/**
* read the cross reference table from a PDF file. When this method is called, the file pointer
* must point to the start of the word "xref" in the file. Reads the xref table and the trailer
* dictionary. If dictionary has a /Prev entry, move file pointer and read new trailer
*
* @param password
*/
private void readTrailer(PDFPassword password)
throws IOException, PDFAuthenticationFailureException,
EncryptionUnsupportedByProductException, EncryptionUnsupportedByPlatformException {
// the table of xrefs
this.objIdx = new PDFXref[50];
int pos = this.buf.position();
PDFDecrypter newDefaultDecrypter = null;
// read a bunch of nested trailer tables
while (true) {
// make sure we are looking at an xref table
if (!nextItemIs("xref")) {
this.buf.position(pos);
readTrailer15(password);
return;
// throw new PDFParseException("Expected 'xref' at start of table");
}
// read a bunch of linked tabled
while (true) {
// read until the word "trailer"
PDFObject obj = readObject(-1, -1, IdentityDecrypter.getInstance());
if (obj.getType() == PDFObject.KEYWORD && obj.getStringValue().equals("trailer")) {
break;
}
// read the starting position of the reference
if (obj.getType() != PDFObject.NUMBER) {
throw new PDFParseException("Expected number for first xref entry");
}
int refstart = obj.getIntValue();
// read the size of the reference table
obj = readObject(-1, -1, IdentityDecrypter.getInstance());
if (obj.getType() != PDFObject.NUMBER) {
throw new PDFParseException("Expected number for length of xref table");
}
int reflen = obj.getIntValue();
// skip a line
readLine();
if (refstart == 1) { // Check and try to fix incorrect Object Number Start
int startPos = this.buf.position();
try {
byte[] refline = new byte[20];
this.buf.get(refline);
if (refline[17] == 'f') { // free
PDFXref objIndex = new PDFXref(refline);
if (objIndex.getID() == 0
&& objIndex.getGeneration() == 65535) { // The highest generation number possible
refstart--;
}
}
} catch (Exception e) { // in case of error ignore
}
this.buf.position(startPos);
}
// extend the objIdx table, if necessary
if (refstart + reflen >= this.objIdx.length) {
PDFXref nobjIdx[] = new PDFXref[refstart + reflen];
System.arraycopy(this.objIdx, 0, nobjIdx, 0, this.objIdx.length);
this.objIdx = nobjIdx;
}
// read reference lines
for (int refID = refstart; refID < refstart + reflen; refID++) {
// each reference line is 20 bytes long
byte[] refline = new byte[20];
this.buf.get(refline);
// ignore this line if the object ID is already defined
if (this.objIdx[refID] != null) {
continue;
}
// see if it's an active object
if (refline[17] == 'n') {
this.objIdx[refID] = new PDFXref(refline);
} else {
this.objIdx[refID] = new PDFXref(null);
}
}
}
// at this point, the "trailer" word (not EOL) has been read.
PDFObject trailerdict = readObject(-1, -1, IdentityDecrypter.getInstance());
if (trailerdict.getType() != PDFObject.DICTIONARY) {
throw new IOException("Expected dictionary after \"trailer\"");
}
// read the root object location
if (this.root == null) {
this.root = trailerdict.getDictRef("Root");
if (this.root != null) {
this.root.setObjectId(PDFObject.OBJ_NUM_TRAILER, PDFObject.OBJ_NUM_TRAILER);
}
}
// read the encryption information
if (this.encrypt == null) {
this.encrypt = trailerdict.getDictRef("Encrypt");
if (this.encrypt != null) {
this.encrypt.setObjectId(PDFObject.OBJ_NUM_TRAILER, PDFObject.OBJ_NUM_TRAILER);
}
if (this.encrypt != null && !PDFDecrypterFactory.isFilterExist(this.encrypt)) {
this.encrypt = null; // the filter is not located at this trailer, we will try later again
} else {
newDefaultDecrypter =
PDFDecrypterFactory.createDecryptor(
this.encrypt, trailerdict.getDictRef("ID"), password);
}
}
if (this.info == null) {
this.info = trailerdict.getDictRef("Info");
if (this.info != null) {
if (!this.info.isIndirect()) {
throw new PDFParseException("Info in trailer must be an indirect reference");
}
this.info.setObjectId(PDFObject.OBJ_NUM_TRAILER, PDFObject.OBJ_NUM_TRAILER);
}
}
// support for hybrid-PDFs containing an additional compressed-xref-stream
