Make the ISO8601 date transcoder configurable (#94)

Make the ISO8601 date transcoder configurable

### Motivation

Fixes apple/swift-openapi-generator#389.

### Modifications

Add a way to configure the existing `ISO8601DateTranscoder`.

### Result

Adopters can more easily use e.g. fractional seconds-based transcoder.

### Test Plan

Added unit tests.


Reviewed by: simonjbeaumont

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#94

Sources/OpenAPIRuntime/Conversion/Configuration.swift

@@ -25,14 +25,37 @@ public protocol DateTranscoder: Sendable {
 }
 
 /// A transcoder for dates encoded as an ISO-8601 string (in RFC 3339 format).
-public struct ISO8601DateTranscoder: DateTranscoder {
+public struct ISO8601DateTranscoder: DateTranscoder, @unchecked Sendable {
+
+    /// The lock protecting the formatter.
+    private let lock: NSLock
+
+    /// The underlying date formatter.
+    private let locked_formatter: ISO8601DateFormatter
+
+    /// Creates a new transcoder with the provided options.
+    /// - Parameter options: Options to override the default ones. If you provide nil here, the default options
+    ///   are used.
+    public init(options: ISO8601DateFormatter.Options? = nil) {
+        let formatter = ISO8601DateFormatter()
+        if let options { formatter.formatOptions = options }
+        lock = NSLock()
+        lock.name = "com.apple.swift-openapi-generator.runtime.ISO8601DateTranscoder"
+        locked_formatter = formatter
+    }
 
     /// Creates and returns an ISO 8601 formatted string representation of the specified date.
-    public func encode(_ date: Date) throws -> String { ISO8601DateFormatter().string(from: date) }
+    public func encode(_ date: Date) throws -> String {
+        lock.lock()
+        defer { lock.unlock() }
+        return locked_formatter.string(from: date)
+    }
 
     /// Creates and returns a date object from the specified ISO 8601 formatted string representation.
     public func decode(_ dateString: String) throws -> Date {
-        guard let date = ISO8601DateFormatter().date(from: dateString) else {
+        lock.lock()
+        defer { lock.unlock() }
+        guard let date = locked_formatter.date(from: dateString) else {
             throw DecodingError.dataCorrupted(
                 .init(codingPath: [], debugDescription: "Expected date string to be ISO8601-formatted.")
             )
@@ -44,6 +67,11 @@ public struct ISO8601DateTranscoder: DateTranscoder {
 extension DateTranscoder where Self == ISO8601DateTranscoder {
     /// A transcoder that transcodes dates as ISO-8601–formatted string (in RFC 3339 format).
     public static var iso8601: Self { ISO8601DateTranscoder() }
+
+    /// A transcoder that transcodes dates as ISO-8601–formatted string (in RFC 3339 format) with fractional seconds.
+    public static var iso8601WithFractionalSeconds: Self {
+        ISO8601DateTranscoder(options: [.withInternetDateTime, .withFractionalSeconds])
+    }
 }
 
 extension JSONEncoder.DateEncodingStrategy {

Tests/OpenAPIRuntimeTests/Conversion/Test_Configuration.swift

@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftOpenAPIGenerator open source project
+//
+// Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+import XCTest
+@_spi(Generated) import OpenAPIRuntime
+
+final class Test_Configuration: Test_Runtime {
+
+    func testDateTranscoder_iso8601() throws {
+        let transcoder: any DateTranscoder = .iso8601
+        XCTAssertEqual(try transcoder.encode(testDate), testDateString)
+        XCTAssertEqual(testDate, try transcoder.decode(testDateString))
+    }
+
+    func testDateTranscoder_iso8601WithFractionalSeconds() throws {
+        let transcoder: any DateTranscoder = .iso8601WithFractionalSeconds
+        XCTAssertEqual(try transcoder.encode(testDateWithFractionalSeconds), testDateWithFractionalSecondsString)
+        XCTAssertEqual(testDateWithFractionalSeconds, try transcoder.decode(testDateWithFractionalSecondsString))
+    }
+}

Tests/OpenAPIRuntimeTests/Test_Runtime.swift

@@ -42,6 +42,10 @@ class Test_Runtime: XCTestCase {
 
     var testDateString: String { "2023-01-18T10:04:11Z" }
 
+    var testDateWithFractionalSeconds: Date { Date(timeIntervalSince1970: 1_674_036_251.123) }
+
+    var testDateWithFractionalSecondsString: String { "2023-01-18T10:04:11.123Z" }
+
     var testDateEscapedString: String { "2023-01-18T10%3A04%3A11Z" }
 
     var testDateStringData: Data { Data(testDateString.utf8) }