//========================================================================
//
// XRef.cc
//
// Copyright 1996-2003 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

//------------------------------------------------------------------------
// ObjectStream
//------------------------------------------------------------------------

class ObjectStream {
public:

  // Create an object stream, using object number <objStrNum>,
  // generation 0.
  ObjectStream(XRef *xref, int objStrNumA);

  ~ObjectStream();

  // Return the object number of this object stream.
  int getObjStrNum() { return objStrNum; }

  // Get the <objIdx>th object from this stream, which should be
  // object number <objNum>, generation 0.
  Object *getObject(int objIdx, int objNum, Object *obj);

private:

  int objStrNum;		// object number of the object stream
  int nObjects;			// number of objects in the stream
  Object *objs;			// the objects (length = nObjects)
  int *objNums;			// the object numbers (length = nObjects)
};

ObjectStream::ObjectStream(XRef *xref, int objStrNumA) {
  Stream *str;
  Parser *parser;
  int *offsets;
  Object objStr, obj1, obj2;
  int first, i;

  objStrNum = objStrNumA;
  nObjects = 0;
  objs = NULL;
  objNums = NULL;

  if (!xref->fetch(objStrNum, 0, &objStr)->isStream()) {
    goto err1;
  }

  if (!objStr.streamGetDict()->lookup("N", &obj1)->isInt()) {
    obj1.free();
    goto err1;
  }
  nObjects = obj1.getInt();
  obj1.free();
  if (nObjects <= 0) {
    goto err1;
  }

  if (!objStr.streamGetDict()->lookup("First", &obj1)->isInt()) {
    obj1.free();
    goto err1;
  }
  first = obj1.getInt();
  obj1.free();
  if (first < 0) {
    goto err1;
  }

  if (nObjects*sizeof(int)/sizeof(int) != nObjects) {
    error(-1, "Invalid 'nObjects'");
    goto err1;
  }
 
  objs = new Object[nObjects];
  objNums = (int *)gmalloc(nObjects * sizeof(int));
  offsets = (int *)gmalloc(nObjects * sizeof(int));

  // parse the header: object numbers and offsets
  objStr.streamReset();
  obj1.initNull();
  str = new EmbedStream(objStr.getStream(), &obj1, gTrue, first);
  parser = new Parser(xref, new Lexer(xref, str));
  for (i = 0; i < nObjects; ++i) {
    parser->getObj(&obj1);
    parser->getObj(&obj2);
    if (!obj1.isInt() || !obj2.isInt()) {
      obj1.free();
      obj2.free();
      delete parser;
      gfree(offsets);
      goto err1;
    }
    objNums[i] = obj1.getInt();
    offsets[i] = obj2.getInt();
    obj1.free();
    obj2.free();
    if (objNums[i] < 0 || offsets[i] < 0 ||
	(i > 0 && offsets[i] < offsets[i-1])) {
      delete parser;
      gfree(offsets);
      goto err1;
    }
  }
  while (str->getChar() != EOF) ;
  delete parser;

  // skip to the first object - this shouldn't be necessary because
  // the First key is supposed to be equal to offsets[0], but just in
  // case...
  for (i = first; i < offsets[0]; ++i) {
    objStr.getStream()->getChar();
  }

  // parse the objects
  for (i = 0; i < nObjects; ++i) {
    obj1.initNull();
    if (i == nObjects - 1) {
      str = new EmbedStream(objStr.getStream(), &obj1, gFalse, 0);
    } else {
      str = new EmbedStream(objStr.getStream(), &obj1, gTrue,
			    offsets[i+1] - offsets[i]);
    }
    parser = new Parser(xref, new Lexer(xref, str));
    parser->getObj(&objs[i]);
    while (str->getChar() != EOF) ;
    delete parser;
  }

  gfree(offsets);

 err1:
  objStr.free();
  return;
}

ObjectStream::~ObjectStream() {
  int i;

  if (objs) {
    for (i = 0; i < nObjects; ++i) {
      objs[i].free();
    }
    delete[] objs;
  }
  gfree(objNums);
}

Object *ObjectStream::getObject(int objIdx, int objNum, Object *obj) {
  if (objIdx < 0 || objIdx >= nObjects || objNum != objNums[objIdx]) {
    return obj->initNull();
  }
  return objs[objIdx].copy(obj);
}

