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Fix #82, #86 repairs corrupt xref sections
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@hhrutter
hhrutter committed Jun 10, 2019
1 parent 33da2dd commit 86b3445
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Showing 2 changed files with 199 additions and 57 deletions.
1 change: 1 addition & 0 deletions pkg/pdfcpu/context.go
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Expand Up @@ -156,6 +156,7 @@ type ReadContext struct {
FileName string // The input PDF-File.
FileSize int64
rs io.ReadSeeker
EolCount int // 1 or 2 characters used for eol.
BinaryTotalSize int64 // total stream data
BinaryImageSize int64 // total image stream data
BinaryFontSize int64 // total font stream data (fontfiles)
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255 changes: 198 additions & 57 deletions pkg/pdfcpu/read.go
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Expand Up @@ -764,7 +764,38 @@ func parseTrailerDict(trailerDict Dict, ctx *Context) (*int64, error) {
return offset, nil
}

func scanLine(s *bufio.Scanner) (string, error) {
func scanLineRaw(s *bufio.Scanner) (string, error) {
if ok := s.Scan(); !ok {
if s.Err() != nil {
return "", s.Err()
}
return "", errors.New("scanner: returning nothing")
}
return s.Text(), nil
}

func scanLine(s *bufio.Scanner) (s1 string, err error) {
for i := 0; i <= 1; i++ {
s1, err = scanLineRaw(s)
if err != nil {
return "", err
}
if len(s1) > 0 {
break
}
}

// Remove comment.
i := strings.Index(s1, "%")
if i >= 0 {
s1 = s1[:i]
}

return s1, nil
}

// scanLine ignores comments and empty lines.
func scanLineOrig(s *bufio.Scanner) (string, error) {
for i := 0; i <= 1; i++ {
if ok := s.Scan(); !ok {
err := s.Err()
Expand Down Expand Up @@ -906,6 +937,39 @@ func scanTrailerDict(s *bufio.Scanner, startTag bool) (string, error) {
return buf.String(), nil
}

func processTrailer(ctx *Context, s *bufio.Scanner, line string) (*int64, error) {

var trailerString string

if line != "trailer" {
trailerString = line[7:]
log.Read.Printf("processTrailer: trailer leftover: <%s>\n", trailerString)
} else {
log.Read.Printf("line (len %d) <%s>\n", len(line), line)
}

trailerString, err := scanTrailer(s, trailerString)
if err != nil {
return nil, err
}

log.Read.Printf("processTrailer: trailerString: (len:%d) <%s>\n", len(trailerString), trailerString)

o, err := parseObject(&trailerString)
if err != nil {
return nil, err
}

trailerDict, ok := o.(Dict)
if !ok {
return nil, errors.New("processTrailer: corrupt trailer dict")
}

log.Read.Printf("processTrailer: trailerDict:\n%s\n", trailerDict)

return parseTrailerDict(trailerDict, ctx)
}

// Parse xRef section into corresponding number of xRef table entries.
func parseXRefSection(s *bufio.Scanner, ctx *Context) (*int64, error) {

Expand Down Expand Up @@ -950,42 +1014,7 @@ func parseXRefSection(s *bufio.Scanner, ctx *Context) (*int64, error) {

log.Read.Println("parseXRefSection: parsing trailer dict..")

var trailerString string

if line != "trailer" {
trailerString = line[7:]
log.Read.Printf("parseXRefSection: trailer leftover: <%s>\n", trailerString)
} else {
log.Read.Printf("line (len %d) <%s>\n", len(line), line)
}

trailerString, err = scanTrailer(s, trailerString)
if err != nil {
return nil, err
}

log.Read.Printf("parseXRefSection: trailerString: (len:%d) <%s>\n", len(trailerString), trailerString)

o, err := parseObject(&trailerString)
if err != nil {
return nil, err
}

trailerDict, ok := o.(Dict)
if !ok {
return nil, errors.New("parseXRefSection: corrupt trailer dict")
}

log.Read.Printf("parseXRefSection: trailerDict:\n%s\n", trailerDict)

offset, err := parseTrailerDict(trailerDict, ctx)
if err != nil {
return nil, err
}

log.Read.Println("parseXRefSection end")

return offset, nil
return processTrailer(ctx, s, line)
}

// Get version from first line of file.
Expand All @@ -994,22 +1023,40 @@ func parseXRefSection(s *bufio.Scanner, ctx *Context) (*int64, error) {
// if present, shall be used instead of the version specified in the Header.
// Save PDF Version from header to xRefTable.
// The header version comes as the first line of the file.
func headerVersion(rs io.ReadSeeker) (*Version, error) {
// eolCount is the number of characters used for eol (1 or 2).
func headerVersion(rs io.ReadSeeker) (v *Version, eolCount int, err error) {

log.Read.Println("headerVersion begin")

var errCorruptHeader = errors.New("headerVersion: corrupt pfd file - no header version available")

// Get first line of file which holds the version of this PDFFile.
// We call this the header version.

