`open-stack-frame` endpoint broken: ERR_HTTP_HEADERS_SENT when Rozenite middleware is active

[lukas-preply]

Summary

When Rozenite middleware is active (WITH_ROZENITE=true), the Metro /open-stack-frame POST endpoint — used by React Native to open source files in the user's editor — is broken. The file never opens, and the Metro console logs:

Could not open trial.spec.ts in the editor.

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (node:_http_outgoing:642:11)
    at app.handle (.../node_modules/@rozenite/middleware/node_modules/express/lib/application.js:161:9)
    at handle (.../node_modules/connect/index.js:91:14)
    at call (.../node_modules/connect/index.js:239:7)
    at Immediate.next (.../node_modules/connect/index.js:183:5)
    at process.processImmediate (node:internal/timers:506:21)

Steps to Reproduce

1. Start Metro with Rozenite enabled:

   WITH_ROZENITE=true react-native start

2. Send a POST request to open a file in the editor:

   curl -X POST "http://localhost:8081/open-stack-frame" \
     -H "Content-Type: application/json" \
     -d '{"file":"src/some/file.ts","lineNumber":1}'

3. File does not open; Metro console shows the error above.

Root Cause Analysis

The middleware chain looks like this:

connect → ... → openStackFrameMiddleware → Rozenite Express middleware → ...

The issue is a collision between openStackFrameMiddleware (from @react-native-community/cli-server-api) and Rozenite's Express middleware:

1. openStackFrameMiddleware handles the POST, calls launchEditor(), writes res.writeHead(200); res.end(), and then falls through to next() — this is a pre-existing bug in the RN CLI middleware (it always calls next() even after ending the response).

2. Rozenite's Express middleware (getMiddleware() in @rozenite/middleware) receives the request via next() and its app.handle() attempts to set response headers — but the response is already sent.

3. This causes ERR_HTTP_HEADERS_SENT, and depending on timing, it may also interfere with launchEditor()'s ability to spawn the editor process.

Relevant code

openStackFrameMiddleware.js (RN CLI — note the unconditional next() call):

const handler = (req, res, next) => {
    if (req.method === 'POST') {
      // ... handles request, sends response ...
      res.writeHead(200);
      res.end();
    }
    next(); // ← called even after res.end() for POST requests
};

Rozenite middleware (@rozenite/middleware/dist/index.js):

app.use((req, _, next) => {
    assert(req.url, "req.url is required");
    logger.debug(`Incoming request: ${req.url}`);
    if (req.url.includes("/rozenite")) {
      req.url = req.url.replace("/rozenite", "");
    }
    next();
});
// ... express.static() catch-all that tries to set headers

Expected Behavior

POST /open-stack-frame should open the specified file in the user's editor, regardless of whether Rozenite middleware is active.

Suggested Fix

Rozenite's middleware could guard against already-finished responses:

app.use((req, res, next) => {
    if (res.headersSent) {
        return; // Response already handled by a previous middleware
    }
    // ... existing logic
});

Alternatively, Rozenite could avoid registering as a catch-all middleware and instead only handle routes under its own namespace (/rozenite/*).

Environment

• @rozenite/middleware: 1.3.0
• @rozenite/metro: 1.3.0
• react-native: 0.81.5
• @react-native-community/cli-server-api: from @react-native-community/cli 20.0.2
• Node: ≥ 24
• macOS