TypeScript: Vercel AI SDK

// securdGuard.ts
// Held and blocked names resolve to the policy's block page address.
// Put that address (from the console, Sites > your site) in SECURD_BLOCK_ADDRS.
import { promises as dns } from "node:dns";

const BLOCK_ADDRS = new Set((process.env.SECURD_BLOCK_ADDRS ?? "").split(",").filter(Boolean));

export class SecurdHeld extends Error {
  constructor(public host: string, public agentRole: string) {
    super(`${host} is held or blocked for ${agentRole}`);
  }
}

export async function securdGuard(host: string, agentRole: string): Promise<void> {
  let answers: string[];
  try {
    answers = (await dns.lookup(host, { all: true })).map((a) => a.address);
  } catch {
    console.warn(JSON.stringify({ event: "securd.unresolved", agentRole, host }));
    throw new SecurdHeld(host, agentRole);
  }
  if (answers.some((a) => BLOCK_ADDRS.has(a))) {
    console.warn(JSON.stringify({ event: "securd.held", agentRole, host }));
    throw new SecurdHeld(host, agentRole);
  }
}

import { tool } from "ai";
import { z } from "zod";
import { securdGuard, SecurdHeld } from "./securdGuard";

const AGENT_ROLE = "chat-assistant";

export const fetchJson = tool({
  description: "GET JSON from an approved API.",
  parameters: z.object({ url: z.string().url() }),
  execute: async ({ url }) => {
    const host = new URL(url).hostname;
    try {
      await securdGuard(host, AGENT_ROLE);
    } catch (e) {
      if (e instanceof SecurdHeld) return { status: "held", host, reason: e.message };
      throw e;
    }
    return (await fetch(url)).json();
  },
});