Go: add PDF 1.5 cross-reference stream support
This is not particularly complete, but it works (again) for Cairo.
This commit is contained in:
parent
55a17a69b7
commit
0b837b3a0e
GPG Key ID:
A0420B94F92B9493
2
LICENSE
2
LICENSE
@ -1,4 +1,4 @@
|
||||
Copyright (c) 2017 - 2021, Přemysl Eric Janouch <p@janouch.name>
|
||||
Copyright (c) 2017 - 2024, Přemysl Eric Janouch <p@janouch.name>
|
||||
|
||||
Permission to use, copy, modify, and/or distribute this software for any
|
||||
purpose with or without fee is hereby granted.
|
||||
|
||||
@ -33,7 +33,8 @@ Runtime dependencies: libcrypto (OpenSSL 1.1 API)
|
||||
$ cd builddir
|
||||
$ ninja
|
||||
|
||||
In addition to the C++ version, also included is a native Go port:
|
||||
In addition to the C++ version, also included is a native Go port,
|
||||
which has enhanced PDF 1.5 support:
|
||||
|
||||
$ go get janouch.name/pdf-simple-sign/cmd/pdf-simple-sign
|
||||
|
||||
|
||||
439
pdf/pdf.go
439
pdf/pdf.go
@ -1,5 +1,5 @@
|
||||
//
|
||||
// Copyright (c) 2018 - 2021, Přemysl Eric Janouch <p@janouch.name>
|
||||
// Copyright (c) 2018 - 2024, Přemysl Eric Janouch <p@janouch.name>
|
||||
//
|
||||
// Permission to use, copy, modify, and/or distribute this software for any
|
||||
// purpose with or without fee is hereby granted.
|
||||
@ -18,6 +18,8 @@ package pdf
|
||||
|
||||
import (
|
||||
"bytes"
|
||||
"compress/zlib"
|
||||
"encoding/binary"
|
||||
"encoding/hex"
|
||||
"errors"
|
||||
"fmt"
|
||||
@ -120,6 +122,13 @@ func NewDict(d map[string]Object) Object {
|
||||
return Object{Kind: Dict, Dict: d}
|
||||
}
|
||||
|
||||
func NewStream(d map[string]Object, s []byte) Object {
|
||||
if d == nil {
|
||||
d = make(map[string]Object)
|
||||
}
|
||||
return Object{Kind: Stream, Dict: d, Stream: s}
|
||||
}
|
||||
|
||||
func NewIndirect(o Object, n, generation uint) Object {
|
||||
return Object{Kind: Indirect, N: n, Generation: generation,
|
||||
Array: []Object{o}}
|
||||
@ -477,8 +486,9 @@ func (o *Object) Serialize() string {
|
||||
// -----------------------------------------------------------------------------
|
||||
|
||||
type ref struct {
|
||||
offset int64 // file offset or N of the next free entry
|
||||
offset int64 // file offset, or N of the next free entry, or index
|
||||
generation uint // object generation
|
||||
compressed *uint // PDF 1.5: N of the containing compressed object
|
||||
nonfree bool // whether this N is taken (for a good zero value)
|
||||
}
|
||||
|
||||
@ -671,16 +681,159 @@ func (u *Updater) parse(lex *Lexer, stack *[]Object) (Object, error) {
|
||||
}
|
||||
}
|
||||
|
||||
func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
|
||||
func (u *Updater) loadXrefEntry(
|
||||
n uint, r ref, loadedEntries map[uint]struct{}) {
|
||||
if _, ok := loadedEntries[n]; ok {
|
||||
return
|
||||
}
|
||||
if lenXref := uint(len(u.xref)); n >= lenXref {
|
||||
u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
|
||||
}
|
||||
loadedEntries[n] = struct{}{}
|
||||
|
||||
u.xref[n] = r
|
||||
}
|
||||
|
||||
func (u *Updater) loadXrefStream(
|
||||
lex *Lexer, stack []Object, loadedEntries map[uint]struct{}) (
|
||||
Object, error) {
|
||||
var object Object
|
||||
for {
|
||||
var err error
|
||||
if object, err = u.parse(lex, &stack); err != nil {
|
||||
return New(End), fmt.Errorf("invalid xref table: %s", err)
|
||||
} else if object.Kind == End {
|
||||
return newError("invalid xref table")
|
||||
}
|
||||
|
||||
// For the sake of simplicity, keep stacking until we find an object.
