Writing some tests, namely the fake game server

tests/FakeGameServer/Program.cs

@@ -1 +1,205 @@
-Console.WriteLine("Hello, World!");
+// A stand-in for VintagestoryServer, used by tests. It copies the behavior measured
+// on 1.22.7 (see the design doc) and can be told to misbehave through environment
+// variables:
+//   FAKE_MODE          Normal | NoReady | FailOnStart | CrashAfterReady | IgnoreStop | IgnoreAll
+//   FAKE_STARTUP_MS    delay before the ready line (default 500)
+//   FAKE_STOP_MS       time the shutdown sequence takes (default 200)
+//   FAKE_CRASH_AFTER_MS  delay between ready and the crash in CrashAfterReady (default 300)
+//   FAKE_CRASH_EXIT_CODE exit code used when crashing (default 0, like the real game)
+//   FAKE_STDIN_EOF     "stop" makes the server stop when stdin closes (default: ignore it)
+//
+// Deliberate differences from the real game:
+//   - --dataPath is required, so a test can never touch a default location.
+//   - Only strict JSON is accepted by --setconfig, not the relaxed syntax.
+//   - If a value-taking flag swallows --dataPath, this exits with 2 where the real
+//     game would fall back to its default path.
+
+using System.Runtime.InteropServices;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using FakeGameServer;
+using static FakeGameServer.FakeOutput;
+
+const int SetConfigSuccessExitCode = 200;
+
+var cli = CommandLine.Parse(args);
+if (cli.DataPath is null)
+{
+    await Console.Error.WriteLineAsync("fake: --dataPath is required, refusing to use a default location");
+    return 2;
+}
+
+var fake = FakeSettings.FromEnvironment();
+var dataPath = Path.GetFullPath(cli.DataPath);
+Directory.CreateDirectory(dataPath);
+
+Log("Server Notification", "Server logger started.");
+Log("Server Notification", "Game Version: v0.0.0 (Fake)");
+
+var configPath = Path.Combine(dataPath, "serverconfig.json");
+JsonObject config;
+if (File.Exists(configPath))
+{
+    config = JsonNode.Parse(File.ReadAllText(configPath))?.AsObject() ?? new JsonObject();
+}
+else
+{
+    Log("Server Notification", "serverconfig.json not found, creating new one");
+    config = new JsonObject
+    {
+        ["ServerName"] = "Vintage Story Server",
+        ["Port"] = 42420,
+        ["MaxClients"] = 16,
+    };
+}
+
+if (cli.SetConfig is not null)
+{
+    JsonObject patch;
+    try
+    {
+        patch = JsonNode.Parse(cli.SetConfig)?.AsObject() ?? throw new JsonException("null value");
+    }
+    catch (Exception ex) when (ex is JsonException or InvalidOperationException)
+    {
+        // Unverified: whether the real game leaves a config file behind after this failure.
+        // The fake does not.
+        var first = cli.SetConfig.TrimStart('-').FirstOrDefault();
+        return Crash(
+            dataPath,
+            fake.CrashExitCode,
+            "Newtonsoft.Json.JsonReaderException: Unexpected character encountered while " +
+            $"parsing value: {first}. Path '', line 0, position 0.");
+    }
+
+    foreach (var (key, value) in patch.ToList())
+    {
+        config[key] = value?.DeepClone();
+        Log("Server Notification", $"Ok, value {value} set for {key}.");
+    }
+
+    File.WriteAllText(configPath, config.ToJsonString(JsonOptions.Indented));
+    return SetConfigSuccessExitCode;
+}
+
+File.WriteAllText(configPath, config.ToJsonString(JsonOptions.Indented));
+var port = cli.Port ?? config["Port"]?.GetValue<int>() ?? 42420;
+
+using var shutdown = new CancellationTokenSource();
+var gate = new object();
+string? stopReason = null;
+var stopViaConsole = false;
+
+void RequestStop(string reason, bool viaConsole)
+{
+    lock (gate)
+    {
+        if (stopReason is not null)
+        {
+            return;
+        }
+
+        stopReason = reason;
+        stopViaConsole = viaConsole;
+    }
+
+    shutdown.Cancel();
+}
+
+void OnSignal(PosixSignalContext context)
+{
+    context.Cancel = true;
+    if (fake.Mode != FakeMode.IgnoreAll)
+    {
+        RequestStop("Shutdown via signal", false);
+    }
+}
+
+using var sigterm = PosixSignalRegistration.Create(PosixSignal.SIGTERM, OnSignal);
+using var sigint = PosixSignalRegistration.Create(PosixSignal.SIGINT, OnSignal);
+
+_ = Task.Run(async () =>
+{
+    string? line;
+    while ((line = await Console.In.ReadLineAsync()) is not null)
+    {
+        line = line.Trim();
+        if (line.Length == 0)
+        {
+            continue;
+        }
+
+        Log("Server Notification", $"Handling Console Command {line}");
+        var ignoresStop = fake.Mode is FakeMode.IgnoreStop or FakeMode.IgnoreAll;
+        if (line == "/stop" && !ignoresStop)
+        {
+            RequestStop("Shutdown via server command", true);
+        }
+    }
+
+    if (fake.StdinEofStopsServer)
+    {
+        RequestStop("stdin closed", false);
+    }
+});
+
+Log("Server Event", "Launching server...");
+Log("Server Notification", "Entering runphase Configuration");
+Log("Server Notification", "Loading savegame");
+
+try
+{
+    await Task.Delay(fake.StartupMs, shutdown.Token);
+}
+catch (OperationCanceledException)
+{
+    // A stop request during startup is handled below.
+}
+
+if (!shutdown.IsCancellationRequested)
+{
+    if (fake.Mode == FakeMode.FailOnStart)
+    {
+        return Crash(dataPath, fake.CrashExitCode, $"Fake failure: could not bind port {port}");
+    }
+
+    if (fake.Mode != FakeMode.NoReady)
+    {
+        Log("Server Event", $"Dedicated Server now running on Port {port} and all ips!");
+    }
+
+    var wait = fake.Mode == FakeMode.CrashAfterReady ? fake.CrashAfterMs : Timeout.Infinite;
+    try
+    {
+        await Task.Delay(wait, shutdown.Token);
+    }
+    catch (OperationCanceledException)
+    {
+        // Stop requested.
+    }
+
+    if (!shutdown.IsCancellationRequested)
+    {
+        return Crash(dataPath, fake.CrashExitCode, "Fake failure: simulated crash while running");
+    }
+}
+
+string reason;
+bool viaConsole;
+lock (gate)
+{
+    reason = stopReason ?? "unknown";
+    viaConsole = stopViaConsole;
+}
+
+Log("Server Notification", $"Server stop requested, begin shutdown sequence. Stop reason: {reason}");
+Log("Server Notification", "Entering runphase Shutdown");
+await Task.Delay(fake.StopMs);
+Log("Server Event", "World saved!");
+Log("Server Event", "Stopped the server!");
+if (viaConsole)
+{
+    Log("Server Notification", "Shut down command executed");
+}
+
+return 0;