import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import {
Root,
RootsListChangedNotificationSchema,
} from "@modelcontextprotocol/sdk/types.js";
// Track roots by session id
export const roots: Map<string | undefined, Root[]> = new Map<
string | undefined,
Root[]
>();
/**
* Get the latest the client roots list for the session.
*
* - Request and cache the roots list for the session if it has not been fetched before.
* - Return the cached roots list for the session if it exists.
*
* When requesting the roots list for a session, it also sets up a `roots/list_changed`
* notification handler. This ensures that updates are automatically fetched and handled
* in real-time.
*
* This function is idempotent. It should only request roots from the client once per session,
* returning the cached version thereafter.
*
* @param {McpServer} server - An instance of the MCP server used to communicate with the client.
* @param {string} [sessionId] - An optional session id used to associate the roots list with a specific client session.
*
* @throws {Error} In case of a failure to request the roots from the client, an error log message is sent.
*/
export const syncRoots = async (server: McpServer, sessionId?: string) => {
const clientCapabilities = server.server.getClientCapabilities() || {};
const clientSupportsRoots: boolean = clientCapabilities.roots !== undefined;
// Fetch the roots list for this client
if (clientSupportsRoots) {
// Function to request the updated roots list from the client
const requestRoots = async () => {
try {
// Request the updated roots list from the client
const response = await server.server.listRoots();
if (response && "roots" in response) {
// Store the roots list for this client
roots.set(sessionId, response.roots);
// Notify the client of roots received
await server.sendLoggingMessage(
{
level: "info",
logger: "everything-server",
data: `Roots updated: ${response.roots.length} root(s) received from client`,
},
sessionId
);
} else {
await server.sendLoggingMessage(
{
level: "info",
logger: "everything-server",
data: "Client returned no roots set",
},
sessionId
);
}
} catch (error) {
await server.sendLoggingMessage(
{
level: "error",
logger: "everything-server",
data: `Failed to request roots from client: ${
error instanceof Error ? error.message : String(error)
}`,
},
sessionId
);
}
};
// If the roots have not been synced for this client,
// set notification handler and request initial roots
if (!roots.has(sessionId)) {
// Set the list changed notification handler
server.server.setNotificationHandler(
RootsListChangedNotificationSchema,
requestRoots
);
// Request the initial roots list immediately
await requestRoots();
}
// Return the roots list for this client
return roots.get(sessionId);
}
};
