path: root/rlp/encode.go

package rlp

import (
    "fmt"
    "io"
    "math/big"
    "reflect"
)

// TODO: put encbufs in a sync.Pool.
//     Doing that requires zeroing the buffers after use.
//     encReader will need to drop it's buffer when done.

var (
    // Common encoded values.
    // These are useful when implementing EncodeRLP.
    EmptyString = []byte{0x80}
    EmptyList   = []byte{0xC0}
)

// Encoder is implemented by types that require custom
// encoding rules or want to encode private fields.
type Encoder interface {
    // EncodeRLP should write the RLP encoding of its receiver to w.
    // If the implementation is a pointer method, it may also be
    // called for nil pointers.
    //
    // Implementations should generate valid RLP. The data written is
    // not verified at the moment, but a future version might. It is
    // recommended to write only a single value but writing multiple
    // values or no value at all is also permitted.
    EncodeRLP(io.Writer) error
}

// Flat wraps a value (which must encode as a list) so
// it encodes as the list's elements.
//
// Example: suppose you have defined a type
//
//     type foo struct { A, B uint }
//
// Under normal encoding rules,
//
//     rlp.Encode(foo{1, 2}) --> 0xC20102
//
// This function can help you achieve the following encoding:
//
//     rlp.Encode(rlp.Flat(foo{1, 2})) --> 0x0102
func Flat(val interface{}) Encoder {
    return flatenc{val}
}

type flatenc struct{ val interface{} }

func (e flatenc) EncodeRLP(out io.Writer) error {
    // record current output position
    var (
        eb          = out.(*encbuf)
        prevstrsize = len(eb.str)
        prevnheads  = len(eb.lheads)
    )
    if err := eb.encode(e.val); err != nil {
        return err
    }
    // check that a new list header has appeared
    if len(eb.lheads) == prevnheads || eb.lheads[prevnheads].offset == prevstrsize-1 {
        return fmt.Errorf("rlp.Flat: %T did not encode as list", e.val)
    }
    // remove the new list header
    newhead := eb.lheads[prevnheads]
    copy(eb.lheads[prevnheads:], eb.lheads[prevnheads+1:])
    eb.lheads = eb.lheads[:len(eb.lheads)-1]
    eb.lhsize -= newhead.tagsize()
    return nil
}

// Encode writes the RLP encoding of val to w. Note that Encode may
// perform many small writes in some cases. Consider making w
// buffered.
//
// Encode uses the following type-dependent encoding rules:
//
// If the type implements the Encoder interface, Encode calls
// EncodeRLP. This is true even for nil pointers, please see the
// documentation for Encoder.
//
// To encode a pointer, the value being pointed to is encoded. For nil
// pointers, Encode will encode the zero value of the type. A nil
// pointer to a struct type always encodes as an empty RLP list.
//
// Struct values are encoded as an RLP list of all their encoded
// public fields. Recursive struct types are supported.
//
// To encode slices and arrays, the elements are encoded as an RLP
// list of the value's elements. Note that arrays and slices with
// element type uint8 or byte are always encoded as an RLP string.
//
// A Go string is encoded as an RLP string.
//
// An unsigned integer value is encoded as an RLP string. Zero always
// encodes as an empty RLP string. Encode also supports *big.Int.
//
// An interface value encodes as the value contained in the interface.
//
// Boolean values are not supported, nor are signed integers, floating
// point numbers, maps, channels and functions.
func Encode(w io.Writer, val interface{}) error {
    if outer, ok := w.(*encbuf); ok {
        // Encode was called by some type's EncodeRLP.
        // Avoid copying by writing to the outer encbuf directly.
        return outer.encode(val)
    }
    eb := newencbuf()
    if err := eb.encode(val); err != nil {
        return err
    }
    return eb.toWriter(w)
}

// EncodeBytes returns the RLP encoding of val.
// Please see the documentation of Encode for the encoding rules.
func EncodeToBytes(val interface{}) ([]byte, error) {
    eb := newencbuf()
    if err := eb.encode(val); err != nil {
        return nil, err
    }
    return eb.toBytes(), nil
}

