/
file.go
726 lines (625 loc) · 16.3 KB
/
file.go
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package pdf
// NOTE for encryption:
// encrypt during Add
// decrypt during Get
import (
"bytes"
"errors"
"fmt"
"github.com/edsrzf/mmap-go"
"io"
"os"
"sort"
)
type freeObject uint // generation number for next use of the object number where this is stored
// File manages access to objects stored in a PDF file.
// Contains the non-managed keys from the file trailer.
type File struct {
filename string
file *os.File
mmap mmap.MMap
created bool
// cross reference for existing objects
// indirect object for new objects
// free object for newly freed objects
// map key is the object number
// make sure generation number is >= existing generation number when modifying
objects map[uint]interface{}
size uint // max object number + 1
prev Integer
// The catalog dictionary for the PDF document contained in the file.
Root ObjectReference
// The Document's encryption dictionary
Encrypt Dictionary
// The document's information dictionary
Info ObjectReference
// An array of two byte-strings constituting a file identifier for the file.
ID Array
}
// Open opens a PDF file for manipulation of its objects.
func Open(filename string) (*File, error) {
file := &File{
filename: filename,
objects: map[uint]interface{}{},
}
var err error
file.file, err = os.Open(filename)
if err != nil {
return nil, err
}
file.mmap, err = mmap.Map(file.file, mmap.RDONLY, 0)
if err != nil {
err2 := file.Close()
if err2 != nil {
return nil, fmt.Errorf("%v %v", err, err2)
}
return nil, err
}
// check pdf file header
if !bytes.Equal(file.mmap[:7], []byte("%PDF-1.")) {
err := file.Close()
if err != nil {
return nil, errors.New("file does not have PDF header; " + err.Error())
}
return nil, errors.New("file does not have PDF header")
}
err = file.loadReferences()
if err != nil {
err2 := file.Close()
if err2 != nil {
return nil, fmt.Errorf("%v %v", err, err2)
}
return nil, err
}
return file, nil
}
// Create creates a new PDF file with no objects.
func Create(filename string) (*File, error) {
file := &File{
filename: filename,
objects: map[uint]interface{}{},
created: true,
size: 1,
}
// create enough of the pdf so that
// appends will not break things
f, err := os.Create(filename)
if err != nil {
return nil, err
}
defer func() {
err := f.Close()
if err != nil {
panic(err)
}
}()
_, err = f.Write([]byte("%PDF-1.7"))
if err != nil {
return nil, err
}
return file, nil
}
// Get returns the referenced object.
// When the object does not exist, Null is returned.
func (f *File) Get(ref ObjectReference) Object {
// fmt.Println("getting: ", ref)
objectRaw, ok := f.objects[ref.ObjectNumber]
if !ok {
return Null{fmt.Errorf("%s not found", ref)}
}
var object Object
switch typed := objectRaw.(type) {
case crossReference: // existing object
switch typed[0] {
case 0: // free entry
return Null{fmt.Errorf("%s is a free object", ref)}
case 1: // normal
offset := typed[1] - 1
obj, _, err := parseIndirectObject(f.mmap[offset:])
if err != nil {
return Null{fmt.Errorf("Error parsing %s", ref)}
}
iobj, ok := obj.(IndirectObject)
if !ok {
return Null{fmt.Errorf("%v is not an indirect object", ref)}
}
if iobj.Object == nil {
return Null{fmt.Errorf("%v's object is nil", ref)}
}
object = iobj.Object
case 2: // in object stream
// get the object stream
objectStreamRef := ObjectReference{ObjectNumber: typed[1]}
objectStream, ok := f.Get(objectStreamRef).(Stream)
if !ok {
return Null{fmt.Errorf("%v should be in object stream %v, but %v is not a stream", ref, objectStreamRef, objectStreamRef)}
}
// parse the index (object number and offset pairs)
index := []Integer{}
N := int(objectStream.Dictionary[Name("N")].(Integer))
stream, err := objectStream.Decode()
if err != nil {
return Null{fmt.Errorf("could not decode %v", objectStreamRef)}
