aws api gateway and lamda - how to get event.body

Question

I'm new to aws and I have a strange problem of getting the body of event inside my lamda handler function.

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        body: event.body
    };
    return response;
};

When I run test I get

Response:
{
  "statusCode": 200
}

However when I only return event

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        body: event <=====
    };
    return response;
};

I get

Response:
{
  "statusCode": 200,
  "body": {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
  }
}

I'm using node 8.10. Does anybody knows what I'm doing wrong here?

Answer 1

The test event in to Lambda console is exactly what you get as the event parameter in your Lambda handler. When you put {"a":1} , you get {"a":1} .

You can simulate a different event types of AWS service (SNS, S3, API Gateway) selecting a template from the combobox.

As you are returning a HTTP response, you want probably to simulate an API Gateway event, it could look like this:

{
  "body": "{\"a\":1}",
  "pathParameters": {
    "id": "XXX"
  },
  "resource": "/myres",
  "path": "/myres",
  "httpMethod": "GET",
  "isBase64Encoded": true,
  "requestContext": {
    "authorizer": {
      "tenantId": "TEST"
    },
    "accountId": "123456789012",
    "resourceId": "123456",
    "stage": "test",
    "requestId": "test-request-id",
    "requestTime": "09/Apr/2015:12:34:56 +0000",
    "requestTimeEpoch": 1428582896000,
    "path": "/myres",
    "resourcePath": "/myres,
    "httpMethod": "GET",
    "apiId": "1234567890",
    "protocol": "HTTP/1.1"
  }
}

Then you will get the body in event.body as JSON string - you can convert it into an object by JSON.parse(event.body) .

When returning, you have to serialize the response body with JSON.stringify :

return {
    statusCode: 200,
    body: JSON.stingify({your:'object'})
};

Answer 2

Change

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        body: event.body
    };
    return response;
};

to

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        body: JSON.stringify(event.body)
    };
    return response;
};

The body you return in API Gateway must be stringified, otherwise it doesn't know how to deal with the response.