/**
* 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.
*
* OPTIONAL SPREADSHEET-BACKED RESPONSE CACHE:
* Set CACHE_SPREADSHEET_ID to a valid Google Sheet ID (must be owned by
* the same account). When enabled, public GET requests are stored in the
* sheet and served from there on repeat visits, reducing UrlFetchApp
* quota consumption. The cache is Vary-aware (Accept-Encoding and
* Accept-Language are hashed into the compound cache key). Leave
* CACHE_SPREADSHEET_ID as-is to disable caching entirely — zero overhead.
*
* DEPLOYMENT:
* 1. Go to https://script.google.com → New project
* 2. Delete the default code, paste THIS entire file
* 3. Change AUTH_KEY below to your own secret
* 4. (Optional) Set CACHE_SPREADSHEET_ID to enable caching
* 5. Click Deploy → New deployment
* 6. Type: Web app | Execute as: Me | Who has access: Anyone
* 7. Copy the Deployment ID into config.json as "script_id"
*
* CHANGE THE AUTH KEY BELOW TO YOUR OWN SECRET!
*/
const AUTH_KEY = "CHANGE_ME_TO_A_STRONG_SECRET";
// Active-probing defense. When false (production default), bad AUTH_KEY
// requests get a decoy HTML page that looks like a placeholder Apps
// Script web app instead of the JSON `{"e":"unauthorized"}` body. This
// makes the deployment indistinguishable from a forgotten-but-public
// Apps Script project to active scanners that POST malformed payloads
// looking for proxy endpoints.
//
// Set to `true` during initial setup if a misconfigured client is
// hitting "unauthorized" and you want the explicit JSON error to debug
// — then flip back to false before the deployment is widely shared.
// (Inspired by #365 Section 3, mhrv-rs v1.8.0+.)
const DIAGNOSTIC_MODE = false;
// ── Optional Spreadsheet Cache ──────────────────────────────
// Set to a valid Spreadsheet ID to enable response caching.
// Leave as-is to disable caching entirely (zero overhead).
const CACHE_SPREADSHEET_ID = "CHANGE_ME_TO_CACHE_SPREADSHEET_ID";
const CACHE_SHEET_NAME = "RelayCache";
const CACHE_META_SHEET_NAME = "RelayMeta";
const CACHE_META_CURSOR_CELL = "A1";
// ── Cache Tuning ────────────────────────────────────────────
const CACHE_MAX_ROWS = 5000; // circular buffer capacity
const CACHE_MAX_BODY_BYTES = 35000; // skip responses larger than ~35 KB
const CACHE_DEFAULT_TTL_SECONDS = 86400; // 24-hour fallback when no Cache-Control
// ── Vary-Aware Cache Key ────────────────────────────────────
// These request headers are hashed into the compound cache key
// alongside the URL so that responses with different encodings
// or languages never collide in the cache. Covers ~95 % of
// real-world Vary usage without inspecting the response.
const VARY_KEY_HEADERS = ["accept-encoding", "accept-language"];
// Keep browser capability headers (sec-ch-ua*, sec-fetch-*) intact.
// Some modern apps, notably Google Meet, use them for browser gating.
const SKIP_HEADERS = {
host: 1, connection: 1, "content-length": 1,
"transfer-encoding": 1, "proxy-connection": 1, "proxy-authorization": 1,
"priority": 1, te: 1,
};
// Headers that disqualify a request from the cache path.
const CACHE_BUSTING_HEADERS = {
authorization: 1, cookie: 1, "x-api-key": 1,
"proxy-authorization": 1, "set-cookie": 1,
};
// HTML body for the bad-auth decoy. Mimics a minimal Apps Script-style
// placeholder page — no proxy-shaped JSON, nothing distinctive enough
// for a probe to fingerprint as a tunnel endpoint.
const DECOY_HTML =
'Web App' +
'The script completed but did not return anything.
