MongoError: Topology is closed, please connect despite established database connection

Question

I am writing a web application that uses asynchronous database requests as a part of the api. Currently, I have an async express route that awaits function returns from async functions. Both of these functions return booleans and both query the database. One works correctly, however the second one does not.

Here is the MongoClient setup:

const MongoClient = require('mongodb').MongoClient;
const uri = config.uri;                         // Contains custom url for accessing database
const client = new MongoClient(uri, { useUnifiedTopology: true}, { useNewUrlParser: true }, { connectTimeoutMS: 30000 }, { keepAlive: 1});

where config is from a file imported as.

const config = require("./config.js");

and functions properly.

Here is the express setup:

app.post("/signup", async function(request, response) {
  log("POST request at /signup");

  log("BEFORE UNIQUE USER");
  const isUniqueUser = await validateUniqueUser(request.body.email, request.body.password);
  log(isUniqueUser);
  const status = {
    status: null
  };
  if (isUniqueUser) {
    log("AFTER UNIQUE USER");
    let userCreated = await createPracticeProfile(request.body.email, request.body.password);
    log("user created: " + userCreated);
    if (userCreated) {
      status.status = "user_created";
    }
    response.json(status);
  } else {
    response.json(status);
  }

  console.log("********************************end");
});

The console outputs:

BEFORE UNIQUE USER

true (which it should be)

AFTER UNIQUE USER

MongoError: Topology is closed.

user created: undefined

***...***end

Here is the function for validating that a user is unique:

/*  VALIDATE_UNIQUE_USER
USE: ensure user does not have existing profile
PARAMS: email (string), password (string)
RETURN: isUniqueUser (bool)
*/
async function validateUniqueUser(email, password) {
  // connect to database
  const database = await client.connect().catch(err => {
    log("ERROR while connecting to database at: validateUniqueUser");
    console.log(err);
    client.close();
  });

  // database connection failed
  if (!database) {
    return false;
  }

  // connection successful => find user
  let user;
  try {
    user = await database.db("guitar-practice-suite").collection("users").findOne({email: email});
  } catch(err) {
    log("ERROR while finding user in database at: validateUniqueUser");
    console.log(err);
    client.close();
    return false;
  } finally {
    client.close();
    // user not found (unique)
    if (user === null || user === undefined) {
      return true;
    }
    return false;
  }
}

Here is the function for inserting the user into the collections:

/* CREATE_PRACTICE_PROFILE
USE: insert a practice profile into the database
PARAMS: email (string), password (string)
RETURN: userCreated (bool)
*/
async function createPracticeProfile(email, password) {
  // hash password
  let hashedPassword;
  try {
    hashedPassword = await new Promise((resolve, reject) => {
      bcrypt.hash(password, null, null, function(err, hash) {
        if (err) {
          reject(err);
        }
        resolve(hash)
      });
    });
  } catch(err) {
    log("ERROR while hashing password at: createPracticeProfile");
    console.log(err);
    return false;
  }

  // connect to database
  const database = await client.connect().catch(err => {
    log("ERROR while connecting to database at: validateUniqueUser");
    console.log(err);
    client.close();
  });

  // database connection failed
  if (!database) {
    return false;
  }

  // database connection successful => insert user into database
  let insertUserToUsers;
  let insertUserToExercises;
  let insertUserToCustomExercises;
  try {
    insertUserToUsers = await database.db("guitar-practice-suite").collection("users").insertOne({email: email, password: hashedPassword});
    insertUserToExercises = await database.db("guitar-practice-suite").collection("exercises").insertOne({email: email});
    insertUserToCustomExercises = await database.db("guitar-practice-suite").collection("custom-exercises").insertOne({email: email, exercises: []});
  } catch(err) {
    log("ERROR while inserting user into database at: createPracticeProfile");
    console.log(err);
    client.close();
    return false;
  } finally {
    client.close();
    return insertUserToUsers && insertUserToExercises && insertUserToCustomExercises;
  }
}

Answer 1

I've found the solution to the problem, but I'm not sure I understand the reasoning. The client.close() in the finally block of the validateUniqueUser function. It was closing the connection before the connection in the createPracticeProfile function was finished inserting the user.

When that line is taken out, the function works.