Koa EventSource Streaming (SSE)

index.js

const PassThrough = require('stream').PassThrough;
const Router = require('koa-66');
const router = new Router();
const Koa = require('koa');
const app = new Koa();

// ...

const sse = (event, data) => {
  return `event:${ event }\ndata: ${ data }\n\n`
}

router.get(`/json/data/:source`, ctx => {
  const stream = new PassThrough();
  const { source } = ctx.params;
  const { db } = app.context; // or whatever :)
  const reader = db.createReader(source); // or whatever :)
  const send = (data) => {
    let { type, msg } = data; // or whatever :)
    stream.write(sse(type, msg));
  }
  
  reader.on('data', send);
  ctx.req.on('close', () => ctx.res.end());
  ctx.req.on('finish', () => ctx.res.end());
  ctx.req.on('error', () => ctx.res.end());
  ctx.type = 'text/event-stream';
  ctx.body = stream;
});

app.use(router.routes());
app.listen(3000);

@sclark39, sse() needs to be a function declaration to work from where it's placed. Otherwise, try:

...
const sse = (event, data) => {
  return `event:${ event }\ndata: ${ data }\n\n`
}

router.get(`/json/data/:source`, ctx => { ... });

Defining sse() before it's called should fix the problem.

  ctx.req.on('close', () => ctx.res.end());
  ctx.req.on('finish', () => ctx.res.end());
  ctx.req.on('error', () => ctx.res.end());

fixes the issue @sclark39 mentioned