Proper fix for invalid startxref.

mlaukala · mlaukala · commit 236c74c17acf · 2018-06-06T10:13:17.000-07:00
diff --git a/src/PdfSharp/Pdf.Advanced/PdfTrailer.cs b/src/PdfSharp/Pdf.Advanced/PdfTrailer.cs
@@ -75,7 +75,7 @@ public PdfTrailer(PdfCrossReferenceStream trailer)
             if (id != null)
                 Elements.SetValue(Keys.ID, id);
         }
-
+        
         public int Size
         {
             get { return Elements.GetInteger(Keys.Size); }
@@ -218,6 +218,37 @@ internal void Finish()
             _document._irefTable.IsUnderConstruction = false;
         }
 
+        /// <summary>
+        /// Constructs the PdfTrailer from a document.
+        /// </summary>
+        /// <param name="parser">the parser used to read the file.</param>
+        internal void ConstructFromDocument(Parser parser)
+        {
+            // TODO - May need to also search for encryption related trailer info
+            PdfCrossReferenceTable xrefTable = _document._irefTable;
+            Elements.SetInteger(Keys.Size, xrefTable.ObjectTable.Count);
+
+            // find the root.
+            PdfDictionary rootToUse = null;
+            foreach (var reference in xrefTable.AllReferences)
+            {
+                PdfObject obj = parser.ReadObject(null, reference.ObjectID, false, false);
+                if (obj is PdfDictionary dObj)
+                {
+                    if (dObj.Elements[PdfCatalog.Keys.Type] as PdfName == "/Catalog")
+                    {
+                        if (rootToUse == null)
+                            rootToUse = dObj;
+                        else if (dObj.ObjectID.GenerationNumber > rootToUse.ObjectID.GenerationNumber)
+                            rootToUse = dObj;
+                    }
+                }
+            }
+
+            if (rootToUse != null)
+                Elements.SetReference(Keys.Root, rootToUse);
+        }
+
         /// <summary>
         /// Predefined keys of this dictionary.
         /// </summary>
diff --git a/src/PdfSharp/Pdf.IO/Lexer.cs b/src/PdfSharp/Pdf.IO/Lexer.cs
@@ -117,7 +117,10 @@ public bool TryScanNextToken(out Symbol symbol, out int position)
                 case '%':
                     // Eat comments, the parser doesn't handle them
                     //return symbol = ScanComment();
-                    ScanComment();
+                    symbol = _symbol = ScanComment();
+                    // Do not eat EOF
+                    if (symbol == Symbol.Eof)
+                        return true;
                     goto Again;
 
                 case '/':
diff --git a/src/PdfSharp/Pdf.IO/Parser.cs b/src/PdfSharp/Pdf.IO/Parser.cs
@@ -1110,62 +1110,31 @@ internal PdfTrailer ReadTrailer()
             if (idx == -1)
                 throw new Exception("The StartXRef table could not be found, the file cannot be opened.");
 
-            ReadSymbol(Symbol.StartXRef);
-			int startxref = _lexer.Position = ReadInteger();
-			
-			// Must be before the first 'goto valid_xref;' statement.
-			int xref_offset = 0;
-
-			// Check for valid startxref
-			if (IsValidXref())
-			{
-				goto valid_xref;
-			}
-
-			// If we reach this point, we have an invalid startxref
-			// First look for bytes preceding "%PDF-". Some pdf producers ignore these.
-			if (length >= 1024)
-			{
-				// "%PDF-" should be in this range
-				string header = _lexer.ReadRawString(0, 1024);
-				idx = header.IndexOf("%PDF-", StringComparison.Ordinal);
-			}
-			else
-			{
-				string header = _lexer.ReadRawString(0, length);
-				idx = header.IndexOf("%PDF-", StringComparison.Ordinal);
-			}
-
-			if (idx > 0)
-			{
-				//_lexer.ByteOffset = idx;
-				_lexer.Position = startxref + idx;
-				if (IsValidXref())
-				{
-					xref_offset = idx;
-					goto valid_xref;
-				}
-			}
-
-			_lexer.Position = startxref;
+            Symbol s = ReadSymbol(Symbol.StartXRef);
+			_lexer.Position = ReadInteger();
+
+            // Producer: iText1.3.1 by lowagie.com (based on itext-paulo-154)
+            // Problem: certificate data added to the start of file. Invalid startxref byte offset
+            // Fix: We could search for the a valid xref table but all byte offsets are probably incorrect.
+            // Probably best to just recreate the xref table.
+            // https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf 7.5.5
+            
 			// Check for valid startxref
 			if (!IsValidXref())
 			{
-				PdfTrailer trailer = TryRecreateXRefTableAndTrailer(_document._irefTable);
-				if (trailer == null)
+                PdfTrailer trailer;
+                bool bSuccess = TryRecreateXRefTableAndTrailer(out trailer, _document);
+				if (!bSuccess)
 					throw new Exception("Could not recreate the xref table or trailer.");
 