' +
'';
// ── Request Handlers ────────────────────────────────────────
function _decoyOrError(jsonBody) {
if (DIAGNOSTIC_MODE) return _json(jsonBody);
return ContentService
.createTextOutput(DECOY_HTML)
.setMimeType(ContentService.MimeType.HTML);
}
function doPost(e) {
try {
var req = JSON.parse(e.postData.contents);
if (req.k !== AUTH_KEY) return _decoyOrError({ e: "unauthorized" });
// Batch mode: { k, q: [...] }
if (Array.isArray(req.q)) return _doBatch(req.q);
// Single mode
return _doSingle(req);
} catch (err) {
// Parse failures of the request body are also probe-shaped — a real
// mhrv-rs client never sends invalid JSON. Decoy for the same reason.
return _decoyOrError({ e: String(err) });
}
}
// `doGet` is what active scanners hit first (HTTP GET probes are cheaper
// than POSTs). Apps Script defaults to a "Script function not found" page
// here which is a fine-enough decoy on its own, but explicitly returning
// the same harmless placeholder makes the response identical to the
// bad-auth POST decoy — one less fingerprint vector.
function doGet(e) {
return ContentService
.createTextOutput(DECOY_HTML)
.setMimeType(ContentService.MimeType.HTML);
}
// ── Single Request ─────────────────────────────────────────
function _doSingle(req) {
if (!req.u || typeof req.u !== "string" || !req.u.match(/^https?:\/\//i)) {
return _json({ e: "bad url" });
}
// ── Optional cache path ────────────────────────────────
// Only entered when CACHE_SPREADSHEET_ID is configured and
// the request qualifies as a public, cachable GET.
if (_canUseCache(req)) {
var cached = _getFromCache(req.u, req.h);
if (cached) {
return _json({
s: cached.status,
h: JSON.parse(cached.headers),
b: cached.body,
cached: true,
});
}
var fetchResult = _fetchAndCache(req.u, req.h);
if (fetchResult) {
return _json({
s: fetchResult.status,
h: JSON.parse(fetchResult.headers),
b: fetchResult.body,
cached: false,
});
}
// If _fetchAndCache returns null (spreadsheet unavailable),
// fall through to the normal relay path below.
}
// ── Normal relay (cache disabled or unavailable) ────────
var opts = _buildOpts(req);
var resp = UrlFetchApp.fetch(req.u, opts);
return _json({
s: resp.getResponseCode(),
h: _respHeaders(resp),
b: Utilities.base64Encode(resp.getContent()),
});
}
// ── Batch Request ──────────────────────────────────────────
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: _respHeaders(resp),
b: Utilities.base64Encode(resp.getContent()),
});
}
}
return _json({ q: results });
}
// ── Request Building ───────────────────────────────────────
function _buildOpts(req) {
var opts = {
method: (req.m || "GET").toLowerCase(),
muteHttpExceptions: true,
followRedirects: req.r !== false,
validateHttpsCertificates: true,
escaping: false,
};
if (req.h && typeof req.h === "object") {
var headers = {};
for (var k in req.h) {
if (req.h.hasOwnProperty(k) && !SKIP_HEADERS[k.toLowerCase()]) {
headers[k] = req.h[k];
}
}
opts.headers = headers;
}
if (req.b) {
opts.payload = Utilities.base64Decode(req.b);
if (req.ct) opts.contentType = req.ct;
}
return opts;
}
function _respHeaders(resp) {
try {
if (typeof resp.getAllHeaders === "function") {
return resp.getAllHeaders();
}
} catch (err) {}
return resp.getHeaders();
}
function doGet(e) {
return HtmlService.createHtmlOutput(
"My App" +
'' +
"Welcome
This application is running normally.