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

XRef::XRef(BaseStream *strA, GString *ownerPassword, GString *userPassword) {
  Guint pos;
  Object obj;

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

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

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

  // read the xref table
  } else {
    while (readXRef(&pos)) ;

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

  // get the root dictionary (catalog) object
  trailerDict.dictLookupNF("Root", &obj);
  if (obj.isRef()) {
    rootNum = obj.getRefNum();
    rootGen = obj.getRefGen();
    obj.free();
  } else {
    obj.free();
    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);
  }
  if (objStr) {
    delete objStr;
  }
}

// Read the 'startxref' position.
Guint XRef::getStartXref() {
  char buf[xrefSearchSize+1];
  char *p;
  int c, n, 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) ;
  lastXRefPos = strToUnsigned(p);

  return lastXRefPos;
}

// Read one xref table section.  Also reads the associated trailer
// dictionary, and returns the prev pointer (if any).
GBool XRef::readXRef(Guint *pos) {
  Parser *parser;
  Object obj;
  GBool more;

  // start up a parser, parse one token
  obj.initNull();
  parser = new Parser(NULL,
	     new Lexer(NULL,
	       str->makeSubStream(start + *pos, gFalse, 0, &obj)));
  parser->getObj(&obj);

  // parse an old-style xref table
  if (obj.isCmd("xref")) {
    obj.free();
    more = readXRefTable(parser, pos);

  // parse an xref stream
  } else if (obj.isInt()) {
    obj.free();
    if (!parser->getObj(&obj)->isInt()) {
      goto err1;
    }
    obj.free();
    if (!parser->getObj(&obj)->isCmd("obj")) {
      goto err1;
    }
    obj.free();
    if (!parser->getObj(&obj)->isStream()) {
      goto err1;
    }
    more = readXRefStream(obj.getStream(), pos);
    obj.free();

  } else {
    goto err1;
  }

  delete parser;
  return more;

 err1:
  obj.free();
  delete parser;
  ok = gFalse;
  return gFalse;
}

GBool XRef::readXRefTable(Parser *parser, Guint *pos) {
  XRefEntry entry;
  GBool more;
  Object obj, obj2;
  Guint pos2;
  int first, n, newSize, i;

  while (1) {
    parser->getObj(&obj);
    if (obj.isCmd("trailer")) {
      obj.free();
      break;
    }
    if (!obj.isInt()) {
      goto err1;
    }
    first = obj.getInt();
    obj.free();
    if (!parser->getObj(&obj)->isInt()) {
      goto err1;
    }
    n = obj.getInt();
    obj.free();
    if (first < 0 || n < 0 || first + n < 0) {
      goto err1;
    }
    if (first + n > size) {
      for (newSize = size ? 2 * size : 1024;
	   first + n > newSize && newSize > 0;
	   newSize <<= 1) ;
      if (newSize < 0) {
	goto err1;
      }
      if (newSize*sizeof(XRefEntry)/sizeof(XRefEntry) != newSize) {
        error(-1, "Invalid 'obj' parameters'");
        goto err1;
      }
 
      entries = (XRefEntry *)grealloc(entries, newSize * sizeof(XRefEntry));
      for (i = size; i < newSize; ++i) {
	entries[i].offset = 0xffffffff;
	entries[i].type = xrefEntryFree;
      }
      size = newSize;
    }
    for (i = first; i < first + n; ++i) {
      if (!parser->getObj(&obj)->isInt()) {
	goto err1;
      }
      entry.offset = (Guint)obj.getInt();
      obj.free();
      if (!parser->getObj(&obj)->isInt()) {
	goto err1;
      }
      entry.gen = obj.getInt();
      obj.free();
      parser->getObj(&obj);
      if (obj.isCmd("n")) {
	entry.type = xrefEntryUncompressed;
      } else if (obj.isCmd("f")) {
	entry.type = xrefEntryFree;
      } else {
	goto err1;
      }
      obj.free();
      if (entries[i].offset == 0xffffffff) {
	entries[i] = entry;
	// 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].type == xrefEntryFree) {
	  i = first = 0;
	  entries[0] = entries[1];
	  entries[1].offset = 0xffffffff;
	}
      }
    }
  }