// EncodeReader returns a reader from which the RLP encoding of val
// can be read. The returned size is the total size of the encoded
// data.
//
// Please see the documentation of Encode for the encoding rules.
func EncodeToReader(val interface{}) (size int, r io.Reader, err error) {
    eb := newencbuf()
    if err := eb.encode(val); err != nil {
        return 0, nil, err
    }
    return eb.size(), &encReader{buf: eb}, nil
}

type encbuf struct {
    str     []byte      // string data, contains everything except list headers
    lheads  []*listhead // all list headers
    lhsize  int         // sum of sizes of all encoded list headers
    sizebuf []byte      // 9-byte auxiliary buffer for uint encoding
}

type listhead struct {
    offset int // index of this header in string data
    size   int // total size of encoded data (including list headers)
}

// encode writes head to the given buffer, which must be at least
// 9 bytes long. It returns the encoded bytes.
func (head *listhead) encode(buf []byte) []byte {
    if head.size < 56 {
        buf[0] = 0xC0 + byte(head.size)
        return buf[:1]
    } else {
        sizesize := putint(buf[1:], uint64(head.size))
        buf[0] = 0xF7 + byte(sizesize)
        return buf[:sizesize+1]
    }
}

func (head *listhead) tagsize() int {
    if head.size < 56 {
        return 1
    }
    return 1 + intsize(uint64(head.size))
}

func newencbuf() *encbuf {
    return &encbuf{sizebuf: make([]byte, 9)}
}

// encbuf implements io.Writer so it can be passed it into EncodeRLP.
func (w *encbuf) Write(b []byte) (int, error) {
    w.str = append(w.str, b...)
    return len(b), nil
}

func (w *encbuf) encode(val interface{}) error {
    rval := reflect.ValueOf(val)
    ti, err := cachedTypeInfo(rval.Type())
    if err != nil {
        return err
    }
    return ti.writer(rval, w)
}

func (w *encbuf) encodeStringHeader(size int) {
    if size < 56 {
        w.str = append(w.str, 0x80+byte(size))
    } else {
        // TODO: encode to w.str directly
        sizesize := putint(w.sizebuf[1:], uint64(size))
        w.sizebuf[0] = 0xB7 + byte(sizesize)
        w.str = append(w.str, w.sizebuf[:sizesize+1]...)
    }
}

func (w *encbuf) encodeString(b []byte) {
    w.encodeStringHeader(len(b))
    w.str = append(w.str, b...)
}

func (w *encbuf) list() *listhead {
    lh := &listhead{offset: len(w.str), size: w.lhsize}
    w.lheads = append(w.lheads, lh)
    return lh
}

func (w *encbuf) listEnd(lh *listhead) {
    lh.size = w.size() - lh.offset - lh.size
    if lh.size < 56 {
        w.lhsize += 1 // length encoded into kind tag
    } else {
        w.lhsize += 1 + intsize(uint64(lh.size))
    }
}

func (w *encbuf) size() int {
    return len(w.str) + w.lhsize
}

func (w *encbuf) toBytes() []byte {
    out := make([]byte, w.size())
    strpos := 0
    pos := 0
    for _, head := range w.lheads {
        // write string data before header
        n := copy(out[pos:], w.str[strpos:head.offset])
        pos += n
        strpos += n
        // write the header
        enc := head.encode(out[pos:])
        pos += len(enc)
    }
    // copy string data after the last list header
    copy(out[pos:], w.str[strpos:])
    return out
}

func (w *encbuf) toWriter(out io.Writer) (err error) {
    strpos := 0
    for _, head := range w.lheads {
        // write string data before header
        if head.offset-strpos > 0 {
            n, err := out.Write(w.str[strpos:head.offset])
            strpos += n
            if err != nil {
                return err
            }
        }
        // write the header
        enc := head.encode(w.sizebuf)
        if _, err = out.Write(enc); err != nil {
            return err
        }
    }
    if strpos < len(w.str) {
        // write string data after the last list header
        _, err = out.Write(w.str[strpos:])
    }
    return err
}

// encReader is the io.Reader returned by EncodeToReader.
// It releases its encbuf at EOF.
type encReader struct {
    buf    *encbuf // the buffer we're reading from. this is nil when we're at EOF.
    lhpos  int     // index of list header that we're reading
    strpos int     // current position in string buffer
    piece  []byte  // next piece to be read
}

func (r *encReader) Read(b []byte) (n int, err error) {
    for {
        if r.piece = r.next(); r.piece == nil {
            return n, io.EOF
        }
        nn := copy(b[n:], r.piece)
        n += nn
        if nn < len(r.piece) {
            // piece didn't fit, see you next time.
            r.piece = r.piece[nn:]
            return n, nil
        }
        r.piece = nil
    }
    panic("not reached")
}

