Snowpack custom headers plugin

package.json

{
  "name": "snowpack-custom-headers",
  "version": "0.0.1",
  "description": "",
  "main": "snowpack-custom-headers.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Samuel Seay",
  "license": "MIT",
  "dependencies": {
    "http-proxy": "^1.18.1",
    "execa": "^5.1.1"
  }
}

proxy-server.js

const http = require("http"),
  httpProxy = require("http-proxy");

var proxy = httpProxy.createProxyServer({});

const {
  sch_headers: headers,
  sch_port: port,
  sch_secure: secure,
  sch_hostname: hostname,
  sch_proxy_port: proxy_port,
} = process.env;

const headersObj = headers.split(",").reduce((acc, curr) => {
  return {
    ...acc,
    [curr.split(":")[0]]: curr.split(":")[1],
  };
}, {});

proxy.on("proxyRes", function (proxyRes, req, res, options) {
  Object.entries(headersObj).forEach(([key, val]) => {
    proxyRes.headers[key] = val;
  });
});

var server = http.createServer(function (req, res) {
  proxy.web(req, res, {
    target: `${secure === "true" ? "https" : "http"}://${hostname}:${port}`,
  });
});

console.log(`Proxying headers on port ${proxy_port}`);

server.listen(proxy_port);

snowpack-custom-headers.js

const execa = require("execa");

module.exports = function (snowpackConfig, pluginOptions) {
  return {
    name: "snowpack-custom-headers",
    async run({ log }) {
      const port = pluginOptions.port || "9001";
      log(`proxying headers on port ${port}`);

      const workerPromise = execa.node(`./proxy-server.js`, {
        env: {
          sch_proxy_port: port,
          sch_port: snowpackConfig.devOptions.port,
          sch_hostname: snowpackConfig.devOptions.hostname,
          sch_secure: snowpackConfig.devOptions.secure,
          sch_headers: Object.entries(pluginOptions.headers)
            .map(([key, val]) => `${key}:${val}`)
            .join(","),
        },
        extendEnv: true,
        windowsHide: false,
        cwd: __dirname,
      });

      try {
        execa.commandSync(
          `open "${snowpackConfig.devOptions.secure ? "https://" : "http://"}${
            snowpackConfig.devOptions.hostname
          }:${port}"`,
          { shell: true }
        );
      } catch (err) {
        console.log(err);
      }

      const { stdout, stderr } = workerPromise;

      function dataListener(chunk) {
        let stdOutput = chunk.toString();
        log("WORKER_MSG", { msg: stdOutput });
      }

      stdout && stdout.on("data", dataListener);
      stderr && stderr.on("data", dataListener);

      return workerPromise.catch((err) => {
        if (/ENOENT/.test(err.message)) {
          log("WORKER_MSG", {
            msg: 'WARN: "snowpack custom headers" run failed.',
          });
        }
        throw err;
      });
    },
  };
};

snowpack.config.mjs

export default {
  devOptions: {
    open: "none",
    port: 9000,
  },

  plugins: [
    [
      "snowpack-custom-headers",
      {
        headers: {
          "Cross-Origin-Opener-Policy": "same-origin",
          "Cross-Origin-Embedder-Policy": "require-corp",
        },
      },
    ],
  ],
};