Amazon Lambda in C# - JsonReaderException

Question

I am attempting to write an AWS Lambda function in C#. I have the AWS Toolkit for Visual Studio 2015. I created a project with the AWS Lambda Project (.Net Core) and then selected the Empty Function option. Which gave me the following code:

UPDATE & ANSWER 02/24/17 - The comment marked as the Answer was useful knowledge but was not the actual answer for me. It was @PavelSafronov's comment in that answer that did the trick. I was either passing nothing in (and getting the error) or I assumed it wanted ME to give the information in JSON format so I would enter { "input": "Some string" } and still get the error. Now that I just passed in "Some string" it worked. However, as far as I am concerned, this seems like a bug. A string is by default nullable and the code written by Amazon even assumes it could be by virtual of the input?.ToUpper() where the ?. is checking for null.

Note: I added the LambdaLogger.Log lines and the Constructor to see where I was getting:

using Amazon.Lambda.Core;
using Amazon.Lambda.Serialization.Json;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.
[assembly: LambdaSerializer(typeof(JsonSerializer))]

namespace AWSLambdaTest1 {

  public class Function {

    public Function() {
      LambdaLogger.Log("Within the Constructor");
    }

    public string KevinsTestFunction(string input, ILambdaContext context) {
      LambdaLogger.Log("Within the KTF");
      return input?.ToUpper();
    }

  }
}

The output screen and Solution Explorer were saying:

Errors in C:\Test Projects\AWSLambda1\AWSLambda1\AWSLambda1.xproj
  Unable to resolve 'Amazon.Lambda.Core (>= 1.0.0)' for '.NETCoreApp,Version=v1.0'.

However, this will build and publish to AWS without fail. I can even Invoke it which returns the following - And is my main question:

{
  "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 )"
  ]
}

The Log file showed that the Constructors log message got there but NOT the actual KevingsTestFunction log message.

On a side note, I am able to get the Unable to resolve 'Amazon.Lambda.Core (>= 1.0.0)' for '.NETCoreApp,Version=v1.0' error to go away by adding the following to my project.json file:

"runtimes": {
  "win10-x64": {},
  "win81-x64": {},
  "win8-x64": {},
  "win7-x64": {}
}

Which makes sense on a Windows machine, not so much here on Amazon. Do I need some different runtime(s)?

That change did not change the JsonReaderException exception.

I tried adding "Linux": {} but that made no change either.

I even tried to update the NuGet package Microsoft.NETCore.App from 1.0.0 to 1.1.0 and that did nothing as well and even back to 1.0.1.

I would figure the default example they give you would work, but I am wrong there. It seems like there are issues with the Amazon.Lambda.Serialization.Json.JsonSerializer attribute. Is it possible to just use NewtonSoft?

Re: "However, as far as I am concerned, this seems like a bug. A string is by default nullable..." - unquoted null is valid JSON, and if that is passed into a function that expects a string, the string parameter will be null. This can be verified by using the AWS Lambda Console and specifying null as the test JSON payload, but not the AWS VS Toolkit, as the Toolkit treats unquoted text as string (for convenience) and quotes it before passing it to Lambda. — Pavel Safronov
– Pavel Safronov, Commented Feb 24, 2017 at 18:35

Zaxxon · Accepted Answer · 2017-08-06 22:41:04Z

15

Per Pavel Safronov -

Yes you should be entering a string not a json object if your Lambda Function entry point is:

public string KevinsTestFunction(string input, ILambdaContext context) {

Then the string you could enter is:

"{ \"input\": \"Something\" }"

You could also change the Lambda Functions entry point to:

public string KevinsTestFunction(JObject input, ILambdaContext context) {

Then you can enter a json object like so:

{ "input": "Something" }

If you're not expecting any input and merely polling a SQS queue or DynamoDb table then you could change the Lambda Function's entry point to:

public string KevinsTestFunction(ILambdaContext context) {

Many variations to play around with.

Now per the update in the original question, by default the AWS web console TEST area will set you up with default test data to send to your Lambda Function. That default test data is a JSON object. As noted it is at odds with the default templates for the C# Lambdas (which accept the string input) made available thru Visual Studio via the AWS SDK. Perhaps this is a built in stumbling block (feature) to force us to run into this issue, pull our hair out over it, then realize how versatile the function handler can be...

answered Aug 6, 2017 at 22:41

Zaxxon

6676 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Ajit Goel Over a year ago

I escaped the input string but it did not work. I also tried to use a JObject (instead of the string input) but the Step function is unable to convert the input Json string to JObject. @Pavel Safronov, would you have any inputs?

Zaxxon Over a year ago

Could you provide the raw string (with all the escape characters, etc) that is being passed into the Lambda function?

jmng Over a year ago

This did it for me.

Marcel Bezerra · Accepted Answer · 2018-08-29 18:08:35Z

4

Update the code:

public string KevinsTestFunction(string input, ILambdaContext context) {
  LambdaLogger.Log("Within the KTF");
  return input?.ToUpper();
}

to:

public string KevinsTestFunction(IDictionary input, ILambdaContext context) {
  LambdaLogger.Log("Within the KTF");
  return input["input"]?.ToUpper();
}

Do not forget to

using System.Collections;

answered Aug 29, 2018 at 18:08

Marcel Bezerra

1791 silver badge9 bronze badges

Comments

Tim Gray · Accepted Answer · 2017-02-23 20:43:40Z

3

My experience with AWS Lambda in C# in a little limited, but this is the kind of error I get when the input ("test" data if you are triggering the function from the console) is not in a actual JSON format. The best bet might be to create a dummy input class for your testing purposes and then give the lambda function the equivalent JSON data to get it to serialize properly.

As for your project.json, I have not needed to add the runtimes section for AWS Lambda before. If you do then you will need to select the relevant runtimes from this list: https://learn.microsoft.com/en-us/dotnet/articles/core/rid-catalog

Also here is a example project.json file if you find that useful: https://gist.github.com/TAGray/8cc812065c3b6abcd732b7f6a3bda92a

Hope that helps.

answered Feb 23, 2017 at 20:43

Tim Gray

1366 bronze badges

3 Comments

Grandizer Over a year ago

While in the resultant window when the publish is successful, there is a Test Function | Configuration | Event Sources | Logs option - I am on the Test Function where I put nothing in the Example Request nor in the box below it. I click Invoke and get the JsonReaderException message. I put in valid JSON of { "input": "Something" } and get the same message.

Grandizer Over a year ago

I created a New project the same was as I described, except this time I used the one "With Tests." Figuring that the "Test Function" option may only be a true Test function (grasping at straws here.) Using the Non-test function within this new project, same error JsonReaderException. I am not able to use the full pathing to the actual test function as it is not actually part of the package. I am not doing any of this through the command line (AWS CLI)

Pavel Safronov Over a year ago

The function in the question is expecting a string, so you should be passing in a quoted string. You would pass in JSON objects if your function is expecting a complex type.

Collectives™ on Stack Overflow

Amazon Lambda in C# - JsonReaderException

3 Answers 3

3 Comments

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related