ByteBackpacker

ByteBackpacker is a small utility written in pure Swift to pack value types into a Byte¹ array and unpack them back.

Additionally, there is a Data (formerly NSData) extension to convert Data objects into a Byte array.

¹ Byte is a typealias for UInt8.

Table of Contents

• Installation
• Usage
• API
• Discussion
• Contributions
• Versions
• License

Installation

You have three options:

1. Use Swift Package Manager:

    import PackageDescription
   
    let package = Package(
        name: "TestImport",
        dependencies: [
            .Package(url: "https://github.com/michaeldorner/ByteBackpacker.git")
        ]
    )
   

2. Use Cocoapods: pod 'ByteBackpacker'

3. Copy the ByteBackpacker.swift file (containing the ByteBackpacker class) to your project (not considered as good practice).

Although it can be used in the same way in Objective-C, I had clearly Swift projects in mind. The easiest way for Objective-C users is to embed the ByteBackpacker.framework. Of course, Swift users can also do this, but actually I do not see any advantages.

Usage

Important for a proper usage: ByteBackpacker does only support value types (e.g. numbers, structs, ...), but no reference types (e.g. classes)! For further information see Discussion.

All examples can be seen running in the ByteBackpackerPlayground.playground. Let's have a look on some general use cases:

From Double to [Byte]

let aDouble: Double = 1.0
let aByteArray: [Byte] = ByteBackpacker.pack(aDouble)

From [Byte] to Double

let option_1: Double = ByteBackpacker.unpack(aByteArray)
let option_2 = ByteBackpacker.unpack(aByteArray) as Double
let option_3 = ByteBackpacker.unpack(aByteArray, toType: Double.self)

From Double to Data to [Byte] to Double

var anotherDouble: Double = 2.0
let data = Data(bytes: &anotherDouble, count: MemoryLayout<Double>.size)
var byteArrayFromNSData = data.toByteArray()
let doubleFromByteArray = ByteBackpacker.unpack(byteArrayFromNSData, toType: Double.self)

From [Byte] to Data

let anotherByteArray: [Byte] = [0, 0, 0, 0, 0, 0, 8, 64]
let dataFromByteArray = Data(bytes: anotherByteArray)

API

Byte is a typealias for UInt8.

ByteOrder is an enum for Little Endian and Big Endian. Furthermore, there is the option for asking the platform you are using for the native byte order of the system: ByteOrder.nativeByteOrder. By default .nativeByteOrder is applied for packing and unpacking.

For packing value types into a [Byte], use

open class func pack<T: Any>( _ value: T, byteOrder: ByteOrder = .nativeByteOrder) -> [Byte]

For unpacking a [Byte] into a value type, use either

open class func unpack<T: Any>(_ valueByteArray: [Byte], byteOrder: ByteOrder = .nativeByteOrder) -> T

or otherwise, if you want to use type inference

open class func unpack<T: Any>(_ valueByteArray: [Byte], toType type: T.Type, byteOrder: ByteOrder = .nativeByteOrder) -> T

Discussion

Generics

There is no way for specifying value types in Swift's generics (see here the discussion on stackoverflow). It would be awesome to specify our methods like func (un)pack<T: Any where T: ~AnyClass>(...) to let the compiler check for value types. So far ByteBackpacker ensures the value type with assert(...).

An open question is how to test the assert(...) for this value type check.

I would love to improve this project. Tell me your ideas, here in github, via mail or in codereview.stackexchange.com.

Contributions

To-Do

• Find a solution for making sure, that T is a value type, but not a reference type
• Add documentation to the source code for a nice Xcode integration
• Find a solution for testing assert()

Acknowledgements

Many thanks to

• Martin R for his suggestions in codereview.stackexchange.com
• iCodist for his update to Swift 3 and Xcode 8
• vaggos666 for his remarks to Swift 4

Versions

(Un)fortunately there is a lot of work going on Swift. This made larger changes to ByteBackpacker needed. The following table shows the compatibility.

Swift version	2.0	3.0	4.0 and later
ByteBackpacker 1.0	✓	✗	✗
ByteBackpacker 1.1	✗	✓	✗
ByteBackpacker 1.2 and later	✗	✓	✓

Hopefully the APIs will be stable now.

License

ByteBackpacker is released under the MIT license. See LICENSE for more details.