|
||||
if object.Kind == Indirect {
|
||||
break
|
||||
}
|
||||
|
||||
stack = append(stack, object)
|
||||
}
|
||||
|
||||
// ISO 32000-2:2020 7.5.8.2 Cross-reference stream dictionary
|
||||
stream := object.Array[0]
|
||||
if stream.Kind != Stream {
|
||||
return newError("invalid xref table")
|
||||
}
|
||||
if typ, ok := stream.Dict["Type"]; !ok ||
|
||||
typ.Kind != Name || typ.String != "XRef" {
|
||||
return newError("invalid xref stream")
|
||||
}
|
||||
|
||||
data, err := u.GetStreamData(stream)
|
||||
if err != nil {
|
||||
return New(End), fmt.Errorf("invalid xref stream: %s", err)
|
||||
}
|
||||
|
||||
size, ok := stream.Dict["Size"]
|
||||
if !ok || !size.IsUint() || size.Number <= 0 {
|
||||
return newError("invalid or missing cross-reference stream Size")
|
||||
}
|
||||
|
||||
type pair struct{ start, count uint }
|
||||
pairs := []pair{}
|
||||
if index, ok := stream.Dict["Index"]; !ok {
|
||||
pairs = append(pairs, pair{0, uint(size.Number)})
|
||||
} else {
|
||||
if index.Kind != Array || len(index.Array)%2 != 0 {
|
||||
return newError("invalid cross-reference stream Index")
|
||||
}
|
||||
|
||||
a := index.Array
|
||||
for i := 0; i < len(a); i += 2 {
|
||||
if !a[i].IsUint() || !a[i+1].IsUint() {
|
||||
return newError("invalid cross-reference stream Index")
|
||||
}
|
||||
pairs = append(pairs, pair{uint(a[i].Number), uint(a[i+1].Number)})
|
||||
}
|
||||
}
|
||||
|
||||
w, ok := stream.Dict["W"]
|
||||
if !ok || w.Kind != Array || len(w.Array) != 3 ||
|
||||
!w.Array[0].IsUint() || !w.Array[1].IsUint() || !w.Array[2].IsUint() {
|
||||
return newError("invalid or missing cross-reference stream W")
|
||||
}
|
||||
|
||||
w1 := uint(w.Array[0].Number)
|
||||
w2 := uint(w.Array[1].Number)
|
||||
w3 := uint(w.Array[2].Number)
|
||||
if w2 == 0 {
|
||||
return newError("invalid cross-reference stream W")
|
||||
}
|
||||
|
||||
unit := w1 + w2 + w3
|
||||
if uint(len(data))%unit != 0 {
|
||||
return newError("invalid cross-reference stream length")
|
||||
}
|
||||
|
||||
readField := func(data []byte, width uint) (uint, []byte) {
|
||||
var n uint
|
||||
for ; width != 0; width-- {
|
||||
n = n<<8 | uint(data[0])
|
||||
data = data[1:]
|
||||
}
|
||||
return n, data
|
||||
}
|
||||
|
||||
// ISO 32000-2:2020 7.5.8.3 Cross-reference stream data
|
||||
for _, pair := range pairs {
|
||||
for i := uint(0); i < pair.count; i++ {
|
||||
if uint(len(data)) < unit {
|
||||
return newError("premature cross-reference stream EOF")
|
||||
}
|
||||
|
||||
var f1, f2, f3 uint = 1, 0, 0
|
||||
if w1 > 0 {
|
||||
f1, data = readField(data, w1)
|
||||
}
|
||||
f2, data = readField(data, w2)
|
||||
if w3 > 0 {
|
||||
f3, data = readField(data, w3)
|
||||
}
|
||||
|
||||
var r ref
|
||||
switch f1 {
|
||||
case 0:
|
||||
r.offset = int64(f2)
|
||||
r.generation = f3
|
||||
case 1:
|
||||
r.offset = int64(f2)
|
||||
r.generation = f3
|
||||
r.nonfree = true
|
||||
case 2:
|
||||
r.offset = int64(f3)
|
||||
r.compressed = &f2
|
||||
r.nonfree = true
|
||||
default:
|
||||
// TODO: It should be treated as a reference to the null object.
