xref.cc

来自「source code: Covert TXT to PDF」· CC 代码 · 共 668 行 · 第 1/2 页

//========================================================================
//
// XRef.cc
//
// Copyright 1996-2002 Glyph & Cog, LLC
//
//========================================================================

#include <aconf.h>

#ifdef USE_GCC_PRAGMAS
#pragma implementation
#endif

#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <ctype.h>
#include "gmem.h"
#include "Object.h"
#include "Stream.h"
#include "Lexer.h"
#include "Parser.h"
#include "Dict.h"
#ifndef NO_DECRYPTION
#include "Decrypt.h"
#endif
#include "Error.h"
#include "ErrorCodes.h"
#include "XRef.h"

//------------------------------------------------------------------------

#define xrefSearchSize 1024	// read this many bytes at end of file
				//   to look for 'startxref'

#ifndef NO_DECRYPTION
//------------------------------------------------------------------------
// Permission bits
//------------------------------------------------------------------------

#define permPrint    (1<<2)
#define permChange   (1<<3)
#define permCopy     (1<<4)
#define permNotes    (1<<5)
#define defPermFlags 0xfffc
#endif

//------------------------------------------------------------------------
// XRef
//------------------------------------------------------------------------

XRef::XRef(BaseStream *strA, GString *ownerPassword, GString *userPassword) {
  Guint pos;
  int i;

  ok = gTrue;
  errCode = errNone;
  size = 0;
  entries = NULL;
  streamEnds = NULL;
  streamEndsLen = 0;

  // read the trailer
  str = strA;
  start = str->getStart();
  pos = readTrailer();

  // if there was a problem with the trailer,
  // try to reconstruct the xref table
  if (pos == 0) {
    if (!(ok = constructXRef())) {
      errCode = errDamaged;
      return;
    }

  // trailer is ok - read the xref table
  } else {
    entries = (XRefEntry *)gmalloc(size * sizeof(XRefEntry));
    for (i = 0; i < size; ++i) {
      entries[i].offset = 0xffffffff;
      entries[i].used = gFalse;
    }
    while (readXRef(&pos)) ;

    // if there was a problem with the xref table,
    // try to reconstruct it
    if (!ok) {
      gfree(entries);
      size = 0;
      entries = NULL;
      if (!(ok = constructXRef())) {
	errCode = errDamaged;
	return;
      }
    }
  }

  // now set the trailer dictionary's xref pointer so we can fetch
  // indirect objects from it
  trailerDict.getDict()->setXRef(this);

  // check for encryption
#ifndef NO_DECRYPTION
  encrypted = gFalse;
#endif
  if (checkEncrypted(ownerPassword, userPassword)) {
    ok = gFalse;
    errCode = errEncrypted;
    return;
  }
}

XRef::~XRef() {
  gfree(entries);
  trailerDict.free();
  if (streamEnds) {
    gfree(streamEnds);
  }
}

// Read startxref position, xref table size, and root.  Returns
// first xref position.
Guint XRef::readTrailer() {
  Parser *parser;
  Object obj;
  char buf[xrefSearchSize+1];
  int n;
  Guint pos, pos1;
  char *p;
  int c;
  int i;

  // read last xrefSearchSize bytes
  str->setPos(xrefSearchSize, -1);
  for (n = 0; n < xrefSearchSize; ++n) {
    if ((c = str->getChar()) == EOF)
      break;
    buf[n] = c;
  }
  buf[n] = '\0';

  // find startxref
  for (i = n - 9; i >= 0; --i) {
    if (!strncmp(&buf[i], "startxref", 9))
      break;
  }
  if (i < 0)
    return 0;
  for (p = &buf[i+9]; isspace(*p); ++p) ;
  pos = lastXRefPos = strToUnsigned(p);

  // find trailer dict by looking after first xref table
  // (NB: we can't just use the trailer dict at the end of the file --
  // this won't work for linearized files.)
  str->setPos(start + pos);
  for (i = 0; i < 4; ++i)
    buf[i] = str->getChar();
  if (strncmp(buf, "xref", 4))
    return 0;
  pos1 = pos + 4;
  while (1) {
    str->setPos(start + pos1);
    for (i = 0; i < 35; ++i) {
      if ((c = str->getChar()) == EOF)
	return 0;
      buf[i] = c;
    }
    if (!strncmp(buf, "trailer", 7))
      break;
    p = buf;
    while (isspace(*p)) ++p;
    while ('0' <= *p && *p <= '9') ++p;
    while (isspace(*p)) ++p;
    n = atoi(p);
    while ('0' <= *p && *p <= '9') ++p;
    while (isspace(*p)) ++p;
    if (p == buf)
      return 0;
    pos1 += (p - buf) + n * 20;
  }
  pos1 += 7;