" +
""
);
}
function _json(obj) {
return ContentService.createTextOutput(JSON.stringify(obj)).setMimeType(
ContentService.MimeType.JSON
);
}
// ═══════════════════════════════════════════════════════════
// SPREADSHEET CACHE — SHEET MANAGEMENT
// ═══════════════════════════════════════════════════════════
function _initCacheSheet() {
if (CACHE_SPREADSHEET_ID === "CHANGE_ME_TO_CACHE_SPREADSHEET_ID") {
return null;
}
try {
var ss = SpreadsheetApp.openById(CACHE_SPREADSHEET_ID);
var sheet = ss.getSheetByName(CACHE_SHEET_NAME);
if (!sheet) {
sheet = ss.insertSheet(CACHE_SHEET_NAME);
// Schema: URL_Hash | URL | Status | Headers | Body | Timestamp | Expires_At
sheet.getRange(1, 1, 1, 7).setValues([[
"URL_Hash", "URL", "Status", "Headers", "Body", "Timestamp", "Expires_At"
]]);
}
return sheet;
} catch (e) {
return null;
}
}
function _getMetaSheet() {
if (CACHE_SPREADSHEET_ID === "CHANGE_ME_TO_CACHE_SPREADSHEET_ID") {
return null;
}
try {
var ss = SpreadsheetApp.openById(CACHE_SPREADSHEET_ID);
var sheet = ss.getSheetByName(CACHE_META_SHEET_NAME);
if (!sheet) {
sheet = ss.insertSheet(CACHE_META_SHEET_NAME);
sheet.getRange(CACHE_META_CURSOR_CELL).setValue(2);
sheet.hideSheet();
}
return sheet;
} catch (e) {
return null;
}
}
function _getNextCursor(sheet, metaSheet) {
var cursorRange = metaSheet.getRange(CACHE_META_CURSOR_CELL);
var cursor = cursorRange.getValue();
if (typeof cursor !== "number" || cursor < 2) cursor = 2;
var totalRows = sheet.getDataRange().getNumRows();
if (totalRows < CACHE_MAX_ROWS + 1) {
return totalRows + 1;
}
return cursor;
}
function _advanceCursor(metaSheet, currentRow) {
var nextRow = currentRow + 1;
if (nextRow > CACHE_MAX_ROWS + 1) nextRow = 2;
metaSheet.getRange(CACHE_META_CURSOR_CELL).setValue(nextRow);
}
function _ensureRowsAllocated(sheet) {
var totalRows = sheet.getDataRange().getNumRows();
if (totalRows < CACHE_MAX_ROWS + 1) {
var needed = CACHE_MAX_ROWS + 1 - totalRows;
sheet.insertRowsAfter(totalRows, needed);
}
}
// ═══════════════════════════════════════════════════════════
// SPREADSHEET CACHE — VARY-AWARE COMPOUND KEY
// ═══════════════════════════════════════════════════════════
/**
* Case-insensitive header lookup.
* HTTP header names are case-insensitive per RFC 7230 § 3.2.
*/
function _getHeaderCaseInsensitive(headers, targetKey) {
var target = targetKey.toLowerCase();
for (var k in headers) {
if (headers.hasOwnProperty(k) && k.toLowerCase() === target) {
return headers[k];
}
}
return null;
}
/**
* Compute a compound cache key:
* MD5(URL | header1:value1 | header2:value2 | ...)
*
* Instead of reading the response Vary header (which would require
* fetching first — circular), we preemptively include the request
* headers that are known to cause response variation. This handles
* Vary: Accept-Encoding and Vary: Accept-Language without ever
* inspecting the response.
*
* Values are lowercased and whitespace-stripped so semantically
* identical requests from different clients produce the same hash.
* Missing and empty headers both map to "" (same semantic).
*/
function _getCacheKey(url, reqHeaders) {
var parts = [url];
if (reqHeaders && typeof reqHeaders === "object") {
for (var i = 0; i < VARY_KEY_HEADERS.length; i++) {
var headerName = VARY_KEY_HEADERS[i];
var rawValue = _getHeaderCaseInsensitive(reqHeaders, headerName);
if (rawValue && String(rawValue).trim() !== "") {
parts.push(headerName + ":" + rawValue.toLowerCase().replace(/\s/g, ""));
} else {
parts.push(headerName + ":");
}
}
} else {
for (var j = 0; j < VARY_KEY_HEADERS.length; j++) {
parts.push(VARY_KEY_HEADERS[j] + ":");
}
}
var compoundKey = parts.join("|");
return _md5Hex(compoundKey);
}
function _md5Hex(input) {
var rawHash = Utilities.computeDigest(Utilities.DigestAlgorithm.MD5, input);
return rawHash
.map(function (byte) {
var v = (byte < 0) ? 256 + byte : byte;
return ("0" + v.toString(16)).slice(-2);
})
.join("");
}
// ═══════════════════════════════════════════════════════════
// SPREADSHEET CACHE — CORE LOGIC
// ═══════════════════════════════════════════════════════════
/**
* Returns true if the request is eligible for the cache path:
* public GET, no body, no auth/cookie headers, cache configured.
