avoid infinite loop in brute-force searcher #88

fixes the case where the brute-force searcher becomes stuck in an infinite loop, it may be the case that the problem pdf from #88 has a newline or some other whitespace between its object and generation number so this may cause a failure elsewhere.

src/UglyToad.PdfPig.Tests/Parser/Parts/BruteForceSearcherTests.cs

@@ -84,6 +84,70 @@ startxref
             }
         }
 
+        [Fact]
+        public void ReaderEscapesUnexpectedObject()
+        {
+            const string s = @"%PDF-1.7
+abcd
+
+1 0 obj
+<< /Type /Any >>
+
+endobj
+
+%AZ 0 obj
+11 0 obj
+769
+endobj
+
+%%EOF";
+
+            var bytes = new ByteArrayInputBytes(OtherEncodings.StringAsLatin1Bytes(s));
+
+            var locations = BruteForceSearcher.GetObjectLocations(bytes);
+
+            Assert.Equal(2, locations.Count);
+
+            var expectedLocations = new long[]
+            {
+                s.IndexOf("1 0 obj", StringComparison.OrdinalIgnoreCase),
+                s.IndexOf("11 0 obj", StringComparison.OrdinalIgnoreCase)
+            };
+
+            Assert.Equal(expectedLocations, locations.Values);
+        }
+
+        [Fact]
+        public void ReaderEscapesUnexpectedGenerationNumber()
+        {
+            const string s = @"%PDF-2.0
+abcdefghijklmnop
+
+1 0 obj
+256
+endobj
+
+16-0 obj
+
+5 0 obj
+<< /IsEmpty false >>
+endobj";
+            
+            var bytes = new ByteArrayInputBytes(OtherEncodings.StringAsLatin1Bytes(s));
+
+            var locations = BruteForceSearcher.GetObjectLocations(bytes);
+
+            Assert.Equal(2, locations.Count);
+
+            var expectedLocations = new long[]
+            {
+                s.IndexOf("1 0 obj", StringComparison.OrdinalIgnoreCase),
+                s.IndexOf("5 0 obj", StringComparison.OrdinalIgnoreCase)
+            };
+
+            Assert.Equal(expectedLocations, locations.Values);
+        }
+
         [Fact]
         public void BruteForceSearcherFileOffsetsCorrect()
         {

src/UglyToad.PdfPig/Parser/Parts/BruteForceSearcher.cs

@@ -33,6 +33,9 @@
 
             var results = new Dictionary<IndirectReference, long>();
 
+            var generationBytes = new StringBuilder();
+            var objectNumberBytes = new StringBuilder();
+
             var originPosition = bytes.CurrentOffset;
 
             var currentOffset = (long)MinimumSearchOffset;
@@ -61,7 +64,7 @@
                                 currentlyInObject = false;
                                 loopProtection = 0;
 
-                                for (int i = 0; i < "endobj".Length; i++)
+                                for (var i = 0; i < "endobj".Length; i++)
                                 {
                                     bytes.MoveNext();
                                     currentOffset++;
@@ -102,7 +105,6 @@
 
                 bytes.Seek(offset);
 
-                var generationBytes = new StringBuilder();
                 while (ReadHelper.IsDigit(bytes.CurrentByte) && offset >= MinimumSearchOffset)
                 {
                     generationBytes.Insert(0, (char)bytes.CurrentByte);
@@ -113,12 +115,12 @@
                 // We should now be at the space between object and generation number.
                 if (!ReadHelper.IsSpace(bytes.CurrentByte))
                 {
+                    currentOffset++;
                     continue;
                 }
 
                 bytes.Seek(--offset);
 
-                var objectNumberBytes = new StringBuilder();
                 while (ReadHelper.IsDigit(bytes.CurrentByte) && offset >= MinimumSearchOffset)
                 {
                     objectNumberBytes.Insert(0, (char)bytes.CurrentByte);
@@ -126,11 +128,22 @@
                     bytes.Seek(offset);
                 }
 
+                if (objectNumberBytes.Length == 0 || generationBytes.Length == 0)
+                {
+                    generationBytes.Clear();
+                    objectNumberBytes.Clear();
+                    currentOffset++;
+                    continue;
+                }
+
                 var obj = long.Parse(objectNumberBytes.ToString(), CultureInfo.InvariantCulture);
                 var generation = int.Parse(generationBytes.ToString(), CultureInfo.InvariantCulture);
 
                 results[new IndirectReference(obj, generation)] = bytes.CurrentOffset;
 
+                generationBytes.Clear();
+                objectNumberBytes.Clear();
+
                 currentlyInObject = true;
 
                 currentOffset++;