ExpressJS - Unhandled rejection Error: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

Question

I am able to register and login to the application but I receive the following server error:

"Unhandled rejection Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client" upon registration. I came across similar questions here but none of them resolved my problem.

authController.js:

const User = require("../models/User");
const jwt = require("jsonwebtoken");
const simplecrypt = require("simplecrypt");
const sc = simplecrypt();

process.env.SECRET_KEY = "secret";

exports.postLogin = (req, res, next) => {
  const { username, password } = req.body;
  let validationMessages = [];

  if (!username || !password) {
    validationMessages.push({ message: "Please fill in all fields" });
  }

  if (password.length < 6) {
    validationMessages.push({
      message: "Password should be at least 6 characters"
    });
  }

  if (validationMessages.length > 0) {
    res.sendStatus(403).json(validationMessages);
  } else {
    User.findOne({ where: { username: username } })
      .then(user => {
        if (!user) {
          res.sendStatus(400).json({
            message: "Invalid username or password"
          });
        } else if (password == sc.decrypt(user.password)) {
          const token = jwt.sign(user.dataValues, process.env.SECRET_KEY, {
            expiresIn: 1440 // expires in 24 hours
          });
          res.send(token);
        }
      })
      .catch(err => {
        res.send("Error: " + err);
      });
  }
};

exports.postRegister = (req, res, next) => {
  const { username, password, password2 } = req.body;
  let validationMessages = [];

  //Check required fields
  if (!username || !password || !password2) {
    validationMessages.push({ message: "Please fill in all fields" });
  }

  if (password.length < 6 || password2.length < 6) {
    validationMessages.push({
      message: "Password should be at least 6 characters"
    });
  }

  if (password !== password2) {
    validationMessages.push({
      message: "Passwords do not match"
    });
  }

  if (validationMessages.length > 0) {
    return res.sendStatus(400).json(validationMessages);
  } else {
    User.findOne({ where: { username: username } })
      .then(user => {
        if (user) {
          return res.sendStatus(403).json("User already exists");
        }
        const hashedPassword = sc.encrypt(password);
        User.create({ username: username, password: hashedPassword })
          .then(user => {
            return res.sendStatus(200).send(user);
          })
          .catch(err => {
            throw new Error(err);
          });
      })
      .catch(err => {
        throw new Error(err);
      });
  }
};

exports.getProfile = (req, res, next) => {
  const decoded = jwt.verify(
    req.headers["authorization"],
    process.env.SECRET_KEY
  );
  User.findOne({
    where: {
      id: decoded.id
    }
  })
    .then(user => {
      if (user) {
        res.statusCode(200).json(user);
      } else {
        throw new Error("User does not exist");
      }
    })
    .catch(err => {
      throw new Error(err);
    });
};

I am using Node.JS v12.14.0 and Express.JS v4.17.1 .

Answer 1

I resolved it myself. My problem was using res.sendStatus which sets the given response HTTP status code and sends its string representation as the response body. res.json will set the content-type response header, but at time time the response will already have been sent to the client. So simply res.send() should replace res.sendStatus().