CcittFaxDecodeFilter: do not check for input length, invert bitmap with ref byte and fix #982

src/UglyToad.PdfPig.Tests/Integration/GithubIssuesTests.cs

@@ -7,6 +7,24 @@
 
     public class GithubIssuesTests
     {
+        [Fact]
+        public void Issue982()
+        {
+            var path = IntegrationHelpers.GetSpecificTestDocumentPath("PDFBOX-659-0.pdf");
+
+            using (var document = PdfDocument.Open(path))
+            {
+                for (int p = 1; p <= document.NumberOfPages; ++p)
+                {
+                    var page = document.GetPage(p);
+                    foreach (var pdfImage in page.GetImages())
+                    {
+                        Assert.True(pdfImage.TryGetPng(out _));
+                    }
+                }
+            }
+        }
+
         [Fact]
         public void Issue973()
         {
@@ -25,11 +43,11 @@ public void Issue973()
             using (var document = PdfDocument.Open(path, new ParsingOptions() { UseLenientParsing = false }))
             {
                 var exception = Assert.Throws<InvalidOperationException>(() => document.GetPage(2));
-                Assert.Equal("Cannot execute a pop of the graphics state stack, it would leave the stack empty.", exception.Message);
+                Assert.Equal("Cannot execute a pop of the graphics state stack, it would leave the stack empty.",
+                    exception.Message);
             }
         }
 
-
         [Fact]
         public void Issue959()
         {

src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs

@@ -6,6 +6,8 @@
     using CcittFax;
     using Util;
 
+    // Filter updated from original port because of issue #982
+
     /// <summary>
     /// Decodes image data that has been encoded using either Group 3 or Group 4.
     /// <para>
@@ -62,11 +64,6 @@ private static CcittFaxCompressionType DetermineCompressionType(ReadOnlySpan<byt
             {
                 var compressionType = CcittFaxCompressionType.Group3_1D; // Group 3 1D
 
-                if (input.Length < 20)
-                {
-                    throw new InvalidOperationException("The format is invalid");
-                }
-
                 if (input[0] != 0 || (input[1] >> 4 != 1 && input[1] != 1))
                 {
                     // leading EOL (0b000000000001) not found, search further and
@@ -114,7 +111,8 @@ private static void InvertBitmap(Span<byte> bufferData)
         {
             for (int i = 0, c = bufferData.Length; i < c; i++)
             {
-                bufferData[i] = (byte)(~bufferData[i] & 0xFF);
+                ref byte b = ref bufferData[i];
+                b = (byte)(~b & 0xFF);
             }
         }
     }