Mongodb database connection code breaks app

Question

During development I've been using this mongodb code block to connect to database and it's been working flawlessly, but not when I deploy to Azure.

mongoose
  .connect(
    "mongodb://" +
      process.env.COSMOSDB_HOST +
      ":" +
      process.env.COSMOSDB_PORT +
      "/" +
      process.env.COSMOSDB_DBNAME +
      "?ssl=true&replicaSet=globaldb",
    {
      auth: {
        user: process.env.COSMOSDB_USER,
        password: process.env.COSMOSDB_PASSWORD
      }
    }
  )
  .then(() => console.log("Connection to CosmosDB successful"))
  .catch(err => console.error(err));

I was having trouble getting it to connect when deploying my app to azure so I was given a different mongodb code block to use from azure support

var mongoDBurl = process.env.MONGODB_CONNECTION;
mongoose.connect(mongoDBurl, { useNewUrlParser: true });

var db = mongoose.connection;

db.on('error', console.error.bind(console, 'MongoDB connection error:'));

db.once('open', (callback) => {
    console.log('MongoDB connectted！！');
});

, but when I use this mongodb code instead of the original, then I get Cannot set headers after they are sent to the client when trying to login to my app. Why is that?

login api

router.post("/login", (req, res, next) => {
  let fetchedUser;
  let username;
  User.findOne({ email: req.body.email })
    .then(user => {
      if (!user) {
        return res.status(401).json({
          message: "Auth failed"
        });
      }

      fetchedUser = user;
      username= user.username;
      return bcrypt.compare(req.body.password, user.password);
    })
    .then(result => {
      if (!result) {
        return res.status(401).json({
          message: "Auth failed"
        });
      }
      const token = jwt.sign(
        {
          email: fetchedUser.email,
          userId: fetchedUser._id,
          username: username
        },
        "secret_this_should_be_longer",
        { expiresIn: "1h" }
      );

      res.status(200).json({
        token: token,
        expiresIn: 3600,
        userId: fetchedUser._id,
        username: username
      });
    })
    .catch(err => {
      return res.status(401).json({
        message: "Auth failed"
      });
    });
});

Yooooomi · Accepted Answer · 2020-02-21 18:11:38Z

3

Reason

That's because the return statement in your promise doesn't end your then's queue. You are responding 401 if you don't find a User, then on the second then, you respond 401 again if there is no result.

Express is telling you that you can't send headers twice, which is true. I think there's nothing MongoDB related issue in your code.

Tip: Try converting your route into try/catch/await code to get a better comprehension of what's going on

Possible solution

Edit: this should work

// You don't need next as you're ending the request here and not calling it anyway
router.post("/login", async (req, res) => {
  const user = await User.findOne({ email: req.body.email });

  if (!user) {
    return res.status(401).json({
      message: "Auth failed"
    });
  }

  const { username } = user;

  const goodPassword = bcrypt.compareSync(req.body.password, user.password);

  if (!goodPassword) {
    return res.status(401).json({
      message: "Auth failed"
    });
  }

  const token = jwt.sign( // Double check if this call is synchronous or not (needs await or not)
    {
      email: user.email,
      userId: user._id,
      username: username
    },
    "secret_this_should_be_longer",
    { expiresIn: "1h" }
  );

  // Maybe store the token in the cookies instead of sending back, as you wish !

  res.status(200).json({
    token: token,
    expiresIn: 3600,
    userId: user._id,
    username: username
  });
});

Note that using await's helps you understand your code !

MongoDB Authentication

Concerning your MongoDB Authentication, you need to use the same credentials as in the first method

const { COSMOSDB_HOST, COSMOSDB_PORT, COSMOSDB_DBNAME, COSMOSDB_USER, COSMOSDB_PASSWORD } = process.env;

mongoose.connect(`mongodb://${COSMOSDB_HOST}:${COSMOSDB_PORT}/${COSMOSDB_DBNAME}?ssl=true&replicaSet=globaldb`,
  {
    auth: {
      user: COSMOSDB_USER,
      password: COSMOSDB_PASSWORD,
    },
  },
);

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'MongoDB connection error:'));

db.once('open', (callback) => {
    console.log('MongoDB connected！！');
});

edited Feb 21, 2020 at 18:11

answered Feb 21, 2020 at 16:34

Yooooomi

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5 Comments

user6680 Over a year ago

Your code works flawless with my old mongodb connection code. Thanks for the demonstration, (async is something I'm trying to work on getting better at) but when I try to login with new mongodb connection code, I get this error: pastebin.com/xyKe5VG0 So it's definitely the mongodb connection code that's the problem

Yooooomi Over a year ago

Ok the problem is still not MongoDB, I destructure the User object even if it doesn't exist, you need to access username only after checking if the User is not null. I edited my answer.

user6680 Over a year ago

When using your updated change. I don't get that error anymore, but also const user is returning null const user = await User.findOne({ email: req.body.email }); console.log(user) return; when connecting to new mongodb code. (returns user successfully with old connection code)

Yooooomi Over a year ago

Your mongo.connect is not using the same credentials as your first way, take a look at my edit on my answer

user6680 Over a year ago

I got it working. I think it was also related to not putting outbound IP addresses from app service properties to cosmosdb Virtual Networks, which was set to selected networks. I added them and now I can login. Thanks for your help!

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