_, err := rs.Seek(0, io.SeekStart)
_, err = rs.Seek(0, io.SeekStart)
if err != nil {
return nil, err
return nil, 0, err
}

buf := make([]byte, 10)
buf := make([]byte, 20)
_, err = rs.Read(buf)
if err != nil {
return nil, err
return nil, 0, err
}

b := string(buf)

// Detect the used eol which should be 1 (0x00, 0x0D) or 2 chars (0x0D0A)long.
// %PDF-1.x{eol}
if b[8] == 0x0A {
eolCount = 1
} else if b[8] == 0x0D {
eolCount = 1
if b[9] == 0x0A {
eolCount = 2
}
} else {
return nil, 0, errCorruptHeader
}

// Parse the PDF-Version.
Expand All @@ -1019,17 +1066,113 @@ func headerVersion(rs io.ReadSeeker) (*Version, error) {
s := strings.TrimSpace(string(buf))

if len(s) < 8 || !strings.HasPrefix(s, prefix) {
return nil, errors.New("headerVersion: corrupt pfd file - no header version available")
return nil, 0, errCorruptHeader
}

pdfVersion, err := PDFVersion(s[len(prefix) : len(prefix)+3])
if err != nil {
return nil, errors.Wrapf(err, "headerVersion: unknown PDF Header Version")
return nil, 0, errors.Wrapf(err, "headerVersion: unknown PDF Header Version")
}

log.Read.Printf("headerVersion: end, found header version: %s\n", pdfVersion)

return &pdfVersion, nil
return &pdfVersion, eolCount, nil
}

// bypassXrefSection is a hack for digesting corrupt xref sections.
// It populates the xRefTable by reading in all indirect objects line by line
// and works on the assumption of a single xref section - meaning no incremental updates have been made.
func bypassXrefSection(ctx *Context) error {
var z int64
g := FreeHeadGeneration
ctx.Table[0] = &XRefTableEntry{
Free: true,
Offset: &z,
Generation: &g}

rs := ctx.Read.rs
eolCount := ctx.Read.EolCount
var off, offset int64

rd, err := newPositionedReader(rs, &offset)
if err != nil {
return err
}

s := bufio.NewScanner(rd)
s.Split(scanLines)

bb := []byte{}
var (
withinObj bool
withinXref bool
withinTrailer bool
)

for {
line, err := scanLineRaw(s)
if err != nil {
break
}
if withinXref {
offset += int64(len(line) + eolCount)
if withinTrailer {
bb = append(bb, ' ')
bb = append(bb, line...)
i := strings.Index(line, "startxref")
if i >= 0 {
// Parse trailer.
_, err = processTrailer(ctx, s, string(bb))
return err
}
continue
}
// Ignore all until "trailer".
i := strings.Index(line, "trailer")
if i >= 0 {
bb = append(bb, line...)
withinTrailer = true
}
continue
}
i := strings.Index(line, "xref")
if i >= 0 {
offset += int64(len(line) + eolCount)
withinXref = true
continue
}
if !withinObj {
i := strings.Index(line, "obj")
if i >= 0 {
withinObj = true
off = offset
bb = append(bb, line[:i+3]...)
}
offset += int64(len(line) + eolCount)
continue
}

// within obj
offset += int64(len(line) + eolCount)
bb = append(bb, ' ')
bb = append(bb, line...)
i = strings.Index(line, "endobj")
if i >= 0 {
l := string(bb)
objNr, generation, err := parseObjectAttributes(&l)
if err != nil {
return err
}
of := off
ctx.Table[*objNr] = &XRefTableEntry{
Free: false,
Offset: &of,
Generation: generation}
bb = nil
withinObj = false
}
}
return nil
}

// Build XRefTable by reading XRef streams or XRef sections.
Expand All @@ -1039,12 +1182,13 @@ func buildXRefTableStartingAt(ctx *Context, offset *int64) error {

rs := ctx.Read.rs

hv, err := headerVersion(rs)
hv, eolCount, err := headerVersion(rs)
if err != nil {
return err
}

ctx.HeaderVersion = hv
ctx.Read.EolCount = eolCount

for offset != nil {

Expand All @@ -1063,26 +1207,23 @@ func buildXRefTableStartingAt(ctx *Context, offset *int64) error {

log.Read.Printf("line: <%s>\n", line)

if strings.TrimSpace(line) != "xref" {
if strings.TrimSpace(line) == "xref" {
log.Read.Println("buildXRefTableStartingAt: found xref section")
if offset, err = parseXRefSection(s, ctx); err != nil {
return err
}
} else {

log.Read.Println("buildXRefTableStartingAt: found xref stream")
ctx.Read.UsingXRefStreams = true
rd, err = newPositionedReader(rs, offset)
if err != nil {
return err
}

if offset, err = parseXRefStream(rd, offset, ctx); err != nil {
return err
// Try fix for corrupt single xref section.
return bypassXrefSection(ctx)
}

} else {

log.Read.Println("buildXRefTableStartingAt: found xref section")
if offset, err = parseXRefSection(s, ctx); err != nil {
return err
}

}
}

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