add webhook creation utility

m2d/actions/register-webhook.js

@@ -0,0 +1,50 @@
+// @ts-check
+
+const assert = require("assert").strict
+const passthrough = require("../../passthrough")
+const {discord, db} = passthrough
+
+/**
+ * Look in the database to find webhook credentials for a channel.
+ * (Note that the credentials may be invalid and need to be re-created if the webhook was interfered with from outside.)
+ * @param {string} channelID
+ * @param {boolean} forceCreate create a new webhook no matter what the database says about the state
+ * @returns id and token for a webhook for that channel
+ */
+async function ensureWebhook(channelID, forceCreate = false) {
+	if (!forceCreate) {
+		/** @type {{id: string, token: string} | null} */
+		const row = db.prepare("SELECT webhook_id as id, webhook_token as token FROM webhook WHERE channel_id = ?").get(channelID)
+		if (row) {
+			return {created: false, ...row}
+		}
+	}
+
+	// If we got here, we need to create a new webhook.
+	const webhook = await discord.snow.webhook.createWebhook(channelID, {name: "Out Of Your Element: Matrix Bridge"})
+	assert(webhook.token)
+	db.prepare("REPLACE INTO webhook (channel_id, webhook_id, webhook_token) VALUES (?, ?, ?)").run(channelID, webhook.id, webhook.token)
+	return {
+		id: webhook.id,
+		token: webhook.token,
+		created: true
+	}
+}
+
+/**
+ * @param {string} channelID
+ * @param {(webhook: import("../../types").WebhookCreds) => Promise<T>} callback
+ * @returns Promise<T>
+ * @template T
+ */
+async function withWebhook(channelID, callback) {
+	const webhook = await ensureWebhook(channelID, false)
+	return callback(webhook).catch(e => {
+		console.error(e)
+		// TODO: check if the error was webhook-related and if webhook.created === false, then: const webhook = ensureWebhook(channelID, true); return callback(webhook)
+		throw new Error(e)
+	})
+}
+
+module.exports.ensureWebhook = ensureWebhook
+module.exports.withWebhook = withWebhook

m2d/actions/send-message.js

@@ -0,0 +1,23 @@
+// @ts-check
+
+const assert = require("assert").strict
+const DiscordTypes = require("discord-api-types/v10")
+const passthrough = require("../../passthrough")
+const {sync, discord, db} = passthrough
+
+/** @type {import("./register-webhook")} */
+const registerWebhook = sync.require("./register-webhook")
+
+/**
+ * @param {string} channelID
+ * @param {DiscordTypes.RESTPostAPIWebhookWithTokenJSONBody & {name: string, file: Buffer}[]} data
+ */
+// param {DiscordTypes.RESTPostAPIWebhookWithTokenQuery & {wait: true, disableEveryone?: boolean}} options
+async function sendMessage(channelID, data) {
+   const result = await registerWebhook.withWebhook(channelID, async webhook => {
+      return discord.snow.webhook.executeWebhook(webhook.id, webhook.token, data, {wait: true, disableEveryone: true})
+   })
+   return result
+}
+
+module.exports.sendMessage = sendMessage

test/test.js

@@ -17,3 +17,4 @@ require("../matrix/read-registration.test")
 require("../d2m/converters/message-to-event.test")
 require("../d2m/actions/create-room.test")
 require("../d2m/converters/user-to-mxid.test")
+require("../d2m/actions/register-user.test")

types.d.ts

@@ -9,6 +9,11 @@ export type AppServiceRegistrationConfig = {
 	rate_limited: boolean
 }
 
+export type WebhookCreds = {
+	id: string
+	token: string
+}
+
 namespace Event {
 	export type BaseStateEvent = {
 		type: string