|
||||
// We can't currently represent that.
|
||||
return newError("unsupported cross-reference stream contents")
|
||||
}
|
||||
|
||||
u.loadXrefEntry(pair.start+i, r, loadedEntries)
|
||||
}
|
||||
}
|
||||
|
||||
stream.Kind = Dict
|
||||
stream.Stream = nil
|
||||
return stream, nil
|
||||
}
|
||||
|
||||
func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) (
|
||||
Object, error) {
|
||||
var throwawayStack []Object
|
||||
if keyword, _ := u.parse(lex,
|
||||
&throwawayStack); keyword.Kind != Keyword || keyword.String != "xref" {
|
||||
return errors.New("invalid xref table")
|
||||
if object, _ := u.parse(lex,
|
||||
&throwawayStack); object.Kind != Keyword || object.String != "xref" {
|
||||
return u.loadXrefStream(lex, []Object{object}, loadedEntries)
|
||||
}
|
||||
for {
|
||||
object, _ := u.parse(lex, &throwawayStack)
|
||||
if object.Kind == End {
|
||||
return errors.New("unexpected EOF while looking for the trailer")
|
||||
return newError("unexpected EOF while looking for the trailer")
|
||||
}
|
||||
if object.Kind == Keyword && object.String == "trailer" {
|
||||
break
|
||||
@ -688,7 +841,7 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
|
||||
|
||||
second, _ := u.parse(lex, &throwawayStack)
|
||||
if !object.IsUint() || !second.IsUint() {
|
||||
return errors.New("invalid xref section header")
|
||||
return newError("invalid xref section header")
|
||||
}
|
||||
|
||||
start, count := uint(object.Number), uint(second.Number)
|
||||
@ -700,33 +853,29 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
|
||||
off.Number > float64(len(u.Document)) ||
|
||||
!gen.IsInteger() || gen.Number < 0 || gen.Number > 65535 ||
|
||||
key.Kind != Keyword {
|
||||
return errors.New("invalid xref entry")
|
||||
return newError("invalid xref entry")
|
||||
}
|
||||
|
||||
free := true
|
||||
if key.String == "n" {
|
||||
free = false
|
||||
} else if key.String != "f" {
|
||||
return errors.New("invalid xref entry")
|
||||
return newError("invalid xref entry")
|
||||
}
|
||||
|
||||
n := start + i
|
||||
if _, ok := loadedEntries[n]; ok {
|
||||
continue
|
||||
}
|
||||
if lenXref := uint(len(u.xref)); n >= lenXref {
|
||||
u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
|
||||
}
|
||||
loadedEntries[n] = struct{}{}
|
||||
|
||||
u.xref[n] = ref{
|
||||
u.loadXrefEntry(start+i, ref{
|
||||
offset: int64(off.Number),
|
||||
generation: uint(gen.Number),
|
||||
nonfree: !free,
|
||||
}
|
||||
}, loadedEntries)
|
||||
}
|
||||
}
|
||||
return nil
|
||||
|
||||
trailer, _ := u.parse(lex, &throwawayStack)
|
||||
if trailer.Kind != Dict {
|
||||
