how to pass an object to amazon SNS

Question

I see in the examples how to to pass a message string to amazon sns sdk's publish method. However, is there an exmaple of how to pass a custom object as the message? I tried setting "MessageStructure" to "json" but then I get InvalidParameter: Invalid parameter: Message Structure - No default entry in JSON message body error. Where should I be passing the object values into in the params?

Any examples?

    var params = {
        Message: JSON.stringify(item),
        MessageStructure: 'json',
        TopicArn: topic
        //MessageAttributes: item
    };

    return sns.publishAsync(params);

Answer 1

An example is shown here: https://docs.aws.amazon.com/sns/latest/api/API_Publish.html#API_Publish_Example_2

The JSON format for Message is as follows:

{
    "default": "A message.",
    "email": "A message for email.",
    "email-json": "A message for email (JSON).",
    "http": "A message for HTTP.",
    "https": "A message for HTTPS.",
    "sqs": "A message for Amazon SQS." 
} 

So, assuming what you wanted to pass is an object, the way it worked for me was:

const messageObjToSend = {
    ...
}

const params = {
    Message: JSON.stringify({
        default: JSON.stringify( messageObjToSend )
    }),
    MessageStructure: 'json',
    TopicArn: 'arn:aws:sns...'
}

Answer 2

There is no SDK-supported way to pass a custom object as a message-- messages are always strings. You can, of course, make the string a serialized version of your object.

MessageStructure: 'json' is for a different purpose-- when you want to pass different strings to different subscription types. In that case, you make the message a serialized json object with AWS-defined structure, where each element defines the message to send to a particular type of subscription (email, sqs, etc). Even in that case, the messages themselves are just strings.

MessageAttributes are parameters you add to the message to support specific subscription types. If you are using SNS to talk to Apple's IOS notification service, for example, you might have to supply additional message parameters or authentication keys-- MessageAttributes provide a mechanism to do this. This is described in this AWS documentation.