Amazon SNS Message Validator for JavaScript
The Amazon SNS Message Validator for Node.js library allows you to validate
that incoming HTTP(S) POST messages are valid Amazon SNS notifications. This
library is standalone and does not depend on the AWS SDK for JavaScript.
Installation
The npm module's name is sns-validator
. Install with npm or yarn:
npm i sns-validator
or
yarn add sns-validator
Basic Usage
To validate a message, you can instantiate a MessageValidator
object and pass
an SNS message and a callback to its validate
method. The message should be
the result of calling JSON.parse
on the body of the HTTP(S) message sent by
SNS to your endpoint. The callback should take two arguments, the first being
an error and the second being the successfully validated SNS message.
The message validator checks the SigningCertURL
, SignatureVersion
, and
Signature
to make sure they are valid and consistent with the message data.
const MessageValidator = require('sns-validator'),
validator = new MessageValidator();
validator.validate(message).then(message => {
}).catch(err => {
});
Installation
The SNS Message Validator relies on the Node crypto module and is only designed
to work on a server, not in a browser. The validation performed is only
necessary when subscribing HTTP(S)
About Amazon SNS
Amazon Simple Notification Service (Amazon SNS) is a fast, fully-managed,
push messaging service. Amazon SNS can deliver messages to email, mobile devices
(i.e., SMS; iOS, Android and FireOS push notifications), Amazon SQS queues,and
— of course — HTTP/HTTPS endpoints.
With Amazon SNS, you can setup topics to publish custom messages to subscribed
endpoints. However, SNS messages are used by many of the other AWS services to
communicate information asynchronously about your AWS resources. Some examples
include:
- Configuring Amazon Glacier to notify you when a retrieval job is complete.
- Configuring AWS CloudTrail to notify you when a new log file has been written.
- Configuring Amazon Elastic Transcoder to notify you when a transcoding job
changes status (e.g., from "Progressing" to "Complete")
Though you can certainly subscribe your email address to receive SNS messages
from service events like these, your inbox would fill up rather quickly. There
is great power, however, in being able to subscribe an HTTP/HTTPS endpoint to
receive the messages. This allows you to program webhooks for your applications
to easily respond to various events.
Handling Messages
Confirming a Subscription to a Topic
In order to handle a SubscriptionConfirmation
message, you must use the
SubscribeURL
value in the incoming message:
const https = require('https'),
MessageValidator = require('sns-validator'),
validator = new MessageValidator();
validator.validate(message).then(message => {
if (message['Type'] === 'SubscriptionConfirmation') {
https.get(message['SubscribeURL'], function (res) {
});
}
}).catch(err => {
console.error(err);
});
If an incoming message includes multibyte characters and its encoding is utf8,
set the encoding to validator
.
const MessageValidator = require('sns-validator'),
validator = new MessageValidator();
validator.encoding = 'utf8';
Receiving a Notification
To receive a notification, use the same code as the preceding example, but
check for the Notification
message type.
if (message['Type'] === 'Notification') {
console.log(`${message['MessageId']}: ${message['Message']}`);
}
The message body will be a string, and will hold whatever data was published
to the SNS topic.
Unsubscribing
Unsubscribing looks the same as subscribing, except the message type will be
UnsubscribeConfirmation
.
if (message['Type'] === 'UnsubscribeConfirmation') {
https.get(message['SubscribeURL'], (res) => {
});
}