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services/settings.mjs

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+// No Gecko, XPCOM, DOM or filesystem imports in the service contract.
+export const API_VERSION = 1;
+
+export class ServiceError extends Error {
+  constructor(code) {
+    super(code);
+    this.code = code;
+  }
+}
+
+function key(value) {
+  if (
+    typeof value !== 'string' ||
+    !value ||
+    value.length > 128 ||
+    ['__proto__', 'constructor', 'prototype'].includes(value)
+  ) {
+    throw new ServiceError('INVALID_KEY');
+  }
+  return value;
+}
+
+// v1 transports JSON only. Binary images will need a separate attachment contract.
+function jsonValue(value, depth = 0) {
+  if (depth > 20) throw new ServiceError('INVALID_VALUE');
+  if (value === null || typeof value === 'boolean' || typeof value === 'string') return;
+  if (typeof value === 'number' && Number.isFinite(value)) return;
+  if (Array.isArray(value)) {
+    value.forEach((v) => jsonValue(v, depth + 1));
+    return;
+  }
+  if (typeof value === 'object' && Object.getPrototypeOf(value) === Object.prototype) {
+    for (const [k, v] of Object.entries(value)) {
+      key(k);
+      jsonValue(v, depth + 1);
+    }
+    return;
+  }
+  throw new ServiceError('INVALID_VALUE');
+}
+
+export class SettingsService {
+  constructor(storage, { maxBytes = 1024 * 1024 } = {}) {
+    this.storage = storage;
+    this.maxBytes = maxBytes;
+  }
+
+  // Only a trusted host adapter may bind a session. Never take identity or
+  // permissions from an application's RPC payload.
+  bindSession(identity, permissions) {
+    if (typeof identity !== 'string' || !identity) throw new ServiceError('INVALID_IDENTITY');
+    const grants = new Set(permissions);
+    return async (request) => {
+      const id = request && request.id;
+      try {
+        if (!request || request.version !== API_VERSION)
+          throw new ServiceError('API_VERSION_UNSUPPORTED');
+        if (!Number.isSafeInteger(id) || id < 0) throw new ServiceError('INVALID_REQUEST');
+        const { method, params } = request;
+        if (method === 'settings.get') {
+          if (!grants.has('settings.read')) throw new ServiceError('PERMISSION_DENIED');
+          const name = key(params && params.key);
+          const value = await this.storage.get(name);
+          return {
+            version: API_VERSION,
+            id,
+            result: { found: value !== undefined, value: value === undefined ? null : value },
+          };
+        }
+        if (method === 'settings.set') {
+          if (!grants.has('settings.write')) throw new ServiceError('PERMISSION_DENIED');
+          const values = params && params.values;
+          if (!values || Object.getPrototypeOf(values) !== Object.prototype)
+            throw new ServiceError('INVALID_VALUE');
+          const entries = Object.entries(values);
+          if (!entries.length || entries.length > 128) throw new ServiceError('INVALID_VALUE');
+          // Validate the entire request before opening a write transaction.
+          for (const [k, v] of entries) {
+            key(k);
+            jsonValue(v);
+          }
+          if (JSON.stringify(values).length > this.maxBytes)
+            throw new ServiceError('VALUE_TOO_LARGE');
+          await this.storage.setMany(entries);
+          return { version: API_VERSION, id, result: { committed: true } };
+        }
+        throw new ServiceError('METHOD_NOT_SUPPORTED');
+      } catch (error) {
+        return {
+          version: API_VERSION,
+          id,
+          error: { code: error instanceof ServiceError ? error.code : 'STORAGE_ERROR' },
+        };
+      }
+    };
+  }
+}