Koa: Getting 404 or 204 as responses; need guidance on using async / await

[rainesinternationaldev]

Hello!

Total Koa newbie here, also new to the async/await syntax. In the post request below i was wondering how I can properly return the completed variable and attach it to ctx.body.

router.post('/resume', async (ctx) => {
  await form.parse(ctx.req, (err, fields, files) => {
    return sendMail(fields.candidateName, files.attachment)
      .then((completed) => {
        return completed;
      });
  });
})

[PlasmaPower]

router.post('/resume', (ctx) => {
  return form.parse(ctx.req, (err, fields, files) => {
    return sendMail(fields.candidateName, files.attachment)
      .then((completed) => {
        ctx.body = completed;
      });
  });
});

Alternatively, using async (like your code does):

router.post('/resume', async (ctx) => {
  ctx.body = await form.parse(ctx.req, (err, fields, files) => {
    return sendMail(fields.candidateName, files.attachment)
      .then((completed) => {
        return completed;
      });
  });
});

[rainesinternationaldev]

Thank you for the incredibly quick reply, @PlasmaPower. Unfortunately the first version gives me a 404 Not Found, and the second suggestion returns a 204 No Content.

The form.parse method comes from the multiparty library.

As for the sendMail function, it works like this:

export const sendMail = (candidateName, attachment) => {
  return new Promise((resolve, reject) => {
    transporter.sendMail({
      from: emailAddress,
      to:   emailAddress,
      subject: `Resume submission from ${candidateName}`,
      text: `Resume submission from ${candidateName}`,
      attachments: attachment
    }, (err) => {
      if (err) reject(err);
      resolve('SENDING COMPLETE');
    })
  });
}

Thanks in advance for your investigation.

[PlasmaPower]

@rainesinternationaldev form.parse doesn't return it a promise from what I can tell. It seems to use an event based system. Try this:

router.post('/resume', (ctx) => {
  ctx.body = '';
  return new Promise((resolve, reject) => {
    form.on('error', reject);
    form.on('close', resolve);
    form.parse(ctx.req, (err, fields, files) => {
      sendMail(fields.candidateName, files.attachment)
        .then((completed) => {
          ctx.body += completed + '\n';
        })
        .catch((err) => {
          ctx.body += 'ERROR: ' + err + '\n';
          ctx.status = 500;
        })
    });
  });
});

[rainesinternationaldev]

Wow you are brilliant, I hope you know that!

I had to place the reject and resolve handlers in the .catch and .then blocks, respectively, because apparently the events only fire when the _parsing_ completes; it does not care to wait until sendMail finishes. Otherwise it worked like a charm so I'll close this.

My question now is I thought a response was triggered the moment you assign ctx.body = '';. How does the route know to wait until the Promise is fulfilled?

[PlasmaPower]

@rainesinternationaldev Thanks! :) About the moving of reject and resolve - I'd be a bit careful about that as this will now error to the console if you have more than one upload in your form (as the Promise will resolve multiple times).

I thought a response was triggered the moment you assign ctx.body

Nope, a response is triggered when the returned promise resolves. Also, now you can just set ctx.body instead of appending to it as your code is for one upload only.