Proposal to allow updating client connection

[seanwarmanshine]

• I'm submitting a ...
  [ ] bug report
  [ X ] feature request
  [ ] question about the decisions made in the repository
  [ ] question about how to use this project

• Summary
  Client connections are currently a one-time operation that has it's set up code inside the MongoStore constructor. I like to have a method that allows developers to swap out the client connection after MongoStore has been instantiated.

This feature would address issues where a MongoDB connection is closed, which currently crashes connect-mongo as it's not able to swap out the original disconnected client. It could also be useful for other circumstances.

• Other information (e.g. detailed explanation, stack traces, related issues, suggestions how to fix, links for us to have context, eg. StackOverflow, personal fork, etc.)

I've built a fix for this that basically just moves most of the constructor logic into a method called connectClient and calls that method from the constructor instead:

class MongoStore extends session.Store {
    constructor({ collectionName = 'sessions', ttl = 1209600, mongoOptions = {}, autoRemove = 'native', autoRemoveInterval = 10, touchAfter = 0, stringify = true, crypto, ...required }) {
        super();
        this.crypto = null;
        debug('create MongoStore instance');
        this.connectClient({ collectionName, ttl, mongoOptions, autoRemove, autoRemoveInterval, touchAfter, stringify, crypto, ...required });
    }
    connectClient({ collectionName = 'sessions', ttl = 1209600, mongoOptions = {}, autoRemove = 'native', autoRemoveInterval = 10, touchAfter = 0, stringify = true, crypto, ...required }) {
        const options = {
            collectionName,
            ttl,
            mongoOptions,
            autoRemove,
            autoRemoveInterval,
            // Connection logic etc...
    }
    // Rest of class logic...
}

This allows the developer to swap out a client whenever they want:

const store = MongoStore.create({
  client: mongoose.connection.getClient(),
});

// Later at any time...
store.connectClient({ client: connection.getClient() });