// next returns the next piece of data to be read.
// it returns nil at EOF.
func (r *encReader) next() []byte {
    switch {
    case r.piece != nil:
        // There is still data available for reading.
        return r.piece

    case r.lhpos < len(r.buf.lheads):
        // We're before the last list header.
        head := r.buf.lheads[r.lhpos]
        sizebefore := head.offset - r.strpos
        if sizebefore > 0 {
            // String data before header.
            p := r.buf.str[r.strpos:head.offset]
            r.strpos += sizebefore
            return p
        } else {
            r.lhpos++
            return head.encode(r.buf.sizebuf)
        }

    case r.strpos < len(r.buf.str):
        // String data at the end, after all list headers.
        p := r.buf.str[r.strpos:]
        r.strpos = len(r.buf.str)
        return p

    default:
        return nil
    }
}

var (
    encoderInterface = reflect.TypeOf(new(Encoder)).Elem()
    big0             = big.NewInt(0)
)

// makeWriter creates a writer function for the given type.
func makeWriter(typ reflect.Type) (writer, error) {
    kind := typ.Kind()
    switch {
    case typ.Implements(encoderInterface):
        return writeEncoder, nil
    case kind != reflect.Ptr && reflect.PtrTo(typ).Implements(encoderInterface):
        return writeEncoderNoPtr, nil
    case kind == reflect.Interface:
        return writeInterface, nil
    case typ.AssignableTo(reflect.PtrTo(bigInt)):
        return writeBigIntPtr, nil
    case typ.AssignableTo(bigInt):
        return writeBigIntNoPtr, nil
    case isUint(kind):
        return writeUint, nil
    case kind == reflect.String:
        return writeString, nil
    case kind == reflect.Slice && typ.Elem().Kind() == reflect.Uint8 && !typ.Elem().Implements(encoderInterface):
        return writeBytes, nil
    case kind == reflect.Slice || kind == reflect.Array:
        return makeSliceWriter(typ)
    case kind == reflect.Struct:
        return makeStructWriter(typ)
    case kind == reflect.Ptr:
        return makePtrWriter(typ)
    default:
        return nil, fmt.Errorf("rlp: type %v is not RLP-serializable", typ)
    }
}

func writeUint(val reflect.Value, w *encbuf) error {
    i := val.Uint()
    if i == 0 {
        w.str = append(w.str, 0x80)
    } else if i < 128 {
        // fits single byte
        w.str = append(w.str, byte(i))
    } else {
        // TODO: encode int to w.str directly
        s := putint(w.sizebuf[1:], i)
        w.sizebuf[0] = 0x80 + byte(s)
        w.str = append(w.str, w.sizebuf[:s+1]...)
    }
    return nil
}

func writeBigIntPtr(val reflect.Value, w *encbuf) error {
    return writeBigInt(val.Interface().(*big.Int), w)
}

func writeBigIntNoPtr(val reflect.Value, w *encbuf) error {
    i := val.Interface().(big.Int)
    return writeBigInt(&i, w)
}

func writeBigInt(i *big.Int, w *encbuf) error {
    if cmp := i.Cmp(big0); cmp == -1 {
        return fmt.Errorf("rlp: cannot encode negative *big.Int")
    } else if cmp == 0 {
        w.str = append(w.str, 0x80)
    } else if bits := i.BitLen(); bits < 8 {
        // fits single byte
        w.str = append(w.str, byte(i.Uint64()))
    } else {
        w.encodeString(i.Bytes())
    }
    return nil
}

func writeBytes(val reflect.Value, w *encbuf) error {
    w.encodeString(val.Bytes())
    return nil
}

func writeString(val reflect.Value, w *encbuf) error {
    s := val.String()
    w.encodeStringHeader(len(s))
    w.str = append(w.str, s...)
    return nil
}

func writeEncoder(val reflect.Value, w *encbuf) error {
    return val.Interface().(Encoder).EncodeRLP(w)
}

