Add: open

src/Lua/Standard/IO/FileHandle.cs

@@ -0,0 +1,6 @@
+namespace Lua.Standard.IO;
+
+public class FileHandle(FileStream stream) : LuaUserData
+{
+    public FileStream Stream { get; } = stream;
+}

src/Lua/Standard/IO/OpenFunction.cs

@@ -0,0 +1,44 @@
+namespace Lua.Standard.IO;
+
+public sealed class OpenFunction : LuaFunction
+{
+    public override string Name => "open";
+    public static readonly OpenFunction Instance = new();
+
+    protected override ValueTask<int> InvokeAsyncCore(LuaFunctionExecutionContext context, Memory<LuaValue> buffer, CancellationToken cancellationToken)
+    {
+        var fileName = context.ReadArgument<string>(0);
+        var mode = context.ArgumentCount >= 2
+            ? context.ReadArgument<string>(1)
+            : "r";
+
+        var fileMode = mode switch
+        {
+            "r" or "rb" or "r+" or "r+b" => FileMode.Open,
+            "w" or "wb" or "w+" or "w+b" => FileMode.Create,
+            "a" or "ab" or "a+" or "a+b" => FileMode.Append,
+            _ => throw new LuaRuntimeException(context.State.GetTraceback(), "bad argument #2 to 'open' (invalid mode)"),
+        };
+
+        var fileAccess = mode switch
+        {
+            "r" or "rb" => FileAccess.Read,
+            "w" or "wb" or "a" or "ab" => FileAccess.Write,
+            _ => FileAccess.ReadWrite,
+        };
+
+        try
+        {
+            var stream = File.Open(fileName, fileMode, fileAccess);
+            buffer.Span[0] = new FileHandle(stream);
+            return new(1);
+        }
+        catch (IOException ex)
+        {
+            buffer.Span[0] = LuaValue.Nil;
+            buffer.Span[1] = ex.Message;
+            buffer.Span[2] = ex.HResult;
+            return new(3);
+        }
+    }
+}