Swift Library for working with sequences of Bytes (aka [UInt8])

What's New



What's Changed

Full Changelog: 0.2.2...0.2.3


Test Status

Bytes aims to be your go-to Swift library for transforming basic types to and from buffers of bytes that can be serialized and written to the network, a file, or a database.


Add Bytes as a dependency in your Package.swift file to start using it. Then, add import Bytes to any file you wish to use the library in.

Please check the releases for recommended versions.

dependencies: [
    .package(url: "", .upToNextMinor(from: "0.2.2")),
targets: [
        name: "MyPackage",
        dependencies: [

What is Bytes?

Bytes is a type alias for [UInt8], which means you can use them anywhere a buffer of bytes would be expected. Although extensions on Int, String, UUID, and even enumerations are provided, this library ultimately lets you transform any fixed-size structure to and from Bytes:

struct Example {
    let a: UInt8
    let b: UInt8

func methodThatTakesExample(_ example: Example) { ... }

let example = Example(a: 1, b: 2)

// Turn a Swift type into Bytes:
let bytes = Bytes(casting: example) // [0x01, 0x02]

// Turn Bytes into a Swift type:
let backToExample = try bytes.casting(to: Example.self) // Type is explicit
methodThatTakesExample(try bytes.casting()) // Type is inferred from context

Do note that objects cast to and from Bytes in this way are not stable outside of the program scope, since they mirror the memory layout of the object at that moment in time. It is much more preferable to encode the item directly using the specialized methods on Int, String, UUID, etc…, as they provide a stable and consistent scheme of encoding and decoding objects in memory.


When working with integers, it is preferable to use the bigEndianBytes/ littleEndianBytes and init(bigEndianBytes: Bytes)/init(littleEndianBytes: Bytes) integer-specific properties and initializers when possible, as they will be guaranteed to be cross platform (casting will always use the byte-order native to system memory). Integer overrides are available for all integer types: Int8, UInt8, Int16, UInt16, Int32, UInt32, Int64, and UInt64. Using Int and UInt for serialization is not recommended, as they are different sizes on different platforms.


To make working with Strings and Characters easy and unambiguous, utf8Bytes and init(utf8Bytes: Bytes) are available. These are not null-terminated, though you can achieve that quite easily: "Hello".utf8Bytes + [0].


UUIDs support serialization in both compact byte form (bytes and init(bytes: Bytes)), and human-readable string form (stringBytes and init(stringBytes: Bytes))

Enums, OptionSets, and RawRepresentable

Enums and other types that conform to RawRepresentable are also supported out of the box via rawBytes and init(rawBytes: Bytes). Types who's RawType is an Integer or String/Character can also use the above getters and initializers.

Collections of Integers, UUIDs, Enums, and other Fixed-Size Types

An array or set of Integers can be serialized using bigEndianBytes/ littleEndianBytes, and initialized using init(bigEndianBytes: Bytes)/init(littleEndianBytes: Bytes). The same can be done with collections of UUIDs and RawRepresentable enums by using the APIs specific to their types.

Complex Example

Since Bytes is just an array, all the methods you are used to are available, including working with slices. If you are working with more complex serialization, consider the example below:

struct Versionstamp {
    let transactionCommitVersion: UInt64
    let batchNumber: UInt16
    var userData: UInt16?
    init(transactionCommitVersion: UInt64, batchNumber: UInt16, userData: UInt16? = nil) {
        self.transactionCommitVersion = transactionCommitVersion
        self.batchNumber = batchNumber
        self.userData = userData

    var bytes: Bytes {
        var result = Bytes()
        result.reserveCapacity(userData == nil ? 10 : 12)
        result.append(contentsOf: transactionCommitVersion.bigEndianBytes)
        result.append(contentsOf: batchNumber.bigEndianBytes)
        if let userData = userData {
            result.append(contentsOf: userData.bigEndianBytes)
        return result
    init<Bytes: BytesCollection>(_ bytes: Bytes?) throws {
        guard let bytes = bytes, bytes.count == 10 || bytes.count == 12 else {
            throw Error.invalidVersionstamp
        let transactionCommitVersion = try! UInt64(bigEndianBytes: bytes[0..<8])
        let batchNumber = try! UInt16(bigEndianBytes: bytes[8..<10])
        var userData: UInt16?
        if bytes.count == 12 {
            userData = try! UInt16(bigEndianBytes: bytes[10..<12])
        self.init(transactionCommitVersion: transactionCommitVersion, batchNumber: batchNumber, userData: userData)
    /// Alternatively using the ByteIterator-class of methods, which don't require keeping track of indices since they decode objects in order.
    init<Bytes: BytesCollection>(sequence: Bytes?) throws {
        var iterator = sequence.makeIterator()
            transactionCommitVersion: try UInt64.self),
            batchNumber: try UInt16.self),
            userData: try iterator.nextIfPresent(bigEndian: UInt16.self)
        /// Verify we are at the end of the stream of bytes.
        guard == nil else {
            throw Error.invalidVersionstamp


Bytes can also be used to pull data from AsyncSequence iterators. To learn more, please see Integration with AsyncSequenceReader.

For instance, improving the above example:

#if compiler(>=5.5) && canImport(_Concurrency)

@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
extension AsyncIteratorProtocol where Element == Byte {
    mutating func next(_ type: Versionstamp.Type) async throws -> Versionstamp {
            transactionCommitVersion: try await next(bigEndian: UInt64.self),
            batchNumber: try await next(bigEndian: UInt16.self),
            userData: try await nextIfPresent(bigEndian: UInt16.self)



Contribution is welcome! Please take a look at the issues already available, or start a new issue to discuss a new feature. Although guarantees can't be made regarding feature requests, PRs that fit within the goals of the project and that have been discussed beforehand are more than welcome!

Please make sure that all submissions have clean commit histories, are well documented, and thoroughly tested. Please rebase your PR before submission rather than merge in main. Linear histories are required, so merge commits in PRs will not be accepted.


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Last updated: Wed Mar 15 2023 16:01:37 GMT-0500 (GMT-05:00)