Bug: SNS envelopes assumes data is always a JSON

[dreamorosi]

Expected Behavior

When processing Amazon SNS events using an AWS Lambda function customers can use a built-in envelope to quickly access the contents of the message.

The envelope should be able to process both messages that are plain strings or JSON encoded strings.

Current Behavior

Currently if the Message field is a plain text string, the envelope will throw an error because it always attempts to JSON.parse() it.

For example, this fails:

{
  "Records": [
    {
      "EventVersion": "1.0",
      "EventSubscriptionArn": "arn:aws:sns:us-east-2:123456789012:sns-la ...",
      "EventSource": "aws:sns",
      "Sns": {
        "SignatureVersion": "1",
        "Timestamp": "2019-01-02T12:45:07.000Z",
        "Signature": "tcc6faL2yUC6dgZdmrwh1Y4cGa/ebXEkAi6RibDsvpi+tE/1+82j...65r==",
        "SigningCertUrl": "https://sns.us-east-2.amazonaws.com/SimpleNotification",
        "MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e",
        "Message": "Hello from SNS!",
        "MessageAttributes": {
          "Test": {
            "Type": "String",
            "Value": "TestString"
          },
          "TestBinary": {
            "Type": "Binary",
            "Value": "TestBinary"
          }
        },
        "Type": "Notification",
        "UnsubscribeUrl": "https://sns.us-east-2.amazonaws.com/?Action=Unsubscribe",
        "TopicArn": "arn:aws:sns:us-east-2:123456789012:sns-lambda",
        "Subject": "TestInvoke"
      }
    }
  ]
}

Code snippet

const parsedBody = SnsEnvelope.parse(event, testSchema);

Steps to Reproduce

N/A

Possible Solution

No response

Powertools for AWS Lambda (TypeScript) version

latest

AWS Lambda function runtime

20.x

Packaging format used

npm

Execution logs

Failed to parse envelope. This error was caused by: Unexpected token 'H', "Hello from SNS!" is not valid JSON.

[dreamorosi]

When fixing this, change the it.fails() test to it() in packages/parser/tests/unit/envelopes/sns.test.ts which was introduced in #3248.