return newError("invalid trailer dictionary")
|
||||
}
|
||||
return trailer, nil
|
||||
}
|
||||
|
||||
// -----------------------------------------------------------------------------
|
||||
@ -756,7 +905,6 @@ func NewUpdater(document []byte) (*Updater, error) {
|
||||
loadedXrefs := make(map[int64]struct{})
|
||||
loadedEntries := make(map[uint]struct{})
|
||||
|
||||
var throwawayStack []Object
|
||||
for {
|
||||
if _, ok := loadedXrefs[xrefOffset]; ok {
|
||||
return nil, errors.New("circular xref offsets")
|
||||
@ -766,19 +914,21 @@ func NewUpdater(document []byte) (*Updater, error) {
|
||||
}
|
||||
|
||||
lex := Lexer{u.Document[xrefOffset:]}
|
||||
if err := u.loadXref(&lex, loadedEntries); err != nil {
|
||||
trailer, err := u.loadXref(&lex, loadedEntries)
|
||||
if err != nil {
|
||||
return nil, err
|
||||
}
|
||||
|
||||
trailer, _ := u.parse(&lex, &throwawayStack)
|
||||
if trailer.Kind != Dict {
|
||||
return nil, errors.New("invalid trailer dictionary")
|
||||
}
|
||||
if len(loadedXrefs) == 0 {
|
||||
u.Trailer = trailer.Dict
|
||||
}
|
||||
loadedXrefs[xrefOffset] = struct{}{}
|
||||
|
||||
// TODO: Descend into XRefStm here first, if present,
|
||||
// which is also a linked list.
|
||||
|
||||
// We allow for mixed cross-reference tables and streams
|
||||
// within a single Prev list, although this should never occur.
|
||||
prevOffset, ok := trailer.Dict["Prev"]
|
||||
if !ok {
|
||||
break
|
||||
@ -825,6 +975,100 @@ func (u *Updater) Version(root *Object) int {
|
||||
return 0
|
||||
}
|
||||
|
||||
func (u *Updater) getFromObjStm(nObjStm, n uint) (Object, error) {
|
||||
if nObjStm == n {
|
||||
return newError("ObjStm recursion")
|
||||
}
|
||||
|
||||
stream, err := u.Get(nObjStm, 0)
|
||||
if err != nil {
|
||||
return stream, err
|
||||
}
|
||||
if stream.Kind != Stream {
|
||||
return newError("invalid ObjStm")
|
||||
}
|
||||
if typ, ok := stream.Dict["Type"]; !ok ||
|
||||
typ.Kind != Name || typ.String != "ObjStm" {
|
||||
return newError("invalid ObjStm")
|
||||
}
|
||||
|
||||
data, err := u.GetStreamData(stream)
|
||||
if err != nil {
|
||||
return New(End), fmt.Errorf("invalid ObjStm: %s", err)
|
||||
}
|
||||
entryN, ok := stream.Dict["N"]
|
||||
if !ok || !entryN.IsUint() || entryN.Number <= 0 {
|
||||
return newError("invalid ObjStm N")
|
||||
}
|
||||
entryFirst, ok := stream.Dict["First"]
|
||||
if !ok || !entryFirst.IsUint() || entryFirst.Number <= 0 {
|
||||
return newError("invalid ObjStm First")
|
||||
}
|
||||
|
||||
// NOTE: This means descending into that stream if n is not found here.
|
||||
// It is meant to be an object reference.
