Code.gs

/**
 * DomainFront Relay — Google Apps Script
 *
 * TWO modes:
 *   1. Single:  POST { k, m, u, h, b, ct, r }       → { s, h, b }
 *   2. Batch:   POST { k, q: [{m,u,h,b,ct,r}, ...] } → { q: [{s,h,b}, ...] }
 *      Uses UrlFetchApp.fetchAll() — all URLs fetched IN PARALLEL.
 *
 * DEPLOYMENT:
 *   1. Go to https://script.google.com → New project
 *   2. Delete the default code, paste THIS entire file
 *   3. Click Deploy → New deployment
 *   4. Type: Web app  |  Execute as: Me  |  Who has access: Anyone
 *   5. Copy the Deployment ID into config.json as "script_id"
 *
 * CHANGE THE AUTH KEY BELOW TO YOUR OWN SECRET!
 */

const AUTH_KEY = "ENTER AUTH CODE HERE";

// Leave empty to keep Apps Script's default user agent.
const FORCE_USER_AGENT = "Mozilla/5.0";

// Forward only headers that are usually needed for normal HTTP semantics.
// Add more here if a target site genuinely requires them.
const ALLOW_HEADERS = {
  accept: 1,
  "accept-language": 1,
  "accept-encoding": 1,
  authorization: 1,
  cookie: 1,
  "cache-control": 1,
  pragma: 1,
  range: 1,
  "if-match": 1,
  "if-none-match": 1,
  "if-modified-since": 1,
  "if-unmodified-since": 1,
  "if-range": 1,
};

const SKIP_HEADERS = {
  host: 1, connection: 1, "content-length": 1,
  "transfer-encoding": 1, "proxy-connection": 1, "proxy-authorization": 1,
  "forwarded": 1, "via": 1,
  "x-forwarded-for": 1, "x-forwarded-host": 1, "x-forwarded-proto": 1,
  "x-forwarded-port": 1, "x-forwarded-server": 1,
  "x-real-ip": 1, "x-client-ip": 1, "client-ip": 1,
  "true-client-ip": 1, "cf-connecting-ip": 1, "fastly-client-ip": 1,
  "fly-client-ip": 1, "x-cluster-client-ip": 1, "x-originating-ip": 1,
  "proxy-client-ip": 1, "wl-proxy-client-ip": 1, "x-proxyuser-ip": 1,
  "remote-addr": 1, origin: 1, referer: 1,
  "user-agent": 1,
};

function _trim(s) {
  return String(s).replace(/^\s+|\s+$/g, "");
}

function _headerName(k) {
  return _trim(k).toLowerCase();
}

function _shouldForwardHeader(k) {
  var name = _headerName(k);
  return !!name && ALLOW_HEADERS[name] && !SKIP_HEADERS[name];
}

function doPost(e) {
  try {
    var req = JSON.parse(e.postData.contents);
    if (req.k !== AUTH_KEY) return _json({ e: "unauthorized" });

    // Batch mode: { k, q: [...] }
    if (Array.isArray(req.q)) return _doBatch(req.q);

    // Single mode
    return _doSingle(req);
  } catch (err) {
    return _json({ e: String(err) });
  }
}

function _doSingle(req) {
  if (!req.u || typeof req.u !== "string" || !req.u.match(/^https?:\/\//i)) {
    return _json({ e: "bad url" });
  }
  var opts = _buildOpts(req);
  var resp = UrlFetchApp.fetch(req.u, opts);
  return _json({
    s: resp.getResponseCode(),
    h: resp.getHeaders(),
    b: Utilities.base64Encode(resp.getContent()),
  });
}

function _doBatch(items) {
  var fetchArgs = [];
  var errorMap = {};

  for (var i = 0; i < items.length; i++) {
    var item = items[i];
    if (!item.u || typeof item.u !== "string" || !item.u.match(/^https?:\/\//i)) {
      errorMap[i] = "bad url";
      continue;
    }
    var opts = _buildOpts(item);
    opts.url = item.u;
    fetchArgs.push({ _i: i, _o: opts });
  }

  // fetchAll() processes all requests in parallel inside Google
  var responses = [];
  if (fetchArgs.length > 0) {
    responses = UrlFetchApp.fetchAll(fetchArgs.map(function(x) { return x._o; }));
  }

  var results = [];
  var rIdx = 0;
  for (var i = 0; i < items.length; i++) {
    if (errorMap.hasOwnProperty(i)) {
      results.push({ e: errorMap[i] });
    } else {
      var resp = responses[rIdx++];
      results.push({
        s: resp.getResponseCode(),
        h: resp.getHeaders(),
        b: Utilities.base64Encode(resp.getContent()),
      });
    }
  }
  return _json({ q: results });
}

function _buildOpts(req) {
  var opts = {
    method: (req.m || "GET").toLowerCase(),
    muteHttpExceptions: true,
    followRedirects: req.r !== false,
    validateHttpsCertificates: true,
  };
  if (req.h && typeof req.h === "object") {
    var headers = {};
    for (var k in req.h) {
      if (req.h.hasOwnProperty(k) && _shouldForwardHeader(k)) {
        headers[_trim(k)] = req.h[k];
      }
    }
    if (FORCE_USER_AGENT) headers["User-Agent"] = FORCE_USER_AGENT;
    opts.headers = headers;
  } else if (FORCE_USER_AGENT) {
    opts.headers = { "User-Agent": FORCE_USER_AGENT };
  }
  if (req.b) {
    opts.payload = Utilities.base64Decode(req.b);
    if (req.ct) opts.contentType = req.ct;
  }
  return opts;
}

function doGet(e) {
  return HtmlService.createHtmlOutput(
    "<!DOCTYPE html><html><head><title>My App</title></head>" +
      '<body style="font-family:sans-serif;max-width:600px;margin:40px auto">' +
      "<h1>Welcome</h1><p>This application is running normally.</p>" +
      "</body></html>"
  );
}

function _json(obj) {
  return ContentService.createTextOutput(JSON.stringify(obj)).setMimeType(
    ContentService.MimeType.JSON
  );
}