Update Filters to operate over Spans

src/UglyToad.PdfPig/Filters/Ascii85Filter.cs

@@ -29,18 +29,17 @@
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
-            var inputSpan = input.Span;
             var asciiBuffer = new byte[5];
 
             var index = 0;
 
             using var writer = new ArrayPoolBufferWriter<byte>();
            
-            for (var i = 0; i < inputSpan.Length; i++)
+            for (var i = 0; i < input.Length; i++)
             {
-                var value = inputSpan[i];
+                var value = input[i];
 
                 if (IsWhiteSpace(value))
                 {
@@ -49,7 +48,7 @@
 
                 if (value == EndOfDataBytes[0])
                 {
-                    if (i == inputSpan.Length - 1 || inputSpan[i + 1] == EndOfDataBytes[1])
+                    if (i == input.Length - 1 || input[i + 1] == EndOfDataBytes[1])
                     {
                         if (index > 0)
                         {

src/UglyToad.PdfPig/Filters/AsciiHexDecodeFilter.cs

@@ -1,7 +1,6 @@
 namespace UglyToad.PdfPig.Filters
 {
     using System;
-    using System.Collections.Generic;
     using System.IO;
     using Tokens;
 
@@ -9,7 +8,7 @@
     /// <summary>
     /// Encodes/decodes data using the ASCII hexadecimal encoding where each byte is represented by two ASCII characters.
     /// </summary>
-    internal class AsciiHexDecodeFilter : IFilter
+    internal sealed class AsciiHexDecodeFilter : IFilter
     {
         private static readonly short[] ReverseHex = 
         [
@@ -30,28 +29,27 @@
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
-            var inputSpan = input.Span;
-            var pair = new byte[2];
+            Span<byte> pair = stackalloc byte[2];
             var index = 0;
 
             using (var memoryStream = new MemoryStream())
             using (var binaryWriter = new BinaryWriter(memoryStream))
             {
-                for (var i = 0; i < inputSpan.Length; i++)
+                for (var i = 0; i < input.Length; i++)
                 {
-                    if (inputSpan[i] == '>')
+                    if (input[i] == '>')
                     {
                         break;
                     }
 
-                    if (IsWhitespace(inputSpan[i]) || inputSpan[i] == '<')
+                    if (IsWhitespace(input[i]) || input[i] == '<')
                     {
                         continue;
                     }
 
-                    pair[index] = inputSpan[i];
+                    pair[index] = input[i];
                     index++;
 
                     if (index == 2)

src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs

@@ -1,9 +1,7 @@
 namespace UglyToad.PdfPig.Filters
 {
     using System;
-    using System.Collections.Generic;
     using System.IO;
-    using System.Linq;
     using Tokens;
     using Util;
 
@@ -12,13 +10,13 @@
     ///
     /// Ported from https://github.com/apache/pdfbox/blob/714156a15ea6fcfe44ac09345b01e192cbd74450/pdfbox/src/main/java/org/apache/pdfbox/filter/CCITTFaxFilter.java
     /// </summary>
-    internal class CcittFaxDecodeFilter : IFilter
+    internal sealed class CcittFaxDecodeFilter : IFilter
     {
         /// <inheritdoc />
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             var decodeParms = DecodeParameterResolver.GetFilterParameters(streamDictionary, filterIndex);
 
@@ -38,7 +36,7 @@
 
             var k = decodeParms.GetIntOrDefault(NameToken.K, 0);
             var encodedByteAlign = decodeParms.GetBooleanOrDefault(NameToken.EncodedByteAlign, false);
-            var compressionType = DetermineCompressionType(input.Span, k);
+            var compressionType = DetermineCompressionType(input, k);
             using (var stream = new CcittFaxDecoderStream(new MemoryStream(input.ToArray()), cols, compressionType, encodedByteAlign))
             {
                 var arraySize = (cols + 7) / 8 * rows;

src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs

@@ -329,7 +329,7 @@
 
             if (index != columns)
             {
-                throw new InvalidOperationException("Sum of run-lengths does not equal scan line width: " + index + " > " + columns);
+                throw new InvalidOperationException($"Sum of run-lengths does not equal scan line width: {index} > {columns}");
             }
 
