Why does my Firebase/Postmark email despatch function fail to deploy?

Question

Firebase deployment of my function fails with the following error:

"Function failed on loading user code. This is likely due to a bug in the user code."

Here's the function code:

const postmark = require("postmark");

const functions = require("firebase-functions");
const admin = require("firebase-admin");

admin.initializeApp()

exports.sendPostmarkEmailFunction = functions.firestore.
    document('/postmarklogs/{documentId}').
    onCreate((snapShot, context) => {

        var serverToken = "_my_client_key_";
        var client = new postmark.ServerClient(serverToken);

        try {
            client.sendEmail({
                "From": "_my_depatch_address_",
                "To": "_my_receipt_address_",
                "Subject": snapShot.data().subject,
                "HtmlBody": snapShot.data().message
            });
            return true;
        } catch (error) {
            console.log("Error : " + error.ErrorCode + " : " + error.Message);
            return false;
        }

    });

This code works just fine in the Firebase emulator. As far as I can see, the deployment issue is triggered specifically by the const postmark = require("postmark"); line. If I comment this out, the function deploys - but then of course it doesn't work!

Advice would be greatly appreciated.

Answer 1

Postmark needs to be installed in the project's 'functions' folder. I'd installed it into the body of the project and so Postmark was missing from the 'functions/package.json' file that guides deployment's build stage. The 'functions' folder created by firebase init functions is like a project within a project and needs to be treated as such.

I got onto the problem from the deployment "build" logs Once Postmark had been installed in the 'functions' folder my sendPostmarkEmailFunction function worked perfectly.

In passing, unless you already know this, the Postmark API token really needs to be squirreled securely away in the Firebase environment variable store. Also, while you might be tempted to use an https.onRequest trigger rather than the onCreate() used here, you might like to know that this is likely to land you in endless CORS issues when used with Postmark.