fix: reject non-object JSON-RPC requests

README.md

@@ -27,7 +27,8 @@ configured, so the server is demoable without a live store.
 
 MCP over **Streamable HTTP**: clients POST JSON-RPC 2.0 to `/mcp`. Implements
 `initialize`, `tools/list`, `tools/call`, and `ping`. `tools/list` only advertises
-the tools the calling client is scoped for.
+the tools the calling client is scoped for. Non-object JSON values receive a
+JSON-RPC `-32600` Invalid Request response before dispatch.
 
 ## Auth & scopes
 

src/index.ts

@@ -51,14 +51,18 @@ export default {
       return aiChat(req, env);
     }
 
-    let body: RpcRequest;
+    let body: unknown;
     try {
-      body = (await req.json()) as RpcRequest;
+      body = await req.json();
     } catch {
       return json(rpcError(null, -32700, "parse error"));
     }
 
-    const result = await handle(body, env, caller);
+    if (body === null || typeof body !== "object" || Array.isArray(body)) {
+      return json(rpcError(null, -32600, "invalid request"));
+    }
+
+    const result = await handle(body as RpcRequest, env, caller);
     // Notifications (no id) get a 202 with no body per JSON-RPC.
     if (result === undefined) return new Response(null, { status: 202 });
     return json(result);

test/index.test.mjs

@@ -69,6 +69,25 @@ function mcpRequest(env, body) {
   );
 }
 
+test("rejects non-object JSON-RPC request bodies", async (t) => {
+  const env = {
+    BRIDGEKIT_CLIENTS: JSON.stringify({
+      "client-key": { name: "reader", tools: [], allowWrite: false },
+    }),
+  };
+
+  for (const body of [null, []]) {
+    await t.test(JSON.stringify(body), async () => {
+      const response = await mcpRequest(env, body);
+      assert.deepEqual(await response.json(), {
+        jsonrpc: "2.0",
+        id: null,
+        error: { code: -32600, message: "invalid request" },
+      });
+    });
+  }
+});
+
 test("tools/call rejects non-object arguments", async (t) => {
   let upstreamCalls = 0;
   globalThis.fetch = async () => {