21. Validation

Written by Tim Condon

Note: This update is an early-access release. This chapter has not yet been updated to Vapor 4.

In the previous chapters, you built a fully-functional API and website. Users can send requests and fill in forms to create acronyms, categories and other users. In this chapter, you’ll learn how to use Vapor’s Validation library to verify some of the information users send the application. You’ll create a registration page on the website for users to sign up. Finally, you’ll validate the data from this form and display an error message if the data isn’t correct.

The registration page

Create a new file in Resources/Views called register.leaf. This is the template for the registration page. Open register.leaf and add the following:

#set("content") {
  <h1>#(title)</h1>

  <form method="post">
    <div class="form-group">
      <label for="name">Name</label>
      <input type="text" name="name" class="form-control"
       id="name"/>
    </div>

    <div class="form-group">
      <label for="username">Username</label>
      <input type="text" name="username" class="form-control"
       id="username"/>
    </div>

    <div class="form-group">
      <label for="password">Password</label>
      <input type="password" name="password"
       class="form-control" id="password"/>
    </div>

    <div class="form-group">
      <label for="confirmPassword">Confirm Password</label>
      <input type="password" name="confirmPassword"
       class="form-control" id="confirmPassword"/>
    </div>

    <button type="submit" class="btn btn-primary">
      Register
    </button>
  </form>
}

#embed("base")

This is very similar to the templates for creating an acronym and logging in. The template contains four input fields for:

• name
• username
• password
• password confirmation

Save the file. Next, open WebsiteController.swift and at the bottom of the file add the following context for the registration page:

struct RegisterContext: Encodable {
  let title = "Register"
}

Next, below logoutHandler(_:), add the following route handler for the registration page:

func registerHandler(_ req: Request) throws -> Future<View> {
  let context = RegisterContext()
  return try req.view().render("register", context)
}

Like the other routes handlers, this creates a context then calls render(_:_:) to render register.leaf.

Next, at the bottom of WebsiteController.swift, create the Content for the POST request for registration:

struct RegisterData: Content {
  let name: String
  let username: String
  let password: String
  let confirmPassword: String
}

This Content type matches the expected data received from the registration POST request. The variables match the names of the inputs in register.leaf. Next, add the following after registerHandler(_:) to create a route handler for this POST request:

// 1
func registerPostHandler(
  _ req: Request,
  data: RegisterData
) throws -> Future<Response> {
  // 2
  let password = try BCrypt.hash(data.password)
  // 3
  let user = User(
    name: data.name,
    username: data.username,
    password: password)
  // 4
  return user.save(on: req).map(to: Response.self) { user in
    // 5
    try req.authenticateSession(user)
    // 6
    return req.redirect(to: "/")
  }
}

Here’s what’s going on in the route handler:

1. Define a route handler that accepts a request and the decoded RegisterData.

2. Hash the password submitted to the form.

3. Create a new User, using the data from the form and the hashed password.

4. Save the new user and unwrap the returned future.

5. Authenticate the session for the new user. This automatically logs users in when they register, thereby providing a nice user experience when signing up with the site.

6. Return a redirect back to the home page.

Next, in boot(router:) add the following below authSessionRoutes.post("logout", use: logoutHandler):

// 1
authSessionRoutes.get("register", use: registerHandler)
// 2
authSessionRoutes.post(RegisterData.self, at: "register",
                       use: registerPostHandler)

Here’s what this does:

1. Connect a GET request for /register to registerHandler(_:).
2. Connect a POST request for /register to registerPostHandler(_:data:). Decode the request’s body to RegisterData.

Finally, open base.leaf. Before the closing </ul> in the navigation bar, add the following:

#// 1
#if(!userLoggedIn) {
  #// 2
  <li class="nav-item #if(title == "Register"){active}">
    #// 3
    <a href="/register" class="nav-link">Register</a>
  </li>
}

Here’s what the new Leaf code does:

1. Check to see if there’s a logged in user. You only want to display the register link if there’s no user logged in.
2. Add a new navigation link to the navigation bar. Set the active class if the current page is the Register page.
3. Add a link to the new /register route.

Save the template then build and run the project in Xcode. Visit http://localhost:8080 in your browser. You’ll see the new navigation link:

Click Register and you’ll see the new register page:

If you fill out the form and click Register, the app takes you to the home page. Notice the Log out button in the top right; this confirms that registration automatically logged you in.

