Feature Request: support logging `Set` & `Map` types

[hfahlbusch]

Expected Behaviour

If I enter a Set as a value of the LogItemExtraInput it should print it's elements like the console.log() and not return {}.
I was thinking there were no data in the set and searched a while for the error.

Current Behaviour

Set with elements will be printed as {}

Code snippet

import { Logger } from '@aws-lambda-powertools/logger';

const log = new Logger({
logLevel: 'DEBUG'
});
const a = new Set();
a.add(1);
a.add(2);

log.debug('My set not logged properly', { data: a});

//{"level":"DEBUG","message":"My set not logged properly","service":"service_undefined","timestamp":"2023-08-12T14:27:00.205Z","data":{}}

console.log('My set logged', a);
// My set logged Set(2) { 1, 2 }

Steps to Reproduce

1. Create new node project
2. Install powertools logger in node modules
3. Copy code snippet from above
4. Run and see missing Set data

Possible Solution

I digged a little into the code.
It seems the extra input is stringified with JSON.stringify which cannot handle Sets in the expected way, because the values are not properties of the Set.

Could be added to the getReplacer() in Logger.js that also handles bigints.
Maybe convert Set to an array [...mySet] or create string representation manually.

Powertools for AWS Lambda (TypeScript) version

latest

AWS Lambda function runtime

18.x

Packaging format used

npm

Execution logs

Example in the logs:

{
    "logLevel": "DEBUG",
    "message": "Modified products and documents",
    "awsRegion": "eu-central-1",
    "service": "cache-invalidation",
    "timestamp": "2023-08-12T13:43:30.197Z",
    "correlationIds": {
        "xRayTraceId": "xxxxxxxxxxxxxxxxxxxxxxxx"
    },
    "durationInMs": 1291,
    "changedAfter": "2023-08-09T22:59:56.820Z",
    "numberOfProducts": 4,
    "numberOfDocuments": 5,
    "productIds": [
        [
            "PROD1",
            "sv-se"
        ],
        [
            "PROD2",
            "no-no"
        ],
        [
            "PROD3",
            "da-dk"
        ],
        [
            "PROD4",
            "no-no"
        ]
    ],
    "documentIds": {}
}

[boring-cyborg]

Thanks for opening your first issue here! We'll come back to you as soon as we can.
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[dreamorosi]

Hi @hfahlbusch thank you for taking the time to open this issue.

Before emitting a log the Logger utility calls JSON.stringify() on the log object.

Like you mentioned Set, as well as Map and others complex types, is not natively JSON-serializable (docs) so the behavior is not a bug but a missing feature.

I think it could be a good addition to the library so I'm going to change the issue type and mark it as feature request.

If there's interest we could definitely add support for those types after agreeing on a format to use.

[hfahlbusch]

Yeah, you are right!
I had a different mental model in my head, I was assuming it behaves more like the console.log not knowing that it's basically a JSON.stringify(). So that's why I framed it as a bug.

I guess with the advent of Sets and Maps it would be a good addition. In my opinion it brings some more comfort.
But for me even the confusion was causing more trouble, than "just transforming the Set to an array" to see it's values.

I would suggest to convert Set to Array and Map to Object, so it stays valid JSON or are you thinking about "arbitrary" strings to make them distinguishable?
(Maybe easy processing of logs as input for another tool could be also a factor here.)