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Turn sequence of data into struct
.package(url: "https://github.com/bigearsenal/BufferLayoutSwift.git", from: "0.9.0")


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What is it?

This library is a clear way to parse sequence of bytes (Data) into your custom struct in order. See buffer-layout-js for more informations.


To run the tests, clone the repo, and run pod install from the Example directory first.

Example decoding a struct from sequence of bytes:

let bytes: [UInt8] = [
    3,0,0,0,1,2,3, // a vector with length = 3 (3,0,0,0) 
    4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // uint128
    1, // uint8
        1, // uint8 (nested)
            0,0, // uint16 (nestedOfNested)
            3,0,0,0, // uint32 (nestedOfNested)
        1,3,0,3,1,0,0,1, //uint64 (nested)
    3,0,0,0, // uint32
    1,3,0,3,1,0,0,1, // uint64?
    0 // bool
private struct VecU8: BufferLayoutProperty {
    let length: UInt32
    let bytes: [UInt8]
    static func fromData(_ data: Data) throws -> (value: VecU8, bytesUsed: Int) {
        // first 4 bytes for length
        let length = try UInt32.fromData(data).value
        guard data.count >= 4+Int(length) else {
            throw BufferLayoutSwift.Error.bytesLengthIsNotValid
        let value = VecU8(length: length, bytes: Array(data[4..<4+Int(length)]))
        return (value: value, bytesUsed: 4 + Int(length))
    func encode() throws -> Data {
        try length.encode() +

private struct MyNumberCollection: BufferLayout {
    // parsable
    let vecu8: VecU8
    let uint128: UInt128
    let uint8: UInt8
    let uint16: UInt16 // excluded -> default to 0
    let nested: MyNestedNumberCollection
    let uint32: UInt32?
    let uint64: UInt64
    let int32: Int32
    let bool: Bool
    // non-parsable part
    var optionalString: String?
    let string: String
    static func injectOtherProperties(typeInfo: TypeInfo, currentInstance: inout MyNumberCollection) throws {
        let stringProp = try typeInfo.property(named: "string")
        try stringProp.set(value: "test", on: &currentInstance)
    static var excludedPropertyNames: [String] {["uint16"]}

private struct MyNestedNumberCollection: BufferLayout, Equatable {
    let uint8: UInt8
    let nested: MyNestedOfNestedNumberCollection
    let uint64: UInt64

private struct MyNestedOfNestedNumberCollection: BufferLayout, Equatable {
    let uint16: UInt16
    let uint32: UInt32
let test = try MyNumberCollection.fromData(Data(array)).value
XCTAssertEqual(test.vecu8.bytes, [1,2,3])
XCTAssertEqual(test.uint128, 4)
XCTAssertEqual(test.uint8, 1)
XCTAssertEqual(test.uint16, 0) // excluded
XCTAssertEqual(test.nested, .init(uint8: 1, nested: .init(uint16: 0, uint32: 3) , uint64: 72057598383227649))
XCTAssertEqual(test.uint32, 3)
XCTAssertEqual(test.uint64, 72057598383227649)
XCTAssertEqual(test.bool, false)
XCTAssertEqual(test.string, "test")

XCTAssertEqual([UInt8](https://raw.github.com/bigearsenal/BufferLayoutSwift/master/try test.encode()), array)



BufferLayoutSwift is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'BufferLayoutSwift'

Define your struct which conforms to BufferLayout and all properties conform to BufferLayoutProperty. Note that UInt8, UInt16, UInt32, ... are already conformed to BufferLayoutProperty by default.

private struct MyStruct: BufferLayout {
    var uint8: UInt8
    var uint16: UInt16
    var uint32: UInt32
    var uint64: UInt64
    var int32: Int32

If you want to exclude some properties from parsing, you can add excludedPropertyNames: [String] to your struct. All these properties and non-BufferLayoutProperty will be ignored.

private struct MyStruct: BufferLayout {
    static var excludedPropertyNames: [String] {["uint16"]}

If you want to modify some non-parsable property after parsing needed properties from data, implement optional method static func injectOtherProperties(typeInfo: TypeInfo, currentInstance: inout MyStruct) throws. This function will be called on the bottom of init(buffer:). Example:

private struct MyStruct: BufferLayout {
    static func injectOtherProperties(typeInfo: TypeInfo, currentInstance: inout MyStruct) throws {
        let stringProp = try typeInfo.property(named: "myProperty") // get property 
        try stringProp.set(value: "test", on: &currentInstance) // dynamically set its property

Now you can create instances of MyStruct by calling fallable init(data: Data) throws. See example for more informations

Supported BufferLayoutProperty:

There are some prefined BufferLayoutProperty , note that BufferLayout is also conform to BufferLayoutProperty for recursion.

extension UInt8: BufferLayoutProperty {}
extension UInt16: BufferLayoutProperty {}
extension UInt32: BufferLayoutProperty {}
extension UInt64: BufferLayoutProperty {}

extension Int8: BufferLayoutProperty {}
extension Int16: BufferLayoutProperty {}
extension Int32: BufferLayoutProperty {}
extension Int64: BufferLayoutProperty {}

extension Bool: BufferLayoutProperty {}
extension Optional: BufferLayoutProperty where Wrapped: BufferLayoutProperty {}

You can define custom BufferLayoutProperty by conforming your type to BufferLayoutProperty. For example: get PublicKey from buffer layout with 32 bytes:

extension PublicKey: BufferLayoutProperty {
    public static func getNumberOfBytes() throws -> Int {

    public init(buffer: Data) throws {
        guard bytes.count == numberOfBytes else {
            throw BufferLayoutSwift.Error.bytesLengthIsNotValid
        // return public key from data
        self = buffer.toPublicKey()

    public func encode() throws -> Data {


  1. 'Runtime'


Chung Tran, bigearsenal@gmail.com


BufferLayoutSwift is available under the MIT license. See the LICENSE file for more info.


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