operate

fn operate(userdata: ?*anyopaque, operation: Io.Operation) Io.Cancelable!Io.Operation.Result {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    switch (operation) {
        .file_read_streaming => |o| return .{
            .file_read_streaming = fileReadStreaming(t, o.file, o.data) catch |err| switch (err) {
                error.Canceled => |e| return e,
                else => |e| e,
            },
        },
        .file_write_streaming => |o| return .{
            .file_write_streaming = fileWriteStreaming(t, o.file, o.header, o.data, o.splat) catch |err| switch (err) {
                error.Canceled => |e| return e,
                else => |e| e,
            },
        },
        .device_io_control => |*o| return .{ .device_io_control = try deviceIoControl(o) },
        .net_receive => |*o| return .{ .net_receive = o: {
            if (!have_networking) break :o .{ error.NetworkDown, 0 };
            if (is_windows) break :o netReceiveWindows(t, o.socket_handle, o.message_buffer, o.data_buffer, o.flags);
            netReceivePosix(o.socket_handle, &o.message_buffer[0], o.data_buffer, o.flags, false) catch |err| switch (err) {
                error.Canceled => |e| return e,
                error.WouldBlock => unreachable,
                else => |e| break :o .{ e, 0 },
            };
            break :o .{ null, 1 };
        } },
        .net_send => |*o| return .{
            .net_send = o: {
                if (!have_networking) break :o .{ error.NetworkDown, 0 };
                if (is_windows) break :o netSendWindows(t, o.socket_handle, o.messages, o.flags);
                const send_err, const sent = netSendPosix(t, o.socket_handle, o.messages, o.flags, false);
                if (send_err) |err| switch (err) {
                    error.Canceled => |e| if (sent == 0) {
                        return e;
                    } else {
                        // Leave the `error.Canceled` for later, but don't try to send any more messages.
                        recancelInner();
                        break :o .{ null, sent };
                    },
                    error.WouldBlock => unreachable,
                    else => |e| break :o .{ e, sent },
                };
                break :o .{ null, sent };
            },
        },
        .net_read => |o| return .{
            .net_read = netRead(o.socket_handle, o.data) catch |err| switch (err) {
                error.Canceled => |e| return e,
                else => |e| e,
            },
        },
        .net_write => |o| return .{
            .net_write = (if (is_windows)
                netWriteWindows(o.socket_handle, o.header, o.data, o.splat)
            else
                netWritePosix(o.socket_handle, o.header, o.data, o.splat)) catch |err| switch (err) {
                error.Canceled => |e| return e,
                else => |e| e,
            },
        },
    }
}