From 94f105809a30fbe39b933241e10b64ae337b155c Mon Sep 17 00:00:00 2001
From: BobLd <38405645+BobLd@users.noreply.github.com>
Date: Tue, 31 Dec 2024 12:56:38 +0000
Subject: [PATCH] Return a copy of the ArrayPoolBufferWriter buffer in Ascii85,
 AsciiHex and RunLength filters and fix #964

---
 .../Filters/Ascii85FilterTests.cs             | 68 +++++++++++++++++--
 src/UglyToad.PdfPig/Filters/Ascii85Filter.cs  |  4 +-
 .../Filters/AsciiHexDecodeFilter.cs           |  2 +-
 .../Filters/RunLengthFilter.cs                |  2 +-
 4 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/src/UglyToad.PdfPig.Tests/Filters/Ascii85FilterTests.cs b/src/UglyToad.PdfPig.Tests/Filters/Ascii85FilterTests.cs
index 857f01c2c..8e1fba65b 100644
--- a/src/UglyToad.PdfPig.Tests/Filters/Ascii85FilterTests.cs
+++ b/src/UglyToad.PdfPig.Tests/Filters/Ascii85FilterTests.cs
@@ -22,7 +22,11 @@ public void DecodesWikipediaExample()
 
             var result = filter.Decode(bytes, dictionary, 0);
 
-            var text = Encoding.ASCII.GetString(result.ToArray());
+#if !NET
+            string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+            string text = Encoding.ASCII.GetString(result.Span);
+#endif
 
             Assert.Equal("Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, " +
                          "that by a perseverance of delight in the continued and indefatigable generation of knowledge, " +
@@ -37,7 +41,11 @@ public void ReplacesZWithEmptyBytes()
 
             var result = filter.Decode(bytes, dictionary, 1);
 
-            var text = Encoding.ASCII.GetString(result.ToArray());
+#if !NET
+            string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+            string text = Encoding.ASCII.GetString(result.Span);
+#endif
 
             Assert.Equal("Man \0\0\0\0is d", text);
         }
@@ -104,8 +112,12 @@ public void DecodesEncodedPdfContent()
 
             var result = filter.Decode(Encoding.ASCII.GetBytes(input), dictionary, 0);
 
-            var text = Encoding.ASCII.GetString(result.ToArray());
-            
+#if !NET
+            string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+            string text = Encoding.ASCII.GetString(result.Span);
+#endif
+
             Assert.Equal(PdfContent.Replace("\r\n", "\n"), text);
         }
 
@@ -124,11 +136,57 @@ public void DecodesEncodedPdfContentMissingEndOfDataSymbol()
 
             var result = filter.Decode(Encoding.ASCII.GetBytes(input), dictionary, 0);
 
-            var text = Encoding.ASCII.GetString(result.ToArray());
+#if !NET
+            string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+            string text = Encoding.ASCII.GetString(result.Span);
+#endif
 
             Assert.Equal(PdfContent.Replace("\r\n", "\n"), text);
         }
 
+        [Fact]
+        public void DecodeParallel()
+        {
+            Parallel.For(0, 100_000, i =>
+            {
+                if (i % 2 == 0)
+                {
+                    var bytes = Encoding.ASCII.GetBytes("9jqo^zBlbD-");
+
+                    var result = filter.Decode(bytes, dictionary, 1);
+
+#if !NET
+                    string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+                    string text = Encoding.ASCII.GetString(result.Span);
+#endif
+
+                    Assert.Equal("Man \0\0\0\0is d", text);
+                }
+                else
+                {
+                    const string input =
+                        @"0d&.mDdmGg4?O`>9P&*SFD)dS2E2gC4pl@QEb/Zr$8N_r$:7]!01IZ=0eskNAdU47<+?7h+B3Ol2_m!C+?)#1+B1
+`9>:<KhASu!rA7]9oF*)G6@;U'.@ps6t@V$[&ART*lARTXoCj@HP2DlU*/0HBI+B1r?0H_r%1a#ac$<nof.3LB""+=MAS+D58'ATD3qCj@.
+           F@;@;70ea^uAKYi.Eb-A7E+*6f+EV:*DBN1?0ek+_+B1r?<%9""=ASu!rA7]9oF*)G6@;U'<.3MT)$8<SS1,pCU6jd-H;e7
+C#1,U1&Ft""Og2'=;YEa`c,ASu!rA8,po+Dk\3BQ%F&+CT;%+CQ]A1,'h!Ft""Oh2'=;UBl%3eCh4`'DBMbD7O]H>0H_br.:""&q8d[6p/M
+T()<(%'A;f?Ma+CT;%+E_a:A0>K&EZek1D/aN,F)u&6DBNA*A0>f4BOu4*+EM76E,9eK+B3(_<%9""p.!0AMEb031ATMF#F<G%,DIIR2+Cno
+&@3B9%+CT.1.3LK*+=KNS6V0ilAoD^,@<=+N>p**=$</Jt-rY&$AKYo'+EV:.+Cf>,E,oN2F(oQ1+D#G#De*R""B-;&&FD,T'F!+n3AKY4b
+F*22=@:F%a+=SF4C'moi+=Li?EZeh0FD)e-@<>p#@;]TuBl.9kATKCFGA(],AKYo5BOu4*+CT;%+C#7pF_Pr+@VfTuDf0B:+=SF4C'moi+=
+Li?EZek1DKKT1F`2DD/TboKAKY](@:s.m/h%oBC'mC/$>""*cF*)G6@;Q?_DIdZpC&~>";
 