*/
function _canUseCache(req) {
if ((req.m || "GET") !== "GET") return false;
if (req.b) return false;
if (!req.u || !req.u.match(/^https?:\/\//i)) return false;
if (CACHE_SPREADSHEET_ID === "CHANGE_ME_TO_CACHE_SPREADSHEET_ID") return false;
if (req.h && typeof req.h === "object") {
for (var k in req.h) {
if (req.h.hasOwnProperty(k) && CACHE_BUSTING_HEADERS[k.toLowerCase()]) {
return false;
}
}
}
return true;
}
/**
* Extract max-age (seconds) from a Cache-Control header value.
* Returns 0 if the directive forbids caching (no-cache / no-store /
* private). Falls back to CACHE_DEFAULT_TTL_SECONDS when no header
* is present. Clamped to [60, 2592000] (1 min – 30 days).
*/
function _parseMaxAge(cacheControlHeader) {
if (!cacheControlHeader) return CACHE_DEFAULT_TTL_SECONDS;
var lower = cacheControlHeader.toLowerCase();
if (
lower.indexOf("no-cache") !== -1 ||
lower.indexOf("no-store") !== -1 ||
lower.indexOf("private") !== -1
) {
return 0;
}
var match = lower.match(/max-age=(\d+)/);
if (match) {
var ttl = parseInt(match[1], 10);
return Math.max(60, Math.min(ttl, 2592000));
}
return CACHE_DEFAULT_TTL_SECONDS;
}
/**
* Rewrite time-sensitive headers so the client sees accurate
* Date, Age, and Cache-Control values reflecting cache age.
*/
function _refreshCachedHeaders(headersJson, timestamp) {
var headers = JSON.parse(headersJson);
var cachedAt = new Date(timestamp);
var now = new Date();
var ageSeconds = Math.floor((now.getTime() - cachedAt.getTime()) / 1000);
if (ageSeconds < 0) ageSeconds = 0;
headers["Date"] = now.toUTCString();
headers["Age"] = String(ageSeconds);
var originalCc = headers["Cache-Control"] || headers["cache-control"];
if (originalCc) {
headers["X-Original-Cache-Control"] = originalCc;
}
var remainingMaxAge = Math.max(0, _parseMaxAge(originalCc) - ageSeconds);
headers["Cache-Control"] = "public, max-age=" + remainingMaxAge;
headers["X-Cache"] = "HIT from relay-spreadsheet";
headers["X-Cached-At"] = cachedAt.toUTCString();
return JSON.stringify(headers);
}
/**
* Retrieve a cached response by compound cache key.
* Uses TextFinder for O(log n) lookup. Skips expired entries.
* Returns null on miss, expired entry, or unavailable sheet.
*/
function _getFromCache(url, reqHeaders) {
var sheet = _initCacheSheet();
if (!sheet) return null;
var hash = _getCacheKey(url, reqHeaders);
var finder = sheet.createTextFinder(hash).matchEntireCell(true);
var found = finder.findNext();
if (found) {
var row = sheet.getRange(found.getRow(), 1, 1, 7).getValues()[0];
var expiresAt = row[6];
if (expiresAt && expiresAt instanceof Date && expiresAt < new Date()) {
return null;
}
return {
status: row[2],
headers: _refreshCachedHeaders(row[3], row[5]),
body: row[4],
};
}
return null;
}
/**
* Fetch a URL and store the response in the spreadsheet cache
* using a circular buffer (O(1) writes). Skips storage when the
* encoded body exceeds CACHE_MAX_BODY_BYTES or when Cache-Control
* forbids caching. Returns the fetch result regardless.
