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authorFelix Lange <fjl@twurst.com>2014-11-14 03:31:48 +0800
committerFelix Lange <fjl@twurst.com>2014-11-17 08:49:47 +0800
commit74266d5bbd95ac07882b09230aec876bf7704f69 (patch)
tree101cd83defc7d396f42500bbf080243fb8571acf /rlp/decode.go
parent9509322ecd8e709ce8a17442836b6ff15ba2edff (diff)
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rlp: new package for streaming RLP decoder
Diffstat (limited to 'rlp/decode.go')
-rw-r--r--rlp/decode.go666
1 files changed, 666 insertions, 0 deletions
diff --git a/rlp/decode.go b/rlp/decode.go
new file mode 100644
index 000000000..1a51e7130
--- /dev/null
+++ b/rlp/decode.go
@@ -0,0 +1,666 @@
+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 {
+ 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
+ }
+}