Basic validation

Vapor provides a validation module to help you check data and models. Open WebsiteController, and add the following at the bottom:

// 1
extension RegisterData: Validatable, Reflectable {
  // 2
  static func validations() throws
    -> Validations<RegisterData> {
    // 3
    var validations = Validations(RegisterData.self)
    // 4
    try validations.add(\.name, .ascii)
    // 5
    try validations.add(\.username,
                        .alphanumeric && .count(3...))
    // 6
    try validations.add(\.password, .count(8...))
    // 7
    return validations
  }
}

Here’s what this does:

1. Extend RegisterData to make it conform to Validatable and Reflectable. Validatable allows you to validate types with Vapor. Reflectable provides a way to discover the internal components of a type.
2. Implement validations() as required by Validatable.
3. Create a Validations instance to contain the various validators.
4. Add a validator to ensure RegisterData’s name contains only ASCII characters. Note: Be careful when adding restrictions on names like this. Some countries, such as China, don’t have names with ASCII characters.
5. Add a validator to ensure the username contains only alphanumeric characters and is at least 3 characters long. .count(_:) takes a Swift Range, allowing you to create both open-ended and closed ranges, if required.
6. Add a validator to ensure the password is at least 8 characters long.
7. Return the validations for Vapor to test.

As you can see, Vapor allows you to create powerful validations on models or incoming data. Because you use key paths, Vapor creates type-safe validations. Be aware the .ascii validator works only on String types. It won’t work on Int, for example.

In registerPostHandler(_:data:), add the following at the top of the method:

do {
  try data.validate()
} catch {
  return req.future(req.redirect(to: "/register"))
}

This calls validate() on the decoded RegisterData, checking each validator you added previously. validate() can throw ValidationError. In an API, you can let this error propagate back to the user but, on a website, that doesn’t make for a good user experience. In this case, you redirect the user back to the “register” page.

Build and run, then visit the “register” page in your browser. If you enter information that doesn’t match the validators, the app sends you back to try again.

Custom validation

If you’ve been following closely, you’ll notice a flaw in the validation: Nothing ensures the passwords match! Vapor’s validation library doesn’t provide a built-in way to check that two strings match. However, it’s easy to add custom validators. In the validations() for RegisterData, before return validations, add the following:

// 1
validations.add("passwords match") { model in
  // 2
  guard model.password == model.confirmPassword else {
    // 3
    throw BasicValidationError("passwords don’t match")
  }
}

Here’s what the new validator does:

1. Use Validation’s add(_:_:) to add a custom validator for RegisterData. This takes a readable description as the first parameter. The second parameter is a closure that should throw if validation fails.
2. Verify that password and confirmPassword match.
3. If they don’t, throw BasicValidationError.

Build and run, then try registering a user with mismatched password. The application redirects you back to the “register” form.

Displaying an error

Currently, when a user fills out the form incorrectly, the application redirects back to the form with no indication anything went wrong. Open register.leaf and add the following under <h1>#(title)</h1>:

#if(message) {
  <div class="alert alert-danger" role="alert">
    Please fix the following errors:<br />
    #(message)
  </div>
}

If the page context includes message, this displays it in a new <div>. You style the new message appropriately by setting the alert and alert-danger classes. Open WebsiteController.swift, and add the following to the end of RegisterContext:

let message: String?

init(message: String? = nil) {
  self.message = message
}

This is the message to display on the registration page. Remember that Leaf handles nil gracefully, allowing you to use the default value in the normal case.

This is the flag the template uses. In registerHandler(_:), replace:

let context = RegisterContext()

With the following:

let context: RegisterContext
if let message = req.query[String.self, at: "message"] {
  context = RegisterContext(message: message)
} else {
  context = RegisterContext()
}

This checks the request’s query. If message exists — i.e., the URL is /register?message=some-string — the route handler includes it in the context Leaf uses to render the page.

Finally, in registerPostHandler(_:data:), replace the catch block with:

catch (let error) {
  let redirect: String
  if let error = error as? ValidationError,
    let message = error.reason.addingPercentEncoding(
      withAllowedCharacters: .urlQueryAllowed) {
    redirect = "/register?message=\(message)"
  } else {
    redirect = "/register?message=Unknown+error"
  }
  return req.future(req.redirect(to: redirect))
}

When validation fails, the route handler extracts the message from the ValidationError, escapes it properly for inclusion in a URL, and adds it to the redirect URL. Then, it redirects the user back to the registration page. Build and run, then visit http://localhost:8080/register in your browser.

Submit the empty form and you’ll see the new message:

Where to go from here?

In this chapter, you learned how to use Vapor’s validation library to check request’s data. You can apply validation to models and other types as well.

In the next chapter, you’ll learn how to integrate the TIL application with an OAuth provider. This lets you delegate login and registration to online services such Google or GitHub, allowing users to sign in with an existing account.