fix: don't call onMessage callback twice when it throws

.changeset/onmessage-callback-error.md

@@ -0,0 +1,5 @@
+---
+'@callstack/react-native-brownfield': patch
+---
+
+`ReactNativeBrownfield.onMessage` no longer calls the callback a second time, with the raw message text, when the callback throws. The error now propagates instead of being swallowed.

packages/react-native-brownfield/src/__tests__/onMessage.test.ts

@@ -0,0 +1,73 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const native = vi.hoisted(() => ({
+  listener: undefined as ((payload: { text: string }) => void) | undefined,
+  remove: vi.fn(),
+}));
+
+vi.mock('react-native', () => ({
+  Platform: { OS: 'ios' },
+  NativeModules: {},
+}));
+vi.mock('../NativeReactNativeBrownfieldModule', () => ({
+  default: {
+    onBrownfieldMessage: (listener: (payload: { text: string }) => void) => {
+      native.listener = listener;
+      return { remove: native.remove };
+    },
+  },
+}));
+
+import ReactNativeBrownfield from '../index';
+
+function emit(text: string) {
+  native.listener?.({ text });
+}
+
+describe('onMessage', () => {
+  beforeEach(() => {
+    native.listener = undefined;
+    native.remove.mockClear();
+  });
+
+  it('passes parsed JSON to the callback', () => {
+    const callback = vi.fn();
+    ReactNativeBrownfield.onMessage(callback);
+
+    emit('{"text":"hello","id":1}');
+
+    expect(callback).toHaveBeenCalledExactlyOnceWith({
+      data: { text: 'hello', id: 1 },
+    });
+  });
+
+  it('passes the raw text when the message is not valid JSON', () => {
+    const callback = vi.fn();
+    ReactNativeBrownfield.onMessage(callback);
+
+    emit('not json');
+
+    expect(callback).toHaveBeenCalledExactlyOnceWith({ data: 'not json' });
+  });
+
+  it('does not call the callback again when it throws', () => {
+    const error = new Error('callback failed');
+    const callback = vi.fn(() => {
+      throw error;
+    });
+    ReactNativeBrownfield.onMessage(callback);
+
+    expect(() => emit('{"text":"hello"}')).toThrow(error);
+    expect(callback).toHaveBeenCalledExactlyOnceWith({
+      data: { text: 'hello' },
+    });
+  });
+
+  it('removes the native subscription', () => {
+    const subscription = ReactNativeBrownfield.onMessage(vi.fn());
+
+    subscription.remove();
+
+    expect(native.remove).toHaveBeenCalledOnce();
+  });
+});

packages/react-native-brownfield/src/index.ts

@@ -96,11 +96,13 @@ const ReactNativeBrownfield = {
   ): { remove: () => void } => {
     const subscription = ReactNativeBrownfieldModule.onBrownfieldMessage(
       (payload) => {
+        let data: unknown;
         try {
-          callback({ data: JSON.parse(payload.text) });
+          data = JSON.parse(payload.text);
         } catch {
-          callback({ data: payload.text });
+          data = payload.text;
         }
+        callback({ data });
       }
     );
     return { remove: () => subscription.remove() };