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// Copyright (c) 2011 CZ.NIC z.s.p.o. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// blame: jnml, labs.nic.cz
package storage
import (
"errors"
"fmt"
"io/ioutil"
"math"
"os"
)
//TODO -> exported type w/ exported fields
type memaccessor struct {
f *os.File
fi *FileInfo
b []byte
}
// Implementation of Accessor.
func (m *memaccessor) BeginUpdate() error { return nil }
// Implementation of Accessor.
func (f *memaccessor) EndUpdate() error { return nil }
// NewMem returns a new Accessor backed by an os.File. The returned Accessor
// keeps all of the store content in memory. The memory and file images are
// synced only by Sync and Close. Recomended for small amounts of data only
// and content which may be lost on process kill/crash. NewMem return the
// Accessor or an error of any.
//
// NOTE: The returned Accessor implements BeginUpdate and EndUpdate as a no op.
func NewMem(f *os.File) (store Accessor, err error) {
a := &memaccessor{f: f}
if err = f.Truncate(0); err != nil {
return
}
var fi os.FileInfo
if fi, err = a.f.Stat(); err != nil {
return
}
a.fi = NewFileInfo(fi, a)
store = a
return
}
// OpenMem return a new Accessor backed by an os.File. The store content is
// loaded from f. The returned Accessor keeps all of the store content in
// memory. The memory and file images are synced only Sync and Close.
// Recomended for small amounts of data only and content which may be lost on
// process kill/crash. OpenMem return the Accessor or an error of any.
//
// NOTE: The returned Accessor implements BeginUpdate and EndUpdate as a no op.
func OpenMem(f *os.File) (store Accessor, err error) {
a := &memaccessor{f: f}
if a.b, err = ioutil.ReadAll(a.f); err != nil {
a.f.Close()
return
}
var fi os.FileInfo
if fi, err = a.f.Stat(); err != nil {
a.f.Close()
return
}
a.fi = NewFileInfo(fi, a)
store = a
return
}
// Close implements Accessor. Specifically it synchronizes the memory and file images.
func (a *memaccessor) Close() (err error) {
defer func() {
a.b = nil
if a.f != nil {
if e := a.f.Close(); e != nil && err == nil {
err = e
}
}
a.f = nil
}()
return a.Sync()
}
func (a *memaccessor) Name() string {
return a.f.Name()
}
func (a *memaccessor) ReadAt(b []byte, off int64) (n int, err error) {
if off < 0 || off > math.MaxInt32 {
return -1, fmt.Errorf("ReadAt: illegal offset %#x", off)
}
rq, fp := len(b), int(off)
if fp+rq > len(a.b) {
return -1, fmt.Errorf("ReadAt: illegal rq %#x @ offset %#x, len %#x", rq, fp, len(a.b))
}
copy(b, a.b[fp:])
return
}
func (a *memaccessor) Stat() (fi os.FileInfo, err error) {
i := a.fi
i.FSize = int64(len(a.b))
fi = i
return
}
// Sync implements Accessor. Specifically it synchronizes the memory and file images.
func (a *memaccessor) Sync() (err error) {
var n int
if n, err = a.f.WriteAt(a.b, 0); n != len(a.b) {
return
}
return a.f.Truncate(int64(len(a.b)))
}
func (a *memaccessor) Truncate(size int64) (err error) {
defer func() {
if e := recover(); e != nil {
err = e.(error)
}
}()
if size > math.MaxInt32 {
panic(errors.New("truncate: illegal size"))
}
a.b = a.b[:int(size)]
return
}
func (a *memaccessor) WriteAt(b []byte, off int64) (n int, err error) {
if off < 0 || off > math.MaxInt32 {
return -1, errors.New("WriteAt: illegal offset")
}
rq, fp, size := len(b), int(off), len(a.b)
if need := rq + fp; need > size {
if need <= cap(a.b) {
a.b = a.b[:need]
} else {
nb := make([]byte, need, 2*need)
copy(nb, a.b)
a.b = nb
}
}
copy(a.b[int(off):], b)
return
}
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