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stream.go
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stream.go
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// Copyright (c) Faye Amacker. All rights reserved.
// Licensed under the MIT License. See LICENSE in the project root for license information.
package cbor
import (
"bytes"
"errors"
"io"
"reflect"
)
// Decoder reads and decodes CBOR values from io.Reader.
type Decoder struct {
r io.Reader
d decoder
buf []byte
off int // next read offset in buf
bytesRead int
}
// NewDecoder returns a new decoder that reads and decodes from r using
// the default decoding options.
func NewDecoder(r io.Reader) *Decoder {
return defaultDecMode.NewDecoder(r)
}
// Decode reads CBOR value and decodes it into the value pointed to by v.
func (dec *Decoder) Decode(v interface{}) error {
_, err := dec.readNext()
if err != nil {
// Return validation error or read error.
return err
}
dec.d.reset(dec.buf[dec.off:])
err = dec.d.value(v)
// Increment dec.off even if decoding err is not nil because
// dec.d.off points to the next CBOR data item if current
// CBOR data item is valid but failed to be decoded into v.
// This allows next CBOR data item to be decoded in next
// call to this function.
dec.off += dec.d.off
dec.bytesRead += dec.d.off
return err
}
// Skip skips to the next CBOR data item (if there is any),
// otherwise it returns error such as io.EOF, io.UnexpectedEOF, etc.
func (dec *Decoder) Skip() error {
n, err := dec.readNext()
if err != nil {
// Return validation error or read error.
return err
}
dec.off += n
dec.bytesRead += n
return nil
}
// NumBytesRead returns the number of bytes read.
func (dec *Decoder) NumBytesRead() int {
return dec.bytesRead
}
// Buffered returns a reader for data remaining in Decoder's buffer.
// Returned reader is valid until the next call to Decode or Skip.
func (dec *Decoder) Buffered() io.Reader {
return bytes.NewReader(dec.buf[dec.off:])
}
// readNext() reads next CBOR data item from Reader to buffer.
// It returns the size of next CBOR data item.
// It also returns validation error or read error if any.
func (dec *Decoder) readNext() (int, error) {
var readErr error
var validErr error
for {
// Process any unread data in dec.buf.
if dec.off < len(dec.buf) {
dec.d.reset(dec.buf[dec.off:])
off := dec.off // Save offset before data validation
validErr = dec.d.wellformed(true, false)
dec.off = off // Restore offset
if validErr == nil {
return dec.d.off, nil
}
if validErr != io.ErrUnexpectedEOF {
return 0, validErr
}
// Process last read error on io.ErrUnexpectedEOF.
if readErr != nil {
if readErr == io.EOF {
// current CBOR data item is incomplete.
return 0, io.ErrUnexpectedEOF
}
return 0, readErr
}
}
// More data is needed and there was no read error.
var n int
for n == 0 {
n, readErr = dec.read()
if n == 0 && readErr != nil {
// No more data can be read and read error is encountered.
// At this point, validErr is either nil or io.ErrUnexpectedEOF.
if readErr == io.EOF {
if validErr == io.ErrUnexpectedEOF {
// current CBOR data item is incomplete.
return 0, io.ErrUnexpectedEOF
}
}
return 0, readErr
}
}
// At this point, dec.buf contains new data from last read (n > 0).
}
}
// read() reads data from Reader to buffer.
// It returns number of bytes read and any read error encountered.
// Postconditions:
// - dec.buf contains previously unread data and new data.
// - dec.off is 0.
func (dec *Decoder) read() (int, error) {
// Grow buf if needed.
const minRead = 512
if cap(dec.buf)-len(dec.buf)+dec.off < minRead {
oldUnreadBuf := dec.buf[dec.off:]
dec.buf = make([]byte, len(dec.buf)-dec.off, 2*cap(dec.buf)+minRead)
dec.overwriteBuf(oldUnreadBuf)
}
// Copy unread data over read data and reset off to 0.
if dec.off > 0 {
dec.overwriteBuf(dec.buf[dec.off:])
}
// Read from reader and reslice buf.
n, err := dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
dec.buf = dec.buf[0 : len(dec.buf)+n]
return n, err
}
func (dec *Decoder) overwriteBuf(newBuf []byte) {
n := copy(dec.buf, newBuf)
dec.buf = dec.buf[:n]
dec.off = 0
}
// Encoder writes CBOR values to io.Writer.
