Multiple async actions in response to a request

I’m new to Koa (and backend-dev in general) and I’m trying to set up a simple signup api. When a user posts to /api/user, bcrypt hashes the password and the user information is stored in a database. In my code it successfully does this but Node returns “headers have already been sent” error and returns a 404 response to the client. I have no trouble doing either of these async actions on their own but when I try to figure out a way to do them one after the other the headers always get sent early.

Here is my code:

async function createUser (ctx, req, next) {
  try {
    let d = new Date()
    await db.none('INSERT INTO users(email, username, hash, created, permissions) VALUES($1, $2, $3, $4, $5)', [req.email, req.username, req.pass, d, 'user'])
    ctx.status = 200
    next()
  } catch (e) {
    if (e.constraint === 'users_email_uindex') {
      ctx.response.body = 'This email address is already in use'
    } else if (e.constraint === 'users_username_uindex') {
      ctx.response.body = 'This username is already in use'
    }
    ctx.status = 400
    console.log(e)
    next()
  }
}

userService.post('/', async (ctx, next) => {
  console.log('POST /api/user/')
  let req = ctx.request.body
  try {
    await bcrypt.hash(req.pass, 10, (e, hash) => {
      if (e) {
        console.log(e)
      }
      req.pass = hash
      createUser(ctx, req, next)
    })
  } catch (e) {
    console.log(e)
  }
})

[uniibu]

Using your code i would do it like this:

Changes:(Node v8.x+)

• Use of ctx.body instead of ctx.response.body
• Added ctx.body on createUser successful db insert, instead of just ctx.status 200
• Removed next on createUser
• Uses Node v8+ for util.promisify
• Added constant bchash which is a promisified version of bcrypt.hash

const bcrypt = require("bcrypt")
const {promisify} = require('util')
const bchash = promisify(bcrypt.hash);

async function createUser(ctx, req) {
    try {
        let d = new Date();
        await db.none('INSERT INTO users(email, username, hash, created, permissions) VALUES($1, $2, $3, $4, $5)', [req.email, req.username, req.pass, d, 'user']);
        // simply setting ctx.status = 200 wont work, it will return as 204 No Content, so ctx.body must be set if you want a blank 200 response
        ctx.body = '';
    } catch (e) {
        console.log(e);
        ctx.status = 400;
        if (e.constraint === 'users_email_uindex') {
            ctx.body = 'This email address is already in use';
        } else if (e.constraint === 'users_username_uindex') {
            ctx.body = 'This username is already in use';
        }
    }
}

userService.post('/', async ctx => {
    console.log('POST /api/user/');
    let req = ctx.request.body;
    try {
        req.pass = await bchash(req.pass, 10);
        await createUser(ctx, req);
    } catch (e) {
        console.log(e);
    }
});

Changes:(Node < v8.x)

• Pretty much the same as the first example except this does not use Node v8’s util promisify
• Uses Node’s native Promise

async function createUser(ctx, req) {
    try {
        let d = new Date();
        await db.none('INSERT INTO users(email, username, hash, created, permissions) VALUES($1, $2, $3, $4, $5)', [req.email, req.username, req.pass, d, 'user']);
        ctx.body = '';
    } catch (e) {
        console.log(e);
        ctx.status = 400;
        if (e.constraint === 'users_email_uindex') {
            ctx.body = 'This email address is already in use';
        } else if (e.constraint === 'users_username_uindex') {
            ctx.body = 'This username is already in use';
        }
    }
}

async function bchash(pw, rounds) {
    return new Promise((resolve, reject) => {
        bcrypt.hash(pw, rounds, (err, hash) => {
            if (err)
                reject(err);
            else
                resolve(hash);
        });
    });
}

userService.post('/', async ctx => {
    console.log('POST /api/user/');
    let req = ctx.request.body;
    try {
        req.pass = await bchash(req.pass, 10);
        await createUser(ctx, req);
    } catch (e) {
        console.log(e);
    }
});

Changes:(My ow version, Node v8+)

• Simplified the routes controller to a single async function
• Uses ctx.throw for error handling

const bcrypt = require("bcrypt")
const {promisify} = require('util')
const bchash = promisify(bcrypt.hash);

async function createUser(ctx) {
    let req = ctx.request.body;
    let d = new Date();
    try {
        req.pass = await bchash(req.pass, 10);
        await db.none('INSERT INTO users(email, username, hash, created, permissions) VALUES($1, $2, $3, $4, $5)', [req.email, req.username, req.pass, d, 'user']);
        ctx.body = 'Success';
    } catch (e) {
        console.log(e);
        if (e.constraint === 'users_email_uindex') {
            ctx.throw('This email address is already in use', 400);
        } else if (e.constraint === 'users_username_uindex') {
            ctx.throw('This username is already in use', 400);
        }
    }
}
userService.post('/', createUser);

NOTE: I did not include whatever module you use for your router, but it should basically be the same with most router syntax.

[uniibu]

Glad to be of help. My best guess is that you are using a lower version of bcrypt(<1.x) which doesn’t support promises. The latest version of bcrypt (1.0.2) supports promises. So in case you update your bcrypt module, you could use await directly like req.pass = await bcrypt.hash(req.pass, 10)

In regards with ctx.throw i just followed the one on docs https://github.com/koajs/koa/wiki/Error-Handling, which is probably outdated due to changes from http-errors

Cheers!