Add backend.readSeeker

This struct implements an io.ReadSeeker on top of a backend. This is the
easiest way to make the packer compatible to the new backend without
loading a complete pack into a bytes.Buffer.
This commit is contained in:
Alexander Neumann 2016-02-20 23:59:07 +01:00
parent b114ab7108
commit 482fc9f51d
2 changed files with 177 additions and 0 deletions

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@ -0,0 +1,63 @@
package backend
import (
"errors"
"io"
)
type readSeeker struct {
be Backend
h Handle
t Type
name string
offset int64
size int64
}
// NewReadSeeker returns an io.ReadSeeker for the given object in the backend.
func NewReadSeeker(be Backend, h Handle) io.ReadSeeker {
return &readSeeker{be: be, h: h}
}
func (rd *readSeeker) Read(p []byte) (int, error) {
n, err := rd.be.Load(rd.h, p, rd.offset)
rd.offset += int64(n)
return n, err
}
func (rd *readSeeker) Seek(offset int64, whence int) (n int64, err error) {
switch whence {
case 0:
rd.offset = offset
case 1:
rd.offset += offset
case 2:
if rd.size == 0 {
rd.size, err = rd.getSize()
if err != nil {
return 0, err
}
}
pos := rd.size + offset
if pos < 0 {
return 0, errors.New("invalid offset, before start of blob")
}
rd.offset = pos
return rd.offset, nil
default:
return 0, errors.New("invalid value for parameter whence")
}
return rd.offset, nil
}
func (rd *readSeeker) getSize() (int64, error) {
stat, err := rd.be.Stat(rd.h)
if err != nil {
return 0, err
}
return stat.Size, nil
}

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@ -0,0 +1,114 @@
package backend_test
import (
"bytes"
"io"
"math/rand"
"restic/backend"
"restic/backend/mem"
"testing"
. "restic/test"
)
func abs(a int) int {
if a < 0 {
return -a
}
return a
}
func loadAndCompare(t testing.TB, rd io.ReadSeeker, size int, offset int64, expected []byte) {
var (
pos int64
err error
)
if offset >= 0 {
pos, err = rd.Seek(offset, 0)
} else {
pos, err = rd.Seek(offset, 2)
}
if err != nil {
t.Errorf("Seek(%d, 0) returned error: %v", offset, err)
return
}
if offset >= 0 && pos != offset {
t.Errorf("pos after seek is wrong, want %d, got %d", offset, pos)
} else if offset < 0 && pos != int64(size)+offset {
t.Errorf("pos after relative seek is wrong, want %d, got %d", int64(size)+offset, pos)
}
buf := make([]byte, len(expected))
n, err := rd.Read(buf)
// if we requested data beyond the end of the file, ignore
// ErrUnexpectedEOF error
if offset > 0 && len(buf) > size && err == io.ErrUnexpectedEOF {
err = nil
buf = buf[:size]
}
if offset < 0 && len(buf) > abs(int(offset)) && err == io.ErrUnexpectedEOF {
err = nil
buf = buf[:abs(int(offset))]
}
if n != len(buf) {
t.Errorf("Load(%d, %d): wrong length returned, want %d, got %d",
len(buf), offset, len(buf), n)
return
}
if err != nil {
t.Errorf("Load(%d, %d): unexpected error: %v", len(buf), offset, err)
return
}
buf = buf[:n]
if !bytes.Equal(buf, expected) {
t.Errorf("Load(%d, %d) returned wrong bytes", len(buf), offset)
return
}
}
func TestReadSeeker(t *testing.T) {
b := mem.New()
length := rand.Intn(1<<24) + 2000
data := Random(23, length)
id := backend.Hash(data)
handle := backend.Handle{Type: backend.Data, Name: id.String()}
err := b.Save(handle, data)
if err != nil {
t.Fatalf("Save() error: %v", err)
}
for i := 0; i < 50; i++ {
l := rand.Intn(length + 2000)
o := rand.Intn(length + 2000)
if rand.Float32() > 0.5 {
o = -o
}
d := data
if o > 0 && o < len(d) {
d = d[o:]
} else {
o = len(d)
d = d[:0]
}
if l > 0 && l < len(d) {
d = d[:l]
}
rd := backend.NewReadSeeker(b, handle)
loadAndCompare(t, rd, len(data), int64(o), d)
}
}