MaxJsonLength Error when decoding jsonstring using System.Web.Helpers.Json.Decode

Question

Hi Team,

I got an error when decoding jsonstring using System.Web.Helpers.Json.Decode. How to set maxJsonLength while using System.Web.Helpers.Json.Decode method.

Errors: System.ArgumentException -- Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property. Parameter name: input at System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit) at System.Web.Helpers.Json.Decode(String value)

Thanks in advance

Answer 1

Hi @Sandeep Reddy Pinniti ,
I suggest you could create System.Web.Script.Serialization.JavaScriptSerializer, which allows access to the MaxJsonLength property:

JavaScriptSerializer ser = new JavaScriptSerializer();  
ser.MaxJsonLength = Int32.MaxValue;  
var jsonArtikel = ser.Serialize(Model);  

Best regards,
Yijing Sun

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Answer 2

Hi @Sandeep Reddy Pinniti ,
The following is a tested and working DynamicJsonObjectFormatter. It has a static method dynamic DynamicJsonObjectFormatter.Decode(string json) that duplicates System.Web.Helpers.Json.Decode, but gives you control of the max length:

public class DynamicJsonObjectFormatter : BufferedMediaTypeFormatter  
{  
    private static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);  
  
    public static dynamic Decode(string json, int maxLength=0)  
    {  
        try  
        {  
            if (string.IsNullOrEmpty(json))  
                return null;  
            var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();  
            if( maxLength>0) {  
                serializer.MaxJsonLength = maxLength;  
            }  
            var deserialized = serializer.DeserializeObject(json);  
            if (deserialized != null)  
            {  
                var dictValues = deserialized as IDictionary<string, object>;  
                if (dictValues != null)  
                    return new DynamicJsonObject(dictValues);  
                var arrayValues = deserialized as object[];  
                if (arrayValues != null)  
                {  
                    return new DynamicJsonArray(arrayValues);  
                }  
            }  
            log.Error("Internal: Attempt to deserialize unrecognized JSON string as DynamicJsonObject");  
        }  
        catch (Exception ex)  
        {  
            log.Error("Internal: exception deserializing JSON", ex);  
        }  
        return null;  
    }  
    override public object ReadFromStream(Type type, System.IO.Stream readStream, System.Net.Http.HttpContent content, IFormatterLogger formatterLogger)  
    {  
        System.IO.StreamReader strdr = null;  
        try  
        {  
            strdr = new System.IO.StreamReader(readStream);  
            string json = strdr.ReadToEnd();  
            int maxLength = 33554432; //Int32.MaxValue;  
            return Decode(json, maxLength);  
        }  
        catch (Exception ex)  
        {  
            log.Error("Internal: exception deserializing JSON", ex);  
        }  
        finally  
        {  
            if (strdr != null)  
            {  
                strdr.Dispose();  
            }  
        }  
        return null;  
    }  
  
    public DynamicJsonObjectFormatter()  
    {  
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/json"));  
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/json"));  
        //SupportedEncodings.Add(new UTF8Encoding(false, true));  
    }  
  
    public override bool CanReadType(Type type)  
    {  
        return (type == typeof(DynamicJsonObject)) || (type == typeof(DynamicJsonArray));  
    }  
  
    public override bool CanWriteType(Type type)  
    {  
        return false;  
    }  
  
}  

(Note: the strdr.ReadToEnd() may also give you an issue with large files. It's size limit can be controlled with

<system.web>  
    <httpRuntime targetFramework="4.6.2" maxRequestLength="200000" />  
    <!-- maxRequestLength is in KB, not B -->  
</system.web>  

in your Web.config file.
Best regards,
Yijing Sun

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