|
||||
if extends, ok := stream.Dict["Extends"]; ok && extends.Kind != Nil {
|
||||
return newError("ObjStm extensions are unsupported")
|
||||
}
|
||||
|
||||
count := uint(entryN.Number)
|
||||
first := uint(entryFirst.Number)
|
||||
if first > uint(len(data)) {
|
||||
return newError("invalid ObjStm First")
|
||||
}
|
||||
|
||||
lex1 := Lexer{data[:first]}
|
||||
data = data[first:]
|
||||
|
||||
type pair struct{ n, offset uint }
|
||||
pairs := []pair{}
|
||||
for i := uint(0); i < count; i++ {
|
||||
var throwawayStack []Object
|
||||
objN, _ := u.parse(&lex1, &throwawayStack)
|
||||
objOffset, _ := u.parse(&lex1, &throwawayStack)
|
||||
if !objN.IsUint() || !objOffset.IsUint() {
|
||||
return newError("invalid ObjStm pairs")
|
||||
}
|
||||
pairs = append(pairs, pair{uint(objN.Number), uint(objOffset.Number)})
|
||||
}
|
||||
for i, pair := range pairs {
|
||||
if pair.offset > uint(len(data)) ||
|
||||
i > 0 && pairs[i-1].offset >= pair.offset {
|
||||
return newError("invalid ObjStm pairs")
|
||||
}
|
||||
}
|
||||
|
||||
for i, pair := range pairs {
|
||||
if pair.n != n {
|
||||
continue
|
||||
}
|
||||
|
||||
if i+1 < len(pairs) {
|
||||
data = data[pair.offset:pairs[i+1].offset]
|
||||
} else {
|
||||
data = data[pair.offset:]
|
||||
}
|
||||
|
||||
lex2 := Lexer{data}
|
||||
var stack []Object
|
||||
for {
|
||||
object, err := u.parse(&lex2, &stack)
|
||||
if err != nil {
|
||||
return object, err
|
||||
} else if object.Kind == End {
|
||||
break
|
||||
} else {
|
||||
stack = append(stack, object)
|
||||
}
|
||||
}
|
||||
if len(stack) == 0 {
|
||||
return newError("empty ObjStm object")
|
||||
}
|
||||
return stack[0], nil
|
||||
}
|
||||
return newError("object not found in ObjStm")
|
||||
}
|
||||
|
||||
// Get retrieves an object by its number and generation--may return
|
||||
// Nil or End with an error.
|
||||
func (u *Updater) Get(n, generation uint) (Object, error) {
|
||||
@ -833,8 +1077,13 @@ func (u *Updater) Get(n, generation uint) (Object, error) {
|
||||
}
|
||||
|
||||
ref := u.xref[n]
|
||||
if !ref.nonfree || ref.generation != generation ||
|
||||
ref.offset >= int64(len(u.Document)) {
|
||||
if !ref.nonfree || ref.generation != generation {
|
||||
return New(Nil), nil
|
||||
}
|
||||
|
||||
if ref.compressed != nil {
|
||||
return u.getFromObjStm(*ref.compressed, n)
|
||||
} else if ref.offset >= int64(len(u.Document)) {
|
||||
return New(Nil), nil
|
||||
}
|
||||
|
||||
@ -889,8 +1138,8 @@ type BytesWriter interface {
|
||||
WriteString(s string) (n int, err error)
|
||||
}
|
||||
|
||||
// Update appends an updated object to the end of the document. The fill
|
||||
// callback must write exactly one PDF object.
|
||||
// Update appends an updated object to the end of the document.
|
||||
// The fill callback must write exactly one PDF object.
|
||||
func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
|
||||
oldRef := u.xref[n]
|
||||
u.updated[n] = struct{}{}
|
||||
@ -910,20 +1159,62 @@ func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
|
||||
u.Document = buf.Bytes()
|
||||
}
|
||||
|
||||
// FlushUpdates writes an updated cross-reference table and trailer.
|
||||
func (u *Updater) FlushUpdates() {
|
||||
updated := make([]uint, 0, len(u.updated))
|
||||
for n := range u.updated {
|
||||
updated = append(updated, n)
|
||||
func (u *Updater) flushXRefStm(updated []uint, buf *bytes.Buffer) {
|
||||
// The cross-reference stream has to point to itself.
