CODEWITHSUNDEEP
c#amazon-web-servicesaws-lambda
vmasanas
vmasanas

Reputation: 515

How to test a very simple AWS Lambda

I've create a very simple lambda function in VS.NET and uploaded to AWS.

namespace HelloWorld
{
    public class SayHi
    {
        public string FunctionHandler(string name, ILambdaContext context)
        {
            return name?.ToUpper();
        }
    }
}

When I test this withing VS.NET it works and all is good.

But if I try to test this from within AWS I can't make it work. I configured a test event with the following json:

{
  "name": "sample text"
}

but when I try to run this I always get the error:

{

  "errorType": "JsonSerializerException",
  "errorMessage": "Error converting the Lambda event JSON payload to a string. JSON strings must be quoted, for example \"Hello World\" in order to be converted to a string: The JSON value could not be converted to System.String. Path: $ | LineNumber: 0 | BytePositionInLine: 1.",
  "stackTrace": [
    "at Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer.Deserialize[T](Stream requestStream)",
    "at lambda_method(Closure , Stream , Stream , LambdaContextInternal )"
  ],
  "cause": {
    "errorType": "JsonException",
    "errorMessage": "The JSON value could not be converted to System.String. Path: $ | LineNumber: 0 | BytePositionInLine: 1.",
    "stackTrace": [
      "at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& readStack, Utf8JsonReader& reader, Exception ex)",
      "at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)",
      "at System.Text.Json.JsonSerializer.ReadCore(Type returnType, JsonSerializerOptions options, Utf8JsonReader& reader)",
      "at System.Text.Json.JsonSerializer.ParseCore(ReadOnlySpan`1 utf8Json, Type returnType, JsonSerializerOptions options)",
      "at System.Text.Json.JsonSerializer.Deserialize[TValue](ReadOnlySpan`1 utf8Json, JsonSerializerOptions options)",
      "at Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer.Deserialize[T](Stream requestStream)"
    ],
    "cause": {
      "errorType": "InvalidOperationException",
      "errorMessage": "Cannot get the value of a token type 'StartObject' as a string.",
      "stackTrace": [
        "at System.Text.Json.Utf8JsonReader.GetString()",
        "at System.Text.Json.Serialization.Converters.JsonConverterString.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)",
        "at System.Text.Json.JsonPropertyInfoNotNullable`4.OnRead(ReadStack& state, Utf8JsonReader& reader)",
        "at System.Text.Json.JsonPropertyInfo.Read(JsonTokenType tokenType, ReadStack& state, Utf8JsonReader& reader)",
        "at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)"
      ]
    }
  }
}

What am I missing here?

Upvotes: 2

Views: 4055

Answers (2)

Khatibzadeh
Khatibzadeh

Reputation: 470

you can change the serializer for the input parameter (that I recommend not to do so). but by default, c# lambda expects the input parameter to be in JSON format.

there is a good blog post regarding Lambda in C#.

based on your sample, the input object for the lambda method should be a class, not a simple string variable, the first input should be an object like the following:

public class InputObject
{
   public string Name {get;set;}
}

and your method input should change to the following:

namespace HelloWorld
{
    public class SayHi
    {
        public string FunctionHandler(InputObject inputObject, ILambdaContext context)
        {
            //your logic
        }
    }
}

Upvotes: 2

Philip Pittle
Philip Pittle

Reputation: 12295

When testing in the Lambda Console, you need the input to be a plain string rather than the default json:

"sample text"

enter image description here

Otherwise the default lambda serializer isn't sure how to convert a json document to a string:

enter image description here

Upvotes: 1

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