frontend api proxy

proxy.ts

import httpProxy from "http-proxy";
import { NextApiRequest, NextApiResponse } from "next";
import { env } from "runtime-injector";

export const config = {
  api: {
    bodyParser: false,
    externalResolver: true,
  },
};

const isDev = process.env.NODE_ENV === "development";

const isCorsHeader = (header: string) =>
  header.toLowerCase().startsWith("access-control-");

const getQueryString = (req: NextApiRequest) => {
  const url = req.url;
  if (!url) return "";
  const indexStart = url.indexOf("?");
  if (indexStart === -1) return "";
  return url.substring(indexStart);
};

let server: any;
const proxy = httpProxy.createProxy().on("proxyRes", (proxyRes, req, res) => {
  const origin = req.headers.origin || "*";

  // Rewrite CORS header
  if ("origin" in req.headers) {
    res.setHeader("access-control-allow-origin", origin);
    res.setHeader("access-control-allow-credentials", "true");
  }

  if (req.headers["access-control-request-method"]) {
    res.setHeader(
      "access-control-allow-methods",
      req.headers["access-control-request-method"]
    );
  }

  if (req.headers["access-control-request-headers"]) {
    res.setHeader(
      "access-control-allow-headers",
      req.headers["access-control-request-headers"]
    );
  }
});

const Page = async (req: NextApiRequest, res: NextApiResponse<any>) => {
  if (!isDev) {
    res.status(400).end();
    return;
  }

  const proxyTarget = env.NEXT_PUBLIC_PROXY_TARGET;
  const proxyTargetCms = env.NEXT_PUBLIC_PROXY_TARGET_CMS;
  const wsProxyTarget = env.NEXT_PUBLIC_CRYPTO_WS_PROXY_TARGET;

  if (!proxyTarget) {
    res.status(500).send({
      error:
        "environment variable `NEXT_PUBLIC_PROXY_TARGET` needs to be presented for api proxy to work",
    });
    return;
  }

  if (!proxyTargetCms) {
    res.status(500).send({
      error:
        "environment variable `NEXT_PUBLIC_PROXY_TARGET_CMS` needs to be presented for api proxy to work",
    });
    return;
  }

  const { slug = [] } = req.query;

  const target =
    Array.isArray(slug) && slug[0] === "cms" ? proxyTargetCms : proxyTarget;

  const path = Array.isArray(slug) ? slug.join("/") : slug;
  const queryString = getQueryString(req);
  req.url = path + queryString;

  if (wsProxyTarget /* enable WebSocket proxying */ && !server) {
    server = (res.socket as any)?.server;
    server.on("upgrade", (req: any, socket: any, head: any) => {
      if (!req.url.startsWith("/api/proxy/ws")) return;

      req.url = req.url.replace(/^\/api\/proxy\/ws/, "");
      req.headers.host = wsProxyTarget.replace(/^wss?:\/\//, "");

      proxy.ws(req, socket, head, {
        target: wsProxyTarget,
      });
    });
  }

  proxy.web(req, res, {
    changeOrigin: true,
    target: target,
    cookieDomainRewrite: "localhost",
  });
};

export default Page;