Swift 2.1 [UInt8] --utf8--> String?

Question

I know questions like this exist on both Stack Overflow and elsewhere. But it seems to have evolved a lot as well.

Given a list of UInt8 (a swift byte a

Answer 1

let buffUInt8: Array<UInt8> = [97, 98, 115, 100, 114, 102, 103, 104, 0]

// you need Int8 array
let buffInt8 = buffUInt8.map{ Int8(bitPattern: $0)}
let str = String.fromCString(buffInt8) // "absdrfgh"

alternatively you can use

String.fromCStringRepairingIllFormedUTF8(cs: UnsafePointer<CChar>) -> (String?, hadError: Bool)

Answer 2

I actually ended up needing to do this for a stream of UInt8 and was curious how hard utf8 decoding is. It's definitely not a one liner, but through the following direct implementation together:

import UIKit

let bytes:[UInt8] = [0xE2, 0x82, 0xEC, 0x00]

var g = bytes.generate()

extension String {
    init(var utf8stream:IndexingGenerator<[UInt8]>) {
        var result = ""
        var codepoint:UInt32 = 0
        while let byte = utf8stream.next() where byte != 0x00 {
            codepoint = UInt32(byte)
            var extraBytes = 0
            if byte & 0b11100000 == 0b11000000 {
                extraBytes = 1
                codepoint &= 0b00011111
            }
            else if byte & 0b11110000 == 0b11100000 {
                extraBytes = 2
                codepoint &= 0b00001111
            }
            else if byte & 0b11111000 == 0b11110000 {
                extraBytes = 3
                codepoint &= 0b00000111
            }
            else if byte & 0b11111100 == 0b11111000 {
                extraBytes = 4
                codepoint &= 0b00000011
            }
            else if byte & 0b11111110 == 0b11111100 {
                extraBytes = 5
                codepoint &= 0b00000001
            }
            for _ in 0..<extraBytes {
                if let additionalByte = utf8stream.next() {
                    codepoint <<= 6
                    codepoint |= UInt32(additionalByte & 0b00111111)
                }
            }
            result.append(UnicodeScalar(codepoint))
        }
        self = result
    }
}

String(utf8stream: g)

Answer 3

Xcode 8 • Swift 3

extension Collection where Iterator.Element == UInt8 {
    var bytes: [UInt8] { return Array(self) }
    var data: Data { return Data(self) }
    var string: String? { return String(data: data, encoding: .utf8) }
}

extension String {
    var data: Data { return Data(utf8) }
}

usage:

let sentence = "Hello World"

let utf8View = sentence.utf8
let bytes = utf8View.bytes     // [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100]

let data1 = sentence.data
print(data1 as NSData)         // <48656c6c 6f20576f 726c64>

let data2 = utf8View.data
let data3 = bytes.data
let string1 = utf8View.string  // "Hello World"
let string2 = bytes.string     // "Hello World"
let string3 = data1.string     // "Hello World"