  // read trailer dict
  obj.initNull();
  parser = new Parser(NULL,
	     new Lexer(NULL,
	       str->makeSubStream(start + pos1, gFalse, 0, &obj)));
  parser->getObj(&trailerDict);
  if (trailerDict.isDict()) {
    trailerDict.dictLookupNF("Size", &obj);
    if (obj.isInt())
      size = obj.getInt();
    else
      pos = 0;
    obj.free();
    trailerDict.dictLookupNF("Root", &obj);
    if (obj.isRef()) {
      rootNum = obj.getRefNum();
      rootGen = obj.getRefGen();
    } else {
      pos = 0;
    }
    obj.free();
  } else {
    pos = 0;
  }
  delete parser;

  // return first xref position
  return pos;
}

// Read an xref table and the prev pointer from the trailer.
GBool XRef::readXRef(Guint *pos) {
  Parser *parser;
  Object obj, obj2;
  char s[20];
  GBool more;
  int first, newSize, n, i, j;
  int c;

  // seek to xref in stream
  str->setPos(start + *pos);

  // make sure it's an xref table
  while ((c = str->getChar()) != EOF && isspace(c)) ;
  s[0] = (char)c;
  s[1] = (char)str->getChar();
  s[2] = (char)str->getChar();
  s[3] = (char)str->getChar();
  if (!(s[0] == 'x' && s[1] == 'r' && s[2] == 'e' && s[3] == 'f')) {
    goto err2;
  }

  // read xref
  while (1) {
    while ((c = str->lookChar()) != EOF && isspace(c)) {
      str->getChar();
    }
    if (c == 't') {
      break;
    }
    for (i = 0; (c = str->getChar()) != EOF && isdigit(c) && i < 20; ++i) {
      s[i] = (char)c;
    }
    if (i == 0) {
      goto err2;
    }
    s[i] = '\0';
    first = atoi(s);
    while ((c = str->lookChar()) != EOF && isspace(c)) {
      str->getChar();
    }
    for (i = 0; (c = str->getChar()) != EOF && isdigit(c) && i < 20; ++i) {
      s[i] = (char)c;
    }
    if (i == 0) {
      goto err2;
    }
    s[i] = '\0';
    n = atoi(s);
    while ((c = str->lookChar()) != EOF && isspace(c)) {
      str->getChar();
    }
    // check for buggy PDF files with an incorrect (too small) xref
    // table size
    if (first + n > size) {
      newSize = size + 256;
      entries = (XRefEntry *)grealloc(entries, newSize * sizeof(XRefEntry));
      for (i = size; i < newSize; ++i) {
	entries[i].offset = 0xffffffff;
	entries[i].used = gFalse;
      }
      size = newSize;
    }
    for (i = first; i < first + n; ++i) {
      for (j = 0; j < 20; ++j) {
	if ((c = str->getChar()) == EOF) {
	  goto err2;
	}
	s[j] = (char)c;
      }
      if (entries[i].offset == 0xffffffff) {
	s[10] = '\0';
	entries[i].offset = strToUnsigned(s);
	s[16] = '\0';
	entries[i].gen = atoi(&s[11]);
	if (s[17] == 'n') {
	  entries[i].used = gTrue;
	} else if (s[17] == 'f') {
	  entries[i].used = gFalse;
	} else {
	  goto err2;
	}
	// PDF files of patents from the IBM Intellectual Property
	// Network have a bug: the xref table claims to start at 1
	// instead of 0.
	if (i == 1 && first == 1 &&
	    entries[1].offset == 0 && entries[1].gen == 65535 &&
	    !entries[1].used) {
	  i = first = 0;
	  entries[0] = entries[1];
	  entries[1].offset = 0xffffffff;
	}
      }
    }
  }

  // read prev pointer from trailer dictionary
  obj.initNull();
  parser = new Parser(NULL,
	     new Lexer(NULL,
	       str->makeSubStream(str->getPos(), gFalse, 0, &obj)));
  parser->getObj(&obj);
  if (!obj.isCmd("trailer")) {
    goto err1;
  }
  obj.free();
  parser->getObj(&obj);
  if (!obj.isDict()) {
    goto err1;
  }
  obj.getDict()->lookupNF("Prev", &obj2);
  if (obj2.isInt()) {
    *pos = (Guint)obj2.getInt();
    more = gTrue;
  } else {
    more = gFalse;
  }
  obj.free();
  obj2.free();

  delete parser;