 				_document._trailer = trailer;
 				return _document._trailer;
 			}
-
-			valid_xref:
-			_lexer.Position = startxref + xref_offset;
-
+            
 			// Read all trailers.
 			while (true)
             {
-                PdfTrailer trailer = ReadXRefTableAndTrailer(_document._irefTable, xref_offset);
+                PdfTrailer trailer = ReadXRefTableAndTrailer(_document._irefTable);
                 // 1st trailer seems to be the best.
                 if (_document._trailer == null)
                     _document._trailer = trailer;
@@ -1186,114 +1155,101 @@ internal PdfTrailer ReadTrailer()
         /// <returns></returns>
         private bool IsValidXref()
         {
-            int length = _lexer.PdfLength;
             int position = _lexer.Position;
-            // Make sure not inside a stream.
-
-            string content = "";
-            int content_pos = position;
-            while (true)
+            try
             {
-                // look for stream and endstream in 1k chunks.
-                int read_length = Math.Min(1024, length - content_pos);
-                content += _lexer.ReadRawString(content_pos, read_length);
-
-                int ss = content.IndexOf("stream", StringComparison.Ordinal);
-                int es = content.IndexOf("endstream", StringComparison.Ordinal);
-                int eof = content.IndexOf("%%EOF", StringComparison.Ordinal);
+                Symbol symbol = ScanNextToken();
+                if (symbol == Symbol.XRef) // xref table
+                {
+                    _lexer.Position = position;
+                    return true;
+                }
 
-                if (ss != es)
+                if (symbol == Symbol.Integer) // Linearization parameter dictionary
                 {
-                    if (ss == -1)
-                    {
-                        if (eof != -1 && eof < es)
-                            break;
-                        else
-                            return false;
-                    }
-                    else if (es == -1)
-                        break;
-                    else if (ss < es)
-                        break;
-                    else if (ss > es)
+                    // Just because we have an integer, doesn't mean the startxref is actually valid
+                    if (ScanNextToken() == Symbol.Integer && ScanNextToken() == Symbol.Obj)
                     {
-                        if (eof != -1 && eof < ss && eof < es)
-                            break;
-                        else
-                            return false;
+                        _lexer.Position = position;
+                        return true;
                     }
                 }
 
-                if (eof != -1)
-                    break;
-
-                content_pos = content_pos + read_length;
-                if (content_pos + read_length >= length)
-                {
-                    // reached the end of the document without finding either.
-                    break;
-                }
+                _lexer.Position = position;
+                return false;
             }
+            catch
+            {
+                _lexer.Position = position;
+                return false;
+            }
+        }
 
-            _lexer.Position = position;
+        private bool TryRecreateXRefTableAndTrailer(out PdfTrailer trailer, PdfDocument document)
+		{
+            PdfCrossReferenceTable xrefTable = document._irefTable;
+            trailer = null;
+            int length = _lexer.PdfLength;
 
-            Symbol symbol = ScanNextToken();
-            if (symbol == Symbol.XRef)
+            // because some pdf producers put random info before the header, we need to find a proper starting position.
+            // i.e. Producer: iText1.3.1 by lowagie.com (based on itext-paulo-154)
+            int startIdx = -1;
+            string contents = "";
+            for (int i = 0, pos = 0; startIdx == -1 && pos < length; i++, pos = 1024 * i)
             {
-                return true;
+                int len = Math.Min(1024, length - pos);
+                contents = $"{contents}{_lexer.ReadRawString(pos, len)}";
+                startIdx = contents.IndexOf("%PDF-1.", StringComparison.Ordinal);
             }
 
-            if (symbol == Symbol.Integer)
+            if (startIdx == -1)
+                return false;
+
+            // Don't look past the last %%EOF marker
+            int endIdx = -1;
+            contents = "";
+            for (int i = 1; endIdx == -1; i++)
             {
-                // Just because we have an integer, doesn't mean the startxref is actually valid
-                if (ScanNextToken() == Symbol.Integer && ScanNextToken() == Symbol.Obj)
+                int pos = length - (1024 * i);
+                int len = 1024;
+
+                if (pos < 0)
                 {
-                    return true;
+                    len = len + pos;
+                    pos = 0;
                 }
-            }
 
