Get inner JSON content as string without deserializing

Question

I've got a file with JSON content like this:

{
  "Data": {
    "A": {
      "A1": "S",
      "A2": 0.0
    }
  },
  "NoData": "text"
}

What I want to achieve is to get the inner json of "Data" as a string. I do not want it to be deserialized as an object. I already tried to deserialize it with Json.NET JsonConvert.DeserializeObject<TestClass> where Test class is defined as

class Testclass
{
  public string Data {get; set;}
  public string NoData {get; set;}
}

But this results in Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: {. Path 'Data', line 2, position 11.

The data in "Data" is cryptographically signed by a remote server and the signature needs to be checked. But I do not necessarily have the same classes the data was serialized with at the clients side. That's why I want to do as few conversions as possible. So deserializing and serializing again may change the original string in "data". All spaces and linebreaks have to stay intact.

Answer 1

 {
    "A": {
      "A1": "S",
      "A2": 0.0
    }
  }

is a JSON Object Use JToken datatype

class JsonConverterObjectToString : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return (objectType == typeof(JTokenType));
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            JToken token = JToken.Load(reader);
            if (token.Type == JTokenType.Object)
            {
                return token.ToString();
            }
            return null;
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            //serializer.Serialize(writer, value);

            //serialize as actual JSON and not string data
            var token = JToken.Parse(value.ToString());
            writer.WriteToken(token.CreateReader());

        }
    }

Otherwise use JsonConverter like this

  JsonConvert.DeserializeObject<Testclass>(json, 
                new JsonConverterObjectToString());

Answer 2

    using Newtonsoft.Json;
    using Newtonsoft.Json.Linq;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace ConsoleApp5
    {
        class Testclass
        {
            public string Data { get; set; }
            public string NoData { get; set; }
        }
        class JsonConverterObjectToString : JsonConverter
        {
            public override bool CanConvert(Type objectType)
            {
                return (objectType == typeof(string));
            }

            public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
            {
                JToken token = JToken.Load(reader);
                if (token.Type == JTokenType.Object)
                {
                    return token.ToString();
                }
                return null;
            }

            public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
            {
                //serializer.Serialize(writer, value);

                //serialize as actual JSON and not string data
                var token = JToken.Parse(value.ToString());
                writer.WriteToken(token.CreateReader());

            }
        }
        class Program
        {

            static void Main(string[] args)
            {
                var json = "{\r\n  \"Data\": {\r\n    \"A\": {\r\n      \"A1\": \"S\",\r\n      \"A2\": 0.0\r\n    }\r\n  },\r\n  \"NoData\": \"text\"\r\n}";
                var jObj = JsonConvert.DeserializeObject<Testclass>(json, new JsonConverterObjectToString());
                var jObjStrin = JsonConvert.SerializeObject(jObj, new JsonConverterObjectToString());
 Console.WriteLine(jObjString);
            }
        }
    }

we can able to JToken to string with the same format Please check the image. the Data has serialized again the same format using the same Convertor

Answer 3

I had implemented a naive JSON parser just for solving this specific problem, here's the code:

Method:

static string ExtractInnerJsonObject(ReadOnlySpan<byte> jsonPayload, ReadOnlySpan<char> targetField, bool preserveWhiteSpaces = false)
{
    const int TYPE_OTHER = 0;
    const int TYPE_OBJECT = 1;
    const int TYPE_STRING = 2;
    const int TYPE_ARRAY = 3;

    ReadOnlySpan<char> jsonPayloadString = Encoding.UTF8.GetString(jsonPayload).AsSpan();

    int objectDepth = 0;
    int lastWhiteSpacePosition = 0;
    int fieldNameStartPosition = 0;
    int fieldNameEndPosition = 0;
    int valueStartPosition = 0;
    int valueEndPosition = 0;
    int detectedValueType = TYPE_OTHER;

    bool isValueTypeDetected = false;

    bool isValueScanStarted = false;
    bool isValueScanCompleted = false;

    bool isTargetField = false;
    bool isFieldNameScanStarted = false;
    bool isFieldNameScanCompleted = false;


    for (int i = 0; i < jsonPayloadString.Length; i++)
    {
        char c = jsonPayloadString[i];

