Add shared JSON file helpers

src/fs-json.ts

@@ -0,0 +1,21 @@
+import fs from 'node:fs/promises';
+import path from 'node:path';
+
+// readJsonFile reads a JSON file and returns undefined when the file does not exist.
+export async function readJsonFile<T = unknown>(filePath: string): Promise<T | undefined> {
+  try {
+    const content = await fs.readFile(filePath, 'utf8');
+    return JSON.parse(content) as T;
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+      return undefined;
+    }
+    throw error;
+  }
+}
+
+// writeJsonFile writes a JSON object to disk, ensuring parent directories are created first.
+export async function writeJsonFile(filePath: string, data: unknown): Promise<void> {
+  await fs.mkdir(path.dirname(filePath), { recursive: true });
+  await fs.writeFile(filePath, JSON.stringify(data, null, 2), 'utf8');
+}

src/oauth.ts

@@ -12,6 +12,7 @@ import type {
   OAuthTokens,
 } from '@modelcontextprotocol/sdk/shared/auth.js';
 import type { ServerDefinition } from './config.js';
+import { readJsonFile, writeJsonFile } from './fs-json.js';
 
 const CALLBACK_HOST = '127.0.0.1';
 const CALLBACK_PATH = '/callback';
@@ -61,25 +62,6 @@ async function ensureDirectory(dir: string) {
   await fs.mkdir(dir, { recursive: true });
 }
 
-// readJsonFile returns undefined for missing files instead of throwing.
-async function readJsonFile<T>(filePath: string): Promise<T | undefined> {
-  try {
-    const raw = await fs.readFile(filePath, 'utf8');
-    return JSON.parse(raw) as T;
-  } catch (error) {
-    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
-      return undefined;
-    }
-    throw error;
-  }
-}
-
-// writeJsonFile persists JSON data to disk, creating parent directories as needed.
-async function writeJsonFile(filePath: string, data: unknown) {
-  await ensureDirectory(path.dirname(filePath));
-  await fs.writeFile(filePath, JSON.stringify(data, null, 2), 'utf8');
-}
-
 // FileOAuthClientProvider persists OAuth session artifacts to disk and captures callback redirects.
 class FileOAuthClientProvider implements OAuthClientProvider {
   private readonly tokenPath: string;

tests/fs-json.test.ts

@@ -0,0 +1,35 @@
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { readJsonFile, writeJsonFile } from '../src/fs-json.js';
+
+describe('fs-json helpers', () => {
+  let tempDir: string;
+
+  beforeEach(async () => {
+    tempDir = await fs.mkdtemp(path.join(os.tmpdir(), 'mcporter-fs-json-'));
+  });
+
+  afterEach(async () => {
+    await fs.rm(tempDir, { recursive: true, force: true });
+  });
+
+  it('returns undefined when reading a missing file', async () => {
+    const missingPath = path.join(tempDir, 'missing.json');
+    const value = await readJsonFile<Record<string, string>>(missingPath);
+    expect(value).toBeUndefined();
+  });
+
+  it('writes JSON and reads it back, ensuring parent directories are created', async () => {
+    const nestedPath = path.join(tempDir, 'nested', 'config.json');
+    const payload = { apiKey: 'secret', retries: 2 };
+    await writeJsonFile(nestedPath, payload);
+
+    const roundTripped = await readJsonFile<typeof payload>(nestedPath);
+    expect(roundTripped).toEqual(payload);
+
+    const raw = await fs.readFile(nestedPath, 'utf8');
+    expect(raw).toContain('\n  "apiKey"');
+  });
+});