ebiten/audio/wav/sectionreader.go
2024-07-14 22:56:26 +09:00

80 lines
1.9 KiB
Go

// Copyright 2024 The Ebitengine 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 wav
import (
"fmt"
"io"
)
// sectionReader is similar to io.SectionReader but takes an io.Reader instead of io.ReaderAt.
type sectionReader struct {
src io.Reader
offset int64
size int64
pos int64
}
// newSectionReader creates a new sectionReader.
func newSectionReader(src io.Reader, offset int64, size int64) *sectionReader {
return &sectionReader{
src: src,
offset: offset,
size: size,
}
}
// Read is implementation of io.Reader's Read.
func (s *sectionReader) Read(p []byte) (int, error) {
if s.pos >= s.size {
return 0, io.EOF
}
if s.pos+int64(len(p)) > s.size {
p = p[:s.size-s.pos]
}
n, err := s.src.Read(p)
s.pos += int64(n)
return n, err
}
// Seek is implementation of io.Seeker's Seek.
//
// If the underlying source is not an io.Seeker, Seek panics.
func (s *sectionReader) Seek(offset int64, whence int) (int64, error) {
seeker, ok := s.src.(io.Seeker)
if !ok {
panic("wav: s.src must be io.Seeker but not")
}
switch whence {
case io.SeekStart:
offset += s.offset
case io.SeekCurrent:
case io.SeekEnd:
offset += s.offset + s.size
whence = io.SeekStart
}
n, err := seeker.Seek(offset, whence)
if err != nil {
return 0, err
}
s.pos = n - s.offset
if s.pos < 0 || s.pos > s.size {
return 0, fmt.Errorf("wav: position is out of range")
}
return s.pos, nil
}