Improve Code Quality (#818)

* Make AdobeFontMetricsLigature a struct

* Make AdobeFontMetricsCharacterSize a struct

* Eliminate allocation in CompactFontFormatData

* Pass TransformationMatrix  by reference

* Seal Encoding classes

* Make SubTableHeaderEntry a readonly struct

* Introduce StringSplitter and eliminate various allocations in GlyphListFactory

* Eliminate a few substring allocations

* Use char overload on StringBuilder

* Eliminate virtual calls on stringIndex

* Optimize ReadHelper ReadLong and ReadInt methods

* Add additional readonly annotations to PdfRectangle

* Optimize NameTokenizer

* Eliminate allocation in TrueTypeGlyphTableSubsetter

* Use empty arrays

* Eliminate allocations in OperationWriteHelper.WriteHex

* Use simplified DecryptCbc method on .NET 6+

* Fix windows-1252 encoding not working on net6.0 and 8.0

* Update int buffers to exact unsigned max length and eliminate additional byte allocation

* Fix typo

* Remove unused constant

src/UglyToad.PdfPig.Core/PdfRectangle.cs

@@ -16,22 +16,22 @@ public struct PdfRectangle
         /// <summary>
         /// Top left point of the rectangle.
         /// </summary>
-        public PdfPoint TopLeft { get; }
+        public readonly PdfPoint TopLeft { get; }
 
         /// <summary>
         /// Top right point of the rectangle.
         /// </summary>
-        public PdfPoint TopRight { get; }
+        public readonly PdfPoint TopRight { get; }
 
         /// <summary>
         /// Bottom right point of the rectangle.
         /// </summary>
-        public PdfPoint BottomRight { get; }
+        public readonly PdfPoint BottomRight { get; }
 
         /// <summary>
         /// Bottom left point of the rectangle.
         /// </summary>
-        public PdfPoint BottomLeft { get; }
+        public readonly PdfPoint BottomLeft { get; }
 
         /// <summary>
         /// Centroid point of the rectangle.

src/UglyToad.PdfPig.Core/ReadHelper.cs

@@ -1,8 +1,8 @@
 namespace UglyToad.PdfPig.Core
 {
     using System;
+    using System.Buffers.Text;
     using System.Collections.Generic;
-    using System.Globalization;
     using System.Text;
 
 #if NET8_0_OR_GREATER
@@ -41,8 +41,6 @@ public static class ReadHelper
             '\f'
         ];
 
-        private static readonly int MaximumNumberStringLength = long.MaxValue.ToString("D").Length;
-
         /// <summary>
         /// Read a string from the input until a newline.
         /// </summary>
@@ -134,7 +132,7 @@ public static bool IsEndOfName(int ch)
         /// </remarks>
         public static bool IsWhitespace(byte c)
         {
-            return c == 0 || c == 32 || c == AsciiLineFeed || c == AsciiCarriageReturn || c == 9 || c == 12;
+            return c is 0 or 32 or AsciiLineFeed or AsciiCarriageReturn or 9 or 12;
         }
 
         /// <summary>
@@ -198,25 +196,24 @@ public static bool IsString(IInputBytes bytes, string s)
         public static long ReadLong(IInputBytes bytes)
         {
             SkipSpaces(bytes);
-            long retval;
 
-            StringBuilder longBuffer = ReadStringNumber(bytes);
+            Span<byte> buffer = stackalloc byte[19]; // max formatted uint64 length
 
-            try
+            ReadNumberAsUtf8Bytes(bytes, buffer, out int bytesRead);
+
+            ReadOnlySpan<byte> longBytes = buffer.Slice(0, bytesRead);
+
+            if (Utf8Parser.TryParse(longBytes, out long result, out _))
             {
-                retval = long.Parse(longBuffer.ToString(), CultureInfo.InvariantCulture);
+                return result;
             }
-            catch (FormatException e)
+            else
             {
-                var bytesToReverse = OtherEncodings.StringAsLatin1Bytes(longBuffer.ToString());
-                bytes.Seek(bytes.CurrentOffset - bytesToReverse.Length);
+                bytes.Seek(bytes.CurrentOffset - bytesRead);
 