        if (c == '{')
        {
            objectDepth++;

            if (isValueScanStarted && !isValueScanCompleted && !isValueTypeDetected)
            {
                detectedValueType = TYPE_OBJECT;
                isValueTypeDetected = true;
            }
        }
        else if (c == '}')
        {
            objectDepth--;

            if (isValueScanStarted && !isValueScanCompleted && detectedValueType == TYPE_OBJECT && objectDepth == 1)
            {
                valueEndPosition = i;
                isValueScanCompleted = true;
            }

            if (isValueScanStarted && !isValueScanCompleted && detectedValueType == TYPE_OTHER)
            {
                valueEndPosition = i - 1;
                isValueScanCompleted = true;
            }
        }
        else if (c == '"')
        {
            if (!isValueScanStarted)
            {
                if (!isFieldNameScanStarted)
                {
                    fieldNameStartPosition = i + 1;
                    isFieldNameScanStarted = true;
                }
                else
                {
                    fieldNameEndPosition = i - 1;
                    isFieldNameScanCompleted = true;
                }
            }
            else
            {
                if (!isValueTypeDetected)
                {
                    detectedValueType = TYPE_STRING;
                    isValueTypeDetected = true;
                }
                else
                {
                    if (!isValueScanCompleted && detectedValueType == TYPE_STRING)
                    {
                        valueEndPosition = i;
                        isValueScanCompleted = true;
                    }
                }
            }
        }
        else if (c == ':')
        {
            if (!isValueScanStarted)
            {
                valueStartPosition = i + 1;
                isValueScanStarted = true;
            }
        }
        else if (c == ',')
        {
            if (isValueScanStarted && !isValueScanCompleted && detectedValueType == TYPE_OTHER)
            {
                valueEndPosition = i - 1;
                isValueScanCompleted = true;
            }
        }
        else if (c == '[')
        {
            if (isValueScanStarted && !isValueScanCompleted && !isValueTypeDetected)
            {
                detectedValueType = TYPE_ARRAY;
                isValueTypeDetected = true;
            }
        }
        else if (c == ']')
        {
            if (isValueScanStarted && !isValueScanCompleted && detectedValueType == TYPE_ARRAY)
            {
                valueEndPosition = i;
                isValueScanCompleted = true;
            }
        }
        else if (char.IsWhiteSpace(c))
        {
            lastWhiteSpacePosition = i;
        }

        if (isFieldNameScanStarted && isFieldNameScanCompleted)
        {
            ReadOnlySpan<char> fieldName = jsonPayloadString[fieldNameStartPosition..(fieldNameEndPosition + 1)];

            if (fieldName.Equals(targetField, StringComparison.Ordinal))
            {
                isTargetField = true;
            }

            isFieldNameScanStarted = false;
            isFieldNameScanCompleted = false;
        }

        if (isValueScanStarted && isValueScanCompleted)
        {
            if (isTargetField)
            {
                ReadOnlySpan<char> value = jsonPayloadString[valueStartPosition..(valueEndPosition + 1)];

                if (preserveWhiteSpaces)
                {
                    return value.ToString();
                }
                else
                {
                    return value.ToString().Trim();
                }
            }

            isValueScanStarted = false;
            isValueScanCompleted = false;
            isValueTypeDetected = false;
            detectedValueType = TYPE_OTHER;
        }

    }

    return null;
}

Usage:

byte[] jsonPayloadReceivedFromSomewhere = Encoding.UTF8.GetBytes(
@"{
  ""Data"": {
    ""A"": {
      ""A1"": ""S"",
      ""A2"": 0.0
    }
  },
  ""NoData"":             ""hello
world!!@#$%^&*()_+-=[]{}|\/?><,.`01234     56789
""
, ""TestArray"":            [1, 2, 3 , 4, 5], ""TestBoolean"" :       true   
,        ""TestDouble""       :  123.45678
, ""TestInteger"" :-9999



}");

string a = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "Data");
string b = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "NoData");
string c = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "InvalidField");
string d = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "TestArray");
string e = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "TestBoolean");
string f = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "TestDouble");
string g = ExtractInnerJsonObject(jsonPayloadReceivedFromSomewhere, "TestInteger");

Result: