349 lines
13 KiB
C#
349 lines
13 KiB
C#
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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace Swan.Formatters
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{
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/// <summary>
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/// A very simple, light-weight JSON library written by Mario
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/// to teach Geo how things are done
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///
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/// This is an useful helper for small tasks but it doesn't represent a full-featured
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/// serializer such as the beloved Json.NET.
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/// </summary>
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public partial class Json
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{
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/// <summary>
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/// A simple JSON Deserializer.
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/// </summary>
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private class Deserializer
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{
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#region State Variables
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private readonly object? _result;
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private readonly string _json;
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private Dictionary<string, object> _resultObject;
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private List<object> _resultArray;
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private ReadState _state = ReadState.WaitingForRootOpen;
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private string? _currentFieldName;
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private int _index;
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#endregion
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private Deserializer(string json, int startIndex)
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{
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_json = json;
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for (_index = startIndex; _index < _json.Length; _index++)
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{
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switch (_state)
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{
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case ReadState.WaitingForRootOpen:
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WaitForRootOpen();
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continue;
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case ReadState.WaitingForField when char.IsWhiteSpace(_json, _index):
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continue;
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case ReadState.WaitingForField when (_resultObject != null && _json[_index] == CloseObjectChar)
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|| (_resultArray != null && _json[_index] == CloseArrayChar):
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// Handle empty arrays and empty objects
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_result = _resultObject ?? _resultArray as object;
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return;
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case ReadState.WaitingForField when _json[_index] != StringQuotedChar:
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throw CreateParserException($"'{StringQuotedChar}'");
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case ReadState.WaitingForField:
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{
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var charCount = GetFieldNameCount();
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_currentFieldName = Unescape(_json.SliceLength(_index + 1, charCount));
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_index += charCount + 1;
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_state = ReadState.WaitingForColon;
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continue;
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}
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case ReadState.WaitingForColon when char.IsWhiteSpace(_json, _index):
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continue;
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case ReadState.WaitingForColon when _json[_index] != ValueSeparatorChar:
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throw CreateParserException($"'{ValueSeparatorChar}'");
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case ReadState.WaitingForColon:
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_state = ReadState.WaitingForValue;
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continue;
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case ReadState.WaitingForValue when char.IsWhiteSpace(_json, _index):
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continue;
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case ReadState.WaitingForValue when (_resultObject != null && _json[_index] == CloseObjectChar)
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|| (_resultArray != null && _json[_index] == CloseArrayChar):
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// Handle empty arrays and empty objects
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_result = _resultObject ?? _resultArray as object;
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return;
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case ReadState.WaitingForValue:
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ExtractValue();
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continue;
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}
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if (_state != ReadState.WaitingForNextOrRootClose || char.IsWhiteSpace(_json, _index)) continue;
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if (_json[_index] == FieldSeparatorChar)
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{
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if (_resultObject != null)
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{
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_state = ReadState.WaitingForField;
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_currentFieldName = null;
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continue;
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}
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_state = ReadState.WaitingForValue;
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continue;
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}
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if ((_resultObject == null || _json[_index] != CloseObjectChar) &&
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(_resultArray == null || _json[_index] != CloseArrayChar))
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{
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throw CreateParserException($"'{FieldSeparatorChar}' '{CloseObjectChar}' or '{CloseArrayChar}'");
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}
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_result = _resultObject ?? _resultArray as object;
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return;
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}
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}
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internal static object? DeserializeInternal(string json) => new Deserializer(json, 0)._result;
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private void WaitForRootOpen()
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{
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if (char.IsWhiteSpace(_json, _index)) return;
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switch (_json[_index])
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{
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case OpenObjectChar:
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_resultObject = new Dictionary<string, object>();
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_state = ReadState.WaitingForField;
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return;
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case OpenArrayChar:
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_resultArray = new List<object>();
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_state = ReadState.WaitingForValue;
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return;
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default:
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throw CreateParserException($"'{OpenObjectChar}' or '{OpenArrayChar}'");
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}
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}
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private void ExtractValue()
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{
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// determine the value based on what it starts with
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switch (_json[_index])
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{
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case StringQuotedChar: // expect a string
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ExtractStringQuoted();
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break;
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case OpenObjectChar: // expect object
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case OpenArrayChar: // expect array
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ExtractObject();
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break;
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case 't': // expect true
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ExtractConstant(TrueLiteral, true);
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break;
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case 'f': // expect false
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ExtractConstant(FalseLiteral, false);
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break;
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case 'n': // expect null
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ExtractConstant(NullLiteral, null);
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break;
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default: // expect number
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ExtractNumber();
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break;
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}
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_currentFieldName = null;
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_state = ReadState.WaitingForNextOrRootClose;
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}
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private static string Unescape(string str)
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{
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// check if we need to unescape at all
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if (str.IndexOf(StringEscapeChar) < 0)