}
offset := 0
for i := 0; i < N*2; i++ {
obj, n, err := parseNumeric(stream[offset:])
if err != nil {
return Null{fmt.Errorf("unable to parse numeric %v", stream[offset:])}
}
index = append(index, obj.(Integer))
offset += n
}
// find the offset for the object we are looking for
start := typed[2] * 2
objectNumber := index[start]
offset = int(index[start+1])
// if the index from the cross reference is wrong,
// find the correct offset
if objectNumber != Integer(ref.ObjectNumber) {
objectNumber = Integer(ref.ObjectNumber)
for i := 0; i < len(index); i += 2 {
if index[i] == objectNumber {
offset = int(index[i+1])
break
}
}
}
// grab the object
first := int(objectStream.Dictionary[Name("First")].(Integer))
object, _, err = parseObject(stream[first+offset:])
if err != nil {
return Null{fmt.Errorf("unable to parse object %v", stream[first+offset:])}
}
default:
panic(typed[0])
}
case IndirectObject: // new object
if typed.Object == nil {
fmt.Println("+++++++++++++++++indirect object's object is nil")
}
object = typed.Object
case freeObject: // newly freed object
return Null{fmt.Errorf("%v freed after pdf was loaded", ref)}
default:
panic(fmt.Sprintf("unhandled type: %T", object))
}
// deal with streams that have refs to lengths
if streamObj, ok := object.(Stream); ok {
if lengthRef, ok := streamObj.Dictionary["Length"].(ObjectReference); ok {
length := f.Get(lengthRef).(Integer)
streamObj.Dictionary["Length"] = length
streamObj.Stream = streamObj.Stream[:int(length)]
}
object = streamObj
}
return object
}
// Add returns the object reference of the object after adding it to the file.
// An IndirectObject's ObjectReference will be used,
// otherwise a free ObjectReference will be used.
//
// If an IndirectObject's ObjectReference also refers to an existing
// object, the newly added IndirectObject will mask the existing one.
// Only the most recently added object will be Saved to disk.
// GenerationNumber must be greater than or equal to the largest existing
// GenerationNumber for that ObjectNumber.
func (f *File) Add(obj Object) (ObjectReference, error) {
// TODO: handle non indirect-objects
ref := ObjectReference{}
switch typed := obj.(type) {
case IndirectObject:
ref.ObjectNumber = typed.ObjectNumber
ref.GenerationNumber = typed.GenerationNumber
// fmt.Println("adding:", ref)
// check to see if the generation number works
existing, ok := f.objects[ref.ObjectNumber]
if ok {
// determine the minimum allowed generation number
var minGenerationNumber uint
switch typed := existing.(type) {
case crossReference: // existing object
switch typed[0] {
case 0: // free entry
minGenerationNumber = typed[2]
case 1: // normal
minGenerationNumber = typed[2]
case 2: // in object stream
// objects in object streams must have a
// generation number of 0
minGenerationNumber = 0
default:
panic(typed[0])
}
case IndirectObject: // new object
minGenerationNumber = typed.GenerationNumber
case freeObject: // newly freed object
minGenerationNumber = uint(typed)
default:
panic(fmt.Sprintf("unhandled type: %T", typed))
}
if ref.GenerationNumber < minGenerationNumber {
// TODO: make better error
ref.GenerationNumber = minGenerationNumber
return ref, errors.New("Generation number is too small...")
}
}
f.objects[ref.ObjectNumber] = typed
default:
// TODO: reuse free object numbers
objectNumber := f.size
f.size++
ref.ObjectNumber = objectNumber
f.objects[objectNumber] = IndirectObject{
ObjectReference: ref,
Object: obj,
}
// panic(obj)
}
return ref, nil
}
func writeLineBreakTo(w io.Writer) (int64, error) {
n, err := w.Write([]byte{'\n', '\n'})
return int64(n), err
}
// Save appends the objects that have been added to the File
// to the file on disk. After saving, the File is still usable
// and will act as though it were just Open'ed.
