node-server doesn't flush headers until content is written to it

[td0m]

What version of Hono are you using?

4.7.11

What runtime/platform is your app running on? (with version if possible)

Node v23.8.0

What steps can reproduce the bug?

on @hono/node-server@1.14.3. make SSE endpoint that waits before sending content:

router.get("/foo", (c) => {
  return streamSSE(c, async (sse) => {
    // headers don't get written for a minute
    await sse.sleep(60_000);
    await sse.write("hi");
  });
});

What is the expected behavior?

Headers getting flushed. You can see this e.g. by visiting in Chrome and checking the status header:

What do you see instead?

Headers not getting flushed until we sse.write:

Additional information

I believe headers getting flushed is the expected behaviour. I tested the exact same code in Deno, works as expected.

[yusukebe]

This may not be a honojs/hono issue but a@hono/node-server issue. I'll transfer the issue.

[usualoma]

I will look into it