|
||||
// XXX: We only duplicate Update code here due to how we currently buffer.
|
||||
n := u.Allocate()
|
||||
updated = append(updated, n)
|
||||
|
||||
u.updated[n] = struct{}{}
|
||||
u.xref[n] = ref{
|
||||
offset: int64(buf.Len() + 1),
|
||||
generation: 0,
|
||||
nonfree: true,
|
||||
}
|
||||
sort.Slice(updated, func(i, j int) bool {
|
||||
return updated[i] < updated[j]
|
||||
|
||||
index, b := []Object{}, []byte{}
|
||||
write := func(f1 byte, f2, f3 uint64) {
|
||||
b = append(b, f1)
|
||||
b = binary.BigEndian.AppendUint64(b, f2)
|
||||
b = binary.BigEndian.AppendUint64(b, f3)
|
||||
}
|
||||
for i := 0; i < len(updated); {
|
||||
start, stop := updated[i], updated[i]+1
|
||||
for i++; i < len(updated) && updated[i] == stop; i++ {
|
||||
stop++
|
||||
}
|
||||
|
||||
index = append(index,
|
||||
NewNumeric(float64(start)), NewNumeric(float64(stop-start)))
|
||||
for ; start < stop; start++ {
|
||||
ref := u.xref[start]
|
||||
if ref.compressed != nil {
|
||||
write(2, uint64(*ref.compressed), uint64(ref.offset))
|
||||
} else if ref.nonfree {
|
||||
write(1, uint64(ref.offset), uint64(ref.generation))
|
||||
} else {
|
||||
write(0, uint64(ref.offset), uint64(ref.generation))
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
u.Trailer["Size"] = NewNumeric(float64(u.xrefSize))
|
||||
u.Trailer["Index"] = NewArray(index)
|
||||
u.Trailer["W"] = NewArray([]Object{
|
||||
NewNumeric(1), NewNumeric(8), NewNumeric(8),
|
||||
})
|
||||
|
||||
buf := bytes.NewBuffer(u.Document)
|
||||
startXref := buf.Len() + 1
|
||||
buf.WriteString("\nxref\n")
|
||||
for _, key := range []string{
|
||||
"Filter", "DecodeParms", "F", "FFilter", "FDecodeParms", "DL"} {
|
||||
delete(u.Trailer, key)
|
||||
}
|
||||
|
||||
stream := NewStream(u.Trailer, b)
|
||||
fmt.Fprintf(buf, "\n%d 0 obj\n%s\nendobj", n, stream.Serialize())
|
||||
}
|
||||
|
||||
func (u *Updater) flushXRef(updated []uint, buf *bytes.Buffer) {
|
||||
buf.WriteString("\nxref\n")
|
||||
for i := 0; i < len(updated); {
|
||||
start, stop := updated[i], updated[i]+1
|
||||
for i++; i < len(updated) && updated[i] == stop; i++ {
|
||||
@ -932,8 +1223,9 @@ func (u *Updater) FlushUpdates() {
|
||||
|
||||
fmt.Fprintf(buf, "%d %d\n", start, stop-start)
|
||||
for ; start < stop; start++ {
|
||||
// XXX: We should warn about any object streams here.
|
||||
ref := u.xref[start]
|
||||
if ref.nonfree {
|
||||
if ref.nonfree && ref.compressed == nil {
|
||||
fmt.Fprintf(buf, "%010d %05d n \n", ref.offset, ref.generation)
|
||||
} else {
|
||||
fmt.Fprintf(buf, "%010d %05d f \n", ref.offset, ref.generation)
|
||||
@ -950,9 +1242,34 @@ func (u *Updater) FlushUpdates() {
|
||||
|
||||
u.Trailer["Size"] = NewNumeric(float64(u.xrefSize))
|
||||
trailer := NewDict(u.Trailer)
|
||||
fmt.Fprintf(buf, "trailer\n%s", trailer.Serialize())
|
||||
}
|
||||
|
||||
fmt.Fprintf(buf, "trailer\n%s\nstartxref\n%d\n%%%%EOF\n",
|
||||
trailer.Serialize(), startXref)
|
||||
// FlushUpdates writes an updated cross-reference table and trailer.
