fix: ignore invalid json messages only

Author: Sahar Shemesh

src/shared/stdio.ts

@@ -1,4 +1,3 @@
-import { ZodError } from 'zod';
 import { JSONRPCMessage, JSONRPCMessageSchema } from '../types.js';
 
 /**
@@ -35,8 +34,8 @@ export function deserializeMessage(line: string): JSONRPCMessage | null {
     try {
         return JSONRPCMessageSchema.parse(JSON.parse(line));
     } catch (error: unknown) {
-        // When Non JSONRPC message is received (parsing error or schema validation error), return null
-        if (error instanceof ZodError || error instanceof SyntaxError) {
+        // When non-JSON messages are received, we simply ignore them.
+        if (error instanceof SyntaxError) {
             return null;
         }
         throw error;

test/shared/stdio.test.ts

@@ -1,5 +1,6 @@
 import { JSONRPCMessage } from '../../src/types.js';
 import { ReadBuffer } from '../../src/shared/stdio.js';
+import { ZodError } from 'zod/v4';
 
 const testMessage: JSONRPCMessage = {
     jsonrpc: '2.0',
@@ -34,9 +35,16 @@ test('should be reusable after clearing', () => {
     expect(readBuffer.readMessage()).toEqual(testMessage);
 });
 
-test('should override invalid messages and return null', () => {
+test('should override invalid json message and return null', () => {
     const readBuffer = new ReadBuffer();
 
     readBuffer.append(Buffer.from('invalid message\n'));
     expect(readBuffer.readMessage()).toBeNull();
 });
+
+test('should throw validation error on invalid JSON-RPC message', () => {
+    const readBuffer = new ReadBuffer();
+    const invalidJsonRpcMessage = '{"jsonrpc":"2.0","method":123}\n';
+    readBuffer.append(Buffer.from(invalidJsonRpcMessage));
+    expect(() => readBuffer.readMessage()).toThrowError(ZodError);
+});