yabridge/README.md

# yabridge

Yet Another way to use Windows VST2 plugins in Linux VST hosts.

## TODOs

There are a few things that should be done before making this public, including:

- Implement missing features:
  - GUIs. Right now I'm just ignoring all of the opcodes related to GUIs so that
    the plugins don't crash when you open their GUI.
  - Check whether sidechaining and ~~MPE~~ work since they're unofficial additions
    to the VST 2.4 spec. Should either work out of the box or with a minor
    adjustment. MPE works!
- add missing details if any to the architecture section.
- Document what this has been tested on and what does or does not work.
- Document wine32 support.

## Usage

There are two ways to use yabridge.

### Symlinking (recommended)

The recommended way to use yabridge is through symbolic links. This allows you
to update yabridge for all of your plugins in one go, and it also avoids having
to install it globally.

You can either use the precompiled binaries from the GitHub releases section, or
you could build yabridge directly from source. If you use the precompiled
binaries, then simply extract them to `~/.local/share/yabridge` or any other
place in your home directory. If you choose to build from source, then you can
directly use the binaries from the `build/` directory. For the section below I'm
going to assume you've placed the files in `~/.local/share/yabridge`.

To set up yabridge for a VST plugin called
`~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.dll`, simply create a
symlink from `~/.local/share/yabridge/libyabridge.so` to
`~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so` like so:

```shell
ln -s ~/.local/share/yabridge/libyabridge.so "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so"
```

For instance, if you wanted to set up yabridge for any of the VST plugins under
`~/.wine/drive_c/Program Files/Steinberg/VstPlugins`, you could do something
like this:

```shell
find "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins" -type f -iname '*.dll' -print0 \
  | sed -z 's/\.dll$/.so/' \
  | xargs -0 -n1 ln -sf ~/.local/share/yabridge/libyabridge.so
```

### Copying

It's also possible to use yabridge by making copies of `libyabridge.so` instead
of creating symlinks. This is not recommended as it makes updating a hassle. If
you choose to do this, then you'll have to make sure `yabridge-host.exe` and
`yabridge-host.exe.so` are somewhere in your search path as otherwise yabridge
won't know where to find them. Either copy them to `/usr/local/bin` (not
recommended) or to `~/.local/bin` and make sure that the directory is in your
`PATH` environment variable.

## Building

To compile yabridge, you'll need [Meson](https://mesonbuild.com/index.html) and
the following dependencies:

- gcc (tested using GCC 9.2)
- A Wine installation with `wiengcc` and the development headers.
- Boost

The following dependencies are included as a Meson wrap:

- bitsery

The project can then be compiled as follows:

```shell
meson setup --buildtype=release --cross-file cross-wine64.conf build
ninja -C build
```

When developing or debugging yabridge you can change the build type to either
`debug` enable debug symbols and disable optimizations.

## Debugging

Wine's error messages and warning are typically very helpful whenever a plugin
doesn't work right away. Sadly this information is not always available. For
instance Bitwig hides a plugin's STDOUT and STDERR streams from you. To make it
easier to debug malfunctioning plugins, yabridge offers two environment
variables:

- `YABRIDGE_DEBUG_FILE=<path>` allows you to write the Wine VST host's STDOUT
  and STDERR messages to a file. For example, you could launch your DAW with
  `env YABRIDGE_DEBUG_FILE=/tmp/yabridge.log <daw>`,
  and then use `tail -F /tmp/yabridge.log` to keep track of that file. If this
  option is not absent then yabridge will write its debug messages to STDERR
  instead.
- `YABRIDGE_DEBUG_LEVEL={0,1}` allows you to set the verbosity of the debug
  information. Every level increases the verbosity of the debug information:

  - A value of `0` (the default) means that yabridge will only output messages
    from the Wine process and some basic information such as the plugin being
    loaded and the wineprefix being used.
  - A value of `1` will log information about all events and function calls
    being sent between the VST host and the plugin. This can be very verbose but
    it makes it easier to see if yabridge is handling things incorrectly.

  More detailed information about these levels can be found in
  `src/common/logging.h`.

### Attaching a debugger

When needed, I found the easiest way to debug the plugin to be to load it in an
instance of Carla with gdb attached:

```shell
env YABRIDGE_DEBUG_FILE=/tmp/yabridge.log YABRIDGE_DEBUG_LEVEL=1 carla --gdb
```

Doing the same thing with the Wine VST host is also possible but it's a bit
tricky. I have not had any success with attaching winedbg to running processes.
The only thing that seems to work is to modify `host-bridge.cpp` to not launch
`yabridge-host.exe` normally, but to instead start a new (detached) terminal
emulator process running the Wine host through `winedbg --gdb`. I wouldn't
recommended doing this if you can avoid it.