|
||||
func (u *Updater) FlushUpdates() {
|
||||
updated := make([]uint, 0, len(u.updated))
|
||||
for n := range u.updated {
|
||||
updated = append(updated, n)
|
||||
}
|
||||
sort.Slice(updated, func(i, j int) bool {
|
||||
return updated[i] < updated[j]
|
||||
})
|
||||
|
||||
// It does not seem to be possible to upgrade a PDF file
|
||||
// from trailer dictionaries to cross-reference streams,
|
||||
// so keep continuity either way.
|
||||
//
|
||||
// (Downgrading from cross-reference streams using XRefStm would not
|
||||
// create a true hybrid-reference file, although it should work.)
|
||||
buf := bytes.NewBuffer(u.Document)
|
||||
startXref := buf.Len() + 1 /* '\n' */
|
||||
if typ, _ := u.Trailer["Type"]; typ.Kind == Name && typ.String == "XRef" {
|
||||
u.flushXRefStm(updated, buf)
|
||||
} else {
|
||||
u.flushXRef(updated, buf)
|
||||
}
|
||||
|
||||
fmt.Fprintf(buf, "\nstartxref\n%d\n%%%%EOF\n", startXref)
|
||||
u.Document = buf.Bytes()
|
||||
}
|
||||
|
||||
@ -971,6 +1288,36 @@ func NewDate(ts time.Time) Object {
|
||||
return NewString(string(buf))
|
||||
}
|
||||
|
||||
// GetStreamData returns the actual data stored in a stream object,
|
||||
// applying any filters.
|
||||
func (u *Updater) GetStreamData(stream Object) ([]byte, error) {
|
||||
if f, ok := stream.Dict["F"]; ok && f.Kind != Nil {
|
||||
return nil, errors.New("stream data in other files are unsupported")
|
||||
}
|
||||
|
||||
// Support just enough to decode a common cross-reference stream.
|
||||
if filter, ok := stream.Dict["Filter"]; !ok {
|
||||
return stream.Stream, nil
|
||||
} else if filter.Kind != Name || filter.String != "FlateDecode" {
|
||||
return nil, errors.New("unsupported stream Filter")
|
||||
}
|
||||
|
||||
// TODO: Support << /Columns N /Predictor 12 >>
|
||||
// which usually appears in files with cross-reference streams.
|
||||
if parms, ok := stream.Dict["DecodeParms"]; ok && parms.Kind != Nil {
|
||||
return nil, errors.New("DecodeParms are not supported")
|
||||
}
|
||||
|
||||
r, err := zlib.NewReader(bytes.NewReader(stream.Stream))
|
||||
if err != nil {
|
||||
return nil, err
|
||||
}
|
||||
|
||||
var b bytes.Buffer
|
||||
_, err = b.ReadFrom(r)
|
||||
return b.Bytes(), err
|
||||
}
|
||||
|
||||
// GetFirstPage retrieves the first page of the given page (sub)tree reference,
|
||||
// or returns a Nil object if unsuccessful.
|
||||
func (u *Updater) GetFirstPage(node Object) Object {
|
||||
@ -1274,7 +1621,7 @@ func Sign(document []byte, key crypto.PrivateKey, certs []*x509.Certificate,
|
||||
})
|
||||
|
||||
// 8.6.1 Interactive Form Dictionary
|
||||
if _, ok := root.Dict["AcroForm"]; ok {
|
||||
if acroform, ok := root.Dict["AcroForm"]; ok && acroform.Kind != Nil {
|
||||
return nil, errors.New("the document already contains forms, " +
|
||||
"they would be overwritten")
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user