DRY two factor code handling in pasteboard, fix leading zero loss

[allendav]

Fixes #557

To test, e.g. with WooCommerce iOS

• Build
• Ensure all unit tests pass, including the two new tests added for this under PasteboardTests
• Update WooCommerce iOS' Podfile to point at a local clone of this branch
• Build WooCommerce iOS with this pod
• Launch
• Sign in to WordPress.com using an account with 2FA enabled
• At the 2FA code prompt, swipe back to the home screen and open your authenticator app
• Select a 2FA code with a leading zero and tap it to copy it
• Swipe back into the WooCommerce iOS app
• Ensure the 2FA code (all six digits) is automatically pasted for you
• Don't actually complete login. Instead, return to the authenticator app and grab a 2FA code without a leading zero.
• Swipe back into the WooCommerce iOS app
• Ensure the 2FA code (all six digits) is automatically pasted for you
• Lastly, do it again but this time grab the code for your actual login and ensure you can complete login with it.

[allendav]

Interesting. It isn't the cast after all. It is how .number pattern matching is working with the pasteboard, i.e.:

                pasteboard.detectValues(for: [.number]) { valuesResult in
                    switch valuesResult {
                        case .success(let twofactorcode):
                            let foo = twofactorcode.first
                            foo?.value

returns 11234 when the pasteboard contains 011234

[allendav]

LOL. I've been digging into this more today. Finally have a robust sequence for pulling out two factor codes. Will update the PR with it tomorrow:

import UIKit

let pasteboard = UIPasteboard.general

pasteboard.string = "123123" /// Try different values here like 123456 123 123123123 asvab 3.1415 -99 etc

/// Detects a two factor authorization code in the pasteboard (if present)
/// and calls the completion with it, prepended as needed with zeros to yield six digits
func detectTwoFactorCode(completion: @escaping (Result<String, Error>) -> Void) {
    pasteboard.detectPatterns(for: [.number]) { result in
        var twoFactorCode: String = ""

        switch result {
            case .success(let detections):
                if detections.isEmpty {
                    completion(.success(""))
                    return
                }
                
                pasteboard.detectValues(for: [.number]) { valuesResult in
                    switch valuesResult {
                        case .success(let match):
                            if let matchedNumber = match.first?.value as? NSNumber {
                                twoFactorCode = matchedNumber.stringValue
                                
                                /// Reject numbers with decimal points or signs in them
                                let possibleCodeSet = CharacterSet(charactersIn: twoFactorCode)
                                if !possibleCodeSet.isSubset(of: CharacterSet.decimalDigits) {
                                    completion(.success(""))
                                    return
                                }
                                
                                /// Reject numbers with more than 6 digits
                                if twoFactorCode.count > 6 {
                                    completion(.success(""))
                                    return
                                }
                                
                                /// Prepend zeros to get to 6 digits
                                while twoFactorCode.count < 6 {
                                    twoFactorCode = "0" + twoFactorCode
                                }

                                completion(.success(twoFactorCode))
                                return
                            }
                        case .failure(let error):
                            completion(.failure(error))
                            return
                    }
                }
            case .failure(let error):
                completion(.failure(error))
                return
        }
    }
}

detectTwoFactorCode() { result in
    switch result {
    case .success(let twoFactorCode):
        twoFactorCode
    case .failure(_):
        "Failure"
    }
}

[bjtitus]

Just a few minor code suggestions. Otherwise, everything looks good!

[bjtitus]

Minor thing, but I wonder if the length should be a parameter of this method. If not, it should probably go as a constant at the top. I think I prefer making it a parameter with a default value, though.

public func detectAuthenticatorCode(length: Int = 6, completion: @escaping (Result<String, Error>) -> Void)

[allendav]

Fixed in e109be8

[bjtitus]

Can you remove this generated header?

We generally keep them out of the projects, but there's no good linter rule available to do it. 😞

[allendav]

Fixed in c96f997

[bjtitus]

It's pretty annoying that Apple is stripping the leading zeros and doesn't mention it.
We should file feedback to have them at least add it to the docs or, better yet, don't strip the leading digits in case they're significant...

[allendav]

We should file feedback...

Agreed. Done. Feedback ID FB8974839

[allendav]

All feedback addressed. Ready for next round of review. Thank you @bjtitus !

[bjtitus]

👍 Looks good to me!

Thanks for fixing this @allendav!