Does https://github.com/koajs/send need to be updated with the new logic?

This is a huge breaking change as it breaks fs.createReadStream support. Instead, you'll have to make sure you'll handle the stream's errors before it reaches the koa response logic. This is good as you'd want to do this for all streams anyways. You can have an upstream middleware like:

app.use(async (ctx, next) {
  await next()

  // check if the object is a stream
  if (ctx.body?.readable && typeof ctx.body?.pipe === 'function') {
    await new Promise((resolve, reject) => { // wait for it to be either readable or throw an error
      ctx.body.on('readable', () => resolve())
      ctx.body.on('error', (err) => reject(err)) // TODO handle errors
    })
  }
})

closes #1420

I don't know why the middleware is not working for me however hard I try(I noticed there is a syntax error, nevertheless), I read through the source code and implemented an alternative.

# Can an AI know that it doesn't know

const isRootCauseErrorENOENT = (err) => {
  if (err instanceof Error) {
    let rootCauseErr = err;
    while (rootCauseErr.cause instanceof Error) {
      rootCauseErr = rootCauseErr.cause;
    }
    return rootCauseErr.code === 'ENOENT';
  }
  return false;
};

app.on('error', (err, ctx) => {
  if (isRootCauseErrorENOENT(err)) {
    // After breaking change introduced in koajs@3.0.0 https://github.com/koajs/koa/pull/1861
    err.status = 404;
  } else {
    console.error('Server error.', err, ctx);
  }
});