Plugins best practices

[jsardev]

So I'm working with fastify some time already and I truly love it! 😄 After some time I came to a reflection about plugins and I'm not sure if I get it right.

Let me explain my case in an example:

My app needs some posts and tags API. These two could be easily separate microservices so I'd like to split them into plugins:

users.js

module.exports = async fastify => {
    const db = somedb('conn.string');
    fastify.get('/users/:id', (request, reply) => {
        // db operations
    });
    // other endpoints
}

tags.js

module.exports = async fastify => {
    const db = somedb('conn.string');
    fastify.get('/tags/:id', (request, reply) => {
        // db operations
    });
    // other endpoints
}

Alright! Everything is cool. But... I duplicate database access code right now, and if I'd like even more plugins I'd duplicate this even more.

fastify-plugin to the rescue! I will create a shared database plugin which will decorate the fastify instance with a db wrapper, use it in my root server file and just use it in all my plugins:

server.js

fastify.register(require('dbplugin'), { connstring: '...' });
fastify.register(require('./users'));
fastify.register(require('./tags'));

users.js/tags.js

module.exports = async fastify => {
    // use fastify.db() here
 }

And here my concerns come into play:

1. Doesn't relying on shared plugins (via fastify-plugin) break encapsulation? It would make sense if I could use fastify-plugin dependencies field, but nothing like this is available in pure fastify plugins and I have no clear indicator that tells me that I forgot to provide a dependency to the encapsulated plugin
2. Relying on shared plugins also makes testing harder, as I need to remember and provide all required plugins in the test (with all configurations)

So my question is: is it a better practice to encapsulate every dependency in a plugin, or rather provide all the shared functionality from a higher-level fastify instance? If the latter, then how do I ensure that these dependencies are present (should I do a manual check?)

I hope I've explained my issue well so it's clear. If not, just ask 😄

[mcollina]

First, you should likely await for getting a database instance:

module.exports = async fastify => {
    const db = await somedb('conn.string');
    fastify.get('/users/:id', (request, reply) => {
        // db operations
    });
    // other endpoints
}

The plugin/decorator system makes it clear what are the dependencies.

1. but nothing like this is available in pure fastify plugins

That logic is actually as part of fastify, not fastify-plugin. I think we should just expose it. Would you like to propose some API for this?

Note that they all works via https://github.com/fastify/fastify-plugin/blob/master/index.js#L37.

[jsardev]

First, you should likely await for getting a database instance

Yeah, that was just an example, I didn't want to make it proper code.

The plugin/decorator system makes it clear what are the dependencies

I don't understand how it makes it clear what are the dependencies? If I'm using fastify-mongodb on the app-level and fastify.mongo (or whatever else) on my internal plugin-level then how do I know what kind of dependency does my plugin need?

The dependencies meta key would make it much more clear.

Would you like to propose some API for this?

I'm sorry but I can't right now 😢

[stale]

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