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//
// Copyright (c) SAS Institute Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Microsoft Compound Document File
// Reference: https://www.openoffice.org/sc/compdocfileformat.pdf
// ERRATA: The above document says the 0th sector is always 512 bytes into the
// file. This is not correct. If SectorSize > 512 bytes then the 0th sector is
// SectorSize bytes into the file.
package comdoc
import (
"bytes"
"encoding/binary"
"errors"
"io"
"os"
)
// CDF file open for reading or writing
type ComDoc struct {
File io.ReaderAt
Header *Header
SectorSize int
ShortSectorSize int
FirstSector int64
// MSAT is a list of sector IDs holding a SAT
MSAT []SecID
// SAT is a table where the index is the sector ID and the value is a pointer to the next sector ID in the same stream
SAT []SecID
SSAT []SecID
Files []DirEnt
sectorBuf []byte
changed bool
rootStorage int // index into files
rootFiles []int // index into Files
msatList []SecID // list of sector IDs holding a MSAT
writer *os.File
closer io.Closer
}
// Open a CDF file for reading
func ReadPath(path string) (*ComDoc, error) {
f, err := os.Open(path)
if err != nil {
return nil, err
}
return openFile(f, nil, f)
}
// Open a CDF file for reading and writing
func WritePath(path string) (*ComDoc, error) {
f, err := os.OpenFile(path, os.O_RDWR, 0)
if err != nil {
return nil, err
}
return openFile(f, f, f)
}
// Parse an already-open CDF file for reading
func ReadFile(reader io.ReaderAt) (*ComDoc, error) {
return openFile(reader, nil, nil)
}
// Parse an already-open CDF file for reading and writing
func WriteFile(f *os.File) (*ComDoc, error) {
return openFile(f, f, nil)
}
func openFile(reader io.ReaderAt, writer *os.File, closer io.Closer) (*ComDoc, error) {
header := new(Header)
r := &ComDoc{
File: reader,
Header: header,
writer: writer,
closer: closer,
}
sr := io.NewSectionReader(reader, 0, 512)
if err := binary.Read(sr, binary.LittleEndian, header); err != nil {
return nil, err
}
if !bytes.Equal(header.Magic[:], fileMagic) {
return nil, errors.New("not a compound document file")
}
if header.ByteOrder != byteOrderMarker {
return nil, errors.New("incorrect byte order marker")
}
if header.SectorSize < 5 || header.SectorSize > 28 || header.ShortSectorSize >= header.SectorSize {
return nil, errors.New("unreasonable header values")
}
r.SectorSize = 1 << header.SectorSize
r.ShortSectorSize = 1 << header.ShortSectorSize
if r.SectorSize < 512 {
r.FirstSector = 512
} else {
r.FirstSector = int64(r.SectorSize)
}
r.sectorBuf = make([]byte, r.SectorSize)
if err := r.readMSAT(); err != nil {
return nil, err
}
if err := r.readSAT(); err != nil {
return nil, err
}
if err := r.readShortSAT(); err != nil {
return nil, err
}
if err := r.readDir(); err != nil {
return nil, err
}
return r, nil
}
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