Fixed serialization of negative dates (before epoch)

Sources/MessagePackExtension.swift

@@ -28,7 +28,19 @@ extension MessagePackExtension {
         case let (0, value):
             self.data = packInteger(for: value.bigEndian)
         default:
-            self.data = packInteger(for: UInt32(timestamp.nanoseconds).bigEndian) + packInteger(for: Int64(timestamp.seconds).bigEndian)
+            if timestamp.nanoseconds < 0 {
+                // Adjust these values from
+                // "negative nanosec from nearest larger negative integer"
+                // to
+                // "positive nanosec from nearest smaller nagative integer".
+                let seconds = timestamp.seconds - 1
+                let nanoSeconds = (MessagePackTimestamp.NSEC_MAX + 1) + timestamp.nanoseconds
+                self.data = packInteger(for: UInt32(nanoSeconds).bigEndian) + packInteger(for: Int64(seconds).bigEndian)
+            }
+            else {
+                self.data = packInteger(for: UInt32(timestamp.nanoseconds).bigEndian) + packInteger(for: Int64(timestamp.seconds).bigEndian)
+            }
+
         }
     }
 }

Sources/MessagePackTimestamp.swift

@@ -9,6 +9,7 @@
 import Foundation
 
 public struct MessagePackTimestamp: Equatable {
+    internal static let NSEC_MAX: Int64 = 999999999
     public var seconds: Int64
     public var nanoseconds: Int64
 

Tests/MessagePackerTests/TimestampPackedTests.swift

@@ -37,4 +37,17 @@ class TimestampPackedTests: XCTestCase {
         let output = Data([199, 12, 255, 25, 69, 229, 222, 0, 0, 0, 14, 211, 132, 20, 74])
         XCTAssertEqual(try encoder.encode(input), output)
     }
+
+    func testTimestamp96WithNegativeDate() throws {
+        let formatter = DateFormatter()
+        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
+        formatter.locale = Locale(identifier: "en_US_POSIX")
+        formatter.timeZone = TimeZone(abbreviation: "UTC")
+        let date = formatter.date(from: "0023-09-24T00:36:30.078Z")!
+
+        let timestamp = MessagePackTimestamp(date: date)
+        let encoded = try encoder.encode(timestamp)
+        let decoded = try MessagePackDecoder().decode(MessagePackTimestamp.self, from: encoded)
+        XCTAssertEqual(date, Date(timestamp: decoded))
+    }
 }