Adding upstream version 1.2.0.

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

wrapio/limitwrap.go

@@ -0,0 +1,94 @@
+package wrapio
+
+import (
+	"encoding/gob"
+	"io"
+
+	"github.com/djherbis/buffer/limio"
+)
+
+// ReadWriterAt implements io.ReaderAt and io.WriterAt
+type ReadWriterAt interface {
+	io.ReaderAt
+	io.WriterAt
+}
+
+// Wrapper implements a io.ReadWriter and ReadWriterAt such that
+// when reading/writing goes past N bytes, it "wraps" back to the beginning.
+type Wrapper struct {
+	// N is the offset at which to "wrap" back to the start
+	N int64
+	// L is the length of the data written
+	L int64
+	// O is our offset in the data
+	O   int64
+	rwa ReadWriterAt
+}
+
+// NewWrapper creates a Wrapper based on ReadWriterAt rwa.
+// L is the current length, O is the current offset, and N is offset at which we "wrap".
+func NewWrapper(rwa ReadWriterAt, L, O, N int64) *Wrapper {
+	return &Wrapper{
+		L:   L,
+		O:   O,
+		N:   N,
+		rwa: rwa,
+	}
+}
+
+// Len returns the # of bytes in the Wrapper
+func (wpr *Wrapper) Len() int64 {
+	return wpr.L
+}
+
+// Cap returns the "wrap" offset (max # of bytes)
+func (wpr *Wrapper) Cap() int64 {
+	return wpr.N
+}
+
+// Reset seeks to the start (0 offset), and sets the length to 0.
+func (wpr *Wrapper) Reset() {
+	wpr.O = 0
+	wpr.L = 0
+}
+
+// SetReadWriterAt lets you switch the underlying Read/WriterAt
+func (wpr *Wrapper) SetReadWriterAt(rwa ReadWriterAt) {
+	wpr.rwa = rwa
+}
+
+// Read reads from the current offset into p, wrapping at Cap()
+func (wpr *Wrapper) Read(p []byte) (n int, err error) {
+	n, err = wpr.ReadAt(p, 0)
+	wpr.L -= int64(n)
+	wpr.O += int64(n)
+	wpr.O %= wpr.N
+	return n, err
+}
+
+// ReadAt reads from the current offset+off into p, wrapping at Cap()
+func (wpr *Wrapper) ReadAt(p []byte, off int64) (n int, err error) {
+	wrap := NewWrapReader(wpr.rwa, wpr.O+off, wpr.N)
+	r := io.LimitReader(wrap, wpr.L-off)
+	return r.Read(p)
+}
+
+// Write writes p to the end of the Wrapper (at Len()), wrapping at Cap()
+func (wpr *Wrapper) Write(p []byte) (n int, err error) {
+	return wpr.WriteAt(p, wpr.L)
+}
+
+// WriteAt writes p at the current offset+off, wrapping at Cap()
+func (wpr *Wrapper) WriteAt(p []byte, off int64) (n int, err error) {
+	wrap := NewWrapWriter(wpr.rwa, wpr.O+off, wpr.N)
+	w := limio.LimitWriter(wrap, wpr.N-off)
+	n, err = w.Write(p)
+	if wpr.L < off+int64(n) {
+		wpr.L = int64(n) + off
+	}
+	return n, err
+}
+
+func init() {
+	gob.Register(&Wrapper{})
+}

