JsonReaderException in AWS Lambda C# Function

Question

I have created an aws lambda function using c# in visual studio 2017 and I'm having problems with the parameters. I am trying to get the 'querystringparameter' but every time I put a parameter in my FunctionHandler I get this error.

{
  "errorType": "JsonReaderException",
  "errorMessage": "Unexpected character encountered while parsing value: {. Path '', line 1, position 1.",
  "stackTrace": [
    "at Newtonsoft.Json.JsonTextReader.ReadStringValue(ReadType readType)",
    "at Newtonsoft.Json.JsonTextReader.ReadAsString()",
    "at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(JsonReader reader, JsonContract contract, Boolean hasConverter)",
    "at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)",
    "at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)",
    "at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)",
    "at lambda_method(Closure , Stream , Stream , ContextInfo )"
  ]
}

This is my sample FunctionHandler code :

public string FunctionHandler(APIGatewayProxyRequest request, ILambdaContext context)
        {
            var sample = GetParameters(request.QueryStringParameters, "sample");
            return sample;
        }

What's wrong with this ? Answers would be very much appreciated. Thank you !

UPDATE

Error Message

can you please provide how you are passing the parameters, I mean the format of JSON values — Muhammad Soliman
– Muhammad Soliman, Commented Oct 6, 2017 at 5:37
I pass the parameter via API Gateway when I'm testing it. I've also tried just passing in a string via testing of function in visual studio 2017 but I still get that same error. — anonymous
– anonymous, Commented Oct 6, 2017 at 5:39

Muhammad Soliman · Accepted Answer · 2017-10-06 06:06:23Z

1

The exception means you are not passing your parameter as a valid JSON format. please make sure to pass your parameter in a string quoted format.

public string myFunctionHandler(string param, ILambdaContext context){
....
}

Passing parameter (in a string quoted format) should be looking like:

"{ \"param\": \"value\" }"

If you have an object:

public string myFunctionHandler(JObject param, ILambdaContext context) {
...
}

In this case, you can pass it like this:

{ "param": "value" }

edited Oct 6, 2017 at 6:06

answered Oct 6, 2017 at 5:48

Muhammad Soliman

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2 Comments

anonymous Over a year ago

How about if I want to pass it as a query parameter but not via AWS API Gateway ? Like, api.com/v1?param=sample ...

Abhigna Nagaraja Over a year ago

@anonymous Such query parameter mapping can be configured as mentioned docs.aws.amazon.com/apigateway/latest/developerguide/…

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