## Rationale

I started this project because the alternatives were either unmaintained, not
self-contained or very difficult to work with. With this implementation I'd like
to prioritize maintainability and correctness, with performance being a
secondary goal. Please let me know if you have any suggestions on how to improve
this!

## Architecture

The project consists of two components, a Linux native VST plugin
(`libyabridge.so`) and a VST host that runs under Wine
(`yabridge-host.exe`/`yabridge-host.exe.so`). I'll refer to a copy of or a
symlink to `libyabridge.so` as _the plugin_, the native Linux VST host that's
hosting the plugin as _the native VST host_, the Wine VST host that's hosting a
Windows `.dll` file as _the Wine VST host_, and the Windows VST plugin that's
loaded in the Wine VST host is simply the _Windows VST plugin_. The whole
process works as follows:

1. Some copy of or a symlink to `libyabridge.so` gets loaded as a VST plugin in
   a Linux VST host. This file should have been renamed to match a Windows VST
   plugin `.dll` file in the same directory. For instance, if there's a
   `Serum_x64.dll` file you'd like to bridge, then there should be a symlink to
   `libyabridge.so` named `Serum_x64.so`.
2. The plugin first attempts to locate:

   - The location of `yabridge-host.exe`. For this it will first search for the
     file either alongside `libyabridge.so`. This is useful for development, as
     it allows you to use a symlink from the build directory to cause yabridge
     to use the `yabridge-host.exe` from that same build directory. If this file
     can't be found, then it will fall back to searching through the search path.
   - The wine prefix plugin is located in.
   - The corresponding Windows VST plugin `.dll` file.

3. The plugin then sets up a Unix domain socket endpoint to communicate with the
   Wine VST host somewhere in a temporary directory and starts listening on it.
   I chose to use Unix domain sockets rather than shared memory because this way
   you get low latency communication with without any busy waits or manual
   synchronisation for free. The added benefit is that it also makes it possible
   to send arbitrarily large data without having to split it up into chunks
   first, which is useful for transmitting audio and preset data which may have
   any arbitrary size.
4. The plugin launches the Wine VST host in the detected wine prefix, passing
   the name of the `.dll` file it should be loading and the path to the Unix
   domain socket that was just created.
5. Communication gets set up using multiple sockets over the same end point.
   This allows us to use blocking read operations from multiple threads to
   handle multiple different events without the risk of receiving packets in the
   wrong order. The following types of events get assigned a socket:

   - Calls from the native VST host to the plugin's `dispatch()` function. These
     get forwarded to the Windows VST plugin through the Wine VST host.
   - Host callback calls from the Windows VST plugin loaded into the Wine VST
     host through the `audioMasterCallback` function. These get forwarded to the
     native VST host through the plugin.

     Both the `dispatch()` and `audioMasterCallback()` functions are handled in
     the same way, with some minor variations on how payload data gets
     serialized depending on the opcode of the event being sent.

   - Calls from the native VST host to the plugin's `getParameter()` and
     `setParameter()` functions. Both functions get forwarded to the Windows VST
     plugin through the Wine VST host using a single socket because they're very
     similar and don't need any complicated behaviour.
   - Calls from the native VST host to the plugin's `process()` and
     `processReplacing()` functions. Both functions get forwarded to the Windows
     VST plugin through the Wine VST host using a single socket. The `process()`
     function has been deprecated, so a VST host will never call it if
     `processReplacing()` is supported by the plugin.
   - Updates of the Windows VST plugin's `AEffect` object. This object tells the
     host about the plugin's capabilities. A copy of this is sent over a socket
     from the Wine VST hsot to the plugin after it loads the Windows VST plugin
     so it can return a pointer to it to the native VST host. Whenever this
     struct updates, the Windows VST plugin will call the `audioMasterIOChanged`
     host callback and we'll repeat this process.

   The operations described above are all handled by first serializing the
   function parameters and any payload into an object before they can be sent
   over a socket. The objects used for encoding both the requests and and the
   responses for theses events can be found in `src/common/communication.h`
   along with functions that read and write these objects over streams and
   sockets. The actual binary serialization is handled using
   [bitsery](https://github.com/fraillt/bitsery).

6. The Wine VST host loads the Windows VST plugin and starts forwarding messages
   over the sockets described above.
7. After the Windows VST plugin has started loading we will forward all values
   from the plugin's `AEffect` struct to the Linux native VST plugin using the
   socket described above. After this point the plugin will stop blocking and
   has finished loading.