120 lines
2.4 KiB
Go
120 lines
2.4 KiB
Go
// Copyright 2017 Hajime Hoshi
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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 mp3
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import (
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"errors"
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"io"
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)
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type source struct {
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reader io.Reader
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buf []byte
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pos int64
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}
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func (s *source) Seek(position int64, whence int) (int64, error) {
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seeker, ok := s.reader.(io.Seeker)
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if !ok {
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return 0, errors.New("mp3: source must be io.Seeker")
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}
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s.buf = nil
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n, err := seeker.Seek(position, whence)
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if err != nil {
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return 0, err
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}
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s.pos = n
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return n, nil
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}
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func (s *source) skipTags() error {
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buf := make([]byte, 3)
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if _, err := s.ReadFull(buf); err != nil {
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return err
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}
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switch string(buf) {
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case "TAG":
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buf := make([]byte, 125)
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if _, err := s.ReadFull(buf); err != nil {
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return err
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}
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case "ID3":
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// Skip version (2 bytes) and flag (1 byte)
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buf := make([]byte, 3)
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if _, err := s.ReadFull(buf); err != nil {
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return err
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}
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buf = make([]byte, 4)
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n, err := s.ReadFull(buf)
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if err != nil {
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return err
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}
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if n != 4 {
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return nil
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}
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size := (uint32(buf[0]) << 21) | (uint32(buf[1]) << 14) |
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(uint32(buf[2]) << 7) | uint32(buf[3])
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buf = make([]byte, size)
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if _, err := s.ReadFull(buf); err != nil {
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return err
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}
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default:
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s.Unread(buf)
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}
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return nil
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}
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func (s *source) rewind() error {
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if _, err := s.Seek(0, io.SeekStart); err != nil {
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return err
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}
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s.pos = 0
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s.buf = nil
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return nil
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}
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func (s *source) Unread(buf []byte) {
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s.buf = append(s.buf, buf...)
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s.pos -= int64(len(buf))
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}
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func (s *source) ReadFull(buf []byte) (int, error) {
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read := 0
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if s.buf != nil {
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read = copy(buf, s.buf)
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if len(s.buf) > read {
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s.buf = s.buf[read:]
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} else {
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s.buf = nil
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}
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if len(buf) == read {
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return read, nil
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}
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}
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n, err := io.ReadFull(s.reader, buf[read:])
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if err != nil {
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// Allow if all data can't be read. This is common.
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if err == io.ErrUnexpectedEOF {
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err = io.EOF
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}
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}
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s.pos += int64(n)
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return n + read, err
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}
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