-            return false;
-        }
-
-        private PdfTrailer TryRecreateXRefTableAndTrailer(PdfCrossReferenceTable xrefTable)
-		{
-			// Let's first check for a trailer
-			int length = _lexer.PdfLength;
-
-			int trail_idx;
-			if (length >= 1024)
-			{
-				string trail = _lexer.ReadRawString(length - 1024, 1024);
-				trail_idx = trail.LastIndexOf("trailer", StringComparison.Ordinal);
-				_lexer.Position = length - 1024 + trail_idx;
-			}
-			else
-			{
-				string trail = _lexer.ReadRawString(0, length);
-				trail_idx = trail.LastIndexOf("trailer", StringComparison.Ordinal);
-				_lexer.Position = trail_idx;
-			}
+                contents = $"{_lexer.ReadRawString(pos, len)}{contents}";
+                endIdx = contents.LastIndexOf("%%EOF", StringComparison.Ordinal);
+                if (endIdx != -1)
+                    endIdx = length - contents.Length + endIdx;
 
-			if (trail_idx == -1)
-				return null; //TODO: Look for compressed xref table that should contain the trailer
+                if (pos == 0)
+                    break;
+            }
 
-			ReadSymbol(Symbol.Trailer);
-			ReadSymbol(Symbol.BeginDictionary);
-			PdfTrailer trailer = new PdfTrailer(_document);
-			ReadDictionary(trailer, false);
+            if (endIdx == -1)
+                return false;
 
+            endIdx = endIdx + 5; // This should be where Eof char is
+            
 			// Recreate the xref table.
 			//
 			// When symbol == Symbol.Obj
 			// [0] - generation
 			// [1] - id
 			TokenInfo[] token_stack = new TokenInfo[2];
-			_lexer.Position = 0;
+            
+            _lexer.Position = startIdx;
 			while (true)
 			{
 				Symbol symbol = ScanNextToken(out int position);
-				if (symbol == Symbol.Eof)
-					break;
+                if (symbol == Symbol.Eof)
+                {
+                    // Check if it's the last EOF
+                    if (_lexer.Position >= endIdx)
+                        break; // This is the end of the file.
+                }
 
 				// we need to skip over streams entirely
 				if (symbol == Symbol.BeginStream)
@@ -1327,21 +1283,45 @@ private PdfTrailer TryRecreateXRefTableAndTrailer(PdfCrossReferenceTable xrefTab
 					token_stack[0].Symbol == Symbol.Integer &&
 					token_stack[1].Symbol == Symbol.Integer)
 				{
+                    // TODO:: Do we only need the most recent revision?
 					PdfObjectID objectID = new PdfObjectID(token_stack[1].Number, token_stack[0].Number);
 					if (!xrefTable.Contains(objectID))
 						xrefTable.Add(new PdfReference(objectID, token_stack[1].Position));
 					//ReadObject(null, objectID, false, false); // Can't do this because the object value will never be set after
 					//SkipCharsUntil(Symbol.EndObj); // Can't do this because streams will cause exceptions
 				}
 
-				token_stack[1] = token_stack[0];
+                token_stack[1] = token_stack[0];
 				TokenInfo token_info = new TokenInfo { Symbol = symbol, Position = position };
 				if (symbol == Symbol.Integer)
 					token_info.Number = _lexer.TokenToInteger;
 				token_stack[0] = token_info;
 			}
 
-			return trailer;
+            // find the root.
+//             foreach (var reference in xrefTable.AllReferences)
+//             {
+//                 PdfObject obj = ReadObject(null, reference.ObjectID, false, false);
+//                 if (obj is PdfDictionary dObj)
+//                 {
+//                     if (dObj.Elements[PdfCatalog.Keys.Type] as PdfName == "/Catalog")
+//                     {
+//                         PdfCatalog catalog = new PdfCatalog(dObj);
+//                     }
+//                 }
+//             }
+
+
+
+
+
+
+
+
+            trailer = new PdfTrailer(_document);
+            trailer.ConstructFromDocument(this);
+
+            return true;
 		}
 
 		struct TokenInfo
@@ -1354,7 +1334,7 @@ struct TokenInfo
 		/// <summary>
 		/// Reads cross reference table(s) and trailer(s).
 		/// </summary>
-		private PdfTrailer ReadXRefTableAndTrailer(PdfCrossReferenceTable xrefTable, int xrefOffset)
+		private PdfTrailer ReadXRefTableAndTrailer(PdfCrossReferenceTable xrefTable)
         {
             Debug.Assert(xrefTable != null);
 
@@ -1372,7 +1352,7 @@ private PdfTrailer ReadXRefTableAndTrailer(PdfCrossReferenceTable xrefTable, int
                         int length = ReadInteger();
                         for (int id = start; id < start + length; id++)
                         {
-                            int position = ReadInteger() + xrefOffset;
+                            int position = ReadInteger();
                             int generation = ReadInteger();
                             ReadSymbol(Symbol.Keyword);
                             string token = _lexer.Token;
diff --git a/src/PdfSharp/Pdf.IO/PdfReader.cs b/src/PdfSharp/Pdf.IO/PdfReader.cs
