Serializing DateTimeOffset objects with ISO8601

Failure to do so will lead to inconsistent results, especially with
users that have a custom system-wide date time string.

src/GitHub.Api/Helpers/Constants.cs

@@ -9,6 +9,7 @@ static class Constants
         public const string UsageFile = "usage.json";
         public const string GitInstallPathKey = "GitInstallPath";
         public const string TraceLoggingKey = "EnableTraceLogging";
+        public const string Iso8601Format = "o";
 
         public static readonly Version MinimumGitVersion = new Version(2, 11, 0);
         public static readonly Version MinimumGitLfsVersion = new Version(2, 3, 4);

src/GitHub.Api/OutputProcessors/LogEntryOutputProcessor.cs

@@ -329,8 +329,8 @@ private void ReturnGitLogEntry()
                     Summary = summary,
                     Description = description,
                     CommitID = commitId,
-                    TimeString = time.Value.ToString(DateTimeFormatInfo.CurrentInfo),
-                    CommitTimeString = committerTime.Value.ToString(DateTimeFormatInfo.CurrentInfo)
+                    TimeString = time.Value.ToString(Constants.Iso8601Format),
+                    CommitTimeString = committerTime.Value.ToString(Constants.Iso8601Format)
                 });
             }
 

src/UnityExtension/Assets/Editor/GitHub.Unity/ApplicationCache.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
-using Octokit;
 using UnityEditor;
 using UnityEngine;
 using Application = UnityEngine.Application;
@@ -92,7 +92,6 @@ abstract class ManagedCacheBase<T> : ScriptObjectSingleton<T> where T : Scriptab
         private static readonly TimeSpan DataTimeout = TimeSpan.MaxValue;
 
         [NonSerialized] private DateTimeOffset? lastUpdatedAtValue;
-
         [NonSerialized] private DateTimeOffset? lastVerifiedAtValue;
 
         public event Action CacheInvalidated;
@@ -148,14 +147,22 @@ public DateTimeOffset LastUpdatedAt
             {
                 if (!lastUpdatedAtValue.HasValue)
                 {
-                    lastUpdatedAtValue = DateTimeOffset.Parse(LastUpdatedAtString);
+                    DateTimeOffset result;
+                    if (DateTimeOffset.TryParseExact(LastUpdatedAtString, Constants.Iso8601Format, CultureInfo.InvariantCulture, DateTimeStyles.None, out result))
+                    {
+                        lastUpdatedAtValue = result;
+                    }
+                    else
+                    {
+                        lastUpdatedAtValue = DateTimeOffset.MinValue;
+                    }
                 }
 
                 return lastUpdatedAtValue.Value;
             }
             set
             {
-                LastUpdatedAtString = value.ToString();
+                LastUpdatedAtString = value.ToString(Constants.Iso8601Format);
                 lastUpdatedAtValue = null;
             }
         }
@@ -166,14 +173,22 @@ public DateTimeOffset LastVerifiedAt
             {
                 if (!lastVerifiedAtValue.HasValue)
                 {
-                    lastVerifiedAtValue = DateTimeOffset.Parse(LastVerifiedAtString);
+                    DateTimeOffset result;
+                    if (DateTimeOffset.TryParseExact(LastVerifiedAtString, Constants.Iso8601Format, CultureInfo.InvariantCulture, DateTimeStyles.None, out result))
+                    {
+                        lastVerifiedAtValue = result;
+                    }
+                    else
+                    {
+                        lastVerifiedAtValue = DateTimeOffset.MinValue;
+                    }
                 }
 
                 return lastVerifiedAtValue.Value;
             }
             set
             {
-                LastVerifiedAtString = value.ToString();
+                LastVerifiedAtString = value.ToString(Constants.Iso8601Format);
                 lastVerifiedAtValue = null;
             }
         }