From 19c1e47db2a92455681a31343266d8ec7109d32f Mon Sep 17 00:00:00 2001
From: Frederik Carlier <frederik.carlier@quamotion.mobi>
Date: Tue, 19 Jun 2018 14:40:51 +0200
Subject: [PATCH] Performance improvements - Set the capacity of the dictionary
 of known - Don't allocate a string to check whether a file is a valid binary
 property list

---
 plist-cil/BinaryPropertyListParser.cs | 22 ++++++++--------
 plist-cil/NSDictionary.cs             | 15 +++++++++--
 plist-cil/PropertyListParser.cs       | 36 ++++++++++++++++-----------
 3 files changed, 46 insertions(+), 27 deletions(-)

diff --git a/plist-cil/BinaryPropertyListParser.cs b/plist-cil/BinaryPropertyListParser.cs
index b4c4462..33818e8 100644
--- a/plist-cil/BinaryPropertyListParser.cs
+++ b/plist-cil/BinaryPropertyListParser.cs
@@ -119,20 +119,20 @@ namespace Claunia.PropertyList
         /// <exception cref="PropertyListFormatException">When the property list's format could not be parsed.</exception>
         private NSObject DoParse(ReadOnlySpan<byte> bytes)
         {
-            string magic = Encoding.ASCII.GetString(
-#if NATIVE_SPAN
-                 bytes.Slice(0, 8));
-#else
-                 bytes.Slice(0, 8).ToArray());
-#endif
-
-            if (!magic.StartsWith("bplist", StringComparison.Ordinal))
+            if(bytes.Length < 8
+                || bytes[0] != 'b'
+                || bytes[1] != 'p'
+                || bytes[2] != 'l'
+                || bytes[3] != 'i'
+                || bytes[4] != 's'
+                || bytes[5] != 't')
             {
+                var magic = Encoding.ASCII.GetString(bytes.Slice(0, 8).ToArray());
                 throw new PropertyListFormatException("The given data is no binary property list. Wrong magic bytes: " + magic);
             }
 
-            majorVersion = magic[6] - 0x30; //ASCII number
-            minorVersion = magic[7] - 0x30; //ASCII number
+            majorVersion = bytes[6] - 0x30; //ASCII number
+            minorVersion = bytes[7] - 0x30; //ASCII number
 
             // 0.0 - OS X Tiger and earlier
             // 0.1 - Leopard
@@ -366,7 +366,7 @@ namespace Claunia.PropertyList
                         ReadLengthAndOffset(bytes, objInfo, offset, out int length, out int contentOffset);
 
                         //System.out.println("Parsing dictionary #"+obj);
-                        NSDictionary dict = new NSDictionary();
+                        NSDictionary dict = new NSDictionary(length);
                         for (int i = 0; i < length; i++)
                         {
                             int keyRef = (int)ParseUnsignedInt(bytes.Slice(offset + contentOffset + i * objectRefSize, objectRefSize));
diff --git a/plist-cil/NSDictionary.cs b/plist-cil/NSDictionary.cs
index 8d76a67..721dd4f 100644
--- a/plist-cil/NSDictionary.cs
+++ b/plist-cil/NSDictionary.cs
@@ -49,13 +49,24 @@ namespace Claunia.PropertyList
         // object remains constant accross calls to AssignIDs and ToBinary
         readonly Dictionary<string, NSString> keys;
 
+        /// <summary>
+        /// Creates a new empty NSDictionary with a specific capacity.
+        /// </summary>
+        /// <param name="capacity">
+        /// The capacity of the dictionary.
+        /// </param>
+        public NSDictionary(int capacity)
+        {
+            dict = new Dictionary<string, NSObject>(capacity);
+            keys = new Dictionary<string, NSString>(capacity);
+        }
+
         /// <summary>
         /// Creates a new empty NSDictionary.
         /// </summary>
         public NSDictionary()
+            : this(0)
         {
-            dict = new Dictionary<string, NSObject>();
-            keys = new Dictionary<string, NSString>();
         }
 
         /// <summary>
diff --git a/plist-cil/PropertyListParser.cs b/plist-cil/PropertyListParser.cs
index ac7f572..bfce752 100644
--- a/plist-cil/PropertyListParser.cs
+++ b/plist-cil/PropertyListParser.cs
@@ -49,22 +49,34 @@ namespace Claunia.PropertyList
         /// </summary>
         /// <returns>The type of the property list</returns>
         /// <param name="dataBeginning">The very first bytes of data of the property list (minus any whitespace) as a string</param>
-        static int DetermineType(string dataBeginning)
+        static int DetermineTypeExact(ReadOnlySpan<byte> dataBeginning)
         {
-            dataBeginning = dataBeginning.Trim();
             if (dataBeginning.Length == 0)
             {
                 return TYPE_ERROR_BLANK;
             }
-            if (dataBeginning.StartsWith("bplist"))
-            {
-                return TYPE_BINARY;
-            }
-            if (dataBeginning.StartsWith("(") || dataBeginning.StartsWith("{") || dataBeginning.StartsWith("/"))
+            else if (dataBeginning[0] == '(' || dataBeginning[0] == '{' || dataBeginning[0] == '/')
             {
                 return TYPE_ASCII;
             }
-            return dataBeginning.StartsWith("<") ? TYPE_XML : TYPE_ERROR_UNKNOWN;
+            else if (dataBeginning[0] == '<')
+            {
+                return TYPE_XML;
+            }
+            else if (dataBeginning.Length >= 6
+                && dataBeginning[0] == 'b'
+                && dataBeginning[1] == 'p'
+                && dataBeginning[2] == 'l'
+                && dataBeginning[3] == 'i'
+                && dataBeginning[4] == 's'
+                && dataBeginning[5] == 't')
+            {
+                return TYPE_BINARY;
+            }
+            else
+            {
+                return TYPE_ERROR_UNKNOWN;
+            }
         }
 
         /// <summary>
@@ -90,11 +102,7 @@ namespace Claunia.PropertyList
             }
 
             var header = bytes.Slice(offset, Math.Min(8, bytes.Length - offset));
-#if NATIVE_SPAN
-            return DetermineType(Encoding.ASCII.GetString(header));
-#else
-            return DetermineType(Encoding.ASCII.GetString(header.ToArray(), 0, header.Length));
-#endif
+            return DetermineTypeExact(header);
         }
 
         /// <summary>
@@ -138,7 +146,7 @@ namespace Claunia.PropertyList
             magicBytes[0] = (byte)b;
             int read = fs.Read(magicBytes, 1, 7);
 
-            int type = DetermineType(Encoding.ASCII.GetString(magicBytes, 0, read));
+            int type = DetermineTypeExact(magicBytes.AsSpan(0, read));
             fs.Seek(mark, SeekOrigin.Begin);
             return type;
         }