fix: harden scoped tools and settings persistence

src/main/settings-file-utils.ts

@@ -0,0 +1,99 @@
+import { randomBytes } from 'node:crypto'
+import {
+  mkdir,
+  rename,
+  rm,
+  writeFile
+} from 'node:fs/promises'
+import { dirname } from 'node:path'
+
+export interface SettingsFileOperations {
+  rename: typeof rename
+  writeFile: typeof writeFile
+}
+
+export class UnsupportedSettingsVersionError extends Error {}
+
+const defaultSettingsFileOperations: SettingsFileOperations = {
+  rename,
+  writeFile
+}
+
+function resolveSettingsFileOperations(
+  operations?: Partial<SettingsFileOperations>
+): SettingsFileOperations {
+  return {
+    ...defaultSettingsFileOperations,
+    ...operations
+  }
+}
+
+export function isMissingFileError(error: unknown): boolean {
+  return (
+    error !== null &&
+    typeof error === 'object' &&
+    'code' in error &&
+    error.code === 'ENOENT'
+  )
+}
+
+export function assertSupportedSettingsVersion(
+  value: unknown,
+  currentVersion: number,
+  message: (version: number) => string
+): void {
+  if (
+    value !== null &&
+    typeof value === 'object' &&
+    'version' in value &&
+    typeof value.version === 'number' &&
+    value.version > currentVersion
+  ) {
+    throw new UnsupportedSettingsVersionError(message(value.version))
+  }
+}
+
+export async function isolateCorruptSettingsFile(
+  filePath: string,
+  failureMessage: string,
+  now: () => number = Date.now,
+  operations?: Partial<SettingsFileOperations>
+): Promise<void> {
+  const fileOperations = resolveSettingsFileOperations(operations)
+  const isolatedPath =
+    `${filePath}.corrupt-${now()}-` +
+    randomBytes(6).toString('hex')
+  try {
+    await fileOperations.rename(filePath, isolatedPath)
+  } catch (error) {
+    if (!isMissingFileError(error)) {
+      throw new Error(failureMessage, { cause: error })
+    }
+  }
+}
+
+export async function writeJsonFileAtomically(
+  filePath: string,
+  value: unknown,
+  operations?: Partial<SettingsFileOperations>
+): Promise<void> {
+  const fileOperations = resolveSettingsFileOperations(operations)
+  await mkdir(dirname(filePath), { recursive: true })
+  const temporaryPath =
+    `${filePath}.${process.pid}.` +
+    `${randomBytes(6).toString('hex')}.tmp`
+  try {
+    await fileOperations.writeFile(
+      temporaryPath,
+      `${JSON.stringify(value, null, 2)}\n`,
+      {
+        encoding: 'utf8',
+        mode: 0o600,
+        flag: 'wx'
+      }
+    )
+    await fileOperations.rename(temporaryPath, filePath)
+  } finally {
+    await rm(temporaryPath, { force: true })
+  }
+}