misskey/packages/backend/src/remote/activitypub/kernel/follow.ts

import { IRemoteUser } from '@/models/entities/user.js';
import follow from '@/services/following/create.js';
import { IFollow } from '../type.js';
import DbResolver from '../db-resolver.js';

export default async (actor: IRemoteUser, activity: IFollow): Promise<string> => {
	const dbResolver = new DbResolver();
	const followee = await dbResolver.getUserFromApId(activity.object);

	if (followee == null) {
		return `skip: followee not found`;
	}

	if (followee.host != null) {
		return `skip: フォローしようとしているユーザーはローカルユーザーではありません`;
	}

	await follow(actor, followee, activity.id);
	return `ok`;
};