  // read the trailer dictionary
  if (!parser->getObj(&obj)->isDict()) {
    goto err1;
  }

  // get the 'Prev' pointer
  obj.getDict()->lookupNF("Prev", &obj2);
  if (obj2.isInt()) {
    *pos = (Guint)obj2.getInt();
    more = gTrue;
  } else if (obj2.isRef()) {
    // certain buggy PDF generators generate "/Prev NNN 0 R" instead
    // of "/Prev NNN"
    *pos = (Guint)obj2.getRefNum();
    more = gTrue;
  } else {
    more = gFalse;
  }
  obj2.free();

  // save the first trailer dictionary
  if (trailerDict.isNone()) {
    obj.copy(&trailerDict);
  }

  // check for an 'XRefStm' key
  if (obj.getDict()->lookup("XRefStm", &obj2)->isInt()) {
    pos2 = (Guint)obj2.getInt();
    readXRef(&pos2);
    if (!ok) {
      goto err1;
    }
  }
  obj2.free();

  obj.free();
  return more;

 err1:
  obj.free();
  ok = gFalse;
  return gFalse;
}

GBool XRef::readXRefStream(Stream *xrefStr, Guint *pos) {
  Dict *dict;
  int w[3];
  GBool more;
  Object obj, obj2, idx;
  int newSize, first, n, i;

  dict = xrefStr->getDict();

  if (!dict->lookupNF("Size", &obj)->isInt()) {
    goto err1;
  }
  newSize = obj.getInt();
  obj.free();
  if (newSize < 0) {
    goto err1;
  }
  if (newSize > size) {
    if (newSize * sizeof(XRefEntry)/sizeof(XRefEntry) != newSize) {
      error(-1, "Invalid 'size' parameter.");
      return gFalse;
    }
    entries = (XRefEntry *)grealloc(entries, newSize * sizeof(XRefEntry));
    for (i = size; i < newSize; ++i) {
      entries[i].offset = 0xffffffff;
      entries[i].type = xrefEntryFree;
    }
    size = newSize;
  }

  if (!dict->lookupNF("W", &obj)->isArray() ||
      obj.arrayGetLength() < 3) {
    goto err1;
  }
  for (i = 0; i < 3; ++i) {
    if (!obj.arrayGet(i, &obj2)->isInt()) {
      obj2.free();
      goto err1;
    }
    w[i] = obj2.getInt();
    obj2.free();
    if (w[i] < 0 || w[i] > 4) {
      goto err1;
    }
  }
  obj.free();

  xrefStr->reset();
  dict->lookupNF("Index", &idx);
  if (idx.isArray()) {
    for (i = 0; i+1 < idx.arrayGetLength(); i += 2) {
      if (!idx.arrayGet(i, &obj)->isInt()) {
	idx.free();
	goto err1;
      }
      first = obj.getInt();
      obj.free();
      if (!idx.arrayGet(i+1, &obj)->isInt()) {
	idx.free();
	goto err1;
      }
      n = obj.getInt();
      obj.free();
      if (first < 0 || n < 0 ||
	  !readXRefStreamSection(xrefStr, w, first, n)) {
	idx.free();
	goto err0;
      }
    }
  } else {
    if (!readXRefStreamSection(xrefStr, w, 0, newSize)) {
      idx.free();
      goto err0;
    }
  }
  idx.free();

  dict->lookupNF("Prev", &obj);
  if (obj.isInt()) {
    *pos = (Guint)obj.getInt();
    more = gTrue;
  } else {
    more = gFalse;
  }
  obj.free();
  if (trailerDict.isNone()) {
    trailerDict.initDict(dict);
  }

  return more;

 err1:
  obj.free();
 err0:
  ok = gFalse;
  return gFalse;
}

GBool XRef::readXRefStreamSection(Stream *xrefStr, int *w, int first, int n) {
  Guint offset;
  int type, gen, c, newSize, i, j;