PDFObject xrefstmPos = trailerdict.getDictRef("XRefStm");
if (xrefstmPos != null) {
int pos14 = this.buf.position();
this.buf.position(xrefstmPos.getIntValue());
readTrailer15(password);
this.buf.position(pos14);
}
// read the location of the previous xref table
PDFObject prevloc = trailerdict.getDictRef("Prev");
if (prevloc != null) {
this.buf.position(prevloc.getIntValue());
} else {
break;
}
// see if we have an optional Version entry
if (this.root.getDictRef("Version") != null) {
processVersion(this.root.getDictRef("Version").getStringValue());
}
}
// make sure we found a root
if (this.root == null) {
throw new PDFParseException("No /Root key found in trailer dictionary");
}
if (this.encrypt != null && newDefaultDecrypter != null) {
PDFObject permissions = this.encrypt.getDictRef("P");
if (permissions != null && !newDefaultDecrypter.isOwnerAuthorised()) {
int perms = permissions != null ? permissions.getIntValue() : 0;
if (permissions != null) {
this.printable = (perms & 4) != 0;
this.saveable = (perms & 16) != 0;
}
}
// Install the new default decrypter only after the trailer has
// been read, as nothing we're reading passing through is encrypted
this.defaultDecrypter = newDefaultDecrypter;
}
// dereference the root object
this.root.dereference();
}
public boolean resolves(PDFXref ref) {
// it's expected that the object number is relevant
return type != Type.FREE && generation == ref.getGeneration();
}
/**
* Used internally to track down PDFObject references. You should never need to call this.
*
* <p>Since this is the only public method for tracking down PDF objects, it is synchronized. This
* means that the PDFFile can only hunt down one object at a time, preventing the file's location
* from getting messed around.
*
* <p>This call stores the current buffer position before any changes are made and restores it
* afterwards, so callers need not know that the position has changed.
*/
public synchronized PDFObject dereference(PDFXref ref, PDFDecrypter decrypter)
throws IOException {
int id = ref.getID();
// make sure the id is valid and has been read
if (id >= this.objIdx.length || this.objIdx[id] == null) {
return PDFObject.nullObj;
}
// check to see if this is already dereferenced
PDFObject obj = this.objIdx[id].getObject();
if (obj != null) {
return obj;
}
// store the current position in the buffer
int startPos = this.buf.position();
boolean compressed = this.objIdx[id].getCompressed();
if (!compressed) {
int loc = this.objIdx[id].getFilePos();
if (loc < 0) {
return PDFObject.nullObj;
}
// move to where this object is
this.buf.position(loc);
// read the object and cache the reference
obj = readObject(ref.getID(), ref.getGeneration(), decrypter);
} else { // compressed
int compId = this.objIdx[id].getID();
int idx = this.objIdx[id].getIndex();
if (idx < 0) return PDFObject.nullObj;
PDFXref compRef = new PDFXref(compId, 0);
PDFObject compObj = dereference(compRef, decrypter);
int first = compObj.getDictionary().get("First").getIntValue();
int length = compObj.getDictionary().get("Length").getIntValue();
int n = compObj.getDictionary().get("N").getIntValue();
if (idx >= n) return PDFObject.nullObj;
ByteBuffer strm = compObj.getStreamBuffer();
ByteBuffer oldBuf = this.buf;
this.buf = strm;
// skip other nums
for (int i = 0; i < idx; i++) {
PDFObject skip1num = readObject(-1, -1, true, IdentityDecrypter.getInstance());
PDFObject skip2num = readObject(-1, -1, true, IdentityDecrypter.getInstance());
}
PDFObject objNumPO = readObject(-1, -1, true, IdentityDecrypter.getInstance());
PDFObject offsetPO = readObject(-1, -1, true, IdentityDecrypter.getInstance());
int objNum = objNumPO.getIntValue();
int offset = offsetPO.getIntValue();
if (objNum != id) return PDFObject.nullObj;
this.buf.position(first + offset);
obj = readObject(objNum, 0, IdentityDecrypter.getInstance());
this.buf = oldBuf;
}
if (obj == null) {
obj = PDFObject.nullObj;
}
this.objIdx[id].setObject(obj);
// reset to the previous position
this.buf.position(startPos);
return obj;
}
