Koa Stream Response

asyncRoute.js

/*
 * In this example I get an error from my rethinkdb database 
 * ReqlRuntimeError: Connection is closed in.... (basically the first query within exportText())
 */
export default async function downloadTexts (ctx, next) {
  const { qid } = this.params

  console.log('start')
  const stream = await exportText(qid, this._rdbConn, true)

  ctx.body = stream.on('error', err => {
    console.log('Error-handler')
    ctx.onerror(err)
  })
  ctx.set('Content-disposition', 'attachment; filename=' + qid + '.csv')
  ctx.set('Content-type', 'text/csv')
  await next()
}

exportText.js

/*
 * This file is responsible for generating the text
 * Just illustrative to see what is happening
 */
const r = require('rethinkdb')
const rethinkdbStream = require('rethinkdb-stream')
const through2 = require('through2')
const stringify = require('csv-stringify')
const stringifier = stringify()

export default async function exportText (qid, conn, all = false) {

   const someData = await fetchSomeDataCompletelyBefore()

  const textQuery = r.table('texts')
  const textCursor = await textQuery.run(conn)
  const stream = rethinkdbStream(textCursor)

  // Body
  return stream
    .pipe(
      through2.obj(function (t, enc, next) {
        this.push(transform(t))
        next()
      })
    )
    .pipe(stringifier)
}

generatorRoute.js

/*
 *  In this example the resulting file is empty. It seams that the body is sent back before the stream can actually start populating data
 */
export default function* downloadTexts (next) {
  const { qid } = this.params

  console.log('Pre')
  console.time('exportText')
  const stream = yield exportText(qid, this._rdbConn, false)
  console.timeEnd('exportText')
  console.log('Post')
  stream.on('error', err => {
    console.log('Error-handler')
    console.error(err)
  })
  this.body = stream
  this.set('Content-disposition', 'attachment; filename=' + qid + '.csv')
  this.set('Content-type', 'text/csv')
  yield next
}

rethinkMiddleware.js

/*
 * Creates and closes the rethinkdb connection. Somehow the connection is still open, but already "closing".
 */



/*
 * Create a RethinkDB connection, and save it in req._rdbConn
 */
export function* createConnection (next) {
  const options = makeConfig(Config.rethinkdb)
  try {
    var conn = yield r.connect(options)
    this._rdbConn = conn
  } catch (err) {
    console.log('this error')
    this.status = 500
    this.body = err.message || http.STATUS_CODES[this.status]
  }
  yield next
}

/*
 * Close the RethinkDB connection
 */
export function* closeConnection (next) {
  console.log('Closing')
  this._rdbConn.close()
  yield next
}