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unlacer.go
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unlacer.go
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// Copyright 2019 The ebml-go authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ebml
import (
"errors"
"io"
)
// ErrFixedLaceUndivisible means that a length of a fixed lacing data is undivisible.
var ErrFixedLaceUndivisible = errors.New("undivisible fixed lace")
// Unlacer is the interface to read laced frames in Block.
type Unlacer interface {
Read() ([]byte, error)
}
type unlacer struct {
r io.Reader
i int
size []int
}
func (u *unlacer) Read() ([]byte, error) {
if u.i >= len(u.size) {
return nil, io.EOF
}
n := u.size[u.i]
u.i++
b := make([]byte, n)
_, err := io.ReadFull(u.r, b)
return b, err
}
// NewNoUnlacer creates pass-through Unlacer for not laced data.
func NewNoUnlacer(r io.Reader, n int64) (Unlacer, error) {
return &unlacer{r: r, size: []int{int(n)}}, nil
}
// NewXiphUnlacer creates Unlacer for Xiph laced data.
func NewXiphUnlacer(r io.Reader, n int64) (Unlacer, error) {
var nFrame int
var b [1]byte
switch _, err := r.Read(b[:]); err {
case nil:
nFrame = int(b[0]) + 1
case io.EOF:
return nil, io.ErrUnexpectedEOF
default:
return nil, err
}
n--
ul := &unlacer{
r: r,
size: make([]int, nFrame),
}
for i := 0; i < nFrame-1; i++ {
for {
switch _, err := ul.r.Read(b[:]); err {
case nil:
case io.EOF:
return nil, io.ErrUnexpectedEOF
default:
return nil, err
}
n--
ul.size[i] += int(b[0])
if b[0] != 0xFF {
ul.size[nFrame-1] -= ul.size[i]
break
}
}
}
ul.size[nFrame-1] += int(n)
if ul.size[nFrame-1] <= 0 {
return nil, io.ErrUnexpectedEOF
}
return ul, nil
}
// NewFixedUnlacer creates Unlacer for Fixed laced data.
func NewFixedUnlacer(r io.Reader, n int64) (Unlacer, error) {
var nFrame int
var b [1]byte
switch _, err := r.Read(b[:]); err {
case nil:
nFrame = int(b[0]) + 1
case io.EOF:
return nil, io.ErrUnexpectedEOF
default:
return nil, err
}
ul := &unlacer{
r: r,
size: make([]int, nFrame),
}
ul.size[0] = (int(n) - 1) / nFrame
for i := 1; i < nFrame; i++ {
ul.size[i] = ul.size[0]
}
if ul.size[0]*nFrame+1 != int(n) {
return nil, wrapErrorf(
ErrFixedLaceUndivisible, "unlacing %d bytes of %d frames", n-1, nFrame,
)
}
return ul, nil
}
// NewEBMLUnlacer creates Unlacer for EBML laced data.
func NewEBMLUnlacer(r io.Reader, n int64) (Unlacer, error) {
var nFrame int
var b [1]byte
switch _, err := r.Read(b[:]); err {
case nil:
nFrame = int(b[0]) + 1
case io.EOF:
return nil, io.ErrUnexpectedEOF
default:
return nil, err
}
n--
vd := &valueDecoder{}
ul := &unlacer{
r: r,
size: make([]int, nFrame),
}
un64, nRead, err := vd.readVUInt(ul.r)
if err != nil {
return nil, err
}
n64 := int64(un64)
n -= int64(nRead)
ul.size[0] = int(n64)
ul.size[nFrame-1] -= int(n64)
for i := 1; i < nFrame-1; i++ {
n64Diff, nRead, err := vd.readVInt(ul.r)
n64 += int64(n64Diff)
if err != nil {
return nil, err
}
if n64 <= 0 {
return nil, io.ErrUnexpectedEOF
}
n -= int64(nRead)
ul.size[i] = int(n64)
ul.size[nFrame-1] -= int(n64)
}
ul.size[nFrame-1] += int(n)
if ul.size[nFrame-1] <= 0 {
return nil, io.ErrUnexpectedEOF
}
return ul, nil
}