Go: add PDF 1.5 cross-reference stream support
This is not particularly complete, but it works (again) for Cairo.
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LICENSE
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LICENSE
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@ -1,4 +1,4 @@
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Copyright (c) 2017 - 2021, Přemysl Eric Janouch <p@janouch.name>
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Copyright (c) 2017 - 2024, Přemysl Eric Janouch <p@janouch.name>
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Permission to use, copy, modify, and/or distribute this software for any
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purpose with or without fee is hereby granted.
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@ -33,7 +33,8 @@ Runtime dependencies: libcrypto (OpenSSL 1.1 API)
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$ cd builddir
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$ ninja
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In addition to the C++ version, also included is a native Go port:
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In addition to the C++ version, also included is a native Go port,
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which has enhanced PDF 1.5 support:
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$ go get janouch.name/pdf-simple-sign/cmd/pdf-simple-sign
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435
pdf/pdf.go
435
pdf/pdf.go
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@ -1,5 +1,5 @@
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//
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// Copyright (c) 2018 - 2021, Přemysl Eric Janouch <p@janouch.name>
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// Copyright (c) 2018 - 2024, Přemysl Eric Janouch <p@janouch.name>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted.
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@ -18,6 +18,8 @@ package pdf
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import (
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"bytes"
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"compress/zlib"
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"encoding/binary"
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"encoding/hex"
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"errors"
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"fmt"
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@ -120,6 +122,13 @@ func NewDict(d map[string]Object) Object {
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return Object{Kind: Dict, Dict: d}
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}
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func NewStream(d map[string]Object, s []byte) Object {
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if d == nil {
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d = make(map[string]Object)
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}
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return Object{Kind: Stream, Dict: d, Stream: s}
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}
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func NewIndirect(o Object, n, generation uint) Object {
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return Object{Kind: Indirect, N: n, Generation: generation,
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Array: []Object{o}}
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@ -477,8 +486,9 @@ func (o *Object) Serialize() string {
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// -----------------------------------------------------------------------------
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type ref struct {
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offset int64 // file offset or N of the next free entry
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offset int64 // file offset, or N of the next free entry, or index
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generation uint // object generation
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compressed *uint // PDF 1.5: N of the containing compressed object
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nonfree bool // whether this N is taken (for a good zero value)
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}
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@ -671,16 +681,159 @@ func (u *Updater) parse(lex *Lexer, stack *[]Object) (Object, error) {
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}
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}
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func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
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func (u *Updater) loadXrefEntry(
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n uint, r ref, loadedEntries map[uint]struct{}) {
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if _, ok := loadedEntries[n]; ok {
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return
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}
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if lenXref := uint(len(u.xref)); n >= lenXref {
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u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
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}
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loadedEntries[n] = struct{}{}
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u.xref[n] = r
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}
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func (u *Updater) loadXrefStream(
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lex *Lexer, stack []Object, loadedEntries map[uint]struct{}) (
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Object, error) {
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var object Object
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for {
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var err error
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if object, err = u.parse(lex, &stack); err != nil {
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return New(End), fmt.Errorf("invalid xref table: %s", err)
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} else if object.Kind == End {
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return newError("invalid xref table")
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}
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// For the sake of simplicity, keep stacking until we find an object.
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if object.Kind == Indirect {
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break
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}
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stack = append(stack, object)
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}
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// ISO 32000-2:2020 7.5.8.2 Cross-reference stream dictionary
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stream := object.Array[0]
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if stream.Kind != Stream {
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return newError("invalid xref table")
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}
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if typ, ok := stream.Dict["Type"]; !ok ||
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typ.Kind != Name || typ.String != "XRef" {
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return newError("invalid xref stream")
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}
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data, err := u.GetStreamData(stream)
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if err != nil {
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return New(End), fmt.Errorf("invalid xref stream: %s", err)
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}
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size, ok := stream.Dict["Size"]
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if !ok || !size.IsUint() || size.Number <= 0 {
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return newError("invalid or missing cross-reference stream Size")
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}
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type pair struct{ start, count uint }
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pairs := []pair{}
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if index, ok := stream.Dict["Index"]; !ok {
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pairs = append(pairs, pair{0, uint(size.Number)})
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} else {
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if index.Kind != Array || len(index.Array)%2 != 0 {
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return newError("invalid cross-reference stream Index")
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}
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a := index.Array
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for i := 0; i < len(a); i += 2 {
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if !a[i].IsUint() || !a[i+1].IsUint() {
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return newError("invalid cross-reference stream Index")
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}
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pairs = append(pairs, pair{uint(a[i].Number), uint(a[i+1].Number)})
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}
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}
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w, ok := stream.Dict["W"]
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if !ok || w.Kind != Array || len(w.Array) != 3 ||
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!w.Array[0].IsUint() || !w.Array[1].IsUint() || !w.Array[2].IsUint() {
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return newError("invalid or missing cross-reference stream W")
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}
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w1 := uint(w.Array[0].Number)
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w2 := uint(w.Array[1].Number)
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w3 := uint(w.Array[2].Number)
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if w2 == 0 {
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return newError("invalid cross-reference stream W")
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}
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unit := w1 + w2 + w3
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if uint(len(data))%unit != 0 {
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return newError("invalid cross-reference stream length")
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}
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readField := func(data []byte, width uint) (uint, []byte) {
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var n uint
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for ; width != 0; width-- {
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n = n<<8 | uint(data[0])
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data = data[1:]
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}
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return n, data
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}
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// ISO 32000-2:2020 7.5.8.3 Cross-reference stream data
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for _, pair := range pairs {
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for i := uint(0); i < pair.count; i++ {
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if uint(len(data)) < unit {
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return newError("premature cross-reference stream EOF")
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}
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var f1, f2, f3 uint = 1, 0, 0
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if w1 > 0 {
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f1, data = readField(data, w1)
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}
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f2, data = readField(data, w2)
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if w3 > 0 {
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f3, data = readField(data, w3)
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}
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var r ref
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switch f1 {
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case 0:
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r.offset = int64(f2)
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r.generation = f3
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case 1:
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r.offset = int64(f2)
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r.generation = f3
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r.nonfree = true
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case 2:
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r.offset = int64(f3)
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r.compressed = &f2
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r.nonfree = true
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default:
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// TODO: It should be treated as a reference to the null object.
