SQS / SNS nested object parsing

[sdd]

Resolves #102.

Adds a set of alternate structs that you can use if you are working with nested objects inside your SQS and/or SNS messages, instead of plain string messages.

For example, a common use case in AWS is to have a Lambda that subscribes to an SQS Queue that is in turn subscribed to an SNS topic. If you are posting serialized JSON objects to that SNS topic, and intending to deserialize them inside a Lambda, prior to this change you would need to manually deserialize the SNS message from within the body of an SqsMessage, and then do the same to get a deserialized instance of a custom struct out of the message field of that SnsMessage.

So whereas before you might need to do this:

#[derive(Deserialize)]
struct CustomStruct {
   foo: String,
   bar: i32
}

fn lambda_handler(e: LambdaEvent<SqsEvent>) -> Result<(), Error> {
    for sqs_msg in e.payload.records.into_iter() {
        let sns_msg: SnsMessage = serde_json::from_str(&sqs_msg.body)?;
        let obj: CustomStruct = serde_json::from_str(&sns_msg.message)?;
        msg_handler(obj);
    }

    Ok(())
}

fn message_handler(msg: CustomStruct) -> () {
    // ... 
}

This PR allows you to do this much more cleanly:

#[derive(Deserialize)]
struct CustomStruct {
   foo: String,
   bar: i32
}

fn lambda_handler(e: LambdaEvent<SqsEventObj<SnsMessageObj<SolveResponse>>>) -> () {
    for sqs_msg in e.payload.records.into_iter() {
        msg_handler(sqs_msg.body.message);
    }
}

fn message_handler(msg: CustomStruct) -> () {
    // ... 
}

[calavera]

this is a great addition, thanks for putting it together! I have a small request so we don't make compilation time higher when sqs and sns events are not compiled.

[sdd]

You're welcome! I've made serde_with optional now, and only pulled in by the sns and sqs features 👍🏼

[CumpsD]

Is it possible these should be optional? https://github.com/LegNeato/aws-lambda-events/blob/master/aws_lambda_events/src/sns/mod.rs#L136-L137

In my SNS message (being posted on SQS) I dont have these fields?

{
    "Records": [
        {
            "attributes": {
                "AWSTraceHeader": "Root=1-633375e5-6992f4381edc004f3f3beed3;Parent=7428100f69529302;Sampled=0",
                "ApproximateFirstReceiveTimestamp": "1664316902967",
                "ApproximateReceiveCount": "1",
                "MessageDeduplicationId": "9",
                "MessageGroupId": "Geert",
                "SenderId": "xxx",
                "SentTimestamp": "1664316902967",
                "SequenceNumber": "18872809200869103616"
            },
            "awsRegion": "eu-central-1",
            "body": "{\n  \"Type\" : \"Notification\",\n  \"MessageId\" : \"f5458878-95d1-5aad-82d9-d3d5edf775d9\",\n  \"SequenceNumber\" : \"10000000000000027000\",\n  \"TopicArn\" : \"arn:aws:sns:eu-central-1:xxx:dev-events.fifo\",\n  \"Message\" : \"{\\\"CustomerDepositedMoney\\\":{\\\"amount\\\":1000.0,\\\"balance\\\":9000.0}}\",\n  \"Timestamp\" : \"2022-09-27T22:15:02.834Z\",\n  \"UnsubscribeURL\" : \"https://sns.eu-central-1.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:eu-central-1:xxx:dev-events.fifo:aab561d9-73b3-4cdf-b527-9cbfa357eb47\"\n}",
            "eventSource": "aws:sqs",
            "eventSourceARN": "arn:aws:sqs:eu-central-1:xxx:dev-sqs1.fifo",
            "md5OfBody": "4fcc9a1791061d7fc91022734f84850f",
            "messageAttributes": {},
            "messageId": "bd9feb74-23c6-40b7-8b27-8af29b4c140a",
            "receiptHandle": "AQEB8m4uUDMmdKPi0AGmlyV30Eln411zJAi7GTQ0FZdkYOBzDlTwHUdEmXRBqWEa0Re3SwaOvhYx/4kj1DR5mLtJM7adYFj+ovAnUBHljr0gfaQe3WHY0l0vM9RVb/vqUI9weHH5fMCgqYXNanMjoA4KyplNewFvJo/KwxY3cF7LZIpaEZdFREJN5uU1h5u2tQKnCKvMValbToW6JU2LHuArXlo8y9VuS6mIHQVUCDYHn+QCze1JoEWC7EUuiPPaFbT2GjTmCuVr85DpYPH8WyDXvpoaujUWkWoj4rgtVp3AdCA="
        }
    ]
}

Which means my SNS message looks like:

{
  "Type" : "Notification",
  "MessageId" : "f5458878-95d1-5aad-82d9-d3d5edf775d9",
  "SequenceNumber" : "10000000000000027000",
  "TopicArn" : "arn:aws:sns:eu-central-1:xxx:dev-events.fifo",
  "Message" : "{\"CustomerDepositedMoney\":{\"amount\":1000.0,\"balance\":9000.0}}",
  "Timestamp" : "2022-09-27T22:15:02.834Z",
  "UnsubscribeURL" : "https://sns.eu-central-1.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:eu-central-1:xxx:dev-events.fifo:aab561d9-73b3-4cdf-b527-9cbfa357eb47"
}

[CumpsD]

Made a PR for it: #115