//
// NOTE: A new object index will be written on each save,
// taking space in the file on disk
func (f *File) Save() error {
// return f.saveUsingXrefTable()
return f.saveUsingXrefStream()
}
func (f *File) saveUsingXrefTable() error {
info, err := os.Stat(f.filename)
if err != nil {
return err
}
file, err := os.OpenFile(f.filename, os.O_WRONLY|os.O_APPEND, 0666)
if err != nil {
return err
}
defer func() {
err := file.Close()
if err != nil {
panic(err)
}
}()
offset := info.Size() + 1
n, err := writeLineBreakTo(file)
if err != nil {
return err
}
offset += n
xrefs := map[Integer]crossReference{}
xrefs[0] = crossReference{0, 0, 65535}
free := sort.IntSlice{}
for i := range f.objects {
switch typed := f.objects[i].(type) {
case crossReference:
// no-op, don't need to write unchanged objects to file
// however, we do need to handle the free list
// xrefs[Integer(i)] = typed
if typed[0] == 0 {
free = append(free, int(i))
}
case IndirectObject:
xrefs[Integer(i)] = crossReference{1, uint(offset - 1), typed.GenerationNumber}
n, err = typed.writeTo(file)
if err != nil {
return err
}
offset += n
n, err = writeLineBreakTo(file)
if err != nil {
return err
}
offset += n
case freeObject:
xrefs[Integer(i)] = crossReference{0, 0, uint(typed)}
free = append(free, int(i))
default:
panic(fmt.Sprintf("unhandled type: %T", typed))
}
}
// fill in the free linked list
free.Sort()
for i := 0; i < free.Len()-1; i++ {
xref := xrefs[Integer(free[i])]
xref[1] = uint(free[i+1])
xrefs[Integer(free[i])] = xref
}
objects := make(sort.IntSlice, 0, len(xrefs))
for objectNumber := range xrefs {
objects = append(objects, int(objectNumber))
}
objects.Sort()
// group into consecutive sets
groups := []sort.IntSlice{}
groupStart := 0
for i := range objects {
if i == 0 {
continue
}
if objects[i] != objects[i-1]+1 {
groups = append(groups, objects[groupStart:i])
groupStart = i
}
}
// add remaining group
groups = append(groups, objects[groupStart:])
// write as an xref table to file
fmt.Fprintf(file, "xref\n")
for _, group := range groups {
fmt.Fprintf(file, "%d %d\n", group[0], len(group))
for _, objectNumber := range group {
xref := xrefs[Integer(objectNumber)]
fmt.Fprintf(file, "%010d %05d ", xref[1], xref[2])
switch xref[0] {
case 0:
// f entries
fmt.Fprintf(file, "f\r\n")
case 1:
// n entries
fmt.Fprintf(file, "n\r\n")
case 2:
panic("can't be in xref table")
default:
panic("unhandled case")
}
}
}
// Setup create the trailer
fmt.Fprintf(file, "\ntrailer\n")
trailer := Dictionary{}
// Size
// Figure out the highest object number to set Size properly
var maxObjNum uint
for objNum := range f.objects {
if objNum > maxObjNum {
maxObjNum = objNum
}
}
trailer[Name("Size")] = Integer(maxObjNum + 1)
// Prev
if f.prev != 0 {
trailer[Name("Prev")] = f.prev
}
// Root
trailer[Name("Root")] = f.Root
// Encrypt
if len(f.Encrypt) != 0 {
trailer[Name("Encrypt")] = f.Encrypt
}
// Info
if f.Info.ObjectNumber != 0 {
trailer[Name("Info")] = f.Info
}
// ID
if len(f.ID) != 0 {
trailer[Name("ID")] = f.ID
}
_, err = trailer.writeTo(file)
if err != nil {
return err
}
fmt.Fprintf(file, "\nstartxref\n%d\n%%%%EOF", offset-1)
return nil
}
func (f *File) saveUsingXrefStream() error {
info, err := os.Stat(f.filename)
if err != nil {
return err
}
file, err := os.OpenFile(f.filename, os.O_RDWR|os.O_APPEND, 0666)
if err != nil {
return err
}
defer func() {
err := file.Close()
if err != nil {
panic(err)
}
}()
offset := info.Size() + 1
n, err := writeLineBreakTo(file)
if err != nil {
return err
}
offset += n
xrefs := map[Integer]crossReference{}
xrefs[0] = crossReference{0, 0, 65535}
free := sort.IntSlice{0}
for i := range f.objects {
switch typed := f.objects[i].(type) {
case crossReference:
// no-op, don't need to write unchanged objects to file
// however, we do need to handle the free list
// xrefs[Integer(i)] = typed
if typed[0] == 0 {
free = append(free, int(i))
}
case IndirectObject:
xrefs[Integer(i)] = crossReference{1, uint(offset - 1), typed.GenerationNumber}
