chore: fix backend activitypub.ts lints and logic

lints: mostly function signatures
logic: remote user logic is incorrect and overly lengthy,
       public key checks are leaky
TODO:  default export lint

packages/backend/src/server/activitypub.ts

@@ -25,7 +25,7 @@ const router = new Router();
 
 //#region Routing
 
-function inbox(ctx: Router.RouterContext) {
+function inbox(ctx: Router.RouterContext): void {
 	let signature;
 
 	try {
@@ -43,13 +43,13 @@ function inbox(ctx: Router.RouterContext) {
 const ACTIVITY_JSON = 'application/activity+json; charset=utf-8';
 const LD_JSON = 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"; charset=utf-8';
 
-function isActivityPubReq(ctx: Router.RouterContext) {
+function isActivityPubReq(ctx: Router.RouterContext): boolean {
 	ctx.response.vary('Accept');
 	const accepted = ctx.accepts('html', ACTIVITY_JSON, LD_JSON);
 	return typeof accepted === 'string' && !accepted.match(/html/);
 }
 
-export function setResponseType(ctx: Router.RouterContext) {
+export function setResponseType(ctx: Router.RouterContext): void {
 	const accept = ctx.accepts(ACTIVITY_JSON, LD_JSON);
 	if (accept === LD_JSON) {
 		ctx.response.type = LD_JSON;
@@ -77,13 +77,9 @@ router.get('/notes/:note', async (ctx, next) => {
 		return;
 	}
 
-	// リモートだったらリダイレクト
-	if (note.userHost != null) {
-		if (note.uri == null || isSelfHost(note.userHost)) {
-			ctx.status = 500;
-			return;
-		}
-		ctx.redirect(note.uri);
+	if (!isSelfHost(note.userHost)) {
+		if (note.uri != null) ctx.redirect(note.uri);
+		else ctx.status = 500;
 		return;
 	}
 
@@ -132,24 +128,19 @@ router.get('/users/:user/publickey', async ctx => {
 		host: IsNull(),
 	});
 
-	if (user == null) {
+	if (user == null || !Users.isLocalUser(user)) {
 		ctx.status = 404;
 		return;
 	}
 
 	const keypair = await getUserKeypair(user.id);
-
-	if (Users.isLocalUser(user)) {
-		ctx.body = renderActivity(renderKey(user, keypair));
-		ctx.set('Cache-Control', 'public, max-age=180');
-		setResponseType(ctx);
-	} else {
-		ctx.status = 400;
-	}
+	ctx.body = renderActivity(renderKey(user, keypair));
+	ctx.set('Cache-Control', 'public, max-age=180');
+	setResponseType(ctx);
 });
 
 // user
-async function userInfo(ctx: Router.RouterContext, user: User | null) {
+async function userInfo(ctx: Router.RouterContext, user: User | null): void {
 	if (user == null) {
 		ctx.status = 404;
 		return;