Make it easy to issue progress notifications from request handlers

Resolves #34.

src/shared/protocol.ts

@@ -1,5 +1,6 @@
-import { AnyZodObject, ZodLiteral, ZodObject, z } from "zod";
+import { AnyZodObject, ZodLiteral, ZodObject, ZodOptional, z } from "zod";
 import {
+  BaseRequestParamsSchema,
   ErrorCode,
   JSONRPCError,
   JSONRPCNotification,
@@ -312,18 +313,42 @@ export class Protocol<
   /**
    * Registers a handler to invoke when this protocol object receives a request with the given method.
    *
+   * The handler receives a second callback parameter that can be used to emit progress notifications.
+   *
    * Note that this will replace any previous request handler for the same method.
    */
   setRequestHandler<
     T extends ZodObject<{
       method: ZodLiteral<string>;
+      params: ZodOptional<typeof BaseRequestParamsSchema>;
     }>,
   >(
     requestSchema: T,
-    handler: (request: z.infer<T>) => SendResultT | Promise<SendResultT>,
+    handler: (
+      request: z.infer<T>,
+      progress: (progress: Progress) => void,
+    ) => SendResultT | Promise<SendResultT>,
   ): void {
-    this._requestHandlers.set(requestSchema.shape.method.value, (request) =>
-      Promise.resolve(handler(requestSchema.parse(request))),
+    this._requestHandlers.set(
+      requestSchema.shape.method.value,
+      async (request) => {
+        const parsedRequest = requestSchema.parse(request);
+        const progressToken = parsedRequest.params?._meta?.progressToken;
+        const progressHandler =
+          progressToken !== undefined
+            ? (progress: Progress) =>
+                // Sending directly on the transport to avoid typing conflicts
+                this._transport
+                  ?.send({
+                    jsonrpc: "2.0",
+                    method: "notifications/progress",
+                    params: { ...progress, progressToken },
+                  })
+                  .catch((error: Error) => this._onerror(error))
+            : () => {};
+
+        return handler(parsedRequest, progressHandler);
+      },
     );
   }
 

src/types.ts

@@ -15,7 +15,7 @@ export const ProgressTokenSchema = z.union([z.string(), z.number().int()]);
  */
 export const CursorSchema = z.string();
 
-const BaseRequestParamsSchema = z
+export const BaseRequestParamsSchema = z
   .object({
     _meta: z.optional(
       z