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fastJSON

, 26 Apr 2014
Smallest, fastest polymorphic JSON serializer (with Silverlight4 and MonoDroid support)
consoletest-noexe.zip
consoletest.zip
fastjson-noexe.zip
fastjson.zip
fastJSON_2.0.28.1.zip
Consoletest
fastJSON
fastJSON.snk
Properties
UnitTests
Properties
fastjson_v1.1-noexe.zip
fastjson_v1.1.zip
Properties
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fastjson_v1.7.7-silverlight4-noexe.zip
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fastjson_v2.0.0-noexe.zip
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fastjson_v2.0.1-noexe.zip
fastjson_v2.0.1.zip
fastjson_v2.0.10-noexe.zip
fastjson_v2.0.10.zip
fastJSON.nuspec
fastjson_v2.0.11-noexe.zip
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fastJSON.nuspec
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fastJSON-SL.v11.suo
fastJSON.nuspec
fastjson_v2.0.22-noexe.zip
fastjson_v2.0.22.zip
fastJSON.snk
fastjson_v2.0.23-noexe.zip
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fastJSON.snk
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fastjson_v2.0.27-noexe.zip
fastjson_v2.0.27.zip
fastJSON.snk
fastJSON_v2.0.28.zip
fastJSON.snk
fastjson_v2.0.3-noexe.zip
fastjson_v2.0.3.zip
fastjson_v2.0.4-noexe.zip
fastjson_v2.0.4.zip
fastjson_v2.0.5-noexe.zip
fastjson_v2.0.5.zip
fastJSON.nuspec
fastjson_v2.0.6-noexe.zip
fastjson_v2.0.6.zip
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fastjson_v2.0.7-noexe.zip
fastjson_v2.0.7.zip
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fastjson_v2.0.8-noexe.zip
fastjson_v2.0.8.zip
fastJSON.nuspec
fastjson_v2.0.9-noexe.zip
fastjson_v2.0.9.zip
fastJSON.nuspec
fastJSON_v2.1.0.zip
fastJSON.snk
fastJSON_v2.1.1.zip
fastJSON.snk
using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Text;

namespace fastJSON
{
    /// <summary>
    /// This class encodes and decodes JSON strings.
    /// Spec. details, see http://www.json.org/
    /// </summary>
    internal sealed class JsonParser
    {
        enum Token
        {
            None = -1,           // Used to denote no Lookahead available
            Curly_Open,
            Curly_Close,
            Squared_Open,
            Squared_Close,
            Colon,
            Comma,
            String,
            Number,
            True,
            False,
            Null
        }

        readonly char[] json;
        readonly StringBuilder s = new StringBuilder();
        Token lookAheadToken = Token.None;
        int index;
        bool _ignorecase = false;


        internal JsonParser(string json, bool ignorecase)
        {
            this.json = json.ToCharArray();
            _ignorecase = ignorecase;
        }

        public object Decode()
        {
            return ParseValue();
        }

        private Dictionary<string, object> ParseObject()
        {
            Dictionary<string, object> table = new Dictionary<string, object>();

            ConsumeToken(); // {

            while (true)
            {
                switch (LookAhead())
                {

                    case Token.Comma:
                        ConsumeToken();
                        break;

                    case Token.Curly_Close:
                        ConsumeToken();
                        return table;

                    default:
                        {

                            // name
                            string name = ParseString();
                            if (_ignorecase)
                                name = name.ToLower();

                            // :
                            if (NextToken() != Token.Colon)
                            {
                                throw new Exception("Expected colon at index " + index);
                            }

                            // value
                            object value = ParseValue();

                            table[name] = value;
                        }
                        break;
                }
            }
        }

        private List<object> ParseArray()
        {
            List<object> array = new List<object>();
            ConsumeToken(); // [

            while (true)
            {
                switch (LookAhead())
                {

                    case Token.Comma:
                        ConsumeToken();
                        break;

                    case Token.Squared_Close:
                        ConsumeToken();
                        return array;

                    default:
                        array.Add(ParseValue());
                        break;
                }
            }
        }

        private object ParseValue()
        {
            switch (LookAhead())
            {
                case Token.Number:
                    return ParseNumber();

                case Token.String:
                    return ParseString();

                case Token.Curly_Open:
                    return ParseObject();

                case Token.Squared_Open:
                    return ParseArray();

                case Token.True:
                    ConsumeToken();
                    return true;

                case Token.False:
                    ConsumeToken();
                    return false;

                case Token.Null:
                    ConsumeToken();
                    return null;
            }

            throw new Exception("Unrecognized token at index" + index);
        }

        private string ParseString()
        {
            ConsumeToken(); // "

            s.Length = 0;

            int runIndex = -1;

            while (index < json.Length)
            {
                var c = json[index++];

                if (c == '"')
                {
                    if (runIndex != -1)
                    {
                        if (s.Length == 0)
                            return new string(json, runIndex, index - runIndex - 1);

                        s.Append(json, runIndex, index - runIndex - 1);
                    }
                    return s.ToString();
                }

                if (c != '\\')
                {
                    if (runIndex == -1)
                        runIndex = index - 1;

                    continue;
                }

                if (index == json.Length) break;

                if (runIndex != -1)
                {
                    s.Append(json, runIndex, index - runIndex - 1);
                    runIndex = -1;
                }

                switch (json[index++])
                {
                    case '"':
                        s.Append('"');
                        break;

                    case '\\':
                        s.Append('\\');
                        break;

                    case '/':
                        s.Append('/');
                        break;

                    case 'b':
                        s.Append('\b');
                        break;

                    case 'f':
                        s.Append('\f');
                        break;

                    case 'n':
                        s.Append('\n');
                        break;

                    case 'r':
                        s.Append('\r');
                        break;

                    case 't':
                        s.Append('\t');
                        break;

                    case 'u':
                        {
                            int remainingLength = json.Length - index;
                            if (remainingLength < 4) break;

