Generating a non-random UUID, using a hash of multiple strings in Swift

Sufiyan — Thu, 03 Aug 2023 02:35:30 +0000

I was just working with some messy data, and realized I need a deterministic way to generate UUIDs from 2 strings in an iOS project. Looks like the only standard method available is

UUID(uuidString: String)

The problem with this is sometimes we don't have the formatted uuidString, so turns out we need to build it ourselves.

Enough talk, here's the code:

import Foundation
import CommonCrypto

func createHash(from string1: String, and string2: String) -> Data {
    let concatenatedString = string1 + string2
    guard let data = concatenatedString.data(using: .utf8) else {
        return Data()
    }

    var digest = [UInt8](repeating: 0, count: Int(CC_SHA256_DIGEST_LENGTH))
    _ = data.withUnsafeBytes {
        CC_SHA256($0.baseAddress, UInt32(data.count), &digest)
    }

    return Data(digest)
}

func generateNonRandomUUID(from string1: String, and string2: String) -> UUID {
    let hashData = createHash(from: string1, and: string2)

    // Truncate the hash data to 128 bits (16 bytes)
    let truncatedHashData = hashData.prefix(16)

    // Create a byte array (UnsafePointer<UInt8>) from the truncated hash data
    var byteArray: [UInt8] = []
    truncatedHashData.withUnsafeBytes {
        byteArray.append(contentsOf: $0)
    }

    // Create a UUID from the byte array
    let uuid = NSUUID(uuidBytes: byteArray)

    return uuid as UUID
}

Happy coding!

Focused state border width hack with Elm-UI

Sufiyan — Thu, 21 Oct 2021 04:49:58 +0000

I was recently trying to fix the focused styling for textfields in our company design system (https://github.com/PaackEng/paack-ui), and ran into this issue where I wasn't able to update the border width as per the design for the focused state.

So elm-ui lets you specify attributes for the focused state, but these have the type "decorative" attr (apparently the decorative label has something to do with the ephemeral styles).

Unfortunately, border width property has the type attr. After banging my head for a while I realized a good hack - instead of setting the border width for the focused state, I just ended up setting an explicit shadow:

shadow { color = Colors.navyBlue700, offset = ( 0, 0 ), blur = 0, size = 1.2 }

Works perfectly !!!

DEV Community: Sufiyan

Generating a non-random UUID, using a hash of multiple strings in Swift

Focused state border width hack with Elm-UI