DeviceToken Swift Playground for transforming Data into a Hex String

README.md

Device Tokens and Push Notifications

When registering a device to push notifications a device token is provided in the form of Data. It is helpful to transform this stream of bytes into a string to use with HTTP requests and storing with UserDefaults in a human readable way. This DeviceToken type allows for creating an instance either is with data or a hex string and then accessing data and hex string properties. The Swift Playground also includes a series of unit tests which cover the DeviceToken type completely.

• Apple Push Notification Device Tokens (NSHipster)

DeviceToken.swift

import Foundation

struct DeviceToken {
    enum Failure: Error {
        case invalidHexString
    }
    var data: Data
    var hexString: String {
        let result = data.map { String(format: "%02x", $0) }.joined().uppercased()
        return result
    }

    init(data: Data) {
        self.data = data
    }

    init(hexString: String) throws {
        if hexString.count % 2 != 0 {
            throw Failure.invalidHexString
        }
        let length = 2
        let end = hexString.count/length
        let range = 0..<end
        let transformHex: (Int) -> String = {
            String(hexString.dropFirst($0 * length).prefix(length))
        }
        let transformByte: (String) throws -> UInt8 = {
            guard let value = UInt8($0, radix: 16) else {
                throw Failure.invalidHexString
            }
            return value
        }
        let bytes = try range.map(transformHex).map(transformByte)
        let data = Data(bytes)
        self.data = data
    }
}

/** TESTING **/

import XCTest

public class TestObserver: NSObject, XCTestObservation {

    public static func observe() {
        let observer = TestObserver()
        XCTestObservationCenter.shared.addTestObserver(observer)
    }

    public func testCase(_ testCase: XCTestCase, didFailWithDescription description: String, inFile filePath: String?, atLine lineNumber: Int) {
        print("🚫 \(description) line:\(lineNumber)")
    }

    public func testCaseDidFinish(_ testCase: XCTestCase) {
        if testCase.testRun?.hasSucceeded == true {
            print("✅ \(testCase)")
        }
    }

}

class DeviceTokenTests : XCTestCase {

    func testEmptyHexString() {
        guard let deviceToken = try? DeviceToken(hexString: "") else {
            XCTFail()
            return
        }
        XCTAssertEqual(deviceToken.hexString, "")
        XCTAssertEqual(Array(deviceToken.data), [])
    }

    func testMaxHexString() {
        guard let deviceToken = try? DeviceToken(hexString: "FF") else {
            XCTFail()
            return
        }
        XCTAssertEqual(deviceToken.hexString, "FF")
        XCTAssertEqual(Array(deviceToken.data), [255])
    }

    func testVariousHexStringValues() {
        guard let deviceToken = try? DeviceToken(hexString: "FF0110") else {
            XCTFail()
            return
        }
        XCTAssertEqual(deviceToken.hexString, "FF0110")
        XCTAssertEqual(Array(deviceToken.data), [255, 1, 16])
    }

    func testEmptyData() {
        let deviceToken = DeviceToken(data: Data([]))
        XCTAssertEqual(deviceToken.hexString, "")
        XCTAssertEqual(Array(deviceToken.data), [])
    }

    func testMaxData() {
        let deviceToken = DeviceToken(data: Data([255]))
        XCTAssertEqual(deviceToken.hexString, "FF")
        XCTAssertEqual(Array(deviceToken.data), [255])
    }

    func testVariousDataValues() {
        let deviceToken = DeviceToken(data: Data([255, 1, 16]))
        XCTAssertEqual(deviceToken.hexString, "FF0110")
        XCTAssertEqual(Array(deviceToken.data), [255, 1, 16])
    }

    func testInvalidHexStringValues() {
        XCTAssertThrowsError(try DeviceToken(hexString: "FF1"))
        XCTAssertThrowsError(try DeviceToken(hexString: "FF0g"))
    }
}

TestObserver.observe()
DeviceTokenTests.defaultTestSuite.run()