username sanitisation for registration

d2m/converters/user-to-mxid.js

@@ -0,0 +1,74 @@
+// @ts-check
+
+const assert = require("assert")
+
+const passthrough = require("../../passthrough")
+const { sync, db } = passthrough
+
+/**
+ * Downcased and stripped username. Can only include a basic set of characters.
+ * https://spec.matrix.org/v1.6/appendices/#user-identifiers
+ * @param {import("discord-api-types/v10").APIUser} user
+ * @returns {string} localpart
+ */
+function downcaseUsername(user) {
+	// First, try to convert the username to the set of allowed characters
+	let downcased = user.username.toLowerCase()
+		// spaces to underscores...
+		.replace(/ /g, "_")
+		// remove disallowed characters...
+		.replace(/[^a-z0-9._=/-]*/g, "")
+		// remove leading and trailing dashes and underscores...
+		.replace(/(?:^[_-]*|[_-]*$)/g, "")
+	// The new length must be at least 2 characters (in other words, it should have some content)
+	if (downcased.length < 2) {
+		downcased = user.id
+	}
+	return downcased
+}
+
+/** @param {string[]} preferences */
+function* generateLocalpartAlternatives(preferences) {
+	const best = preferences[0]
+	assert.ok(best)
+	// First, suggest the preferences...
+	for (const localpart of preferences) {
+		yield localpart
+	}
+	// ...then fall back to generating number suffixes...
+	let i = 2
+	while (true) {
+		yield best + (i++)
+	}
+}
+
+/**
+ * @param {import("discord-api-types/v10").APIUser} user
+ * @returns {string}
+ */
+function userToSimName(user) {
+	assert.notEqual(user.discriminator, "0000", "cannot create user for a webhook")
+
+	// 1. Is sim user already registered?
+	const existing = db.prepare("SELECT sim_name FROM sim WHERE discord_id = ?").pluck().get(user.id)
+	if (existing) return existing
+
+	// 2. Register based on username (could be new or old format)
+	const downcased = downcaseUsername(user)
+	const preferences = [downcased]
+	if (user.discriminator.length === 4) { // Old style tag? If user.username is unavailable, try the full tag next
+		preferences.push(downcased + user.discriminator)
+	}
+
+	// Check for conflicts with already registered sims
+	/** @type {string[]} */
+	const matches = db.prepare("SELECT sim_name FROM sim WHERE sim_name LIKE ? ESCAPE '@'").pluck().all(downcased + "%")
+	// Keep generating until we get a suggestion that doesn't conflict
+	for (const suggestion of generateLocalpartAlternatives(preferences)) {
+		if (!matches.includes(suggestion)) return suggestion
+	}
+
+	throw new Error(`Ran out of suggestions when generating sim name. downcased: "${downcased}"`)
+}
+
+module.exports.userToSimName = userToSimName