-                throw new InvalidOperationException($"Error: Expected a long type at offset {bytes.CurrentOffset}, instead got \'{longBuffer}\'", e);
+                throw new InvalidOperationException($"Error: Expected a long type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(longBytes)}\'");
             }
-
-            return retval;
         }
-
 
         /// <summary>
         /// Whether the given value is a digit or not.
@@ -231,28 +228,29 @@ public static bool IsDigit(int c)
         /// </summary>
         public static int ReadInt(IInputBytes bytes)
         {
-            if (bytes == null)
+            if (bytes is null)
             {
                 throw new ArgumentNullException(nameof(bytes));
             }
 
             SkipSpaces(bytes);
-            int result;
 
-            var intBuffer = ReadStringNumber(bytes);
+            Span<byte> buffer = stackalloc byte[10]; // max formatted uint32 length
 
-            try
+            ReadNumberAsUtf8Bytes(bytes, buffer, out int bytesRead);
+
+            var intBytes = buffer.Slice(0, bytesRead);
+
+            if (Utf8Parser.TryParse(intBytes, out int result, out _))
             {
-                result = int.Parse(intBuffer.ToString(), CultureInfo.InvariantCulture);
+                return result;
             }
-            catch (Exception e)
+            else
             {
-                bytes.Seek(bytes.CurrentOffset - OtherEncodings.StringAsLatin1Bytes(intBuffer.ToString()).Length);
-
-                throw new PdfDocumentFormatException($"Error: Expected an integer type at offset {bytes.CurrentOffset}", e);
+                bytes.Seek(bytes.CurrentOffset - bytesRead);
+                
+                throw new PdfDocumentFormatException($"Error: Expected an integer type at offset {bytes.CurrentOffset}, instead got \'{OtherEncodings.BytesAsLatin1String(intBytes)}\'");
             }
-
-            return result;
         }
 
         /// <summary>
@@ -304,33 +302,34 @@ public static bool IsValidUtf8(byte[] input)
 #endif
         }
 
-        private static StringBuilder ReadStringNumber(IInputBytes reader)
+        private static void ReadNumberAsUtf8Bytes(IInputBytes reader, scoped Span<byte> buffer, out int bytesRead)
         {
-            byte lastByte;
-            StringBuilder buffer = new StringBuilder();
+            int position = 0;
 
+            byte lastByte;
+
             while (reader.MoveNext() && (lastByte = reader.CurrentByte) != ' ' &&
                    lastByte != AsciiLineFeed &&
                    lastByte != AsciiCarriageReturn &&
-                   lastByte != 60 && //see sourceforge bug 1714707
+                   lastByte != 60 && // see sourceforge bug 1714707
                    lastByte != '[' && // PDFBOX-1845
                    lastByte != '(' && // PDFBOX-2579
                    lastByte != 0)
             {
-                buffer.Append((char)lastByte);
-
-                if (buffer.Length > MaximumNumberStringLength)
+                if (position >= buffer.Length)
                 {
-                    throw new InvalidOperationException($"Number \'{buffer}\' is getting too long, stop reading at offset {reader.CurrentOffset}");
+                    throw new InvalidOperationException($"Number \'{OtherEncodings.BytesAsLatin1String(buffer.Slice(0, position))}\' is getting too long, stop reading at offset {reader.CurrentOffset}");
                 }
+
+                buffer[position++] = lastByte;                
             }
 
             if (!reader.IsAtEnd())
             {
                 reader.Seek(reader.CurrentOffset - 1);
             }
 
-            return buffer;
+            bytesRead = position;
         }
     }
 }

src/UglyToad.PdfPig.Fonts/AdobeFontMetrics/AdobeFontMetricsCharacterSize.cs

@@ -4,7 +4,7 @@
     /// The x and y components of the width vector of the font's characters.
     /// Presence implies that IsFixedPitch is true.
     /// </summary>
-    public class AdobeFontMetricsCharacterSize
+    public readonly struct AdobeFontMetricsCharacterSize
     {
         /// <summary>
         /// The horizontal width.

src/UglyToad.PdfPig.Fonts/AdobeFontMetrics/AdobeFontMetricsLigature.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// A ligature in an Adobe Font Metrics individual character.
     /// </summary>
-    public class AdobeFontMetricsLigature
+    public readonly struct AdobeFontMetricsLigature
     {
         /// <summary>
         /// The character to join with to form a ligature.