  if (first + n < 0) {
    return gFalse;
  }
  if (first + n > size) {
    for (newSize = size ? 2 * size : 1024;
	 first + n > newSize && newSize > 0;
	 newSize <<= 1) ;
    if (newSize < 0) {
      return gFalse;
    }
    if (newSize*sizeof(XRefEntry)/sizeof(XRefEntry) != newSize) {
      error(-1, "Invalid 'size' inside xref table.");
      return gFalse;
    }
    entries = (XRefEntry *)grealloc(entries, newSize * sizeof(XRefEntry));
    for (i = size; i < newSize; ++i) {
      entries[i].offset = 0xffffffff;
      entries[i].type = xrefEntryFree;
    }
    size = newSize;
  }
  for (i = first; i < first + n; ++i) {
    if (w[0] == 0) {
      type = 1;
    } else {
      for (type = 0, j = 0; j < w[0]; ++j) {
	if ((c = xrefStr->getChar()) == EOF) {
	  return gFalse;
	}
	type = (type << 8) + c;
      }
    }
    for (offset = 0, j = 0; j < w[1]; ++j) {
      if ((c = xrefStr->getChar()) == EOF) {
	return gFalse;
      }
      offset = (offset << 8) + c;
    }
    for (gen = 0, j = 0; j < w[2]; ++j) {
      if ((c = xrefStr->getChar()) == EOF) {
	return gFalse;
      }
      gen = (gen << 8) + c;
    }
    if (entries[i].offset == 0xffffffff) {
      switch (type) {
      case 0:
	entries[i].offset = offset;
	entries[i].gen = gen;
	entries[i].type = xrefEntryFree;
	break;
      case 1:
	entries[i].offset = offset;
	entries[i].gen = gen;
	entries[i].type = xrefEntryUncompressed;
	break;
      case 2:
	entries[i].offset = offset;
	entries[i].gen = gen;
	entries[i].type = xrefEntryCompressed;
	break;
      default:
	return gFalse;
      }
    }
  }

  return gTrue;
}

// Attempt to construct an xref table for a damaged file.
GBool XRef::constructXRef() {
  Parser *parser;
  Object newTrailerDict, obj;
  char buf[256];
  Guint pos;
  int num, gen;
  int newSize;
  int streamEndsSize;
  char *p;
  int i;
  GBool gotRoot;

  gfree(entries);
  size = 0;
  entries = NULL;

  error(0, "PDF file is damaged - attempting to reconstruct xref table...");
  gotRoot = gFalse;
  streamEndsLen = streamEndsSize = 0;

  str->reset();
  while (1) {
    pos = str->getPos();
    if (!str->getLine(buf, 256)) {
      break;
    }
    p = buf;

    // got trailer dictionary
    if (!strncmp(p, "trailer", 7)) {
      obj.initNull();
      parser = new Parser(NULL,
		 new Lexer(NULL,
		   str->makeSubStream(start + pos + 7, gFalse, 0, &obj)));
      parser->getObj(&newTrailerDict);
      if (newTrailerDict.isDict()) {
	newTrailerDict.dictLookupNF("Root", &obj);
	if (obj.isRef()) {
	  rootNum = obj.getRefNum();
	  rootGen = obj.getRefGen();
	  if (!trailerDict.isNone()) {
	    trailerDict.free();
	  }
	  newTrailerDict.copy(&trailerDict);
	  gotRoot = gTrue;
	}
	obj.free();
      }
      newTrailerDict.free();
      delete parser;

    // look for object
    } else if (isdigit(*p)) {
      num = atoi(p);
      if (num > 0) {
	do {
	  ++p;
	} while (*p && isdigit(*p));
	if (isspace(*p)) {
	  do {
	    ++p;
	  } while (*p && isspace(*p));
	  if (isdigit(*p)) {
	    gen = atoi(p);
	    do {
	      ++p;
	    } while (*p && isdigit(*p));
	    if (isspace(*p)) {
	      do {
		++p;
	      } while (*p && isspace(*p));
	      if (!strncmp(p, "obj", 3)) {
		if (num >= size) {
		  newSize = (num + 1 + 255) & ~255;
		  if (newSize < 0) {
		    error(-1, "Bad object number");
		    return gFalse;
		  }
                  if (newSize*sizeof(XRefEntry)/sizeof(XRefEntry) != newSize) {
                    error(-1, "Invalid 'obj' parameters.");
                    return gFalse;
                  }
		  entries = (XRefEntry *)
		      grealloc(entries, newSize * sizeof(XRefEntry));
		  for (i = size; i < newSize; ++i) {
		    entries[i].offset = 0xffffffff;
		    entries[i].type = xrefEntryFree;
		  }
		  size = newSize;
		}
		if (entries[num].type == xrefEntryFree ||
		    gen >= entries[num].gen) {
		  entries[num].offset = pos - start;
		  entries[num].gen = gen;
		  entries[num].type = xrefEntryUncompressed;
		}
	      }
	    }
	  }
	}
      }

