Strange error using Flutter app + Deno + MongoDB backend - mongodb

Question

I want to write a simple registration function and this is my code:
auth_screen.dart:
Future<void> _submit() async {
if (!_formKey.currentState!.validate()) {
// Invalid!
return;
}
_formKey.currentState!.save();
setState(() {
_isLoading = true;
});
try {
if (_authMode == AuthMode.Login) {
// Log user in
await Provider.of<Auth>(context, listen: false).login(
_authData['email'] as String,
_authData['password'] as String,
);
} else {
// Sign user up
await Provider.of<Auth>(context, listen: false).signup(
_authData['email'] as String,
_authData['password'] as String,
);
}
} on HttpException catch (error) {
var errorMessage = 'Authentication failed';
print("this is the auth data");
print(_authData);
if (error.toString().contains('EMAIL_EXISTS')) {
errorMessage = 'This email address is already in use.';
} else if (error.toString().contains('INVALID_EMAIL')) {
errorMessage = 'This is not a valid email address';
} else if (error.toString().contains('WEAK_PASSWORD')) {
errorMessage = 'This password is too weak.';
} else if (error.toString().contains('EMAIL_NOT_FOUND')) {
errorMessage = 'Could not find a user with that email.';
} else if (error.toString().contains('INVALID_PASSWORD')) {
errorMessage = 'Invalid password.';
}
_showErrorDialog(errorMessage);
} catch (error) {
var errorMessage = 'Could not authenticate you. Please try again later.' +
error.toString();
_showErrorDialog(errorMessage);
}
setState(() {
_isLoading = false;
});
}
auth.dart:
Future<void> signup(String email, String password) async {
return _authenticate(email, password, 'register');
}
Future<void> _authenticate(
String email, String password, String urlSegment) async {
final url = Uri.parse('http://10.0.2.2:8000/api/$urlSegment');
// final url = Uri.http('http://localhost:8000/api/', 'urlSegment');
try {
final response = await http.post(
url,
body: json.encode(
{
'email': email,
'password': password,
//'returnSecureToken': true,
},
),
);
final responseData = json.decode(response.body);
if (responseData['error'] != null) {
throw HttpException(responseData['error']['message']);
}
_token = responseData['idToken'];
_userId = responseData['localId'];
_expiryDate = DateTime.now().add(
Duration(
seconds: int.parse(
responseData['expiresIn'],
),
),
);
_autoLogout();
notifyListeners();
final prefs = await SharedPreferences.getInstance();
final userData = json.encode(
{
'token': _token,
'userId': _userId,
'expiryDate': _expiryDate!.toIso8601String(),
},
);
prefs.setString('userData', userData);
} catch (error) {
throw error;
}
}
This is the backend(Deno) part of the project:
auth_controller.ts:
async register(ctx: RouterContext) {
const { email, password } = await ctx.request.body().value;
let user = await User.findOne({ email });
if (user) {
ctx.response.status = 422;
ctx.response.body = { message: "Email is already exist" };
return;
}
const hashedPassword = hashSync(password);
user = new User({ email, password: hashedPassword });
await user.save();
ctx.response.status = 201;
ctx.response.body = {
id: user.id,
name: user.name,
email: user.email
};
}
And this is the user.ts class:
export default class User extends BaseModel {
public id: string = "";
public name: string = "";
public email: string = "";
public password: string = "";
constructor({ id = "", name = "", email = "", password = "" }) {
super();
this.id = id;
this.name = name;
this.email = email;
this.password = password;
}
static async findOne(params: object): Promise<User | null> {
const user = await userCollection.findOne(params);
if (!user) {
return null;
}
return new User(User.prepare(user));
}
async save() {
const _id = await userCollection.insertOne(this);
this.id = _id;
return this;
}
}
I get this error message when I want to test the application on Android emulator:
type 'Null' is not a subtype of type 'String'
When I try the backend server using Postman and send post request to http://0.0.0.0:8000/api/register address. I get correct response and it works, but I don't know why do I get Null response using the Flutter app?
I tried to print the variables in both front and backend side of the application and it seems they all are good and correct but I can not understand why do I get this error message?!

Answer 1

probably you got a null value in your map in this part since map return a null value when can't find a key, check if the Map value is not null
try {
if (_authMode == AuthMode.Login) {
// Log user in
await Provider.of<Auth>(context, listen: false).login(
_authData['email'] as String, // can return a null value
_authData['password'] as String, // can return a null value
);
} else {
// Sign user up
await Provider.of<Auth>(context, listen: false).signup(
_authData['email'] as String, // can return a null value
_authData['password'] as String, // can return a null value
);
}
}

Answer 2

Seems you're getting a null as a response value instead of a String.
EDIT:
Future<void> signup(String email, String password) async {
return _authenticate(email, password, 'register');
}
Check email and password are not null. And getting the correct values.

Answer 3

Actually the problem was from these two lines of code:
_token = responseData['idToken'];
_userId = responseData['localId'];
Because it wasn't passing these data in response from the backend side.