             decodedLength = (index + 7) / 8;

src/UglyToad.PdfPig/Filters/DctDecodeFilter.cs

@@ -9,7 +9,7 @@
         public bool IsSupported { get; } = false;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             throw new NotSupportedException("The DST (Discrete Cosine Transform) Filter indicates data is encoded in JPEG format. " +
                                             "This filter is not currently supported but the raw data can be supplied to JPEG supporting libraries.");

src/UglyToad.PdfPig/Filters/FlateFilter.cs

@@ -2,10 +2,8 @@
 {
     using Fonts;
     using System;
-    using System.Collections.Generic;
     using System.IO;
     using System.IO.Compression;
-    using System.Linq;
     using Tokens;
     using Util;
 
@@ -20,7 +18,7 @@
     /// See section 3.3.3 of the spec (version 1.7) for details on the FlateDecode filter.
     /// The flate decode filter may have a predictor function to further compress the stream.
     /// </remarks>
-    internal class FlateFilter : IFilter
+    internal sealed class FlateFilter : IFilter
     {
         // Defaults are from table 3.7 in the spec (version 1.7)
         private const int DefaultColors = 1;
@@ -34,7 +32,7 @@
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             var parameters = DecodeParameterResolver.GetFilterParameters(streamDictionary, filterIndex);
 

src/UglyToad.PdfPig/Filters/IFilter.cs

@@ -1,7 +1,6 @@
 namespace UglyToad.PdfPig.Filters
 {
     using System;
-    using System.Collections.Generic;
     using Tokens;
 
     /// <summary>
@@ -21,6 +20,6 @@
         /// <param name="streamDictionary">The dictionary of the <see cref="StreamToken"/> (or other dictionary types, e.g. inline images) containing these bytes.</param>
         /// <param name="filterIndex">The position of this filter in the pipeline used to encode data.</param>
         /// <returns>The decoded bytes.</returns>
-        byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex);
+        byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex);
     }
 }

src/UglyToad.PdfPig/Filters/Jbig2DecodeFilter.cs

@@ -9,7 +9,7 @@
         public bool IsSupported { get; } = false;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             throw new NotSupportedException("The JBIG2 Filter for monochrome image data is not currently supported. " +
                                             "Try accessing the raw compressed data directly.");

src/UglyToad.PdfPig/Filters/JpxDecodeFilter.cs

@@ -9,7 +9,7 @@
         public bool IsSupported { get; } = false;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             throw new NotSupportedException("The JPX Filter (JPEG2000) for image data is not currently supported. " +
                                             "Try accessing the raw compressed data directly.");

src/UglyToad.PdfPig/Filters/LzwFilter.cs

@@ -29,7 +29,7 @@ namespace UglyToad.PdfPig.Filters
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
             var parameters = DecodeParameterResolver.GetFilterParameters(streamDictionary, filterIndex);
 
@@ -39,7 +39,7 @@ namespace UglyToad.PdfPig.Filters
 
             if (predictor > 1)
             {
-                var decompressed = Decode(input.Span, earlyChange == 1);
+                var decompressed = Decode(input, earlyChange == 1);
 
                 var colors = Math.Min(parameters.GetIntOrDefault(NameToken.Colors, DefaultColors), 32);
                 var bitsPerComponent = parameters.GetIntOrDefault(NameToken.BitsPerComponent, DefaultBitsPerComponent);
@@ -50,7 +50,7 @@ namespace UglyToad.PdfPig.Filters
                 return result;
             }
 
-            var data = Decode(input.Span, earlyChange == 1);
+            var data = Decode(input, earlyChange == 1);
 
             return data;
         }

src/UglyToad.PdfPig/Filters/RunLengthFilter.cs

@@ -1,16 +1,15 @@
 namespace UglyToad.PdfPig.Filters
 {
     using System;
-    using System.Collections.Generic;
-    using System.IO;
     using Tokens;
+    using UglyToad.PdfPig.Core;
 