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// We can't currently represent that.
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return newError("unsupported cross-reference stream contents")
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}
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u.loadXrefEntry(pair.start+i, r, loadedEntries)
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}
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}
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stream.Kind = Dict
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stream.Stream = nil
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return stream, nil
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}
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func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) (
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Object, error) {
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var throwawayStack []Object
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if keyword, _ := u.parse(lex,
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&throwawayStack); keyword.Kind != Keyword || keyword.String != "xref" {
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return errors.New("invalid xref table")
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if object, _ := u.parse(lex,
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&throwawayStack); object.Kind != Keyword || object.String != "xref" {
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return u.loadXrefStream(lex, []Object{object}, loadedEntries)
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}
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for {
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object, _ := u.parse(lex, &throwawayStack)
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if object.Kind == End {
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return errors.New("unexpected EOF while looking for the trailer")
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return newError("unexpected EOF while looking for the trailer")
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}
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if object.Kind == Keyword && object.String == "trailer" {
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break
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@ -688,7 +841,7 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
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second, _ := u.parse(lex, &throwawayStack)
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if !object.IsUint() || !second.IsUint() {
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return errors.New("invalid xref section header")
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return newError("invalid xref section header")
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}
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start, count := uint(object.Number), uint(second.Number)
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@ -700,33 +853,29 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
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off.Number > float64(len(u.Document)) ||
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!gen.IsInteger() || gen.Number < 0 || gen.Number > 65535 ||
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key.Kind != Keyword {
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return errors.New("invalid xref entry")
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return newError("invalid xref entry")
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}
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free := true
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if key.String == "n" {
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free = false
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} else if key.String != "f" {
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return errors.New("invalid xref entry")
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return newError("invalid xref entry")
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}
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n := start + i
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if _, ok := loadedEntries[n]; ok {
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continue
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}
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if lenXref := uint(len(u.xref)); n >= lenXref {
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u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
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}
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loadedEntries[n] = struct{}{}
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u.xref[n] = ref{
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u.loadXrefEntry(start+i, ref{
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offset: int64(off.Number),
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generation: uint(gen.Number),
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nonfree: !free,
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}, loadedEntries)
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}
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}
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trailer, _ := u.parse(lex, &throwawayStack)
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if trailer.Kind != Dict {
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return newError("invalid trailer dictionary")
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}
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return nil
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return trailer, nil
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}
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// -----------------------------------------------------------------------------
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@ -756,7 +905,6 @@ func NewUpdater(document []byte) (*Updater, error) {
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loadedXrefs := make(map[int64]struct{})
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loadedEntries := make(map[uint]struct{})
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var throwawayStack []Object
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for {
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if _, ok := loadedXrefs[xrefOffset]; ok {
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return nil, errors.New("circular xref offsets")
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@ -766,19 +914,21 @@ func NewUpdater(document []byte) (*Updater, error) {
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}
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lex := Lexer{u.Document[xrefOffset:]}
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if err := u.loadXref(&lex, loadedEntries); err != nil {
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trailer, err := u.loadXref(&lex, loadedEntries)
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if err != nil {
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return nil, err
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}
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trailer, _ := u.parse(&lex, &throwawayStack)
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if trailer.Kind != Dict {
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return nil, errors.New("invalid trailer dictionary")
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}
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if len(loadedXrefs) == 0 {
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u.Trailer = trailer.Dict
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}
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loadedXrefs[xrefOffset] = struct{}{}
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// TODO: Descend into XRefStm here first, if present,
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// which is also a linked list.
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// We allow for mixed cross-reference tables and streams
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// within a single Prev list, although this should never occur.
