The Internet Date/Time Format (RFC 3339) with JSON

README.md

The Internet Date/Time Format (RFC 3339) with JSON

Examples how encode/decode RFC 3339 (ISO 8601) dates in JSON by JSONEncoder/JSONDecoder.

Links:

• RFC 3339
• Date format patterns
• ISO8601DateFormatter
• DateFormatter

Sources:

• JSONEncoder
• JSONDecoder
• ISO8601DateFormatter

format.swift

do {
    let options: ISO8601DateFormatter.Options = .withInternetDateTime
    let cfOptions = CFISO8601DateFormatOptions(rawValue: options.rawValue)
    let cfFormatter = CFDateFormatterCreateISO8601Formatter(kCFAllocatorSystemDefault, cfOptions)
    let format = CFDateFormatterGetFormat(cfFormatter) as String
    print(format) // yyyy-MM-dd'T'HH:mm:ssXXXXX
}
do {
    let options: ISO8601DateFormatter.Options = [.withInternetDateTime, .withFractionalSeconds]
    let cfOptions = CFISO8601DateFormatOptions(rawValue: options.rawValue)
    let cfFormatter = CFDateFormatterCreateISO8601Formatter(kCFAllocatorSystemDefault, cfOptions)
    let format = CFDateFormatterGetFormat(cfFormatter) as String
    print(format) // yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX
}

mix.swift

// Decoding with/without fractional seconds

let formatter1 = ISO8601DateFormatter()
formatter1.formatOptions = .withInternetDateTime

let formatter2 = ISO8601DateFormatter()
formatter2.formatOptions = [.withInternetDateTime, .withFractionalSeconds]

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
    let container = try decoder.singleValueContainer()
    let string = try container.decode(String.self)

    if let date = formatter1.date(from: string) {
        return date
    } else if let date = formatter2.date(from: string) {
        return date
    }

    throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date string: \(string)")
})

struct Mix: Decodable {
    let date1: Date
    let date2: Date
}

let json = #"{"date1": "2021-06-19T10:30:00Z", "date2": "2021-06-19T10:30:00.123Z"}"#

do {
    let mix = try decoder.decode(Mix.self, from: json.data(using: .utf8)!)
    print(mix)
} catch {
    print(error)
}

with1.swift

// Encoding & decoding with fractional seconds by .custom strategy

let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]

let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .custom({ (date, encoder) in
    var container = encoder.singleValueContainer()
    try container.encode(formatter.string(from: date))
})

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom({ (decoder) in
    let container = try decoder.singleValueContainer()
    let string = try container.decode(String.self)
    if let date = formatter.date(from: string) {
        return date
    }
    throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date string: \(string)")
})

do {
    let now = Date()
    print("date:   ", now)
    let data = try encoder.encode(now)
    print("encoded:", String(data: data, encoding: .utf8)!)
    let date = try decoder.decode(Date.self, from: data)
    print("decoded:", date)
} catch {
    print(error)
}

with2.swift

// Encoding & decoding with fractional seconds by .formatted strategy
// Date format patterns: https://www.unicode.org/reports/tr35/tr35-31/tr35-dates.html#Date_Format_Patterns

let formatter = DateFormatter()
formatter.locale = .init(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(identifier: "GMT")
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"

let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .formatted(formatter)

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(formatter)

do {
    let now = Date()
    print("date:   ", now)
    let data = try encoder.encode(now)
    print("encoded:", String(data: data, encoding: .utf8)!)
    let date = try decoder.decode(Date.self, from: data)
    print("decoded:", date)
} catch {
    print(error)
}

without.swift

// Encoding & decoding without fractional seconds

let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .iso8601
        
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601

do {
    let now = Date()
    print("date:   ", now)
    let data = try encoder.encode(now)
    print("encoded:", String(data: data, encoding: .utf8)!)
    let date = try decoder.decode(Date.self, from: data)
    print("decoded:", date)
} catch {
    print(error)
}