csharp-sdk-upm/Libs/Newtonsoft.Json/DefaultJsonNameTable.cs

#region License
// Copyright (c) 2007 James Newton-King
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
#endregion

using System;

namespace LC.Newtonsoft.Json
{
    /// <summary>
    /// The default JSON name table implementation.
    /// </summary>
    public class DefaultJsonNameTable : JsonNameTable
    {
        // used to defeat hashtable DoS attack where someone passes in lots of strings that hash to the same hash code
        private static readonly int HashCodeRandomizer;

        private int _count;
        private Entry[] _entries;
        private int _mask = 31;

        static DefaultJsonNameTable()
        {
            HashCodeRandomizer = Environment.TickCount;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="DefaultJsonNameTable"/> class.
        /// </summary>
        public DefaultJsonNameTable()
        {
            _entries = new Entry[_mask + 1];
        }

        /// <summary>
        /// Gets a string containing the same characters as the specified range of characters in the given array.
        /// </summary>
        /// <param name="key">The character array containing the name to find.</param>
        /// <param name="start">The zero-based index into the array specifying the first character of the name.</param>
        /// <param name="length">The number of characters in the name.</param>
        /// <returns>A string containing the same characters as the specified range of characters in the given array.</returns>
        public override string? Get(char[] key, int start, int length)
        {
            if (length == 0)
            {
                return string.Empty;
            }

            int hashCode = length + HashCodeRandomizer;
            hashCode += (hashCode << 7) ^ key[start];
            int end = start + length;
            for (int i = start + 1; i < end; i++)
            {
                hashCode += (hashCode << 7) ^ key[i];
            }
            hashCode -= hashCode >> 17;
            hashCode -= hashCode >> 11;
            hashCode -= hashCode >> 5;

            // make sure index is evaluated before accessing _entries, otherwise potential race condition causing IndexOutOfRangeException
            var index = hashCode & _mask;
            var entries = _entries;

            for (Entry entry = entries[index]; entry != null; entry = entry.Next)
            {
                if (entry.HashCode == hashCode && TextEquals(entry.Value, key, start, length))
                {
                    return entry.Value;
                }
            }

            return null;
        }

        /// <summary>
        /// Adds the specified string into name table.
        /// </summary>
        /// <param name="key">The string to add.</param>
        /// <remarks>This method is not thread-safe.</remarks>
        /// <returns>The resolved string.</returns>
        public string Add(string key)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            int length = key.Length;
            if (length == 0)
            {
                return string.Empty;
            }

            int hashCode = length + HashCodeRandomizer;
            for (int i = 0; i < key.Length; i++)
            {
                hashCode += (hashCode << 7) ^ key[i];
            }
            hashCode -= hashCode >> 17;
            hashCode -= hashCode >> 11;
            hashCode -= hashCode >> 5;
            for (Entry entry = _entries[hashCode & _mask]; entry != null; entry = entry.Next)
            {
                if (entry.HashCode == hashCode && entry.Value.Equals(key, StringComparison.Ordinal))
                {
                    return entry.Value;
                }
            }

            return AddEntry(key, hashCode);
        }

        private string AddEntry(string str, int hashCode)
        {
            int index = hashCode & _mask;
            Entry entry = new Entry(str, hashCode, _entries[index]);
            _entries[index] = entry;
            if (_count++ == _mask)
            {
                Grow();
            }
            return entry.Value;
        }

        private void Grow()
        {
            Entry[] entries = _entries;
            int newMask = (_mask * 2) + 1;
            Entry[] newEntries = new Entry[newMask + 1];

            for (int i = 0; i < entries.Length; i++)
            {
                Entry next;
                for (Entry entry = entries[i]; entry != null; entry = next)
                {
                    int index = entry.HashCode & newMask;
                    next = entry.Next;
                    entry.Next = newEntries[index];
                    newEntries[index] = entry;
                }
            }
            _entries = newEntries;
            _mask = newMask;
        }

        private static bool TextEquals(string str1, char[] str2, int str2Start, int str2Length)
        {
            if (str1.Length != str2Length)
            {
                return false;
            }

            for (int i = 0; i < str1.Length; i++)
            {
                if (str1[i] != str2[str2Start + i])
                {
                    return false;
                }
            }
            return true;
        }

        private class Entry
        {
            internal readonly string Value;
            internal readonly int HashCode;
            internal Entry Next;

            internal Entry(string value, int hashCode, Entry next)
            {
                Value = value;
                HashCode = hashCode;
                Next = next;
            }
        }
    }
}