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prevOffset, ok := trailer.Dict["Prev"]
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if !ok {
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break
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@ -825,6 +975,100 @@ func (u *Updater) Version(root *Object) int {
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return 0
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}
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func (u *Updater) getFromObjStm(nObjStm, n uint) (Object, error) {
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if nObjStm == n {
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return newError("ObjStm recursion")
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}
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stream, err := u.Get(nObjStm, 0)
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if err != nil {
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return stream, err
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}
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if stream.Kind != Stream {
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return newError("invalid ObjStm")
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}
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if typ, ok := stream.Dict["Type"]; !ok ||
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typ.Kind != Name || typ.String != "ObjStm" {
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return newError("invalid ObjStm")
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}
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data, err := u.GetStreamData(stream)
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if err != nil {
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return New(End), fmt.Errorf("invalid ObjStm: %s", err)
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}
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entryN, ok := stream.Dict["N"]
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if !ok || !entryN.IsUint() || entryN.Number <= 0 {
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return newError("invalid ObjStm N")
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}
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entryFirst, ok := stream.Dict["First"]
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if !ok || !entryFirst.IsUint() || entryFirst.Number <= 0 {
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return newError("invalid ObjStm First")
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}
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// NOTE: This means descending into that stream if n is not found here.
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// It is meant to be an object reference.
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if extends, ok := stream.Dict["Extends"]; ok && extends.Kind != Nil {
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return newError("ObjStm extensions are unsupported")
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}
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count := uint(entryN.Number)
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first := uint(entryFirst.Number)
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if first > uint(len(data)) {
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return newError("invalid ObjStm First")
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}
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lex1 := Lexer{data[:first]}
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data = data[first:]
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type pair struct{ n, offset uint }
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pairs := []pair{}
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for i := uint(0); i < count; i++ {
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var throwawayStack []Object
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objN, _ := u.parse(&lex1, &throwawayStack)
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objOffset, _ := u.parse(&lex1, &throwawayStack)
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if !objN.IsUint() || !objOffset.IsUint() {
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return newError("invalid ObjStm pairs")
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}
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pairs = append(pairs, pair{uint(objN.Number), uint(objOffset.Number)})
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}
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for i, pair := range pairs {
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if pair.offset > uint(len(data)) ||
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i > 0 && pairs[i-1].offset >= pair.offset {
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return newError("invalid ObjStm pairs")
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}
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}
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for i, pair := range pairs {
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if pair.n != n {
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continue
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}
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if i+1 < len(pairs) {
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data = data[pair.offset:pairs[i+1].offset]
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} else {
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data = data[pair.offset:]
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}
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lex2 := Lexer{data}
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var stack []Object
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for {
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object, err := u.parse(&lex2, &stack)
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if err != nil {
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return object, err
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} else if object.Kind == End {
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break
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} else {
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stack = append(stack, object)
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}
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}
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if len(stack) == 0 {
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return newError("empty ObjStm object")
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}
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return stack[0], nil
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}
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return newError("object not found in ObjStm")
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}
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// Get retrieves an object by its number and generation--may return
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// Nil or End with an error.
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func (u *Updater) Get(n, generation uint) (Object, error) {
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@ -833,8 +1077,13 @@ func (u *Updater) Get(n, generation uint) (Object, error) {
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}
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ref := u.xref[n]
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if !ref.nonfree || ref.generation != generation ||
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ref.offset >= int64(len(u.Document)) {
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if !ref.nonfree || ref.generation != generation {
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return New(Nil), nil
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}
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if ref.compressed != nil {
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return u.getFromObjStm(*ref.compressed, n)
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} else if ref.offset >= int64(len(u.Document)) {
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return New(Nil), nil
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}
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@ -889,8 +1138,8 @@ type BytesWriter interface {
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WriteString(s string) (n int, err error)
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}
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// Update appends an updated object to the end of the document. The fill
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// callback must write exactly one PDF object.
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// Update appends an updated object to the end of the document.
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// The fill callback must write exactly one PDF object.
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func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
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oldRef := u.xref[n]
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u.updated[n] = struct{}{}
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@ -910,20 +1159,62 @@ func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
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u.Document = buf.Bytes()
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}
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// FlushUpdates writes an updated cross-reference table and trailer.
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func (u *Updater) FlushUpdates() {
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updated := make([]uint, 0, len(u.updated))
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for n := range u.updated {
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func (u *Updater) flushXRefStm(updated []uint, buf *bytes.Buffer) {
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// The cross-reference stream has to point to itself.
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// XXX: We only duplicate Update code here due to how we currently buffer.
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n := u.Allocate()
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updated = append(updated, n)
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u.updated[n] = struct{}{}
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u.xref[n] = ref{
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offset: int64(buf.Len() + 1),
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generation: 0,
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nonfree: true,
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}
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sort.Slice(updated, func(i, j int) bool {
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return updated[i] < updated[j]
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index, b := []Object{}, []byte{}
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write := func(f1 byte, f2, f3 uint64) {
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b = append(b, f1)
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||||
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