With iOS 15 or later we can take advantage of Date ParseStrategy ISO8601FormatStyle. Create an iso8601 with fractional seconds strategy and use it to initialize a new Date using its generic initializer init<T>(_ value: T.ParseInput, strategy: T) throws where T : ParseStrategy, T.ParseOutput == Date. If it fails just try without optional seconds:
Decoding
extension ParseStrategy where Self == Date.ISO8601FormatStyle {
static var iso8601withFractionalSeconds: Self { .init(includingFractionalSeconds: true) }
}
extension JSONDecoder.DateDecodingStrategy {
static let iso8601withOptionalFractionalSeconds = custom {
let string = try $0.singleValueContainer().decode(String.self)
do {
return try .init(string, strategy: .iso8601withFractionalSeconds)
} catch {
return try .init(string, strategy: .iso8601)
}
}
}
Encoding
extension FormatStyle where Self == Date.ISO8601FormatStyle {
static var iso8601withFractionalSeconds: Self { .init(includingFractionalSeconds: true) }
}
extension JSONEncoder.DateEncodingStrategy {
static let iso8601withFractionalSeconds = custom {
var container = $1.singleValueContainer()
try container.encode($0.formatted(.iso8601withFractionalSeconds))
}
}
// Playground testing
struct ISODates: Codable {
let dateWith9FS: Date
let dateWith3FS: Date
let dateWith2FS: Date
let dateWithoutFS: Date
}
let isoDatesJSON = """
{
"dateWith9FS": "2017-06-19T18:43:19.532123456Z",
"dateWith3FS": "2017-06-19T18:43:19.532Z",
"dateWith2FS": "2017-06-19T18:43:19.53Z",
"dateWithoutFS": "2017-06-19T18:43:19Z",
}
"""
let isoDatesData = Data(isoDatesJSON.utf8)
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601withOptionalFractionalSeconds
do {
let isoDates = try decoder.decode(ISODates.self, from: isoDatesData)
print(isoDates.dateWith9FS.formatted(.iso8601withFractionalSeconds))
print(isoDates.dateWith3FS.formatted(.iso8601withFractionalSeconds))
print(isoDates.dateWith2FS.formatted(.iso8601withFractionalSeconds))
print(isoDates.dateWithoutFS.formatted(.iso8601withFractionalSeconds))
} catch {
print(error)
}
Original Post:
You can use two different date formatters (with and without fraction seconds) and create a custom DateDecodingStrategy. In case of failure when parsing the date returned by the API you can throw a DecodingError as suggested by @PauloMattos in comments:
iOS 9, macOS 10.9, tvOS 9, watchOS 2, Xcode 9 or later
The custom ISO8601 DateFormatter:
extension Formatter {
static let iso8601withFractionalSeconds: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
return formatter
}()
static let iso8601: DateFormatter = {
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssXXXXX"
return formatter
}()
}
The custom DateDecodingStrategy:
extension JSONDecoder.DateDecodingStrategy {
static let customISO8601 = custom {
let container = try $0.singleValueContainer()
let string = try container.decode(String.self)
if let date = Formatter.iso8601withFractionalSeconds.date(from: string) ?? Formatter.iso8601.date(from: string) {
return date
}
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
}
}
The custom DateEncodingStrategy:
extension JSONEncoder.DateEncodingStrategy {
static let customISO8601 = custom {
var container = $1.singleValueContainer()
try container.encode(Formatter.iso8601withFractionalSeconds.string(from: $0))
}
}
edit/update:
Xcode 10 • Swift 4.2 or later • iOS 11.2.1 or later
ISO8601DateFormatter now supports formatOptions .withFractionalSeconds:
extension Formatter {
static let iso8601withFractionalSeconds: ISO8601DateFormatter = {
let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
return formatter
}()
static let iso8601: ISO8601DateFormatter = {
let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withInternetDateTime]
return formatter
}()
}
The customs DateDecodingStrategy and DateEncodingStrategy would be the same as shown above.