     /// <inheritdoc />
     /// <summary>
     /// The Run Length filterencodes data in a simple byte-oriented format based on run length.
     /// The encoded data is a sequence of runs, where each run consists of a length byte followed by 1 to 128 bytes of data.
     /// </summary>
-    internal class RunLengthFilter : IFilter
+    internal sealed class RunLengthFilter : IFilter
     {
         private const byte EndOfDataLength = 128;
 
@@ -18,60 +17,55 @@
         public bool IsSupported { get; } = true;
 
         /// <inheritdoc />
-        public byte[] Decode(ReadOnlyMemory<byte> input, DictionaryToken streamDictionary, int filterIndex)
+        public byte[] Decode(ReadOnlySpan<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
-            var inputSpan = input.Span;
-            using (var memoryStream = new MemoryStream())
-            using (var writer = new BinaryWriter(memoryStream))
+            using var output = new ArrayPoolBufferWriter<byte>(input.Length);
+
+            var i = 0;
+            while (i < input.Length)
             {
-                var i = 0;
-                while (i < inputSpan.Length)
+                var runLength = input[i];
+
+                if (runLength == EndOfDataLength)
                 {
-                    var runLength = inputSpan[i];
-
-                    if (runLength == EndOfDataLength)
-                    {
-                        break;
-                    }
-
-                    // if length byte in range 0 - 127 copy the following length + 1 bytes literally to the output.
-                    if (runLength <= 127)
-                    {
-                        var rangeToWriteLiterally = runLength + 1;
-
-                        while (rangeToWriteLiterally > 0)
-                        {
-                            i++;
-
-                            writer.Write(inputSpan[i]);
-
-                            rangeToWriteLiterally--;
-                        }
-
-                        // Move to the following byte.
-                        i++;
-                    }
-                    // Otherwise copy the single following byte 257 - length times (between 2 - 128 times)
-                    else
-                    {
-                        var numberOfTimesToCopy = 257 - runLength;
-
-                        var byteToCopy = inputSpan[i + 1];
-
-                        for (int j = 0; j < numberOfTimesToCopy; j++)
-                        {
-                            writer.Write(byteToCopy);
-                        }
-
-                        // Move to the single byte after the byte to copy.
-                        i += 2;
-                    }
+                    break;
                 }
 
-                writer.Flush();
+                // if length byte in range 0 - 127 copy the following length + 1 bytes literally to the output.
+                if (runLength <= 127)
+                {
+                    var rangeToWriteLiterally = runLength + 1;
 
-                return memoryStream.ToArray();
+                    while (rangeToWriteLiterally > 0)
+                    {
+                        i++;
+
+                        output.Write(input[i]);
+
+                        rangeToWriteLiterally--;
+                    }
+
+                    // Move to the following byte.
+                    i++;
+                }
+                // Otherwise copy the single following byte 257 - length times (between 2 - 128 times)
+                else
+                {
+                    var numberOfTimesToCopy = 257 - runLength;
+
+                    var byteToCopy = input[i + 1];
+
+                    for (int j = 0; j < numberOfTimesToCopy; j++)
+                    {
+                        output.Write(byteToCopy);
+                    }
+
+                    // Move to the single byte after the byte to copy.
+                    i += 2;
+                }
             }
+
+            return output.WrittenSpan.ToArray();
         }
     }
-}
+}

src/UglyToad.PdfPig/PdfExtensions.cs

@@ -63,7 +63,7 @@
             var transform = stream.Data;
             for (var i = 0; i < filters.Count; i++)
             {
-                transform = filters[i].Decode(transform, stream.StreamDictionary, i);
+                transform = filters[i].Decode(transform.Span, stream.StreamDictionary, i);
             }
 
             return transform;
@@ -79,7 +79,7 @@
             var transform = stream.Data;
             for (var i = 0; i < filters.Count; i++)
             {
-                transform = filters[i].Decode(transform, stream.StreamDictionary, i);
+                transform = filters[i].Decode(transform.Span, stream.StreamDictionary, i);
             }
 
             return transform;