Support "Block" operations on ActivityPub

* TODO: inhibit interactions on our side from a blocked Actor

api/src/activity/federation.js

@@ -1,4 +1,27 @@
+async function areActorsValid(actors, ourDomain) {
+	if (!actors instanceof Array && typeof actors !== 'string') {
+		console.error('Unexpected type of "actors" in "federation.doesActorsExistAndOurs"')
+		return false
+	}
+	if (typeof actors === 'string') actors = [actors]
+	for (var i = 0; i < actors.length; i++) {
+		let url
+		try { url = new URL(actors[i]) }
+		catch (e) { return false }
+		if (ourDomain && url.hostname !== apex.domain)
+			return false
+
+		actors[i] = url.href
+		const actor = await apex.store.getObject(actors[i])
+		// TODO: check account is deleted/disabled/banned/...?
+		if (actor === null || actor.type !== 'Person')
+			return false
+	}
+	return true
+}
+
 module.exports = {
+	areActorsValid,
 	inbox: async (msg) => {
 		// TODO: add logging for every matches params
 		if (msg.activity.type === 'Reject' && msg.object.type === 'Follow')
@@ -8,14 +31,20 @@ module.exports = {
 				follow.rejected = true
 				await db.table.objects().replaceOne({ _id: follow._id }, follow)
 			}
-			return true;
+			return true
+		}
+		if (msg.activity.type === 'Block')
+		{
+			if (areActorsValid(msg.activity.object, true))
+				await apex.store.saveObject(msg.activity)
+			return true
 		}
 		if (msg.activity.type === 'Undo')
 		{
 			if (msg.object.type === 'Block') {
 				await db.table.objects().deleteOne(
 					{ id: msg.object.id, type: 'Block' })
-				return true;
+				return true
 			}
 		}