Implement MCP 2026-07-28 (#2286)
Co-authored-by: Matt <77928207+mattzcarey@users.noreply.github.com> Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
This commit is contained in:
Felix Weinberger
GitHub
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e4227d135c
commit
1823aae891
4 changed files with 69131 additions and 9001 deletions
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@ -2,6 +2,7 @@ import type { FastifyInstance } from 'fastify';
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import Fastify from 'fastify';
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import { hostHeaderValidation, localhostHostValidation } from './middleware/hostHeaderValidation';
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import { localhostOriginValidation, originValidation } from './middleware/originValidation';
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/**
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* Options for creating an MCP Fastify application.
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@ -22,6 +23,18 @@ export interface CreateMcpFastifyAppOptions {
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* to restrict which hostnames are allowed.
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*/
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allowedHosts?: string[];
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/**
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* List of allowed origin hostnames for Origin header validation.
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* If provided, Origin validation will be applied using this list (port-agnostic,
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* hostnames only — the same convention as `allowedHosts`).
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*
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* When omitted, Origin validation is automatically enabled for localhost-class
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* binds (the same condition as host validation): requests without an `Origin`
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* header pass, while a present `Origin` whose hostname is not localhost-class
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* is rejected with `403`.
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*/
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allowedOrigins?: string[];
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}
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/**
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@ -54,7 +67,7 @@ export interface CreateMcpFastifyAppOptions {
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* ```
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*/
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export function createMcpFastifyApp(options: CreateMcpFastifyAppOptions = {}): FastifyInstance {
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const { host = '127.0.0.1', allowedHosts } = options;
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const { host = '127.0.0.1', allowedHosts, allowedOrigins } = options;
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const app = Fastify();
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@ -78,5 +91,14 @@ export function createMcpFastifyApp(options: CreateMcpFastifyAppOptions = {}): F
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}
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}
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// Origin validation follows the same arming ladder as host validation:
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// an explicit allowlist wins; otherwise localhost-class binds are protected
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// by default. Requests without an Origin header always pass.
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if (allowedOrigins) {
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app.addHook('onRequest', originValidation(allowedOrigins));
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} else if (['127.0.0.1', 'localhost', '::1'].includes(host)) {
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app.addHook('onRequest', localhostOriginValidation());
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}
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return app;
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}
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@ -1,2 +1,3 @@
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export * from './fastify';
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export * from './middleware/hostHeaderValidation';
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export * from './middleware/originValidation';
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@ -0,0 +1,50 @@
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import { localhostAllowedOrigins, validateOriginHeader } from '@modelcontextprotocol/server';
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import type { FastifyReply, FastifyRequest } from 'fastify';
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/**
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* Fastify onRequest hook for Origin header validation.
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* Validates the `Origin` header hostname (port-agnostic) against an allowed list.
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*
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* Browsers attach an `Origin` header to cross-origin requests; validating it —
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* alongside Host header validation — protects localhost and development servers
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* against DNS rebinding and cross-site request forgery. Requests without an
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* `Origin` header pass (non-browser MCP clients do not send one); a present
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* value that is not allowed, or that cannot be parsed, is rejected with `403`.
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*
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* @param allowedOriginHostnames - List of allowed origin hostnames (without scheme or port).
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* For IPv6, provide the address with brackets (e.g., `[::1]`).
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* @returns Fastify onRequest hook handler
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*
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* @example
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* ```ts
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* app.addHook('onRequest', originValidation(['localhost', '127.0.0.1', '[::1]']));
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* ```
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*/
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export function originValidation(allowedOriginHostnames: string[]) {
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return async (request: FastifyRequest, reply: FastifyReply): Promise<void> => {
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const result = validateOriginHeader(request.headers.origin, allowedOriginHostnames);
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if (!result.ok) {
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await reply.code(403).send({
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jsonrpc: '2.0',
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error: {
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code: -32_000,
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message: result.message
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},
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id: null
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});
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}
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};
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}
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/**
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* Convenience hook for localhost Origin validation.
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* Allows only origins whose hostname is `localhost`, `127.0.0.1`, or `[::1]` (IPv6 localhost).
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*
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* @example
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* ```ts
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* app.addHook('onRequest', localhostOriginValidation());
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* ```
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*/
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export function localhostOriginValidation() {
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return originValidation(localhostAllowedOrigins());
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}
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116
packages/middleware/fastify/test/originValidation.test.ts
Normal file
116
packages/middleware/fastify/test/originValidation.test.ts
Normal file
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@ -0,0 +1,116 @@
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import Fastify from 'fastify';
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import { createMcpFastifyApp } from '../src/fastify';
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import { localhostOriginValidation, originValidation } from '../src/middleware/originValidation';
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describe('@modelcontextprotocol/fastify origin validation', () => {
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describe('originValidation', () => {
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test('should block a disallowed Origin header', async () => {
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const app = Fastify();
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app.addHook('onRequest', originValidation(['localhost']));
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app.get('/health', async () => ({ ok: true }));
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const res = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000', origin: 'http://evil.example.com' }
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});
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expect(res.statusCode).toBe(403);
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expect(res.json()).toEqual(
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expect.objectContaining({
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jsonrpc: '2.0',
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error: expect.objectContaining({
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code: -32_000
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}),
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id: null
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})
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);
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});
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test('should allow an allowed Origin header and requests without an Origin header', async () => {
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const app = Fastify();
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app.addHook('onRequest', localhostOriginValidation());
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app.get('/health', async () => 'ok');
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const allowed = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000', origin: 'http://localhost:5173' }
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});
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expect(allowed.statusCode).toBe(200);
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const noOrigin = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000' }
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});
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expect(noOrigin.statusCode).toBe(200);
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});
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test('should deny malformed Origin values (deny on failure)', async () => {
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const app = Fastify();
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app.addHook('onRequest', localhostOriginValidation());
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app.get('/health', async () => 'ok');
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const res = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000', origin: 'null' }
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});
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expect(res.statusCode).toBe(403);
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});
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});
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describe('createMcpFastifyApp origin arming', () => {
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test('arms localhost origin validation by default', async () => {
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const app = createMcpFastifyApp();
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app.get('/health', async () => 'ok');
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const bad = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000', origin: 'http://evil.example.com' }
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});
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expect(bad.statusCode).toBe(403);
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const good = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'localhost:3000', origin: 'http://localhost:5173' }
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});
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expect(good.statusCode).toBe(200);
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});
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test('uses allowedOrigins when provided', async () => {
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const app = createMcpFastifyApp({ host: '0.0.0.0', allowedHosts: ['myapp.local'], allowedOrigins: ['myapp.local'] });
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app.get('/health', async () => 'ok');
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const good = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'myapp.local:3000', origin: 'https://myapp.local' }
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});
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expect(good.statusCode).toBe(200);
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const bad = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'myapp.local:3000', origin: 'http://evil.example.com' }
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});
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expect(bad.statusCode).toBe(403);
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});
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test('applies no origin validation for 0.0.0.0 without allowedOrigins', async () => {
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const app = createMcpFastifyApp({ host: '0.0.0.0' });
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app.get('/health', async () => 'ok');
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const res = await app.inject({
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method: 'GET',
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url: '/health',
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headers: { host: 'whatever.example.com', origin: 'http://evil.example.com' }
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});
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expect(res.statusCode).toBe(200);
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});
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});
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});
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