wrapio/wrap.go

@@ -0,0 +1,139 @@
+package wrapio
+
+import "io"
+
+// DoerAt is a common interface for wrappers WriteAt or ReadAt functions
+type DoerAt interface {
+	DoAt([]byte, int64) (int, error)
+}
+
+// DoAtFunc is implemented by ReadAt/WriteAt
+type DoAtFunc func([]byte, int64) (int, error)
+
+type wrapper struct {
+	off    int64
+	wrapAt int64
+	doat   DoAtFunc
+}
+
+func (w *wrapper) Offset() int64 {
+	return w.off
+}
+
+func (w *wrapper) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	case 0:
+		w.off = offset
+	case 1:
+		w.off += offset
+	case 2:
+		w.off = (w.wrapAt + offset)
+	}
+	w.off %= w.wrapAt
+	return w.off, nil
+}
+
+func (w *wrapper) DoAt(p []byte, off int64) (n int, err error) {
+	return w.doat(p, off)
+}
+
+// WrapWriter wraps writes around a section of data.
+type WrapWriter struct {
+	*wrapper
+}
+
+// NewWrapWriter creates a WrapWriter starting at offset off, and wrapping at offset wrapAt.
+func NewWrapWriter(w io.WriterAt, off int64, wrapAt int64) *WrapWriter {
+	return &WrapWriter{
+		&wrapper{
+			doat:   w.WriteAt,
+			off:    (off % wrapAt),
+			wrapAt: wrapAt,
+		},
+	}
+}
+
+// Write writes p starting at the current offset, wrapping when it reaches the end.
+// The current offset is shifted forward by the amount written.
+func (w *WrapWriter) Write(p []byte) (n int, err error) {
+	n, err = Wrap(w, p, w.off, w.wrapAt)
+	w.off = (w.off + int64(n)) % w.wrapAt
+	return n, err
+}
+
+// WriteAt writes p starting at offset off, wrapping when it reaches the end.
+func (w *WrapWriter) WriteAt(p []byte, off int64) (n int, err error) {
+	return Wrap(w, p, off, w.wrapAt)
+}
+
+// WrapReader wraps reads around a section of data.
+type WrapReader struct {
+	*wrapper
+}
+
+// NewWrapReader creates a WrapReader starting at offset off, and wrapping at offset wrapAt.
+func NewWrapReader(r io.ReaderAt, off int64, wrapAt int64) *WrapReader {
+	return &WrapReader{
+		&wrapper{
+			doat:   r.ReadAt,
+			off:    (off % wrapAt),
+			wrapAt: wrapAt,
+		},
+	}
+}
+
+// Read reads into p starting at the current offset, wrapping if it reaches the end.
+// The current offset is shifted forward by the amount read.
+func (r *WrapReader) Read(p []byte) (n int, err error) {
+	n, err = Wrap(r, p, r.off, r.wrapAt)
+	r.off = (r.off + int64(n)) % r.wrapAt
+	return n, err
+}
+
+// ReadAt reads into p starting at the current offset, wrapping when it reaches the end.
+func (r *WrapReader) ReadAt(p []byte, off int64) (n int, err error) {
+	return Wrap(r, p, off, r.wrapAt)
+}
+
+// maxConsecutiveEmptyActions determines how many consecutive empty reads/writes can occur before giving up
+const maxConsecutiveEmptyActions = 100
+
+// Wrap causes an action on an array of bytes (like read/write) to be done from an offset off,
+// wrapping at offset wrapAt.
+func Wrap(w DoerAt, p []byte, off int64, wrapAt int64) (n int, err error) {
+	var m, fails int
+
+	off %= wrapAt
+
+	for len(p) > 0 {
+
+		if off+int64(len(p)) < wrapAt {
+			m, err = w.DoAt(p, off)
+		} else {
+			space := wrapAt - off
+			m, err = w.DoAt(p[:space], off)
+		}
+
+		if err != nil && err != io.EOF {
+			return n + m, err
+		}
+
+		switch m {
+		case 0:
+			fails++
+		default:
+			fails = 0
+		}
+
+		if fails > maxConsecutiveEmptyActions {
+			return n + m, io.ErrNoProgress
+		}
+
+		n += m
+		p = p[m:]
+		off += int64(m)
+		off %= wrapAt
+	}
+
+	return n, err
+}

wrapio/wrapio_test.go

@@ -0,0 +1,44 @@
+package wrapio
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestWrapper(t *testing.T) {
+	if file, err := ioutil.TempFile("", "wrap.test"); err == nil {
+		defer os.Remove(file.Name())
+		defer file.Close()
+		file.Write([]byte("abcdef"))
+
+		data := make([]byte, 12)
+
+		w := NewWrapper(file, 6, 1, 6)
+		if n, err := w.ReadAt(data, 1); err == nil || err == io.EOF {
+			if !bytes.Equal(data[:n], []byte("cdefa")) {
+				t.Errorf("Exp cdefa, Got %s", data[:n])
+			}
+		} else {
+			t.Error(err.Error())
+		}
+	}
+}
+
+func TestWrap(t *testing.T) {
+	if file, err := ioutil.TempFile("", "wrap.test"); err == nil {
+		w := NewWrapWriter(file, 0, 3)
+		w.Write([]byte("abcdef"))
+
+		r := NewWrapReader(file, 0, 2)
+		data := make([]byte, 6)
+		r.Read(data)
+		if !bytes.Equal(data, []byte("dedede")) {
+			t.Error("Wrapper error!")
+		}
+		file.Close()
+		os.Remove(file.Name())
+	}
+}