Adding upstream version 1.2.0.

Signed-off-by: Daniel Baumann <daniel@debian.org>

ring.go

@@ -0,0 +1,58 @@
+package buffer
+
+import (
+	"io"
+	"math"
+
+	"github.com/djherbis/buffer/wrapio"
+)
+
+type ring struct {
+	BufferAt
+	L int64
+	*wrapio.WrapReader
+	*wrapio.WrapWriter
+}
+
+// NewRing returns a Ring Buffer from a BufferAt.
+// It overwrites old data in the Buffer when needed (when its full).
+func NewRing(buffer BufferAt) Buffer {
+	return &ring{
+		BufferAt:   buffer,
+		WrapReader: wrapio.NewWrapReader(buffer, 0, buffer.Cap()),
+		WrapWriter: wrapio.NewWrapWriter(buffer, 0, buffer.Cap()),
+	}
+}
+
+func (buf *ring) Len() int64 {
+	return buf.L
+}
+
+func (buf *ring) Cap() int64 {
+	return math.MaxInt64
+}
+
+func (buf *ring) Read(p []byte) (n int, err error) {
+	if buf.L == buf.BufferAt.Cap() {
+		buf.WrapReader.Seek(buf.WrapWriter.Offset(), 0)
+	}
+	n, err = io.LimitReader(buf.WrapReader, buf.L).Read(p)
+	buf.L -= int64(n)
+	return n, err
+}
+
+func (buf *ring) Write(p []byte) (n int, err error) {
+	n, err = buf.WrapWriter.Write(p)
+	buf.L += int64(n)
+	if buf.L > buf.BufferAt.Cap() {
+		buf.L = buf.BufferAt.Cap()
+	}
+	return n, err
+}
+
+func (buf *ring) Reset() {
+	buf.BufferAt.Reset()
+	buf.L = 0
+	buf.WrapReader = wrapio.NewWrapReader(buf.BufferAt, 0, buf.BufferAt.Cap())
+	buf.WrapWriter = wrapio.NewWrapWriter(buf.BufferAt, 0, buf.BufferAt.Cap())
+}