295 lines
15 KiB
TypeScript
295 lines
15 KiB
TypeScript
/**
|
|
* Elicitation — server requests user input. One factory, both protocol eras.
|
|
*
|
|
* The same tools serve both eras with different APIs: on a 2025-era
|
|
* connection (`--legacy`, the `initialize` handshake) the server uses the
|
|
* push-style server→client request flow — `ctx.mcpReq.elicitInput(...)` for
|
|
* form and URL mode, `UrlElicitationRequiredError` for the throw-style URL
|
|
* signal, and `createElicitationCompletionNotifier` for the out-of-band
|
|
* `notifications/elicitation/complete`. On a 2026-07-28 connection there is
|
|
* no server→client request channel: the same tools instead **return**
|
|
* `inputRequired(...)` (multi-round-trip) and the client retries with the
|
|
* collected responses. The protocol carries the request differently; the user
|
|
* experience is the same.
|
|
*
|
|
* One binary, either transport (selected from argv). On HTTP the 2025-era arm
|
|
* is **sessionful** (`NodeStreamableHTTPServerTransport`): push-style
|
|
* `elicitation/create` needs the `initialize`-declared client capabilities and
|
|
* the bidirectional SSE stream of a session, neither of which the per-request
|
|
* stateless legacy fallback can provide.
|
|
*/
|
|
import { randomUUID } from 'node:crypto';
|
|
import type { IncomingMessage, ServerResponse } from 'node:http';
|
|
import { createServer } from 'node:http';
|
|
|
|
import { parseExampleArgs } from '@mcp-examples/shared';
|
|
import { NodeStreamableHTTPServerTransport, toNodeHandler, toWebRequest } from '@modelcontextprotocol/node';
|
|
import type {
|
|
CallToolResult,
|
|
ElicitRequestFormParams,
|
|
ElicitRequestURLParams,
|
|
InputRequiredResult,
|
|
McpRequestContext
|
|
} from '@modelcontextprotocol/server';
|
|
import {
|
|
acceptedContent,
|
|
createMcpHandler,
|
|
inputRequired,
|
|
isInitializeRequest,
|
|
isLegacyRequest,
|
|
McpServer,
|
|
UrlElicitationRequiredError
|
|
} from '@modelcontextprotocol/server';
|
|
import { serveStdio } from '@modelcontextprotocol/server/stdio';
|
|
import * as z from 'zod/v4';
|
|
|
|
// The form schema (with `enumNames` display labels for the enum field).
|
|
const REGISTRATION_SCHEMA: ElicitRequestFormParams['requestedSchema'] = {
|
|
type: 'object',
|
|
properties: {
|
|
username: { type: 'string', title: 'Username', minLength: 3, maxLength: 20 },
|
|
email: { type: 'string', title: 'Email', format: 'email' },
|
|
plan: {
|
|
type: 'string',
|
|
title: 'Plan',
|
|
enum: ['free', 'pro', 'team'],
|
|
enumNames: ['Free tier', 'Pro', 'Team']
|
|
}
|
|
},
|
|
required: ['username', 'email']
|
|
};
|
|
|
|
type Registration = { username: string; email: string; plan?: string };
|
|
|
|
function buildServer(reqCtx: McpRequestContext): McpServer {
|
|
const server = new McpServer({ name: 'elicitation-example', version: '1.0.0' });
|
|
|
|
// ---- Form-mode elicitation -----------------------------------------------
|
|
server.registerTool(
|
|
'register_user',
|
|
{ description: 'Register a new user account by collecting their information' },
|
|
async (ctx): Promise<CallToolResult | InputRequiredResult> => {
|
|
if (reqCtx.era === 'legacy') {
|
|
// 2025-era: push a server→client `elicitation/create` request and
|
|
// await the user's answer in-line.
|
|
const result = await ctx.mcpReq.elicitInput({
|
|
mode: 'form',
|
|
message: 'Please provide your registration information:',
|
|
requestedSchema: REGISTRATION_SCHEMA
|
|
});
|
|
if (result.action !== 'accept' || !result.content) {
|
|
return { content: [{ type: 'text', text: `registration ${result.action}` }] };
|
|
}
|
|
const { username, email, plan } = result.content as Registration;
|
|
return { content: [{ type: 'text', text: `registered ${username} <${email}> (plan: ${plan ?? 'free'})` }] };
|
|
}
|
|
// 2026-07-28: return inputRequired — the client collects the form
|
|
// and retries this same handler with the response attached.
