swift-extras-json

This package provides a json encoder and decoder in Swift (without the use of Foundation or any other dependency). The implementation is RFC8259 compliant. It offers a significant performance improvement compared to the Foundation implementation on Linux.

If you like the idea of using Swift without any dependencies, you might also like our reimplementation of Base64 in Swift: swift-extras-base64

Goals

• does not use Foundation at all
• does not use unsafe Swift syntax
• no external dependencies, only the Swift stdlib required
• faster than Foundation implementation

Currently not supported

• custom encoder and decoder for Data and Date
• parsing/decoding of UTF-16 and UTF-32 encoded json
• transforming CodingKeys to camelCase or snake_case (I want to look into this)

Alternatives

• IkigaJSON super fast encoding and decoding especially for server side Swift code. Depends on SwiftNIO.
• Foundation Coding

Usage

Add swift-extras-json as dependency to your Package.swift:

  dependencies: [
    .package(url: "https://github.com/swift-extras/swift-extras-json.git", .upToNextMajor(from: "0.6.0")),
  ],

Add ExtrasJSON to the target you want to use it in.

  targets: [
    .target(name: "MyFancyTarget", dependencies: [
      .product(name: "ExtrasJSON", package: "swift-extras-json"),
    ])
  ]

Use it as you would use the Foundation encoder and decoder.

import ExtrasJSON

let bytesArray  = try XJSONEncoder().encode(myEncodable)
let myDecodable = try XJSONDecoder().decode(MyDecodable.self, from: bytes)

Use with SwiftNIO ByteBuffer

For maximal performance create an [UInt8] from your ByteBuffer, even though buffer.readableBytesView would technically work as well.

let result = try XJSONDecoder().decode(
  [SampleStructure].self,
  from: buffer.readBytes(length: buffer.readableBytes)!)

let bytes = try XJSONEncoder().encode(encodable)
var buffer = byteBufferAllocator.buffer(capacity: bytes.count)
buffer.writeBytes(bytes)

Use with Vapor 4

Increase the performance of your Vapor 4 API by using swift-extras-json instead of the default Foundation implementation. First you’ll need to implement the conformance to Vapor’s ContentEncoder and ContentDecoder as described in the Vapor docs.

import Vapor
import ExtrasJSON

extension XJSONEncoder: ContentEncoder {
  public func encode<E: Encodable>(
    _ encodable: E,
    to body: inout ByteBuffer,
    headers: inout HTTPHeaders) throws
  {
    headers.contentType = .json
    let bytes = try self.encode(encodable)
    // the buffer's storage is resized in case its capacity is not sufficient
    body.writeBytes(bytes)
  }
}

extension XJSONDecoder: ContentDecoder {
  public func decode<D: Decodable>(
    _ decodable: D.Type,
    from body: ByteBuffer,
    headers: HTTPHeaders) throws -> D
  {
    guard headers.contentType == .json || headers.contentType == .jsonAPI else {
      throw Abort(.unsupportedMediaType)
    }
    var body = body
    return try self.decode(D.self, from: body.readBytes(length: body.readableBytes)!)
  }
}

Next, register the encoder and decoder for use in Vapor:

let decoder = XJSONDecoder()
ContentConfiguration.global.use(decoder: decoder, for: .json)

let encoder = XJSONEncoder()
ContentConfiguration.global.use(encoder: encoder, for: .json)

Performance

All tests have been run on a 2019 MacBook Pro (16” – 2,4 GHz 8-Core Intel Core i9). You can run the tests yourself by cloning this repo and

# change dir to perf tests
$ cd PerfTests

# compile and run in release mode - IMPORTANT ‼️
$ swift run -c release

Encoding

	macOS Swift 5.1	macOS Swift 5.2	Linux Swift 5.1	Linux Swift 5.2
Foundation	2.61s	2.62s	13.03s	12.52s
ExtrasJSON	1.23s	1.25s	1.13s	1.05s
Speedup	~2x	~2x	~10x	~10x

Decoding

	macOS Swift 5.1	macOS Swift 5.2	Linux Swift 5.1	Linux Swift 5.2
Foundation	2.72s	3.04s	10.27s	10.65s
ExtrasJSON	1.70s	1.72s	1.39s	1.16s
Speedup	~1.5x	~1.5x	~7x	~8x

Workarounds

What about Date and Data?

