audio: Add Loop

exp/audio/loop.go

@@ -0,0 +1,68 @@
+// Copyright 2016 Hajime Hoshi
+//
+// 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 audio
+
+import (
+	"io"
+)
+
+type Loop struct {
+	stream ReadSeekCloser
+	size   int64
+	pos    int64
+}
+
+func NewLoop(stream ReadSeekCloser, size int64) ReadSeekCloser {
+	return &Loop{
+		stream: stream,
+		size:   size,
+	}
+}
+
+func (l *Loop) Read(b []byte) (int, error) {
+	n, err := l.stream.Read(b)
+	l.pos += int64(n)
+	l.pos %= l.size
+	if err == io.EOF {
+		if _, err := l.Seek(0, 0); err != nil {
+			return 0, err
+		}
+		err = nil
+	}
+	return n, err
+}
+
+func (l *Loop) Seek(offset int64, whence int) (int64, error) {
+	next := int64(0)
+	switch whence {
+	case 0:
+		next = offset
+	case 1:
+		next = int64(l.pos) + offset
+	case 2:
+		panic("audio: whence must be 0 or 1 for a loop stream")
+	}
+	next %= l.size
+	pos, err := l.stream.Seek(next, 0)
+	if err != nil {
+		return 0, err
+	}
+	l.pos = pos
+	return l.pos, nil
+}
+
+func (l *Loop) Close() error {
+	return l.stream.Close()
+}