Example on how to integrate IkigaJSON with Vapor 4

configure.swift

import Vapor
import IkigaJSON
// ...

public func configure(_ app: Application) throws {
    var decoder = IkigaJSONDecoder()
    decoder.settings.dateDecodingStrategy = .iso8601
    ContentConfiguration.global.use(decoder: decoder, for: .json)

    var encoder = IkigaJSONEncoder()
    encoder.settings.dateDecodingStrategy = .iso8601
    ContentConfiguration.global.use(encoder: encoder, for: .json)

    // ...
}

IkigaJSON+Content.swift

import Vapor
import IkigaJSON

extension IkigaJSONEncoder: ContentEncoder {
    public func encode<E: Encodable>(
        _ encodable: E,
        to body: inout ByteBuffer,
        headers: inout HTTPHeaders
    ) throws {
        headers.contentType = .json
        try self.encodeAndWrite(encodable, into: &body)
    }
}

extension IkigaJSONDecoder: 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)
        }

        return try self.decode(D.self, from: body)
    }
}

Package.swift

// swift-tools-version:5.2
import PackageDescription

let package = Package(
    name: "app",
    platforms: [
       .macOS(.v10_15),
    ],
    products: [
        .executable(name: "Run", targets: ["Run"]),
        .library(name: "App", targets: ["App"]),
    ],
    dependencies: [
        // ...
        .package(url: "https://github.com/Ikiga/IkigaJSON.git", from: "2.0.0")
    ],
    targets: [
        .target(name: "App", dependencies: [
            .product(name: "Vapor", package: "vapor"),
            .product(name: "IkigaJSON", package: "IkigaJSON")
            // ...
        ]),
        // ...
    ]
)