Hono•4mo ago

Server Sent Events

Hello guys! Sorry if this was asked before. I'm trying to implement an event emitter with SSE like this:

const emitter = new EventEmitter();

app.use("/sse/*", async (c, next) => {
  c.header("Content-Type", "text/event-stream");
  c.header("Cache-Control", "no-cache");
  c.header("Connection", "keep-alive");
  await next();
});

app.post('/message', async (c) => {
  const message = 'test';
  emitter.emit('message', message);
  return c.json({message});
})

app.get('/sse', async (c) => {
  return streamSSE(c, async (stream) => {
   
  const handler = async (message: string) => {
      await stream.writeSSE({
        data: message,
        event: "message"
      });
    }

    stream.onAbort(() => {
      console.log('Connection aborted');
    })

    emitter.on('message', handler);
})
})

const emitter = new EventEmitter();

app.use("/sse/*", async (c, next) => {
  c.header("Content-Type", "text/event-stream");
  c.header("Cache-Control", "no-cache");
  c.header("Connection", "keep-alive");
  await next();
});

app.post('/message', async (c) => {
  const message = 'test';
  emitter.emit('message', message);
  return c.json({message});
})

app.get('/sse', async (c) => {
  return streamSSE(c, async (stream) => {
   
  const handler = async (message: string) => {
      await stream.writeSSE({
        data: message,
        event: "message"
      });
    }

    stream.onAbort(() => {
      console.log('Connection aborted');
    })

    emitter.on('message', handler);
})
})

but it seems it goes directly in the onError on frontend because it closes the stream

2 Replies

Mihai AndreiOP•4mo ago

The fix seems to be to add this inside streamSSE:

let isAborted = false
stream.onAbort(() => {
   isAborted = true;
})
while(!isAborted) {
      await stream.sleep(500); 
}

let isAborted = false
stream.onAbort(() => {
   isAborted = true;
})
while(!isAborted) {
      await stream.sleep(500); 
}

Is this the expected way to use SSE in hono?

Mihai AndreiOP•4mo ago

I think i've found something related. It seems i need to use stream instead https://github.com/honojs/hono/issues/2993

GitHub

Stream should not be closed automatically · Issue #2993 · honojs/ho...

What version of Hono are you using? 4.4.6 What runtime/platform is your app running on? Bun What steps can reproduce the bug? Using either stream or streamSSE is not gonna work unless you're us...

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Server Sent Events