Add a way to make it abundantly clear when the client and server are …

…on different versions.

src/Autopelago/GameDefinitions.cs

@@ -17,6 +17,8 @@ private GameDefinitions()
     {
     }
 
+    public required string VersionStamp { get; init; }
+
     // EVERYTHING must be derived from these first few collections. this is important to minimize
     // how much work #52 will be!
     public required ImmutableArray<ItemDefinitionModel> AllItems { get; init; }
@@ -95,6 +97,7 @@ private static GameDefinitions LoadFromEmbeddedResource()
         using StreamReader yamlReader = new(yamlStream, Encoding.UTF8);
         YamlMappingNode map = new DeserializerBuilder().Build().Deserialize<YamlMappingNode>(yamlReader);
 
+        string versionStamp = map["version_stamp"].To<string>();
         YamlMappingNode itemsMap = (YamlMappingNode)map["items"];
         YamlMappingNode regionsMap = (YamlMappingNode)map["regions"];
 
@@ -103,6 +106,8 @@ private static GameDefinitions LoadFromEmbeddedResource()
         ItemKey goalItem = items.AllItems.First(i => i.Name == "Victory").Key;
         return new()
         {
+            VersionStamp = versionStamp,
+
             AllItems = items.AllItems,
             AllLocations = regions.AllLocations,
             AllRegions = regions.AllRegions,

src/Autopelago/GameInitializer.cs

@@ -21,6 +21,11 @@ public sealed class GameAndContext
     public required MultiworldInfo Context { get; init; }
 }
 
+public sealed record AutopelagoWorldMetadata
+{
+    public required string VersionStamp { get; init; }
+}
+
 public sealed record MultiworldInfo
 {
     public required FrozenDictionary<string, FrozenDictionary<long, string>> GeneralItemNameMapping { get; init; }
@@ -42,6 +47,10 @@ public sealed record MultiworldInfo
 [JsonSerializable(typeof(JsonElement))]
 public sealed partial class AuraDataSerializationContext : JsonSerializerContext;
 
+[JsonSerializable(typeof(AutopelagoWorldMetadata))]
+[JsonSourceGenerationOptions(PropertyNamingPolicy = JsonKnownNamingPolicy.SnakeCaseLower)]
+public sealed partial class AutopelagoWorldMetadataSerializationContext : JsonSerializerContext;
+
 public sealed class GameInitializer : ArchipelagoPacketHandler
 {
     private readonly AsyncSubject<GameAndContext> _initializedGame = new();
@@ -167,6 +176,18 @@ private async ValueTask HandleAsync(ConnectResponsePacketModel connectResponse,
         }
 
         ConnectedPacketModel connected = (ConnectedPacketModel)connectResponse;
+
+        if (connected.SlotData.Deserialize(AutopelagoWorldMetadataSerializationContext.Default.AutopelagoWorldMetadata) is not { } autopelagoWorldMetadata ||
+            autopelagoWorldMetadata.VersionStamp != GameDefinitions.Instance.VersionStamp)
+        {
+            throw new InvalidOperationException($"""
+Client and .apworld are from different versions! This client wants to see '{GameDefinitions.Instance.VersionStamp}'.
+To check this yourself, open the .apworld file in 7-zip or something like that, look near the top of
+its 'AutopelagoDefinitions.yml' file for a "version_stamp". If it's not there, or if its value isn't
+the one we were looking for (again, '{GameDefinitions.Instance.VersionStamp}'), then that's why this happened.
+""");
+        }
+
         _slotInfo = connected.SlotInfo.ToFrozenDictionary();
         _slotByPlayerAlias = connected.Players.ToFrozenDictionary(p => p.Alias, p => p.Slot);
         LocationScoutsPacketModel locationScouts = new()

src/Autopelago/PacketModels.cs

@@ -185,6 +185,8 @@ private protected ConnectResponsePacketModel() { }
 
 public sealed record ConnectedPacketModel : ConnectResponsePacketModel
 {
+    private static readonly JsonElement s_emptyObject = CreateJsonElementForEmptyObject();
+
     public required int Team { get; init; }
 
     public required int Slot { get; init; }
@@ -195,11 +197,17 @@ public sealed record ConnectedPacketModel : ConnectResponsePacketModel
 
     public required ImmutableArray<long> CheckedLocations { get; init; }
 
-    public Dictionary<string, JsonElement> SlotData { get; init; } = [];
+    public JsonElement SlotData { get; init; } = s_emptyObject;
 
     public Dictionary<int, SlotModel> SlotInfo { get; init; } = [];
 
     public required int HintPoints { get; init; }
+
+    private static JsonElement CreateJsonElementForEmptyObject()
+    {
+        using JsonDocument document = JsonDocument.Parse("{}");
+        return document.RootElement.Clone();
+    }
 }
 
 public sealed record ConnectionRefusedPacketModel : ConnectResponsePacketModel

src/AutopelagoDefinitions.yml

@@ -1,6 +1,8 @@
 # This file exists in both the client and the server projects.
 # Please make sure that it matches in both places.
 
+version_stamp: '20241218'
+
 items:
   blackbird: 'Lockheed SR-71 Blackbird'
   mongoose_in_a_combat_spacecraft: