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package fusefrontend_reverse
import (
"bytes"
"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"
)
// File header that contains an all-zero File ID
var zeroFileHeader *contentenc.FileHeader
func init() {
zeroFileHeader = contentenc.RandomHeader()
// Overwrite with zeros
zeroFileHeader.Id = make([]byte, contentenc.HEADER_ID_LEN)
}
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
}
// readBackingFile: read from the backing plaintext file, encrypt it, return the
// ciphertext.
// "off" ... ciphertext offset (must be >= HEADER_LEN)
// "length" ... ciphertext length
func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, err error) {
blocks := rf.contentEnc.ExplodeCipherRange(off, length)
// Read the backing plaintext in one go
alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
plaintext := make([]byte, int(alignedLength))
n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
if err != nil && err != io.EOF {
tlog.Warn.Printf("readBackingFile: ReadAt: %s", err.Error())
return nil, err
}
// Truncate buffer down to actually read bytes
plaintext = plaintext[0:n]
// Encrypt blocks
ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, zeroFileHeader.Id, contentenc.ReverseDummyNonce)
// Crop down to the relevant part
lenHave := len(ciphertext)
skip := blocks[0].Skip
endWant := int(skip + length)
if lenHave > endWant {
out = ciphertext[skip:endWant]
} else if lenHave > int(skip) {
out = ciphertext[skip:lenHave]
} // else: out stays empty, file was smaller than the requested offset
return out, nil
}
// Read - FUSE call
func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult, status fuse.Status) {
length := uint64(len(buf))
off := uint64(ioff)
var out bytes.Buffer
var header []byte
// Synthesize file header
if off < contentenc.HEADER_LEN {
header = zeroFileHeader.Pack()
// Truncate to requested part
end := int(off) + len(buf)
if end > len(header) {
end = len(header)
}
header = header[off:end]
// Write into output buffer and adjust offsets
out.Write(header)
hLen := uint64(len(header))
off += hLen
length -= hLen
}
// Read actual file data
if length > 0 {
fileData, err := rf.readBackingFile(off, length)
if err != nil {
return nil, fuse.ToStatus(err)
}
if len(fileData) == 0 {
// If we could not read any actual data, we also don't want to
// return the file header. An empty file stays empty in encrypted
// form.
return nil, fuse.OK
}
out.Write(fileData)
}
return fuse.ReadResultData(out.Bytes()), fuse.OK
}
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