n, err = typed.writeTo(file)
if err != nil {
return err
}
offset += n
n, err = writeLineBreakTo(file)
if err != nil {
return err
}
offset += n
case freeObject:
xrefs[Integer(i)] = crossReference{0, 0, uint(typed)}
free = append(free, int(i))
default:
panic(fmt.Sprintf("unhandled type: %T", typed))
}
}
// Figure out the highest object number to set Size properly
var maxObjNum uint
for objNum := range f.objects {
if objNum > maxObjNum {
maxObjNum = objNum
}
}
// add an xref for the xrefstream
xrefstreamObjectNumber := uint(maxObjNum + 1)
maxObjNum++
xref := crossReference{1, uint(offset - 1), 0}
xrefs[Integer(xrefstreamObjectNumber)] = xref
f.objects[xrefstreamObjectNumber] = xref
// fill in the free linked list
free.Sort()
for i := 0; i < free.Len()-1; i++ {
xref := xrefs[Integer(free[i])]
xref[1] = uint(free[i+1])
xrefs[Integer(free[i])] = xref
}
objects := make(sort.IntSlice, 0, len(xrefs))
for objectNumber := range xrefs {
objects = append(objects, int(objectNumber))
}
objects.Sort()
// group into consecutive sets
groups := []sort.IntSlice{}
groupStart := 0
for i := range objects {
if i == 0 {
continue
}
if objects[i] != objects[i-1]+1 {
groups = append(groups, objects[groupStart:i])
groupStart = i
}
}
groups = append(groups, objects[groupStart:])
// Create the xrefstream dictionary (the trailer)
trailer := Dictionary{}
trailer[Name("Size")] = Integer(maxObjNum + 1)
// Prev
if f.prev != 0 {
trailer[Name("Prev")] = f.prev
}
// Root
trailer[Name("Root")] = f.Root
// Encrypt
if len(f.Encrypt) != 0 {
trailer[Name("Encrypt")] = f.Encrypt
}
// Info
if f.Info.ObjectNumber != 0 {
trailer[Name("Info")] = f.Info
}
// ID
if len(f.ID) != 0 {
trailer[Name("ID")] = f.ID
}
// Add xrefstream specific things to trailer
trailer["Type"] = Name("XRef")
// Index
index := Array{}
// fmt.Println(groups)
for _, group := range groups {
index = append(index, Integer(group[0]), Integer(len(group)))
}
trailer["Index"] = index
// layout for the stream (W)
maxXref := [3]uint{}
for _, xref := range xrefs {
for i := 0; i < len(xref); i++ {
if xref[i] > maxXref[i] {
maxXref[i] = xref[i]
}
}
}
nBytes := [3]int{}
for i := range nBytes {
nBytes[i] = nBytesForInt(int(maxXref[i]))
}
trailer["W"] = Array{Integer(nBytes[0]), Integer(nBytes[1]), Integer(nBytes[2])}
// log.Println(xrefs)
stream := &bytes.Buffer{}
for _, group := range groups {
for _, objectNumber := range group {
xref := xrefs[Integer(objectNumber)]
for i := range xref {
_, err = stream.Write(intToBytes(xref[i], nBytes[i]))
if err != nil {
return err
}
}
}
}
xrefstream := IndirectObject{
ObjectReference: ObjectReference{
ObjectNumber: xrefstreamObjectNumber,
},
Object: Stream{
Dictionary: trailer,
Stream: stream.Bytes(),
},
}
_, err = f.Add(xrefstream)
if err != nil {
return err
}
_, err = xrefstream.writeTo(file)
if err != nil {
return err
}
fmt.Fprintf(file, "\nstartxref\n%d\n%%%%EOF", offset-1)
return nil
}
// Close the File, does not Save.
func (f *File) Close() error {
if f.created {
// don't need to clean up mmap
return nil
}
err := f.mmap.Unmap()
if err != nil {
return err
}
err = f.file.Close()
if err != nil {
return err
}
return nil
}
// Free the object with the specified number.
// Will automatically determine and increment the generation number.
func (f *File) Free(objectNumber uint) {
obj, ok := f.objects[objectNumber]
if !ok {
// object does not exist, and therefore is already free
return
}
switch typed := obj.(type) {
case crossReference: // existing object
switch typed[0] {
case 0: // free entry
// no-op
// the object is already free
case 1: // normal
f.objects[objectNumber] = freeObject(typed[2] + 1)
case 2: // in object stream
// objects in object streams must have a
// generation number of 0
f.objects[objectNumber] = freeObject(1)
default:
panic(typed[0])
}
case IndirectObject: // new object
f.objects[objectNumber] = freeObject(typed.GenerationNumber + 1)
case freeObject: // newly freed object
// no-op
// already free
default:
panic(fmt.Sprintf("unhandled type: %T", typed))
}
}