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After reading <https://www.pulumi.com/blog/simple-serverless-programming-with-google-cloud-functions-and-pulumi/>, I started wondering whether there was a way to easily create a function for pubsub, but where the topic already exists and for ownership reasons shouldn’t be imported?

e.g.

Before:
```// Create a PubSub Topic
let requests = new gcp.pubsub.Topic("requests");
requests.onMessagePublished("newMessage", (data) =&gt; {
    // Print out a log message for every message on the Topic.
    // Change this code to fit your needs!
    console.log(Buffer.from(data.data, "base64").toString());
});```
After:
```// Create a PubSub Topic
let requests = await gcp.pubsub.getTopic("requests");
/// ???
requests.onMessagePublished("newMessage", (data) =&gt; {
    // Print out a log message for every message on the Topic.
    // Change this code to fit your needs!
    console.log(Buffer.from(data.data, "base64").toString());
});```


Might this be acceptable:
```const eventSource = new gcp.pubsub.Topic("event-source", null, {
	retainOnDelete: true,
	import:
		"/projects/&lt;project&gt;/topics/&lt;topic&gt;",
});```

hmm.
Maybe this?
```Topic.prototype.onMessagePublished(requests, ...)```


Though looking at the code, you may as well use `cloudfunctions.CallbackFunction` directly.
<https://github.com/pulumi/pulumi-gcp/blob/master/sdk/nodejs/pubsub/zMixins.ts#L82>

Oh yeah. That looks pretty clean. Thanks!