Date and Data are particular cases for encoding and decoding. They do have default implementations that are kind off special:

• Date will be encoded as a float

  Example: 2020-03-17 16:36:58 +0000 will be encoded as 606155818.503831

• Data will be encoded as a numeric array.

  Example: 0, 1, 2, 3, 255 will be encoded as: [0, 1, 2, 3, 255]

Yes, that is the default implementation. Only Apple knows why it is not ISO 8601 and Base64. 🙃 Since I don’t want to link against Foundation, it is not possible to implement default encoding and decoding strategies for Date and Data like the Foundation implementation does. That’s why, if you want to use another encoding/decoding strategy than the default, you need to overwrite encode(to: Encoder) and init(from: Decoder).

This could look like this:

struct MyEvent: Decodable {

  let eventTime: Date
  
  enum CodingKeys: String, CodingKey {
    case eventTime
  }

  init(from decoder: Decoder) {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    let dateString = try container.decode(String.self, forKey: .eventTime)
    guard let timestamp = MyEvent.dateFormatter.date(from: dateString) else {
      let dateFormat = String(describing: MyEvent.dateFormatter.dateFormat)
      throw DecodingError.dataCorruptedError(forKey: .eventTime, in: container, debugDescription:
        "Expected date to be in format `\(dateFormat)`, but `\(dateString) does not fulfill format`")
    }
    self.eventTime = timestamp
  }
  
  private static let dateFormatter: DateFormatter = MyEvent.createDateFormatter()
  private static func createDateFormatter() -> DateFormatter {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
    formatter.timeZone   = TimeZone(secondsFromGMT: 0)
    formatter.locale     = Locale(identifier: "en_US_POSIX")
    return formatter
  }
}

You can find more information about encoding and decoding custom types in Apple’s documentation.

Of course you can use @propertyWrappers to make this more elegant:

import Foundation

@propertyWrapper
struct DateStringCoding: Decodable {
  var wrappedValue: Date
  
  init(wrappedValue: Date) {
    self.wrappedValue = wrappedValue
  }

  init(from decoder: Decoder) throws {
    let container = try decoder.singleValueContainer()
    let dateString = try container.decode(String.self)
    guard let date = Self.dateFormatter.date(from: dateString) else {
      let dateFormat = String(describing: Self.dateFormatter.dateFormat)
      throw DecodingError.dataCorruptedError(in: container, debugDescription:
            "Expected date to be in format `\(dateFormat)`, but `\(dateString) does not fulfill format`")
    }
    self.wrappedValue = date
  }

  private static let dateFormatter: DateFormatter = Self.createDateFormatter()
  private static func createDateFormatter() -> DateFormatter {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
    formatter.timeZone   = TimeZone(secondsFromGMT: 0)
    formatter.locale     = Locale(identifier: "en_US_POSIX")
    return formatter
  }
}

struct MyEvent: Decodable {
  @DateStringCoding
  var eventTime: Date
}

Checkout a full example in the test file DateCodingTests.

UTF-16 and UTF-32

If your input is UTF-16 or UTF-32 encoded, you can easily convert it to UTF-8:

let utf16 = UInt16[]() // your utf-16 encoded data
let utf8  = Array(String(decoding: utf16, as: Unicode.UTF16.self).utf8)

let utf32 = UInt32[]() // your utf-32 encoded data
let utf8  = Array(String(decoding: utf32, as: Unicode.UTF32.self).utf8)

Contributing

Please feel welcome and encouraged to contribute to swift-extras-json. This is a very young endeavour and help is always welcome.

If you’ve found a bug, have a suggestion, or need help getting started, please open an Issue or a PR. If you use this package, I’d be grateful for sharing your experience.

Focus areas for the time being:

• ensuring safe use of nested containers while encoding and decoding
• supporting camelCase and snakeCase aka KeyEncodingStrategy

Credits

• @weissi thanks for answering all my questions and for opening tickets SR-12125 and SR-12126
• @dinhhungle thanks for your quality assurance. It helped a lot!
• @Ro-M thanks for checking my README.md
• @Trzyipolkostkicukru thanks for your advice on @propertyWrappers and for finding typos.