    } else if (!strncmp(p, "endstream", 9)) {
      if (streamEndsLen == streamEndsSize) {
	streamEndsSize += 64;
        if (streamEndsSize*sizeof(int)/sizeof(int) != streamEndsSize) {
          error(-1, "Invalid 'endstream' parameter.");
          return gFalse;
        }
	streamEnds = (Guint *)grealloc(streamEnds,
				       streamEndsSize * sizeof(int));
      }
      streamEnds[streamEndsLen++] = pos;
    }
  }

  if (gotRoot)
    return gTrue;

  error(-1, "Couldn't find trailer dictionary");
  return gFalse;
}

#ifndef NO_DECRYPTION
GBool XRef::checkEncrypted(GString *ownerPassword, GString *userPassword) {
  Object encrypt, filterObj, versionObj, revisionObj, lengthObj;
  Object ownerKey, userKey, permissions, fileID, fileID1;
  GBool encrypted1;
  GBool ret;

  keyLength = 0;
  encVersion = encRevision = 0;
  ret = gFalse;

  permFlags = defPermFlags;
  ownerPasswordOk = gFalse;
  trailerDict.dictLookup("Encrypt", &encrypt);
  if ((encrypted1 = encrypt.isDict())) {
    ret = gTrue;
    encrypt.dictLookup("Filter", &filterObj);
    if (filterObj.isName("Standard")) {
      encrypt.dictLookup("V", &versionObj);
      encrypt.dictLookup("R", &revisionObj);
      encrypt.dictLookup("Length", &lengthObj);
      encrypt.dictLookup("O", &ownerKey);
      encrypt.dictLookup("U", &userKey);
      encrypt.dictLookup("P", &permissions);
      trailerDict.dictLookup("ID", &fileID);
      if (versionObj.isInt() &&
	  revisionObj.isInt() &&
	  ownerKey.isString() && ownerKey.getString()->getLength() == 32 &&
	  userKey.isString() && userKey.getString()->getLength() == 32 &&
	  permissions.isInt() &&
	  fileID.isArray()) {
	encVersion = versionObj.getInt();
	encRevision = revisionObj.getInt();
	if (lengthObj.isInt()) {
	  keyLength = lengthObj.getInt() / 8;
	} else {
	  keyLength = 5;
	}
	permFlags = permissions.getInt();
	if (encVersion >= 1 && encVersion <= 2 &&
	    encRevision >= 2 && encRevision <= 3) {
	  fileID.arrayGet(0, &fileID1);
	  if (fileID1.isString()) {
	    if (Decrypt::makeFileKey(encVersion, encRevision, keyLength,
				     ownerKey.getString(), userKey.getString(),
				     permFlags, fileID1.getString(),
				     ownerPassword, userPassword, fileKey,
				     &ownerPasswordOk)) {
	      if (ownerPassword && !ownerPasswordOk) {
		error(-1, "Incorrect owner password");
	      }
	      ret = gFalse;
	    } else {
	      error(-1, "Incorrect password");
	    }
	  } else {
	    error(-1, "Weird encryption info");
	  }
	  fileID1.free();
	} else {
	  error(-1, "Unsupported version/revision (%d/%d) of Standard security handler",
		encVersion, encRevision);
	}
      } else {
	error(-1, "Weird encryption info");
      }
      fileID.free();
      permissions.free();
      userKey.free();
      ownerKey.free();
      lengthObj.free();
      revisionObj.free();
      versionObj.free();
    } else {
      error(-1, "Unknown security handler '%s'",
	    filterObj.isName() ? filterObj.getName() : "???");
    }
    filterObj.free();
  }
  encrypt.free();