|
|
const response = ctx.mcpReq.inputResponses?.['form'] as { action?: string } | undefined;
|
|
if (!response) {
|
|
return inputRequired({
|
|
inputRequests: {
|
|
form: inputRequired.elicit({
|
|
message: 'Please provide your registration information:',
|
|
requestedSchema: REGISTRATION_SCHEMA
|
|
})
|
|
}
|
|
});
|
|
}
|
|
const form = acceptedContent<Registration>(ctx.mcpReq.inputResponses, 'form');
|
|
if (!form) {
|
|
return { content: [{ type: 'text', text: `registration ${response.action}` }] };
|
|
}
|
|
return { content: [{ type: 'text', text: `registered ${form.username} <${form.email}> (plan: ${form.plan ?? 'free'})` }] };
|
|
}
|
|
);
|
|
|
|
// ---- Multi-step / chained form elicitation (two sequential prompts) ------
|
|
server.registerTool(
|
|
'plan_trip',
|
|
{ description: 'Plan a trip by collecting a destination and then dates for that destination' },
|
|
async (ctx): Promise<CallToolResult | InputRequiredResult> => {
|
|
const DEST: ElicitRequestFormParams['requestedSchema'] = {
|
|
type: 'object',
|
|
properties: { destination: { type: 'string', title: 'Destination' } },
|
|
required: ['destination']
|
|
};
|
|
const datesFor = (dest: string): ElicitRequestFormParams['requestedSchema'] => ({
|
|
type: 'object',
|
|
properties: {
|
|
departure: { type: 'string', title: `Departure date for ${dest}`, format: 'date' },
|
|
nights: { type: 'integer', title: 'Nights', minimum: 1, maximum: 30 }
|
|
},
|
|
required: ['departure', 'nights']
|
|
});
|
|
if (reqCtx.era === 'legacy') {
|
|
// 2025-era: two sequential `elicitation/create` pushes inside one tool call.
|
|
const step1 = await ctx.mcpReq.elicitInput({ mode: 'form', message: 'Where to?', requestedSchema: DEST });
|
|
if (step1.action !== 'accept' || !step1.content) {
|
|
return { content: [{ type: 'text', text: `trip ${step1.action}` }] };
|
|
}
|
|
const dest = step1.content.destination as string;
|
|
const step2 = await ctx.mcpReq.elicitInput({ mode: 'form', message: 'When?', requestedSchema: datesFor(dest) });
|
|
if (step2.action !== 'accept' || !step2.content) {
|
|
return { content: [{ type: 'text', text: `trip ${step2.action}` }] };
|
|
}
|
|
return {
|
|
content: [
|
|
{ type: 'text', text: `trip planned: ${dest} on ${step2.content.departure} for ${step2.content.nights} nights` }
|
|
]
|
|
};
|
|
}
|
|
// 2026-07-28: two `inputRequired` rounds — the second carries the
|
|
// first answer back via `requestState` (an opaque server-minted
|
|
// string) so the chain survives the stateless retry. See ../mrtr/
|
|
// for integrity-protecting `requestState` in production.
|
|
const dates = acceptedContent<{ departure: string; nights: number }>(ctx.mcpReq.inputResponses, 'dates');
|
|
const destination =
|
|
ctx.mcpReq.requestState<string>() ??
|
|
acceptedContent<{ destination: string }>(ctx.mcpReq.inputResponses, 'dest')?.destination;
|
|
if (!destination) {
|
|
return inputRequired({ inputRequests: { dest: inputRequired.elicit({ message: 'Where to?', requestedSchema: DEST }) } });
|
|
}
|
|
if (!dates) {
|
|
return inputRequired({
|
|
requestState: destination,
|
|
inputRequests: { dates: inputRequired.elicit({ message: 'When?', requestedSchema: datesFor(destination) }) }
|
|
});
|
|
}
|
|
return { content: [{ type: 'text', text: `trip planned: ${destination} on ${dates.departure} for ${dates.nights} nights` }] };
|
|
}
|
|
);
|
|
|
|
// ---- URL-mode elicitation (push style + completion notification) ---------
|
|
server.registerTool(
|
|
'link_account',
|
|
{
|
|
description: 'Link a third-party account by opening a sign-in URL',
|
|
inputSchema: z.object({ provider: z.string() })
|
|
},
|
|
async ({ provider }, ctx): Promise<CallToolResult | InputRequiredResult> => {
|
|
if (reqCtx.era === 'legacy') {
|
|
// 2025-era push style: send `elicitation/create` (mode: 'url')
|
|
// and, in parallel, simulate the out-of-band callback that
|
|
// fires when the user finishes the URL flow by sending
|
|
// `notifications/elicitation/complete` for the same id. The
|
|
// client waits for that notification before answering accept.
|
|
const elicitationId = randomUUID();
|
|
// Tie the completion notification to the in-flight request so on
|
|
// sessionful HTTP it travels over this POST's SSE response stream
|
|
// (rather than the standalone GET stream).
|
|
const notifyComplete = server.server.createElicitationCompletionNotifier(elicitationId, {
|
|
relatedRequestId: ctx.mcpReq.id
|
|
});
|
|
setTimeout(() => void notifyComplete().catch(error => console.error('[server] complete notify failed:', error)), 50);
|
|
const params: ElicitRequestURLParams = {
|
|
mode: 'url',
|
|
message: `Sign in to ${provider} to link your account`,
|
|
url: `https://example.com/oauth/${encodeURIComponent(provider)}/authorize`,
|
|
elicitationId
|
|
};
|
|
const result = await ctx.mcpReq.elicitInput(params);
|
|
return { content: [{ type: 'text', text: result.action === 'accept' ? `linked ${provider}` : `link ${result.action}` }] };
|
|
}
|
|
// 2026-07-28: URL elicitation rides the multi-round-trip flow. No
|
|
// elicitationId / complete notification — correlation is the
|
|
// server's own state across retries.
