How do I convert an escaped JSON string within a JSON object?

Question

I\'m receiving a JSON object from a public API with a property that, itself, is an escaped JSON string.

{
   \"responses\":[
      {
         \"info\":\"keep         


        

Answer 1

Your JSON contains a literal string for the "body" objects that is actually embedded, double-serialized JSON. To deserialize this to a POCO hierarchy without needing to introduce an intermediate string Json surrogate property inside any of your types, you have a few options:

1. You could preprocess your JSON using LINQ to JSON and replace the literal "body" strings with their parsed equivalents:

       var rootToken = JToken.Parse(json);
       foreach (var token in rootToken.SelectTokens("responses[*].body").ToList().Where(t => t.Type == JTokenType.String))
       {
           token.Replace(JToken.Parse((string)token));
       }
   
       var root = rootToken.ToObject();
   

2. You could introduce a generic JsonConverter for the POCO corresponding to each Body object that parses the incoming embedded JSON string literal into a LINQ to JSON hierarchy, then deserializes that:

   public class EmbeddedLiteralConverter : JsonConverter
   {
       public override bool CanConvert(Type objectType)
       {
           return typeof(T).IsAssignableFrom(objectType);
       }
   
       public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
       {
           if (reader.TokenType == JsonToken.Null)
               return null;
           var contract = serializer.ContractResolver.ResolveContract(objectType);
           if (contract is JsonPrimitiveContract)
               throw new JsonSerializationException("Invalid type: " + objectType);
           if (existingValue == null)
               existingValue = contract.DefaultCreator();
           if (reader.TokenType == JsonToken.String)
           {
               var json = (string)JToken.Load(reader);
               using (var subReader = new JsonTextReader(new StringReader(json)))
               {
                   // By populating a pre-allocated instance we avoid an infinite recursion in EmbeddedLiteralConverter.ReadJson()
                   // Re-use the existing serializer to preserve settings.
                   serializer.Populate(subReader, existingValue);
               }
           }
           else
           {
               serializer.Populate(reader, existingValue);
           }
           return existingValue;
       }
   
       public override bool CanWrite { get { return false; } }
   
       public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
       {
           throw new NotImplementedException();
       }
   }
   

   Then use it like:

       var root = JsonConvert.DeserializeObject(json, new EmbeddedLiteralConverter());
   

   Note that the converter checks to see whether the incoming JSON token is a string, and if not, deserializes directly. Thus the converter should be usable when the "body" JSON is and is not double-serialized.

For testing purposes I generated the following target classes using http://json2csharp.com/:

public class Error
{
    public string message { get; set; }
    public string type { get; set; }
    public int code { get; set; }
}

public class Body
{
    public Error error { get; set; }
}

public class Respons
{
    public string info { get; set; }
    public Body body { get; set; }
}

public class RootObject
{
    public List responses { get; set; }
}