*/
function _fetchAndCache(url, reqHeaders) {
var sheet = _initCacheSheet();
if (!sheet) return null;
try {
var response = UrlFetchApp.fetch(url, { muteHttpExceptions: true });
var status = response.getResponseCode();
var headers = _respHeaders(response);
var body = Utilities.base64Encode(response.getContent());
// Cell-size safety gate
if (body.length > CACHE_MAX_BODY_BYTES) {
return { status: status, headers: JSON.stringify(headers), body: body };
}
// TTL extraction
var cacheControl =
headers["Cache-Control"] || headers["cache-control"] || null;
var ttlSeconds = _parseMaxAge(cacheControl);
if (ttlSeconds === 0) {
return { status: status, headers: JSON.stringify(headers), body: body };
}
var hash = _getCacheKey(url, reqHeaders);
var timestamp = new Date();
var expiresAt = new Date(timestamp.getTime() + ttlSeconds * 1000);
// Safety: fallback if Date math produces invalid result
if (isNaN(expiresAt.getTime())) {
expiresAt = new Date(timestamp.getTime() + CACHE_DEFAULT_TTL_SECONDS * 1000);
}
var rowData = [
hash,
url,
status,
JSON.stringify(headers),
body,
timestamp.toISOString(),
expiresAt,
];
// Circular buffer write (O(1))
var metaSheet = _getMetaSheet();
if (metaSheet) {
_ensureRowsAllocated(sheet);
var writeRow = _getNextCursor(sheet, metaSheet);
sheet.getRange(writeRow, 1, 1, 7).setValues([rowData]);
_advanceCursor(metaSheet, writeRow);
} else {
// Fallback: simple append if meta sheet is unavailable
sheet.appendRow(rowData);
}
return { status: status, headers: JSON.stringify(headers), body: body };
} catch (e) {
return null;
}
}
// ═══════════════════════════════════════════════════════════
// SPREADSHEET CACHE — DIAGNOSTICS
// ═══════════════════════════════════════════════════════════
function getCacheStats() {
var sheet = _initCacheSheet();
if (!sheet) {
console.log("Cache is not enabled or spreadsheet unavailable.");
return;
}
var data = sheet.getDataRange().getValues();
var totalEntries = data.length - 1;
var now = new Date();
var expiredCount = 0;
for (var i = 1; i < data.length; i++) {
var expiresAt = data[i][6];
if (expiresAt && expiresAt instanceof Date && expiresAt < now) {
expiredCount++;
}
}
var metaSheet = _getMetaSheet();
var cursorInfo = "N/A";
if (metaSheet) {
cursorInfo = String(metaSheet.getRange(CACHE_META_CURSOR_CELL).getValue());
}
console.log("=== CACHE STATS ===");
console.log("Total rows used: " + totalEntries + " / " + CACHE_MAX_ROWS);
console.log("Active entries: " + (totalEntries - expiredCount));
console.log("Expired entries: " + expiredCount);
console.log("Cursor position: " + cursorInfo);
console.log("Max body size: " + CACHE_MAX_BODY_BYTES + " chars");
console.log("Default TTL: " + CACHE_DEFAULT_TTL_SECONDS + " sec");
console.log("Vary key headers: " + VARY_KEY_HEADERS.join(", "));
if (totalEntries > 0) {
console.log("Oldest entry: " + data[1][5]);
console.log("Newest entry: " + data[data.length - 1][5]);
}
}
function clearExpiredCache() {
var sheet = _initCacheSheet();
if (!sheet) {
console.log("Cache is not enabled.");
return;
}
var data = sheet.getDataRange().getValues();
var now = new Date();
var rowsToClear = [];
for (var i = 1; i < data.length; i++) {
var expiresAt = data[i][6];
if (expiresAt && expiresAt instanceof Date && expiresAt < now) {
rowsToClear.push(i + 1);
}
}
for (var j = 0; j < rowsToClear.length; j++) {
sheet.getRange(rowsToClear[j], 1, 1, 7).clearContent();
}
console.log("Cleared " + rowsToClear.length + " expired entries (" +
(data.length - 1 - rowsToClear.length) + " remaining).");
}
function clearEntireCache() {
var sheet = _initCacheSheet();
if (sheet) {
var totalRows = sheet.getDataRange().getNumRows();
if (totalRows > 1) {
sheet.getRange(2, 1, totalRows - 1, 7).clearContent();
}
}
var metaSheet = _getMetaSheet();
if (metaSheet) {
metaSheet.getRange(CACHE_META_CURSOR_CELL).setValue(2);
}
console.log("Cache wiped. Cursor reset to row 2.");
}