|
|
const auth = ctx.mcpReq.inputResponses?.['auth'] as { action?: string } | undefined;
|
|
if (auth?.action !== 'accept') {
|
|
return inputRequired({
|
|
inputRequests: {
|
|
auth: inputRequired.elicitUrl({
|
|
message: `Sign in to ${provider} to link your account`,
|
|
url: `https://example.com/oauth/${encodeURIComponent(provider)}/authorize`
|
|
})
|
|
}
|
|
});
|
|
}
|
|
return { content: [{ type: 'text', text: `linked ${provider}` }] };
|
|
}
|
|
);
|
|
|
|
// ---- URL-mode elicitation (throw style, 2025-era only) -------------------
|
|
// The error-style signal: the tool THROWS `UrlElicitationRequiredError`
|
|
// (wire `-32042`); the client catches it as a typed error and reads
|
|
// `.elicitations`. There is no 2026-07-28 equivalent — a throw on that era
|
|
// fails loudly with a steer to `inputRequired.elicitUrl(...)`.
|
|
server.registerTool(
|
|
'confirm_payment',
|
|
{
|
|
description: 'Confirm a payment via a browser flow (2025-era throw-style URL elicitation)',
|
|
inputSchema: z.object({ cartId: z.string() })
|
|
},
|
|
async ({ cartId }): Promise<CallToolResult> => {
|
|
throw new UrlElicitationRequiredError([
|
|
{
|
|
mode: 'url',
|
|
message: 'Open the link to confirm payment',
|
|
url: `https://example.com/confirm-payment?cart=${encodeURIComponent(cartId)}`,
|
|
elicitationId: randomUUID()
|
|
}
|
|
]);
|
|
}
|
|
);
|
|
|
|
return server;
|
|
}
|
|
|
|
const { transport, port } = parseExampleArgs();
|
|
|
|
if (transport === 'stdio') {
|
|
void serveStdio(buildServer);
|
|
console.error('[server] serving over stdio');
|
|
} else {
|
|
// --- modern (2026-07-28): per-request, strict so the sessionful arm owns ALL legacy traffic ---
|
|
const modern = toNodeHandler(createMcpHandler(buildServer, { legacy: 'reject' }));
|
|
|
|
// --- legacy (2025): sessionful Streamable HTTP — push-style elicitation
|
|
// requires the session (client capabilities + bidirectional SSE stream) ---
|
|
const sessions = new Map<string, NodeStreamableHTTPServerTransport>();
|
|
const handleLegacy = async (req: IncomingMessage, res: ServerResponse, body: unknown): Promise<void> => {
|
|
const sid = req.headers['mcp-session-id'] as string | undefined;
|
|
if (sid && sessions.has(sid)) {
|
|
await sessions.get(sid)!.handleRequest(req, res, body);
|
|
} else if (!sid && isInitializeRequest(body)) {
|
|
const t = new NodeStreamableHTTPServerTransport({
|
|
sessionIdGenerator: () => randomUUID(),
|
|
onsessioninitialized: id => {
|
|
sessions.set(id, t);
|
|
}
|
|
});
|
|
t.onclose = () => t.sessionId && sessions.delete(t.sessionId);
|
|
await buildServer({ era: 'legacy' } as McpRequestContext).connect(t);
|
|
await t.handleRequest(req, res, body);
|
|
} else {
|
|
res.writeHead(sid ? 404 : 400, { 'content-type': 'application/json' }).end(
|
|
JSON.stringify({
|
|
jsonrpc: '2.0',
|
|
error: sid
|
|
? { code: -32_001, message: 'Session not found' }
|
|
: { code: -32_000, message: 'Bad Request: Session ID required' },
|
|
id: null
|
|
})
|
|
);
|
|
}
|
|
};
|
|
|
|
createServer((req, res) => {
|
|
void (async () => {
|
|
// `toWebRequest` reads the Node body into a web-standard `Request`,
|
|
// so the body now lives in `request`, not `req`. Ask the predicate
|
|
// first — it classifies an internal clone, leaving `request`
|
|
// readable for the `.json()` both arms need (reading `.json()`
|
|
// first would make the predicate's internal clone throw).
|
|
const request = await toWebRequest(req);
|
|
const legacy = await isLegacyRequest(request);
|
|
const body: unknown = req.method === 'POST' ? await request.json().catch(() => {}) : undefined;
|
|
await (legacy ? handleLegacy(req, res, body) : modern(req, res, body));
|
|
})().catch(error => {
|
|
console.error('[server] request error:', error instanceof Error ? error.message : error);
|
|
if (!res.headersSent) res.writeHead(500).end();
|
|
});
|
|
}).listen(port, () => {
|
|
console.error(`[server] listening on http://127.0.0.1:${port}/mcp`);
|
|
});
|
|
}
|