package contentenc // Per-file header // // Format: [ "Version" uint16 big endian ] [ "Id" 16 random bytes ] import ( "bytes" "encoding/binary" "encoding/hex" "fmt" "log" "github.com/rfjakob/gocryptfs/internal/cryptocore" ) const ( // CurrentVersion is the current On-Disk-Format version CurrentVersion = 2 headerVersionLen = 2 // uint16 headerIDLen = 16 // 128 bit random file id // HeaderLen is the total header length HeaderLen = headerVersionLen + headerIDLen ) // FileHeader represents the header stored on each non-empty file. type FileHeader struct { Version uint16 ID []byte } // Pack - serialize fileHeader object func (h *FileHeader) Pack() []byte { if len(h.ID) != headerIDLen || h.Version != CurrentVersion { log.Panic("FileHeader object not properly initialized") } buf := make([]byte, HeaderLen) binary.BigEndian.PutUint16(buf[0:headerVersionLen], h.Version) copy(buf[headerVersionLen:], h.ID) return buf } // allZeroFileID is preallocated to quickly check if the data read from disk is all zero var allZeroFileID = make([]byte, headerIDLen) // ParseHeader - parse "buf" into fileHeader object func ParseHeader(buf []byte) (*FileHeader, error) { if len(buf) != HeaderLen { return nil, fmt.Errorf("ParseHeader: invalid length, want=%d have=%d", HeaderLen, len(buf)) } var h FileHeader h.Version = binary.BigEndian.Uint16(buf[0:headerVersionLen]) if h.Version != CurrentVersion { return nil, fmt.Errorf("ParseHeader: invalid version, want=%d have=%d. Hexdump: %s", CurrentVersion, h.Version, hex.EncodeToString(buf)) } h.ID = buf[headerVersionLen:] if bytes.Equal(h.ID, allZeroFileID) { return nil, fmt.Errorf("ParseHeader: file id is all-zero. Hexdump: %s", hex.EncodeToString(buf)) } return &h, nil } // RandomHeader - create new fileHeader object with random Id func RandomHeader() *FileHeader { var h FileHeader h.Version = CurrentVersion h.ID = cryptocore.RandBytes(headerIDLen) return &h }