windowPostMessageTransport throws when an unrelated postMessage has null data
Assessment
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Newbie friendliness
- 74/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Active
- Tech stack
- typescript
Research direction
Find the getWindowPostMessageTransport implementation and inspect the message listener installed by connect(). Reproduce the issue with a message event whose data is null or undefined, then verify that non-object payloads are ignored while existing target, stream, origin, and MetaMask message handling remain unchanged.
Written by the indexing model from the issue text.
Description
What happened?
getWindowPostMessageTransport().connect() installs a global window.addEventListener('message', ...) listener. That listener receives every postMessage on the page, including messages sent by unrelated scripts or iframes.
The current listener destructures event.data before validating it:
const { target, data } = event.data;
If another page script sends a valid postMessage with null or undefined data, this throws a TypeError before the listener can ignore the unrelated message.
Minimal reproduction
After connect() has registered the message listener, dispatching a message shaped like this is enough to trigger the crash:
messageHandler({
data: null,
origin: location.origin,
} as MessageEvent);
Expected: unrelated/non-object message payloads are ignored, the same as wrong target/stream/origin messages.
Actual: the listener throws while destructuring event.data.
Suggested fix
Add a small guard before destructuring:
if (!event.data || typeof event.data !== 'object') {
return;
}
This keeps the existing MetaMask message handling unchanged while preventing unrelated page messages from surfacing avoidable listener errors.
- Dominant language
- TypeScript
- Stars
- 1
- Forks
- 4
- PR merge metrics
- No merged PRs in 30d
Getting set up
- No Dockerfile or Docker Compose file
- Has a pull request template
- No contributing guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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