList(s *Stream, val reflect.Value, elemdec decoder, maxelem int) error {
    size, err := s.List()
    if err != nil {
        return err
    }
    if size == 0 {
        if val.Kind() == reflect.Slice {
            val.Set(reflect.MakeSlice(val.Type(), 0, 0))
        } else {
            zero(val, 0)
        }
        return s.ListEnd()
    }

    i := 0
    for {
        if i > maxelem {
            return fmt.Errorf("rlp: input List has more than %d elements", maxelem)
        }
        if val.Kind() == reflect.Slice {
            // 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 err
        }
        i++
    }
    if i < val.Len() {
        if val.Kind() == reflect.Array {
            // zero the rest of the array.
            zero(val, i)
        } else {
            val.SetLen(i)
        }
    }
    return s.ListEnd()
}

func decodeByteSlice(s *Stream, val reflect.Value) error {
    kind, _, err := s.Kind()
    if err != nil {
        return err
    }
    if kind == List {
        return decodeList(s, val, decodeUint, maxInt)
    }
    b, err := s.Bytes()
    if err == nil {
        val.SetBytes(b)
    }
    return err
}

var errStringDoesntFitArray = errors.New("rlp: string value doesn't fit into target array")

func decodeByteArray(s *Stream, val reflect.Value) error {
    kind, size, err := s.Kind()
    if err != nil {
        return err
    }
    switch kind {
    case Byte:
        if val.Len() == 0 {
            return errStringDoesntFitArray
        }
        bv, _ := s.Uint()
        val.Index(0).SetUint(bv)
        zero(val, 1)
    case String:
        if uint64(val.Len()) < size {
            return errStringDoesntFitArray
        }
        slice := val.Slice(0, int(size)).Interface().([]byte)
        if err := s.readFull(slice); err != nil {
            return err
        }
        zero(val, int(size))
    case List:
        return decodeList(s, val, decodeUint, val.Len())
    }
    return nil
}

func zero(val reflect.Value, start int) {
    z := reflect.Zero(val.Type().Elem())
    for i := start; i < val.Len(); i++ {
        val.Index(i).Set(z)
    }
}

type field struct {
    index int
    info  *typeinfo
}

func makeStructDecoder(typ reflect.Type) (decoder, error) {
    var fields []field
    for i := 0; i < typ.NumField(); i++ {
        if f := typ.Field(i); f.PkgPath == "" { // exported
            info, err := cachedTypeInfo1(f.Type)
            if err != nil {
                return nil, err
            }
            fields = append(fields, field{i, info})
        }
    }
    dec := func(s *Stream, val reflect.Value) (err error) {
        if _, err = s.List(); err != nil {
            return err
        }
        for _, f := range fields {
            err = f.info.decoder(s, val.Field(f.index))
            if err == EOL {
                // too few elements. leave the rest at their zero value.
                break
            } else if err != nil {
                return err
            }
        }
        if err = s.ListEnd(); err == errNotAtEOL {
            err = errors.New("rlp: input List has too many elements")
        }
        return err
    }
    return dec, nil
}

func makePtrDecoder(typ reflect.Type) (decoder, error) {
    etype := typ.Elem()
    etypeinfo, err := cachedTypeInfo1(etype)
    if err != nil {
        return nil, err
    }
    dec := func(s *Stream, val reflect.Value) (err error) {
        _, size, err := s.Kind()
        if err != nil || size == 0 && s.byteval == 0 {
            val.Set(reflect.Zero(typ)) // set to nil
            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 {
    kind, _, err := s.Kind()
    if err != nil {
        return err
    }
    if kind == List {
        slice := reflect.New(ifsliceType).Elem()
        if err := decodeList(s, slice, decodeInterface, maxInt); 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")

    // Other errors
    ErrExpectedString = errors.New("rlp: expected String or Byte")
    ErrExpectedList   = errors.New("rlp: expected List")
    ErrElemTooLarge   = errors.New("rlp: element is larger than containing list")

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

// 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
    uintbuf []byte

    kind    Kind   // kind of value ahead
    size    uint64 // size of value ahead
    byteval byte   // value of single byte in type tag
    stack   []listpos
}

type listpos struct{ pos, size uint64 }

func NewStream(r ByteReader) *Stream {
    return &Stream{r: r, uintbuf: make([]byte, 8), kind: -1}
}

// 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
        }
        return b, nil
    default:
        return nil, ErrExpectedString
    }
}

// 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:
        s.kind = -1 // rearm Kind
        return uint64(s.byteval), nil
    case String:
        if size > uint64(maxbits/8) {
            return 0, fmt.Errorf("rlp: string is larger than %d bits", maxbits)
        }
        return s.readUint(byte(size))
    default:
        return 0, ErrExpectedString
    }
}

// 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())
    if err != nil {
        return err
    }
    return info.decoder(s, rval.Elem())
}

// 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 {
        if tos != nil && tos.pos == tos.size {
            return 0, 0, EOL
        }
        kind, size, err = s.readKind()
        if err != nil {
            return 0, 0, err
        }
        s.kind, s.size = kind, size
    }
    if tos != nil && tos.pos+s.size > tos.size {
        return 0, 0, ErrElemTooLarge
    }
    return s.kind, s.size, nil
}

func (s *Stream) readKind() (kind Kind, size uint64, err error) {
    b, err := s.readByte()
    if err != nil {
        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)
        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)
        return List, size, err
    }
}

func (s *Stream) readUint(size byte) (uint64, error) {
    if size == 1 {
        b, err := s.readByte()
        if err == io.EOF {
            err = io.ErrUnexpectedEOF
        }
        return uint64(b), err
    }
    start := int(8 - size)
    for i := 0; i < start; i++ {
        s.uintbuf[i] = 0
    }
    err := s.readFull(s.uintbuf[start:])
    return binary.BigEndian.Uint64(s.uintbuf), err
}

func (s *Stream) readFull(buf []byte) (err error) {
    s.willRead(uint64(len(buf)))
    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) {
    s.willRead(1)
    b, err := s.r.ReadByte()
    if len(s.stack) > 0 && err == io.EOF {
        err = io.ErrUnexpectedEOF
    }
    return b, err
}

func (s *Stream) willRead(n uint64) {
    s.kind = -1 // rearm Kind
    if len(s.stack) > 0 {
        s.stack[len(s.stack)-1].pos += n
    }
}