MehtaiPhoneApps MehtaiPhoneApps - 2 months ago 48
iOS Question

Generating Random Bytes in Swift 3.0

I want to generate random bytes using

SecRandomCopyBytes
in Swift 3.0. Here is how I did it in Swift 2.2

private static func generateRandomBytes() -> String? {
let data = NSMutableData(length: Int(32))

let result = SecRandomCopyBytes(kSecRandomDefault, 32, UnsafeMutablePointer<UInt8>(data!.mutableBytes))
if result == errSecSuccess {
return data!.base64EncodedString(options: NSData.Base64EncodingOptions(rawValue: 0))
} else {
print("Problem generating random bytes")
return nil
}
}


In Swift 3, I tried to do it like this, since I know the concept of unsafemutablebytes is different now, but it doesn't allow me to return. If I comment out the return part, it still says
Generic Parameter ResultType could not be inferred


fileprivate static func generateRandomBytes() -> String? {
var keyData = Data(count: 32)
_ = keyData.withUnsafeMutableBytes {mutableBytes in
let result = SecRandomCopyBytes(kSecRandomDefault, keyData.count, mutableBytes)
if result == errSecSuccess {
return keyData.base64EncodedString(options: NSData.Base64EncodingOptions(rawValue: 0))
} else {
print("Problem generating random bytes")
return nil
}
}
return nil
}


Does anyone know how to fix this?

Thanks

Answer

You were close, but return inside the closure returns from the closure, not from the outer function. Therefore only SecRandomCopyBytes() should be called in the closure, and the result passed back.

func generateRandomBytes() -> String? {

    var keyData = Data(count: 32)
    let result = keyData.withUnsafeMutableBytes {
        (mutableBytes: UnsafeMutablePointer<UInt8>) -> Int32 in
        SecRandomCopyBytes(kSecRandomDefault, keyData.count, mutableBytes)
    }
    if result == errSecSuccess {
        return keyData.base64EncodedString()
    } else {
        print("Problem generating random bytes")
        return nil
    }
}

For a "single-expression closure" the closure type can inferred automatically, so this can be shortened to

func generateRandomBytes() -> String? {

    var keyData = Data(count: 32)
    let result = keyData.withUnsafeMutableBytes {
        SecRandomCopyBytes(kSecRandomDefault, keyData.count, $0)
    }
    if result == errSecSuccess {
        return keyData.base64EncodedString()
    } else {
        print("Problem generating random bytes")
        return nil
    }
}
Comments