Allow to specify the MessageAttributes when publishing an event

[alessandrozucca]

In order to be able to use the attribute based filtering, would be nice if the Publisher allowed to specify the MessageAttributes field in sns.PublishInput so basically have something like:

// PublishRaw will emit the byte array to the SNS topic.
// The key will be used as the SNS message subject.
func (p *publisher) PublishRaw(_ context.Context, key string, m []byte, messageAttributes map[string]*MessageAttributeValue) error {
	msg := &sns.PublishInput{
		TopicArn: &p.topic,
		Subject:  &key,
		Message:  aws.String(base64.StdEncoding.EncodeToString(m)),
		MessageAttributes: messageAttributes,
	}

	_, err := p.sns.Publish(msg)
	return err
}

ref. https://aws.amazon.com/blogs/compute/simplify-pubsub-messaging-with-amazon-sns-message-filtering/

[jprobinson]

Howdy @alessandrozucca!

Sorry for the delay, I've been thinking about this one since you posted.

While it does seem handy, I do worry about this leading to a leaky abstraction as we've been trying to find the lowest common denominator between SNS, Kafka & Google PubSub.

I do see that PubSub also has attributes but I haven't found something similar in the Kafka world so I'm a bit hesitant to alter our main interface.

Perhaps we can make a new Publisher interface (similar to the MultiPublisher) and maybe it just wont be implemented for Kafka?

[alessandrozucca]

Hi @jprobinson

Sorry for the delay in the response and happy new year 🎉

I understand your reason for not wanting to change the main interface.

Creating a new Publisher that allows to specify the message attributes makes sense.

In the meanwhile, to get this working, I have already added in a local package an interface (with a third argument map[string]*sns.MessageAttributeValue) and copied your implementation of the publisher allowing the MessageAttibute to be specified.

[coryt]

I get the reason for not adding it, but I would love to see this added in somehow.
I have taken a similar approach to @alessandrozucca and implemented this in a local package.

[taraspos]

@jprobinson what if attributes will be passed via context, so there is no need to change the interface and context will be optionally handled?

Something like:

if v, ok := ctx.Value("MessageAttributes").(map[string]*sns.MessageAttributeValue); ok {
      msg.MessageAttributes = v
}

[alessandrozucca-pp]

Think this issue can be closed - I have just noticed that this has been implemented 😄

[pingsutw]

@trane9991 is possible to do similar thing for google pub/sub? I want to set attribute for my event which will be sent to google pub/sub

if v, ok := ctx.Value("MessageAttributes").(map[string]*sns.MessageAttributeValue); ok {
      msg.MessageAttributes = v
}