Merge pull request modelcontextprotocol#158 from jwvictor/add-sessionid-to-context

Add sessionID to RequestHandlerExtra type for tool invocations so multi-user services can distinguish users

Author: jspahrsummers

src/inMemory.ts

@@ -11,6 +11,7 @@ export class InMemoryTransport implements Transport {
  onclose?: () => void;
  onerror?: (error: Error) => void;
  onmessage?: (message: JSONRPCMessage) => void;
+ sessionId?: string;
 
  /**
  * Creates a pair of linked in-memory transports that can communicate with each other. One should be passed to a Client and one to a Server.

src/server/mcp.test.ts

@@ -323,6 +323,59 @@ describe("tool()", () => {
  mcpServer.tool("tool2", () => ({ content: [] }));
  });
 
+ test("should pass sessionId to tool callback via RequestHandlerExtra", async () => {
+ const mcpServer = new McpServer({
+ name: "test server",
+ version: "1.0",
+ });
+
+ const client = new Client(
+ {
+ name: "test client",
+ version: "1.0",
+ },
+ {
+ capabilities: {
+ tools: {},
+ },
+ },
+ );
+
+ let receivedSessionId: string | undefined;
+ mcpServer.tool("test-tool", async (extra) => {
+ receivedSessionId = extra.sessionId;
+ return {
+ content: [
+ {
+ type: "text",
+ text: "Test response",
+ },
+ ],
+ };
+ });
+
+ const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+ // Set a test sessionId on the server transport
+ serverTransport.sessionId = "test-session-123";
+
+ await Promise.all([
+ client.connect(clientTransport),
+ mcpServer.server.connect(serverTransport),
+ ]);
+
+ await client.request(
+ {
+ method: "tools/call",
+ params: {
+ name: "test-tool",
+ },
+ },
+ CallToolResultSchema,
+ );
+
+ expect(receivedSessionId).toBe("test-session-123");
+ });
+
  test("should allow client to call server tools", async () => {
  const mcpServer = new McpServer({
  name: "test server",

src/shared/protocol.ts

@@ -88,6 +88,11 @@ export type RequestHandlerExtra = {
  * An abort signal used to communicate if the request was cancelled from the sender's side.
  */
  signal: AbortSignal;
+
+ /**
+ * The session ID from the transport, if available.
+ */
+ sessionId?: string;
 };
 
 /**
@@ -307,9 +312,15 @@ export abstract class Protocol<
  const abortController = new AbortController();
  this._requestHandlerAbortControllers.set(request.id, abortController);
 
+ // Create extra object with both abort signal and sessionId from transport
+ const extra: RequestHandlerExtra = {
+ signal: abortController.signal,
+ sessionId: this._transport?.sessionId,
+ };
+
  // Starting with Promise.resolve() puts any synchronous errors into the monad as well.
  Promise.resolve()
- .then(() => handler(request, { signal: abortController.signal }))
+ .then(() => handler(request, extra))
  .then(
  (result) => {
  if (abortController.signal.aborted) {

src/shared/transport.ts

@@ -41,4 +41,9 @@ export interface Transport {
  * Callback for when a message (request or response) is received over the connection.
  */
  onmessage?: (message: JSONRPCMessage) => void;
+
+ /**
+ * The session ID generated for this connection.
+ */
+ sessionId?: string;
 }