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wrapped_read_file.go
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/
wrapped_read_file.go
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// Copyright 2019 Keybase Inc. All rights reserved.
// Use of this source code is governed by a BSD
// license that can be found in the LICENSE file.
package libfs
import (
"context"
"io"
"time"
"github.com/keybase/client/go/kbfs/libkbfs"
"github.com/keybase/client/go/logger"
"github.com/pkg/errors"
billy "gopkg.in/src-d/go-billy.v4"
)
const (
// Debug tag ID for an individual FS operation.
ctxFSOpID = "FSID"
)
type ctxFSTagKey int
const (
ctxFSIDKey ctxFSTagKey = iota
)
// wrappedReadFile is a read-only file that serves data from a given
// `reader` function.
type wrappedReadFile struct {
name string
reader func(context.Context) ([]byte, time.Time, error)
log logger.Logger
// TODO: proper locking for `nextRead` if we ever use it outside
// of libkbfs node-wrapping (which always uses `ReadAt`).
nextRead int
}
var _ billy.File = (*wrappedReadFile)(nil)
func (wrf *wrappedReadFile) getDataAndTime() ([]byte, time.Time) {
ctx := libkbfs.CtxWithRandomIDReplayable(
context.Background(), ctxFSIDKey, ctxFSOpID, nil)
data, t, err := wrf.reader(ctx)
if err != nil {
wrf.log.CDebugf(ctx, "Couldn't read wrapped file: %+v", err)
return nil, time.Time{}
}
return data, t
}
func (wrf *wrappedReadFile) Len() int {
data, _ := wrf.getDataAndTime()
return len(data)
}
func (wrf *wrappedReadFile) Name() string {
return wrf.name
}
func (wrf *wrappedReadFile) Write(_ []byte) (n int, err error) {
return 0, errors.New("wrapped read files can't be written")
}
func (wrf *wrappedReadFile) Read(p []byte) (n int, err error) {
data, _ := wrf.getDataAndTime()
if wrf.nextRead >= len(data) {
return 0, io.EOF
}
n = copy(p, data[wrf.nextRead:])
wrf.nextRead += n
return n, nil
}
func (wrf *wrappedReadFile) ReadAt(p []byte, off int64) (n int, err error) {
data, _ := wrf.getDataAndTime()
if off >= int64(len(data)) {
return 0, io.EOF
}
n = copy(p, data[off:])
return n, nil
}
func (wrf *wrappedReadFile) Seek(offset int64, whence int) (int64, error) {
newOffset := offset
switch whence {
case io.SeekStart:
case io.SeekCurrent:
newOffset = int64(wrf.nextRead) + offset
case io.SeekEnd:
data, _ := wrf.getDataAndTime()
newOffset = int64(len(data)) + offset
}
if newOffset < 0 {
return 0, errors.Errorf("Cannot seek to offset %d", newOffset)
}
wrf.nextRead = int(newOffset)
return newOffset, nil
}
func (wrf *wrappedReadFile) Close() error {
return nil
}
func (wrf *wrappedReadFile) Lock() error {
return errors.New("wrapped read files can't be locked")
}
func (wrf *wrappedReadFile) Unlock() error {
return errors.New("wrapped read files can't be unlocked")
}
func (wrf *wrappedReadFile) Truncate(size int64) error {
return errors.New("wrapped read files can't be truncated")
}
func (wrf *wrappedReadFile) GetInfo() *wrappedReadFileInfo {
data, t := wrf.getDataAndTime()
return &wrappedReadFileInfo{
name: wrf.Name(),
size: int64(len(data)),
mtime: t,
}
}