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:
Přemysl Eric Janouch 2023-06-29 05:01:23 +02:00
parent 55a17a69b7
commit 0b837b3a0e
Signed by: p
GPG Key ID: A0420B94F92B9493
3 changed files with 396 additions and 48 deletions

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@ -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.

View File

@ -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

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@ -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)
}
}
trailer, _ := u.parse(lex, &throwawayStack)
if trailer.Kind != Dict {
return newError("invalid trailer dictionary")
}
return nil
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 {
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")
}