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package fusefrontend_reverse
import (
"fmt"
"io"
"os"
"github.com/hanwen/go-fuse/fuse"
"github.com/hanwen/go-fuse/fuse/nodefs"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
var zeroFileId []byte
func init() {
zeroFileId = make([]byte, 16)
}
type reverseFile struct {
// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
nodefs.File
// Backing FD
fd *os.File
// Content encryption helper
contentEnc *contentenc.ContentEnc
}
func NewFile(fd *os.File, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
return &reverseFile{
File: nodefs.NewDefaultFile(),
fd: fd,
contentEnc: contentEnc,
}, fuse.OK
}
// GetAttr - FUSE call
func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
fmt.Printf("reverseFile.GetAttr fd=%d\n", rf.fd.Fd())
return fuse.ENOSYS
}
// Read - FUSE call
func (rf *reverseFile) Read(buf []byte, off int64) (resultData fuse.ReadResult, status fuse.Status) {
// TODO prefix file header
length := uint64(len(buf))
blocks := rf.contentEnc.ExplodeCipherRange(uint64(off), length)
// Read the backing plaintext in one go
alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
tlog.Warn.Printf("alignedOffset=%d, alignedLength=%d\n", alignedOffset, alignedLength)
plaintext := make([]byte, int(alignedLength))
n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
if err != nil && err != io.EOF {
tlog.Warn.Printf("reverseFile.Read: ReadAt: %s", err.Error())
return nil, fuse.ToStatus(err)
}
// Truncate buffer down to actually read bytes
plaintext = plaintext[0:n]
// Encrypt blocks
ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, zeroFileId)
// Crop down to the relevant part
var out []byte
lenHave := len(ciphertext)
skip := blocks[0].Skip
endWant := int(skip + length)
if lenHave > endWant {
out = plaintext[skip:endWant]
} else if lenHave > int(skip) {
out = plaintext[skip:lenHave]
}
// else: out stays empty, file was smaller than the requested offset
return fuse.ReadResultData(out), fuse.OK
}
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