src/UglyToad.PdfPig.Fonts/CompactFontFormat/CompactFontFormatData.cs

@@ -1,10 +1,8 @@
 namespace UglyToad.PdfPig.Fonts.CompactFontFormat
 {
     using System;
-    using System.Collections.Generic;
     using System.Diagnostics;
     using System.Text;
-    using Core;
 
     /// <summary>
     /// Provides access to the raw bytes of this Compact Font Format file with utility methods for reading data types from it.
@@ -37,14 +35,7 @@ public CompactFontFormatData(ReadOnlyMemory<byte> dataBytes)
         /// </summary>
         public string ReadString(int length, Encoding encoding)
         {
-            var bytes = new byte[length];
-
-            for (var i = 0; i < bytes.Length; i++)
-            {
-                bytes[i] = ReadByte();
-            }
-
-            return encoding.GetString(bytes);
+            return encoding.GetString(ReadSpan(length));
         }
 
         /// <summary>
@@ -86,6 +77,20 @@ public int ReadOffset(int offsetSize)
             return value;
         }
 
+        internal ReadOnlySpan<byte> ReadSpan(int count)
+        {
+            if (Position + count >= dataBytes.Length)
+            {
+                throw new IndexOutOfRangeException($"Cannot read past end of data. Attempted to read to {Position + count} when the underlying data is {dataBytes.Length} bytes long.");
+            }
+
+            var result = dataBytes.Span.Slice(Position + 1, count);
+
+            Position += count;
+
+            return result;
+        }
+
         /// <summary>
         /// Read byte.
         /// </summary>

src/UglyToad.PdfPig.Fonts/CompactFontFormat/CompactFontFormatEncodingReader.cs

@@ -8,7 +8,7 @@
 
     internal static class CompactFontFormatEncodingReader
     {
-        public static Encoding ReadEncoding(CompactFontFormatData data, ICompactFontFormatCharset charset, IReadOnlyList<string> stringIndex)
+        public static Encoding ReadEncoding(CompactFontFormatData data, ICompactFontFormatCharset charset, ReadOnlySpan<string> stringIndex)
         {
             if (data == null)
             {
@@ -32,7 +32,7 @@ public static Encoding ReadEncoding(CompactFontFormatData data, ICompactFontForm
             }
         }
 
-        private static CompactFontFormatFormat0Encoding ReadFormat0Encoding(CompactFontFormatData data, ICompactFontFormatCharset charset, IReadOnlyList<string> stringIndex, byte format)
+        private static CompactFontFormatFormat0Encoding ReadFormat0Encoding(CompactFontFormatData data, ICompactFontFormatCharset charset, ReadOnlySpan<string> stringIndex, byte format)
         {
             var numberOfCodes = data.ReadCard8();
 
@@ -45,7 +45,7 @@ private static CompactFontFormatFormat0Encoding ReadFormat0Encoding(CompactFontF
                 values.Add((code, sid, str));
             }
 
-            IReadOnlyList<CompactFontFormatBuiltInEncoding.Supplement> supplements = new List<CompactFontFormatBuiltInEncoding.Supplement>();
+            IReadOnlyList<CompactFontFormatBuiltInEncoding.Supplement> supplements = [];
             if (HasSupplement(format))
             {
                 supplements = ReadSupplement(data, stringIndex);
@@ -54,7 +54,7 @@ private static CompactFontFormatFormat0Encoding ReadFormat0Encoding(CompactFontF
             return new CompactFontFormatFormat0Encoding(values, supplements);
         }
 
-        private static CompactFontFormatFormat1Encoding ReadFormat1Encoding(CompactFontFormatData data, ICompactFontFormatCharset charset, IReadOnlyList<string> stringIndex, byte format)
+        private static CompactFontFormatFormat1Encoding ReadFormat1Encoding(CompactFontFormatData data, ICompactFontFormatCharset charset, ReadOnlySpan<string> stringIndex, byte format)
         {
             var numberOfRanges = data.ReadCard8();
 
