How to Use KnoxProxy with MCP Servers

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";
import { ProxyAgent, fetch as undiciFetch } from "undici";

const PROXY_HOST = "gw.knoxproxy.com";
const PROXY_PORT = 7000;
const PROXY_USER = process.env.KNOX_PROXY_USER ?? "USER";
const PROXY_PASS = process.env.KNOX_PROXY_PASS ?? "PASS";

function buildProxyUrl(country?: string, sessionId?: string): string {
  let username = PROXY_USER;
  if (country) username += `-country-${country}`;
  if (sessionId) username += `-session-${sessionId}`;
  return `http://${username}:${PROXY_PASS}@${PROXY_HOST}:${PROXY_PORT}`;
}

async function proxiedFetch(
  url: string,
  country?: string,
  sessionId?: string,
): Promise<string> {
  const proxyUrl = buildProxyUrl(country, sessionId);
  const dispatcher = new ProxyAgent(proxyUrl);
  const response = await undiciFetch(url, { dispatcher });
  if (!response.ok) {
    throw new Error(`HTTP ${response.status}: ${response.statusText}`);
  }
  return await response.text();
}

const server = new McpServer({
  name: "web-fetcher",
  version: "1.0.0",
});

server.tool(
  "fetch_page",
  "Fetch a web page through KnoxProxy with optional geo-targeting",
  {
    url: z.string().url().describe("URL to fetch"),
    country: z.string().length(2).optional()
      .describe("ISO country code for geo-targeting (e.g., us, de, jp)"),
  },
  async ({ url, country }) => {
    const html = await proxiedFetch(url, country);
    // Strip HTML tags for cleaner LLM consumption
    const text = html.replace(/<[^>]*>/g, " ").replace(/\s+/g, " ").trim();
    return {
      content: [{ type: "text", text: text.slice(0, 50000) }],
    };
  },
);

server.tool(
  "check_ip",
  "Check the current proxy IP address and location",
  {
    country: z.string().length(2).optional()
      .describe("ISO country code to verify geo-targeting"),
  },
  async ({ country }) => {
    const result = await proxiedFetch("https://httpbin.org/ip", country);
    return {
      content: [{ type: "text", text: result }],
    };
  },
);

const transport = new StdioServerTransport();
await server.connect(transport);