type Encoder struct {
w io.Writer
em *encMode
indefTypes []cborType
}
// NewEncoder returns a new encoder that writes to w using the default encoding options.
func NewEncoder(w io.Writer) *Encoder {
return defaultEncMode.NewEncoder(w)
}
// Encode writes the CBOR encoding of v.
func (enc *Encoder) Encode(v interface{}) error {
if len(enc.indefTypes) > 0 && v != nil {
indefType := enc.indefTypes[len(enc.indefTypes)-1]
if indefType == cborTypeTextString {
k := reflect.TypeOf(v).Kind()
if k != reflect.String {
return errors.New("cbor: cannot encode item type " + k.String() + " for indefinite-length text string")
}
} else if indefType == cborTypeByteString {
t := reflect.TypeOf(v)
k := t.Kind()
if (k != reflect.Array && k != reflect.Slice) || t.Elem().Kind() != reflect.Uint8 {
return errors.New("cbor: cannot encode item type " + k.String() + " for indefinite-length byte string")
}
}
}
buf := getEncodeBuffer()
err := encode(buf, enc.em, reflect.ValueOf(v))
if err == nil {
_, err = enc.w.Write(buf.Bytes())
}
putEncodeBuffer(buf)
return err
}
// StartIndefiniteByteString starts byte string encoding of indefinite length.
// Subsequent calls of (*Encoder).Encode() encodes definite length byte strings
// ("chunks") as one contiguous string until EndIndefinite is called.
func (enc *Encoder) StartIndefiniteByteString() error {
return enc.startIndefinite(cborTypeByteString)
}
// StartIndefiniteTextString starts text string encoding of indefinite length.
// Subsequent calls of (*Encoder).Encode() encodes definite length text strings
// ("chunks") as one contiguous string until EndIndefinite is called.
func (enc *Encoder) StartIndefiniteTextString() error {
return enc.startIndefinite(cborTypeTextString)
}
// StartIndefiniteArray starts array encoding of indefinite length.
// Subsequent calls of (*Encoder).Encode() encodes elements of the array
// until EndIndefinite is called.
func (enc *Encoder) StartIndefiniteArray() error {
return enc.startIndefinite(cborTypeArray)
}
// StartIndefiniteMap starts array encoding of indefinite length.
// Subsequent calls of (*Encoder).Encode() encodes elements of the map
// until EndIndefinite is called.
func (enc *Encoder) StartIndefiniteMap() error {
return enc.startIndefinite(cborTypeMap)
}
// EndIndefinite closes last opened indefinite length value.
func (enc *Encoder) EndIndefinite() error {
if len(enc.indefTypes) == 0 {
return errors.New("cbor: cannot encode \"break\" code outside indefinite length values")
}
_, err := enc.w.Write([]byte{cborBreakFlag})
if err == nil {
enc.indefTypes = enc.indefTypes[:len(enc.indefTypes)-1]
}
return err
}
var cborIndefHeader = map[cborType][]byte{
cborTypeByteString: {cborByteStringWithIndefiniteLengthHead},
cborTypeTextString: {cborTextStringWithIndefiniteLengthHead},
cborTypeArray: {cborArrayWithIndefiniteLengthHead},
cborTypeMap: {cborMapWithIndefiniteLengthHead},
}
func (enc *Encoder) startIndefinite(typ cborType) error {
if enc.em.indefLength == IndefLengthForbidden {
return &IndefiniteLengthError{typ}
}
_, err := enc.w.Write(cborIndefHeader[typ])
if err == nil {
enc.indefTypes = append(enc.indefTypes, typ)
}
return err
}
// RawMessage is a raw encoded CBOR value.
type RawMessage []byte
// MarshalCBOR returns m or CBOR nil if m is nil.
func (m RawMessage) MarshalCBOR() ([]byte, error) {
if len(m) == 0 {
return cborNil, nil
}
return m, nil
}
// UnmarshalCBOR creates a copy of data and saves to *m.
func (m *RawMessage) UnmarshalCBOR(data []byte) error {
if m == nil {
return errors.New("cbor.RawMessage: UnmarshalCBOR on nil pointer")
}
*m = append((*m)[0:0], data...)
return nil
}