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return str;
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var builder = new StringBuilder(str.Length);
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for (var i = 0; i < str.Length; i++)
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{
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if (str[i] != StringEscapeChar)
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{
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builder.Append(str[i]);
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continue;
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}
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if (i + 1 > str.Length - 1)
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break;
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// escape sequence begins here
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switch (str[i + 1])
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{
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case 'u':
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i = ExtractEscapeSequence(str, i, builder);
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break;
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case 'b':
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builder.Append('\b');
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i += 1;
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break;
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case 't':
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builder.Append('\t');
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i += 1;
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break;
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case 'n':
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builder.Append('\n');
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i += 1;
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break;
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case 'f':
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builder.Append('\f');
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i += 1;
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break;
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case 'r':
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builder.Append('\r');
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i += 1;
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break;
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default:
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builder.Append(str[i + 1]);
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i += 1;
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break;
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}
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}
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return builder.ToString();
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}
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private static int ExtractEscapeSequence(string str, int i, StringBuilder builder)
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{
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var startIndex = i + 2;
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var endIndex = i + 5;
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if (endIndex > str.Length - 1)
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{
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builder.Append(str[i + 1]);
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i += 1;
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return i;
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}
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var hexCode = str.Slice(startIndex, endIndex).ConvertHexadecimalToBytes();
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builder.Append(Encoding.BigEndianUnicode.GetChars(hexCode));
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i += 5;
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return i;
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}
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private int GetFieldNameCount()
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{
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var charCount = 0;
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for (var j = _index + 1; j < _json.Length; j++)
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{
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if (_json[j] == StringQuotedChar && _json[j - 1] != StringEscapeChar)
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break;
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charCount++;
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}
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return charCount;
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}
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private void ExtractObject()
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{
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// Extract and set the value
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var deserializer = new Deserializer(_json, _index);
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if (_currentFieldName != null)
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_resultObject[_currentFieldName] = deserializer._result;
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else
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_resultArray.Add(deserializer._result);
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_index = deserializer._index;
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}
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private void ExtractNumber()
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{
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var charCount = 0;
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for (var j = _index; j < _json.Length; j++)
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{
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if (char.IsWhiteSpace(_json[j]) || _json[j] == FieldSeparatorChar
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|| (_resultObject != null && _json[j] == CloseObjectChar)
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|| (_resultArray != null && _json[j] == CloseArrayChar))
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break;
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charCount++;
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}
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// Extract and set the value
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var stringValue = _json.SliceLength(_index, charCount);
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if (decimal.TryParse(stringValue, System.Globalization.NumberStyles.Number, System.Globalization.CultureInfo.InvariantCulture, out var value) == false)
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throw CreateParserException("[number]");
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if (_currentFieldName != null)
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_resultObject[_currentFieldName] = value;
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else
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_resultArray.Add(value);
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_index += charCount - 1;
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}
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private void ExtractConstant(string boolValue, bool? value)
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{
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if (_json.SliceLength(_index, boolValue.Length) != boolValue)
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throw CreateParserException($"'{ValueSeparatorChar}'");
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// Extract and set the value
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if (_currentFieldName != null)
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_resultObject[_currentFieldName] = value;
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else
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_resultArray.Add(value);
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_index += boolValue.Length - 1;
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}
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private void ExtractStringQuoted()
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{
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var charCount = 0;
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var escapeCharFound = false;
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for (var j = _index + 1; j < _json.Length; j++)
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{
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if (_json[j] == StringQuotedChar && !escapeCharFound)
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break;
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escapeCharFound = _json[j] == StringEscapeChar && !escapeCharFound;
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charCount++;
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}
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// Extract and set the value
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var value = Unescape(_json.SliceLength(_index + 1, charCount));
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if (_currentFieldName != null)
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_resultObject[_currentFieldName] = value;
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else
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_resultArray.Add(value);
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_index += charCount + 1;
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}
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private FormatException CreateParserException(string expected)
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{
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var textPosition = _json.TextPositionAt(_index);
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return new FormatException(
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$"Parser error (Line {textPosition.Item1}, Col {textPosition.Item2}, State {_state}): Expected {expected} but got '{_json[_index]}'.");
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}
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/// <summary>
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/// Defines the different JSON read states.
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/// </summary>
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private enum ReadState
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{
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WaitingForRootOpen,
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WaitingForField,
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WaitingForColon,
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WaitingForValue,
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WaitingForNextOrRootClose,
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}
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}
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}
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}
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