Fix for XRef stream parsing when last object not included (#399)

- xrefstream: Fix when Index too short. Instead of appending the number of objects appends higher than the maximum index. Fix object number for XRefs stream table when its own offset encountered. Test case included

pdf/core/crossrefs_test.go

@@ -0,0 +1,46 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
+package core
+
+import (
+	"io/ioutil"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseXRefs(t *testing.T) {
+	objData, err := ioutil.ReadFile("./testdata/obj94_xrefs")
+	require.NoError(t, err)
+
+	p := NewParserFromString(string(objData))
+	_, err = p.parseXrefStream(nil)
+	require.NoError(t, err)
+
+	expected := XrefTable{
+		17: {XType: 0, ObjectNumber: 17, Generation: 0, Offset: 427290, OsObjNumber: 0, OsObjIndex: 0},
+		55: {XType: 0, ObjectNumber: 55, Generation: 0, Offset: 427442, OsObjNumber: 0, OsObjIndex: 0},
+		79: {XType: 0, ObjectNumber: 79, Generation: 0, Offset: 427487, OsObjNumber: 0, OsObjIndex: 0},
+		80: {XType: 0, ObjectNumber: 80, Generation: 0, Offset: 427921, OsObjNumber: 0, OsObjIndex: 0},
+		81: {XType: 0, ObjectNumber: 81, Generation: 0, Offset: 428071, OsObjNumber: 0, OsObjIndex: 0},
+		82: {XType: 0, ObjectNumber: 82, Generation: 0, Offset: 429516, OsObjNumber: 0, OsObjIndex: 0},
+		83: {XType: 0, ObjectNumber: 83, Generation: 0, Offset: 429601, OsObjNumber: 0, OsObjIndex: 0},
+		84: {XType: 0, ObjectNumber: 84, Generation: 0, Offset: 429640, OsObjNumber: 0, OsObjIndex: 0},
+		85: {XType: 0, ObjectNumber: 85, Generation: 0, Offset: 429679, OsObjNumber: 0, OsObjIndex: 0},
+		86: {XType: 0, ObjectNumber: 86, Generation: 0, Offset: 429714, OsObjNumber: 0, OsObjIndex: 0},
+		87: {XType: 0, ObjectNumber: 87, Generation: 0, Offset: 429765, OsObjNumber: 0, OsObjIndex: 0},
+		88: {XType: 0, ObjectNumber: 88, Generation: 0, Offset: 429816, OsObjNumber: 0, OsObjIndex: 0},
+		89: {XType: 0, ObjectNumber: 89, Generation: 0, Offset: 429877, OsObjNumber: 0, OsObjIndex: 0},
+		90: {XType: 0, ObjectNumber: 90, Generation: 0, Offset: 429948, OsObjNumber: 0, OsObjIndex: 0},
+		91: {XType: 0, ObjectNumber: 91, Generation: 0, Offset: 430019, OsObjNumber: 0, OsObjIndex: 0},
+		92: {XType: 0, ObjectNumber: 92, Generation: 0, Offset: 430054, OsObjNumber: 0, OsObjIndex: 0},
+		// Additional object (not in index):
+		// Modified such that offset is 0 and number corrected.
+		94: {XType: 0, ObjectNumber: 94, Generation: 0, Offset: 0, OsObjNumber: 0, OsObjIndex: 0},
+	}
+
+	require.Equal(t, expected, p.xrefs)
+}

pdf/core/parser.go

@@ -840,6 +840,8 @@ func (parser *PdfParser) parseXrefStream(xstm *PdfObjectInteger) (*PdfObjectDict
 		parser.reader = bufio.NewReader(parser.rs)
 	}
 
+	xsOffset := parser.GetFileOffset()
+
 	xrefObj, err := parser.ParseIndirectObject()
 	if err != nil {
 		common.Log.Debug("ERROR: Failed to read xref object")
@@ -967,8 +969,14 @@ func (parser *PdfParser) parseXrefStream(xstm *PdfObjectInteger) (*PdfObjectDict
 
 	if entries == objCount+1 {
 		// For compatibility, expand the object count.
-		common.Log.Debug("BAD file: allowing compatibility (append one object to xref stm)")
-		indexList = append(indexList, objCount)
+		common.Log.Debug("Incompatibility: Index missing coverage of 1 object - appending one - May lead to problems")
+		maxIndex := objCount - 1
+		for _, ind := range indexList {
+			if ind > maxIndex {
+				maxIndex = ind
+			}
+		}
+		indexList = append(indexList, maxIndex+1)
 		objCount++
 	}
 
@@ -1040,6 +1048,14 @@ func (parser *PdfParser) parseXrefStream(xstm *PdfObjectInteger) (*PdfObjectDict
 			common.Log.Trace("- Free object - can probably ignore")
 		} else if ftype == 1 {
 			common.Log.Trace("- In use - uncompressed via offset %b", p2)
+			// If offset (n2) is same as the XRefs table offset, then update the Object number with the
+			// one that was parsed.  Fixes problem where the object number is incorrectly or not specified
+			// in the Index.
+			if n2 == xsOffset {
+				common.Log.Debug("Updating object number for XRef table %d -> %d", objNum, xs.ObjectNumber)
+				objNum = int(xs.ObjectNumber)
+			}
+
 			// Object type 1: Objects that are in use but are not
 			// compressed, i.e. defined by an offset (normal entry)
 			if xr, ok := parser.xrefs[objNum]; !ok || int(n3) > xr.Generation {
@@ -1546,6 +1562,8 @@ func NewParserFromString(txt string) *PdfParser {
 	parser.fileSize = int64(len(txt))
 	parser.streamLengthReferenceLookupInProgress = map[int64]bool{}
 
+	parser.xrefs = XrefTable{}
+
 	return &parser
 }