  // this flag has to be set *after* we read the O/U/P strings
  encrypted = encrypted1;

  return ret;
}
#else
GBool XRef::checkEncrypted(GString *ownerPassword, GString *userPassword) {
  Object obj;
  GBool encrypted;

  trailerDict.dictLookup("Encrypt", &obj);
  if ((encrypted = !obj.isNull())) {
    error(-1, "PDF file is encrypted and this version of the Xpdf tools");
    error(-1, "was built without decryption support.");
  }
  obj.free();
  return encrypted;
}
#endif

GBool XRef::okToPrint(GBool ignoreOwnerPW) {
#ifndef NO_DECRYPTION
  return (!ignoreOwnerPW && ownerPasswordOk) || (permFlags & permPrint);
#else
  return gTrue;
#endif
}

GBool XRef::okToChange(GBool ignoreOwnerPW) {
#ifndef NO_DECRYPTION
  return (!ignoreOwnerPW && ownerPasswordOk) || (permFlags & permChange);
#else
  return gTrue;
#endif
}

GBool XRef::okToCopy(GBool ignoreOwnerPW) {
#ifndef NO_DECRYPTION
  return (!ignoreOwnerPW && ownerPasswordOk) || (permFlags & permCopy);
#else
  return gTrue;
#endif
}

GBool XRef::okToAddNotes(GBool ignoreOwnerPW) {
#ifndef NO_DECRYPTION
  return (!ignoreOwnerPW && ownerPasswordOk) || (permFlags & permNotes);
#else
  return gTrue;
#endif
}

Object *XRef::fetch(int num, int gen, Object *obj) {
  XRefEntry *e;
  Parser *parser;
  Object obj1, obj2, obj3;

  // check for bogus ref - this can happen in corrupted PDF files
  if (num < 0 || num >= size) {
    goto err;
  }

  e = &entries[num];
  switch (e->type) {

  case xrefEntryUncompressed:
    if (e->gen != gen) {
      goto err;
    }
    obj1.initNull();
    parser = new Parser(this,
	       new Lexer(this,
		 str->makeSubStream(start + e->offset, gFalse, 0, &obj1)));
    parser->getObj(&obj1);
    parser->getObj(&obj2);
    parser->getObj(&obj3);
    if (!obj1.isInt() || obj1.getInt() != num ||
	!obj2.isInt() || obj2.getInt() != gen ||
	!obj3.isCmd("obj")) {
      goto err;
    }
#ifndef NO_DECRYPTION
    parser->getObj(obj, encrypted ? fileKey : (Guchar *)NULL, keyLength,
		   num, gen);
#else
    parser->getObj(obj);
#endif
    obj1.free();
    obj2.free();
    obj3.free();
    delete parser;
    break;

  case xrefEntryCompressed:
    if (gen != 0) {
      goto err;
    }
    if (!objStr || objStr->getObjStrNum() != (int)e->offset) {
      if (objStr) {
	delete objStr;
      }
      objStr = new ObjectStream(this, e->offset);
    }
    objStr->getObject(e->gen, num, obj);
    break;

  default:
    goto err;
  }

  return obj;

 err:
  return obj->initNull();
}

Object *XRef::getDocInfo(Object *obj) {
  return trailerDict.dictLookup("Info", obj);
}

// Added for the pdftex project.
Object *XRef::getDocInfoNF(Object *obj) {
  return trailerDict.dictLookupNF("Info", obj);
}

GBool XRef::getStreamEnd(Guint streamStart, Guint *streamEnd) {
  int a, b, m;

  if (streamEndsLen == 0 ||
      streamStart > streamEnds[streamEndsLen - 1]) {
    return gFalse;
  }

  a = -1;
  b = streamEndsLen - 1;
  // invariant: streamEnds[a] < streamStart <= streamEnds[b]
  while (b - a > 1) {
    m = (a + b) / 2;
    if (streamStart <= streamEnds[m]) {
      b = m;
    } else {
      a = m;
    }
  }
  *streamEnd = streamEnds[b];
  return gTrue;
}

Guint XRef::strToUnsigned(char *s) {
  Guint x;
  char *p;
  int i;

  x = 0;
  for (p = s, i = 0; *p && isdigit(*p) && i < 10; ++p, ++i) {
    x = 10 * x + (*p - '0');
  }
  return x;
}