Amazon Lex recurring lambda function error

Question

I have been trying to make a lambda function for a Lex chatbot I'm making, but whenever my intent calls upon the function, it keeps giving me the same error and I am tired of it. I am using node.js. The error message it gives me is:

An error has occurred: Invalid Lambda Response: 
Received invalid response from Lambda: Can not construct instance of
IntentResponse: no String-argument constructor/factory method to
deserialize from String value ('this works') at
[Source: "this works"; line: 1, column: 1

This happens no matter what kind of lambda function I input. Any answers?

exports.handler = (event, context, callback) => { // TODO implement callback(null, "this works"); }; — Gaben
– Gaben, Commented Aug 9, 2017 at 19:18

AndyOS · Accepted Answer · 2017-08-09 22:32:07Z

1

This is happening because all you're sending back is a String, whereas Lex expects replies in specific formats e.g.

"dialogAction": {
    "type": "Close",
    "fulfillmentState": "Fulfilled or Failed",
    "message": {
      "contentType": "PlainText or SSML",
      "content": "Message to convey to the user. For example, Thanks, your pizza has been ordered."
    },
   "responseCard": {
      "version": integer-value,
      "contentType": "application/vnd.amazonaws.card.generic",
      "genericAttachments": [
          {
             "title":"card-title",
             "subTitle":"card-sub-title",
             "imageUrl":"URL of the image to be shown",
             "attachmentLinkUrl":"URL of the attachment to be associated with the card",
             "buttons":[ 
                 {
                    "text":"button-text",
                    "value":"Value sent to server on button click"
                 }
              ]
           } 
       ] 
     }
  }

This code will work:

function close(sessionAttributes, fulfillmentState, message, responseCard) {
    return {
        sessionAttributes,
        dialogAction: {
            type: 'Close',
            fulfillmentState,
            message,
            responseCard,
        },
    };
}

function dispatch(intentRequest, callback) {
    const outputSessionAttributes = intentRequest.sessionAttributes || {};
    callback(close(outputSessionAttributes, 'Fulfilled', { contentType: 'PlainText',
        content: 'Thank you and goodbye' }));
}

function loggingCallback(response, originalCallback) {
    originalCallback(null, response);
}

exports.handler = (event, context, callback) => {
    try {
        console.log("event: " + JSON.stringify(event));
        dispatch(event, (response) => loggingCallback(response, callback));
    } catch (err) {
        callback(err);
    }
};

It simply sends back "Thank you and goodbye" in the required format, in this case with a "dialogAction" type of "Close" - which informs Lex not to expect a response from the user.

There are other types - this and more are all explained in the Lex documentation.

answered Aug 9, 2017 at 22:32

AndyOS

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2 Comments

Gaben Over a year ago

I am very new to AWS Lambda, and so I don't really understand how I get that JSON code out of my javascript.

AndyOS Over a year ago

I'd recommend you go through the tutorials they provide, they are fairly detailed - and show you how to construct the required JSON responses using sample functions like the "close" one I included in my answer. For that one all you need to provide is the "content" - a string.

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