Koa: How to handle ECONNRESET and EPIPE on streaming?

[stepankuzmin]

Consider this example

const fs = require('fs');
const Koa = require('koa');

const app = new Koa();

app.use(async (ctx) => {
  ctx.body = fs.createReadStream('really-large-file');
});

app.listen(4000);

If user aborts request I'm getting either

  Error: read ECONNRESET
      at _errnoException (util.js:1024:11)
      at TCP.onread (net.js:618:25)

or

  Error: write EPIPE
      at _errnoException (util.js:1024:11)
      at WriteWrap.afterWrite [as oncomplete] (net.js:870:14)

What is the proper way to handle this type of errors?

P.S. I have no errors after request aborts with express

const fs = require('fs');
const express = require('express');

const app = express();

app.get('/', (req, res) => {
  fs.createReadStream('really-large-file').pipe(res);
});

app.listen(4000);

P.P.S. I've tried

app.use(async (ctx) => {
  fs.createReadStream('really-large-file').pipe(ctx.res);
  ctx.respond = false;
});

But it had no effect.

[dead-horse]

try koa-onerror to catch this error and handle it manually?

[jonathanong]

depends on how you want to handle the error. once the headers and the stream is already sent, there's not much you can do.

[GuillaumeCisco]

I'm experiencing the same issue using webpackHotMiddleware with ssr. Every time I refresh the page in chrome, the error appears:

Error: read ECONNRESET
      at _errnoException (util.js:1003:13)
      at TCP.onread (net.js:623:25)

in the server log.
As described in this thread, a close is not done correctly : https://github.com/websockets/ws/issues/1256
This thread deals with websocket, but we use event-stream here.

Is there a better way to handle this problem than just hiding the error with koa-onerror ?

[GuillaumeCisco]

Ok just found out resolving this problem in my case is impossible as event-stream does not communicate data to the server. So the server will never know when an user refresh its tab. We have to use a websocket communication to handle this.

I discovered koa-webpack with https://github.com/webpack-contrib/webpack-hot-client which implements a websocket approch and should be better than using koa-error. I will try that ;)

[shellscape]

@GuillaumeCisco just thought I would mention: I wrote webpack-hot-client, and was researching the same ECONNRESET error in a separate project. your comment reminded me that I've already solved this problem in the past. Cheers.

[rvanmil]

I know this is an old issue but in case someone finds it and is unable to get things to work properly (koa-onerror did not work for me), here's how I got this to work (koa 2.7.0).
Looking at the onerror function here: https://github.com/koajs/koa/blob/8b4e2cd3bc6e165a0ea544686346cd79e437bc28/lib/context.js#L121 and here: https://github.com/koajs/koa/blob/8b4e2cd3bc6e165a0ea544686346cd79e437bc28/lib/context.js#L123-L128 once the headers are sent, nothing is done. But the error is emitted as an app-level error.
So I created a handler for the app-level error event:

// Catch and log Koa app-level errors
const app = new Koa()
app.on('error', (error) => {
  if (error.code === 'EPIPE') {
    logger.warn('Koa app-level EPIPE error.', { error })
  } else {
    logger.error('Koa app-level error', { error })
  }
})

And now I'm no longer seeing the Error: write EPIPE messages 😊