Add basic SNS Delivery Policy implementation

[timothepearce]

Statement

It seems that SNS has a default delivery policy that is not applied in the plugin.

serverless-offline-sns/src/sns-server.ts

Lines 248 to 260 in 884298b

	private publishHttp(event, sub, raw) {
	return fetch(sub.Endpoint, {
	method: "POST",
	body: event,
	timeout: 0,
	headers: {
	"x-amz-sns-rawdelivery": "" + raw,
	"Content-Type": "text/plain; charset=UTF-8",
	"Content-Length": Buffer.byteLength(event),
	},
	}).then(res => this.debug(res))
	.catch(ex => this.debug(ex));
	}

The catched request is only logged, no other behavior is implemented.

Question

Do you think this behavior deserves to be implemented in it?
If so, in what form?

Proposal

I think it would be interesting to keep the current behavior of the plugin and add a custom variable to modify it if necessary.

custom:
  serverless-offline-sns:
    retry: 3 # default 0
    retry-interval: 1000 # In ms, default 0

With a retry custom attribute set to 3 and retry-interval set to 1000, we will send again each initial delivery attempt following the rules of the SNS Delivery Policy.

What do you think about it?

[mj1618]

I like it - feel free to raise a PR.

[mj1618]

Sorry for the delayed response