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-rw-r--r--LICENSE2
-rw-r--r--README.adoc3
-rw-r--r--pdf/pdf.go439
3 files changed, 396 insertions, 48 deletions
diff --git a/LICENSE b/LICENSE
index 5e342a0..7511f3e 100644
--- a/LICENSE
+++ b/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.
diff --git a/README.adoc b/README.adoc
index ee356f3..9e32e16 100644
--- a/README.adoc
+++ b/README.adoc
@@ -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
diff --git a/pdf/pdf.go b/pdf/pdf.go
index 92d18e9..1e8cfdc 100644
--- a/pdf/pdf.go
+++ b/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")
- }
-
- 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)...)
+ return newError("invalid xref entry")
}
- 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")
}