bandwidth savings configs

server/src/helpers/bandwidthSavings.js

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+// Bandwidth Savings Helper
+// Purpose: Normalizes bandwidth-saving config and exposes tiny policy helpers.
+// Scope: Keeps cross-service video/tab/spectator decisions consistent without
+// making individual services know raw YAML defaults or legacy config shapes.
+const { loadConfig } = require('./configLoader');
+
+const MULTI_TAB_MODES = new Set(['allowed', 'verifiedOnly', 'notAllowed']);
+const VIDEO_MODES = new Set(['snapshots', 'live']);
+const EXTERNAL_SPECTATOR_ACCESS_MODES = new Set(['off', 'on', 'admin']);
+
+const DEFAULT_BANDWIDTH_SAVINGS = Object.freeze({
+  multiTabProtection: 'verifiedOnly',
+  nonTurnVideo: 'snapshots',
+  externalSpectatorVideo: 'snapshots',
+  externalSpectatorAccess: 'on',
+});
+
+function normalizeEnum(value, allowed, fallback) {
+  /*
+    Config files are hand-edited on the server, so a typo should not crash the
+    process or silently broaden access. Each option falls back to the current
+    conservative behavior unless it exactly matches a known value.
+  */
+  const normalized = typeof value === 'string' ? value.trim() : '';
+  return allowed.has(normalized) ? normalized : fallback;
+}
+
+function buildBandwidthSavingsPolicy(config = loadConfig()) {
+  const raw = config.bandwidthSavings || {};
+  return {
+    multiTabProtection: normalizeEnum(
+      raw.multiTabProtection,
+      MULTI_TAB_MODES,
+      DEFAULT_BANDWIDTH_SAVINGS.multiTabProtection,
+    ),
+    nonTurnVideo: normalizeEnum(
+      raw.nonTurnVideo,
+      VIDEO_MODES,
+      DEFAULT_BANDWIDTH_SAVINGS.nonTurnVideo,
+    ),
+    externalSpectatorVideo: normalizeEnum(
+      raw.externalSpectatorVideo,
+      VIDEO_MODES,
+      DEFAULT_BANDWIDTH_SAVINGS.externalSpectatorVideo,
+    ),
+    externalSpectatorAccess: normalizeEnum(
+      raw.externalSpectatorAccess,
+      EXTERNAL_SPECTATOR_ACCESS_MODES,
+      DEFAULT_BANDWIDTH_SAVINGS.externalSpectatorAccess,
+    ),
+  };
+}
+
+function getBandwidthSavingsPolicy() {
+  /*
+    loadConfig() is cached by configLoader, so rebuilding this small object per
+    caller is cheap while still letting tests pass explicit config objects into
+    buildBandwidthSavingsPolicy().
+  */
+  return buildBandwidthSavingsPolicy(loadConfig());
+}
+
+function shouldEnforceSingleDriverTab({ isVerified = false, isAdmin = false } = {}) {
+  const { multiTabProtection } = getBandwidthSavingsPolicy();
+  if (multiTabProtection === 'allowed') return false;
+  if (multiTabProtection === 'notAllowed') return true;
+  /*
+    verifiedOnly preserves the old behavior: trusted users can run multiple
+    driver tabs for operations/testing, while anonymous users are limited to one
+    active driver surface for fairness and bandwidth.
+  */
+  return !isVerified && !isAdmin;
+}
+
+function shouldUseSnapshotsForNonTurnVideo() {
+  return getBandwidthSavingsPolicy().nonTurnVideo === 'snapshots';
+}
+
+function shouldUseSnapshotsForExternalSpectatorVideo() {
+  return getBandwidthSavingsPolicy().externalSpectatorVideo === 'snapshots';
+}
+
+function canUseExternalSpectatorAccess({
+  isLocal = false,
+  isAdmin = false,
+  hasGrant = false,
+} = {}) {
+  /*
+    Local/LAN spectators are not the upload-bandwidth problem, and admins need
+    to retain access for maintenance. The configured external mode only applies
+    to ordinary non-local spectator sockets.
+  */
+  if (isLocal || isAdmin) return true;
+  const { externalSpectatorAccess } = getBandwidthSavingsPolicy();
+  if (externalSpectatorAccess === 'off') return false;
+  if (externalSpectatorAccess === 'admin') return Boolean(hasGrant);
+  return true;
+}
+
+module.exports = {
+  DEFAULT_BANDWIDTH_SAVINGS,
+  buildBandwidthSavingsPolicy,
+  getBandwidthSavingsPolicy,
+  shouldEnforceSingleDriverTab,
+  shouldUseSnapshotsForNonTurnVideo,
+  shouldUseSnapshotsForExternalSpectatorVideo,
+  canUseExternalSpectatorAccess,
+};