@@ -85,7 +85,7 @@ private static CompactFontFormatFormat1Encoding ReadFormat1Encoding(CompactFontF
         }
 
         private static IReadOnlyList<CompactFontFormatBuiltInEncoding.Supplement> ReadSupplement(CompactFontFormatData dataInput,
-            IReadOnlyList<string> stringIndex)
+            ReadOnlySpan<string> stringIndex)
         {
             var numberOfSupplements = dataInput.ReadCard8();
             var supplements = new CompactFontFormatBuiltInEncoding.Supplement[numberOfSupplements];
@@ -101,13 +101,13 @@ private static CompactFontFormatFormat1Encoding ReadFormat1Encoding(CompactFontF
             return supplements;
         }
 
-        private static string ReadString(int index, IReadOnlyList<string> stringIndex)
+        private static string ReadString(int index, ReadOnlySpan<string> stringIndex)
         {
             if (index >= 0 && index <= 390)
             {
                 return CompactFontFormatStandardStrings.GetName(index);
             }
-            if (index - 391 < stringIndex.Count)
+            if (index - 391 < stringIndex.Length)
             {
                 return stringIndex[index - 391];
             }

src/UglyToad.PdfPig.Fonts/CompactFontFormat/CompactFontFormatIndividualFontParser.cs

@@ -2,7 +2,6 @@
 {
     using System;
     using System.Collections.Generic;
-    using System.Linq;
     using Charsets;
     using CharStrings;
     using Core;
@@ -23,7 +22,7 @@ public CompactFontFormatIndividualFontParser(CompactFontFormatTopLevelDictionary
             this.privateDictionaryReader = privateDictionaryReader;
         }
 
-        public CompactFontFormatFont Parse(CompactFontFormatData data, string name, ReadOnlySpan<byte> topDictionaryIndex, IReadOnlyList<string> stringIndex,
+        public CompactFontFormatFont Parse(CompactFontFormatData data, string name, ReadOnlySpan<byte> topDictionaryIndex, ReadOnlySpan<string> stringIndex,
             CompactFontFormatIndex globalSubroutineIndex)
         {
             var individualData = new CompactFontFormatData(topDictionaryIndex.ToArray());
@@ -127,8 +126,10 @@ public CompactFontFormatFont Parse(CompactFontFormatData data, string name, Read
             return new CompactFontFormatFont(topDictionary, privateDictionary, charset, Union<Type1CharStrings, Type2CharStrings>.Two(charStrings), fontEncoding);
         }
 
-        private static ICompactFontFormatCharset ReadCharset(CompactFontFormatData data, CompactFontFormatTopLevelDictionary topDictionary,
-        CompactFontFormatIndex charStringIndex, IReadOnlyList<string> stringIndex)
+        private static ICompactFontFormatCharset ReadCharset(CompactFontFormatData data,
+            CompactFontFormatTopLevelDictionary topDictionary,
+            CompactFontFormatIndex charStringIndex,
+            ReadOnlySpan<string> stringIndex)
         {
             data.Seek(topDictionary.CharSetOffset);
 
@@ -180,13 +181,13 @@ private static ICompactFontFormatCharset ReadCharset(CompactFontFormatData data,
             }
         }
 
-        private static string ReadString(int index, IReadOnlyList<string> stringIndex)
+        private static string ReadString(int index, ReadOnlySpan<string> stringIndex)
         {
             if (index >= 0 && index <= 390)
             {
                 return CompactFontFormatStandardStrings.GetName(index);
             }
-            if (index - 391 < stringIndex.Count)
+            if (index - 391 < stringIndex.Length)
             {
                 return stringIndex[index - 391];
             }
@@ -213,9 +214,10 @@ private static Type2CharStrings ReadCharStrings(CompactFontFormatData data, Comp
             }
         }
 
-        private CompactFontFormatCidFont ReadCidFont(CompactFontFormatData data, CompactFontFormatTopLevelDictionary topLevelDictionary,
+        private CompactFontFormatCidFont ReadCidFont(CompactFontFormatData data,
+            CompactFontFormatTopLevelDictionary topLevelDictionary,
             int numberOfGlyphs,
-            IReadOnlyList<string> stringIndex,
+            ReadOnlySpan<string> stringIndex,
             CompactFontFormatPrivateDictionary privateDictionary,
             ICompactFontFormatCharset charset,
             CompactFontFormatIndex globalSubroutines,