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