// writeEncoderNoPtr handles non-pointer values that implement Encoder
// with a pointer receiver.
func writeEncoderNoPtr(val reflect.Value, w *encbuf) error {
    if !val.CanAddr() {
        // We can't get the address. It would be possible make the
        // value addressable by creating a shallow copy, but this
        // creates other problems so we're not doing it (yet).
        //
        // package json simply doesn't call MarshalJSON for cases like
        // this, but encodes the value as if it didn't implement the
        // interface. We don't want to handle it that way.
        return fmt.Errorf("rlp: game over: unadressable value of type %v, EncodeRLP is pointer method", val.Type())
    }
    return val.Addr().Interface().(Encoder).EncodeRLP(w)
}

func writeInterface(val reflect.Value, w *encbuf) error {
    if val.IsNil() {
        // Write empty list. This is consistent with the previous RLP
        // encoder that we had and should therefore avoid any
        // problems.
        w.str = append(w.str, 0xC0)
        return nil
    }
    eval := val.Elem()
    ti, err := cachedTypeInfo(eval.Type())
    if err != nil {
        return err
    }
    return ti.writer(eval, w)
}

func makeSliceWriter(typ reflect.Type) (writer, error) {
    etypeinfo, err := cachedTypeInfo1(typ.Elem())
    if err != nil {
        return nil, err
    }
    writer := func(val reflect.Value, w *encbuf) error {
        lh := w.list()
        vlen := val.Len()
        for i := 0; i < vlen; i++ {
            if err := etypeinfo.writer(val.Index(i), w); err != nil {
                return err
            }
        }
        w.listEnd(lh)
        return nil
    }
    return writer, nil
}

func makeStructWriter(typ reflect.Type) (writer, error) {
    fields, err := structFields(typ)
    if err != nil {
        return nil, err
    }
    writer := func(val reflect.Value, w *encbuf) error {
        lh := w.list()
        for _, f := range fields {
            if err := f.info.writer(val.Field(f.index), w); err != nil {
                return err
            }
        }
        w.listEnd(lh)
        return nil
    }
    return writer, nil
}

func makePtrWriter(typ reflect.Type) (writer, error) {
    etypeinfo, err := cachedTypeInfo1(typ.Elem())
    if err != nil {
        return nil, err
    }
    zero := reflect.Zero(typ.Elem())
    kind := typ.Elem().Kind()
    writer := func(val reflect.Value, w *encbuf) error {
        switch {
        case !val.IsNil():
            return etypeinfo.writer(val.Elem(), w)
        case kind == reflect.Struct:
            // encoding the zero value of a struct could trigger
            // infinite recursion, avoid that.
            w.listEnd(w.list())
            return nil
        default:
            return etypeinfo.writer(zero, w)
        }
    }
    return writer, err
}

// putint writes i to the beginning of b in with big endian byte
// order, using the least number of bytes needed to represent i.
func putint(b []byte, i uint64) (size int) {
    switch {
    case i < (1 << 8):
        b[0] = byte(i)
        return 1
    case i < (1 << 16):
        b[0] = byte(i >> 8)
        b[1] = byte(i)
        return 2
    case i < (1 << 24):
        b[0] = byte(i >> 16)
        b[1] = byte(i >> 8)
        b[2] = byte(i)
        return 3
    case i < (1 << 32):
        b[0] = byte(i >> 24)
        b[1] = byte(i >> 16)
        b[2] = byte(i >> 8)
        b[3] = byte(i)
        return 4
    case i < (1 << 40):
        b[0] = byte(i >> 32)
        b[1] = byte(i >> 24)
        b[2] = byte(i >> 16)
        b[3] = byte(i >> 8)
        b[4] = byte(i)
        return 5
    case i < (1 << 48):
        b[0] = byte(i >> 40)
        b[1] = byte(i >> 32)
        b[2] = byte(i >> 24)
        b[3] = byte(i >> 16)
        b[4] = byte(i >> 8)
        b[5] = byte(i)
        return 6
    case i < (1 << 56):
        b[0] = byte(i >> 48)
        b[1] = byte(i >> 40)
        b[2] = byte(i >> 32)
        b[3] = byte(i >> 24)
        b[4] = byte(i >> 16)
        b[5] = byte(i >> 8)
        b[6] = byte(i)
        return 7
    default:
        b[0] = byte(i >> 56)
        b[1] = byte(i >> 48)
        b[2] = byte(i >> 40)
        b[3] = byte(i >> 32)
        b[4] = byte(i >> 24)
        b[5] = byte(i >> 16)
        b[6] = byte(i >> 8)
        b[7] = byte(i)
        return 8
    }
}

// intsize computes the minimum number of bytes required to store i.
func intsize(i uint64) (size int) {
    for size = 1; ; size++ {
        if i >>= 8; i == 0 {
            return size
        }
    }
    panic("not reached")
}