                            // parse the 32 bit hex into an integer codepoint
                            uint codePoint = ParseUnicode(json[index], json[index + 1], json[index + 2], json[index + 3]);
                            s.Append((char)codePoint);

                            // skip 4 chars
                            index += 4;
                        }
                        break;
                }
            }

            throw new Exception("Unexpectedly reached end of string");
        }

        private uint ParseSingleChar(char c1, uint multipliyer)
        {
            uint p1 = 0;
            if (c1 >= '0' && c1 <= '9')
                p1 = (uint)(c1 - '0') * multipliyer;
            else if (c1 >= 'A' && c1 <= 'F')
                p1 = (uint)((c1 - 'A') + 10) * multipliyer;
            else if (c1 >= 'a' && c1 <= 'f')
                p1 = (uint)((c1 - 'a') + 10) * multipliyer;
            return p1;
        }

        private uint ParseUnicode(char c1, char c2, char c3, char c4)
        {
            uint p1 = ParseSingleChar(c1, 0x1000);
            uint p2 = ParseSingleChar(c2, 0x100);
            uint p3 = ParseSingleChar(c3, 0x10);
            uint p4 = ParseSingleChar(c4, 1);

            return p1 + p2 + p3 + p4;
        }

        private long CreateLong(string s)
        {
            long num = 0;
            bool neg = false;
            foreach (char cc in s)
            {
                if (cc == '-')
                    neg = true;
                else if (cc == '+')
                    neg = false;
                else
                {
                    num *= 10;
                    num += (int)(cc - '0');
                }
            }

            return neg ? -num : num;
        }

        private object ParseNumber()
        {
            ConsumeToken();

            // Need to start back one place because the first digit is also a token and would have been consumed
            var startIndex = index - 1;
            bool dec = false;
            do
            {
                if (index == json.Length)
                    break;
                var c = json[index];

                if ((c >= '0' && c <= '9') || c == '.' || c == '-' || c == '+' || c == 'e' || c == 'E')
                {
                    if (c == '.' || c == 'e' || c == 'E')
                        dec = true;
                    if (++index == json.Length)
                        break;                        //throw new Exception("Unexpected end of string whilst parsing number");
                    continue;
                }
                break;
            } while (true);

			if (dec)
			{
				string s = new string(json, startIndex, index - startIndex);
				return double.Parse(s, NumberFormatInfo.InvariantInfo);
			}
			long num;
			return JSON.CreateLong(out num, json, startIndex, index - startIndex);
        }

        private Token LookAhead()
        {
            if (lookAheadToken != Token.None) return lookAheadToken;

            return lookAheadToken = NextTokenCore();
        }

        private void ConsumeToken()
        {
            lookAheadToken = Token.None;
        }

        private Token NextToken()
        {
            var result = lookAheadToken != Token.None ? lookAheadToken : NextTokenCore();

            lookAheadToken = Token.None;

            return result;
        }

        private Token NextTokenCore()
        {
            char c;

            // Skip past whitespace
            do
            {
                c = json[index];

                if (c > ' ') break;
                if (c != ' ' && c != '\t' && c != '\n' && c != '\r') break;

            } while (++index < json.Length);

            if (index == json.Length)
            {
                throw new Exception("Reached end of string unexpectedly");
            }

            c = json[index];

            index++;

            //if (c >= '0' && c <= '9')
            //    return Token.Number;

            switch (c)
            {
                case '{':
                    return Token.Curly_Open;

                case '}':
                    return Token.Curly_Close;

                case '[':
                    return Token.Squared_Open;

                case ']':
                    return Token.Squared_Close;

                case ',':
                    return Token.Comma;

                case '"':
                    return Token.String;

                case '0':
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                case '-':
                case '+':
                case '.':
                    return Token.Number;

                case ':':
                    return Token.Colon;

                case 'f':
                    if (json.Length - index >= 4 &&
                        json[index + 0] == 'a' &&
                        json[index + 1] == 'l' &&
                        json[index + 2] == 's' &&
                        json[index + 3] == 'e')
                    {
                        index += 4;
                        return Token.False;
                    }
                    break;

                case 't':
                    if (json.Length - index >= 3 &&
                        json[index + 0] == 'r' &&
                        json[index + 1] == 'u' &&
                        json[index + 2] == 'e')
                    {
                        index += 3;
                        return Token.True;
                    }
                    break;

                case 'n':
                    if (json.Length - index >= 3 &&
                        json[index + 0] == 'u' &&
                        json[index + 1] == 'l' &&
                        json[index + 2] == 'l')
                    {
                        index += 3;
                        return Token.Null;
                    }
                    break;

            }

            throw new Exception("Could not find token at index " + --index);
        }
    }
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Mehdi Gholam
Architect
United Kingdom United Kingdom
Mehdi first started programming when he was 8 on BBC+128k machine in 6512 processor language, after various hardware and software changes he eventually came across .net and c# which he has been using since v1.0.
He is formally educated as a system analyst Industrial engineer, but his programming passion continues.
 
* Mehdi is the 5th person to get 6 out of 7 Platinums on CodeProject (13th Jan'12)

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