+                    var result = filter.Decode(Encoding.ASCII.GetBytes(input), dictionary, 0);
+
+#if !NET
+                    string text = Encoding.ASCII.GetString(result.ToArray());
+#else
+                    string text = Encoding.ASCII.GetString(result.Span);
+#endif
+
+                    Assert.Equal(PdfContent.Replace("\r\n", "\n"), text);
+                }
+            });
+        }
     }
 }
diff --git a/src/UglyToad.PdfPig/Filters/Ascii85Filter.cs b/src/UglyToad.PdfPig/Filters/Ascii85Filter.cs
index e5a16240b..5fafa0772 100644
--- a/src/UglyToad.PdfPig/Filters/Ascii85Filter.cs
+++ b/src/UglyToad.PdfPig/Filters/Ascii85Filter.cs
@@ -29,7 +29,7 @@ public sealed class Ascii85Filter : IFilter
         /// <inheritdoc />
         public ReadOnlyMemory<byte> Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
-            var asciiBuffer = new byte[5];
+            Span<byte> asciiBuffer = stackalloc byte[5];
 
             var index = 0;
 
@@ -96,7 +96,7 @@ public ReadOnlyMemory<byte> Decode(ReadOnlySpan<byte> input, DictionaryToken str
                 WriteData(asciiBuffer, index, writer);
             }
 
-            return writer.WrittenMemory;
+            return writer.WrittenMemory.ToArray();
         }
 
         private static void WriteData(Span<byte> ascii, int index, ArrayPoolBufferWriter<byte> writer)
diff --git a/src/UglyToad.PdfPig/Filters/AsciiHexDecodeFilter.cs b/src/UglyToad.PdfPig/Filters/AsciiHexDecodeFilter.cs
index c6558b7f2..d66871dcf 100644
--- a/src/UglyToad.PdfPig/Filters/AsciiHexDecodeFilter.cs
+++ b/src/UglyToad.PdfPig/Filters/AsciiHexDecodeFilter.cs
@@ -68,7 +68,7 @@ public ReadOnlyMemory<byte> Decode(ReadOnlySpan<byte> input, DictionaryToken str
                 WriteHexToByte(pair, writer);
             }
 
-            return writer.WrittenMemory;
+            return writer.WrittenMemory.ToArray();
         }
 
         private static void WriteHexToByte(ReadOnlySpan<byte> hexBytes, ArrayPoolBufferWriter<byte> writer)
diff --git a/src/UglyToad.PdfPig/Filters/RunLengthFilter.cs b/src/UglyToad.PdfPig/Filters/RunLengthFilter.cs
index 1a4d102f0..e345d001f 100644
--- a/src/UglyToad.PdfPig/Filters/RunLengthFilter.cs
+++ b/src/UglyToad.PdfPig/Filters/RunLengthFilter.cs
@@ -62,7 +62,7 @@ public ReadOnlyMemory<byte> Decode(ReadOnlySpan<byte> input, DictionaryToken str
                 }
             }
 
-            return output.WrittenMemory;
+            return output.WrittenMemory.ToArray();
         }
     }
 }
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