Add boilerplate for a JACK backend

Cargo.lock

@@ -2096,6 +2096,7 @@ dependencies = [
 name = "nih_plug"
 version = "0.0.0"
 dependencies = [
+ "anyhow",
  "assert_no_alloc",
  "atomic_float",
  "atomic_refcell",

Cargo.toml

@@ -47,7 +47,7 @@ assert_process_allocs = ["dep:assert_no_alloc"]
 # Enables an export target for standalone binaries through the
 # `nih_export_standalone()` function. Disabled by default, as this requires
 # building additional dependencies for audio and MIDI handling.
-standalone = ["dep:baseview", "dep:clap"]
+standalone = ["dep:anyhow", "dep:baseview", "dep:clap"]
 # Enables the `nih_export_vst3!()` macro. Enabled by default. This feature
 # exists mostly for GPL-compliance reasons, since even if you don't use the VST3
 # wrapper you might otherwise still include a couple (unused) symbols from the
@@ -83,6 +83,7 @@ widestring = "1.0.0-beta.1"
 assert_no_alloc = { version = "1.1", optional = true }
 
 # Used for the `standalone` feature
+anyhow = { version = "1.0", optional = true }
 # NOTE: OpenGL support is not needed here, but rust-analyzer gets confused when
 #       some crates do use it and others don't
 baseview = { git = "https://github.com/robbert-vdh/baseview.git", branch = "feature/resize", features = ["opengl"], optional = true }

src/wrapper/standalone.rs

@@ -3,6 +3,7 @@
 
 use clap::{FromArgMatches, IntoApp};
 
+use self::backend::Backend;
 use self::config::WrapperConfig;
 use self::wrapper::{Wrapper, WrapperError};
 use super::util::setup_logger;
@@ -68,14 +69,28 @@ pub fn nih_export_standalone_with_args<P: Plugin, Args: IntoIterator<Item = Stri
     )
     .unwrap_or_else(|err| err.exit());
 
-    nih_log!(
-        "Audio and MIDI IO has not yet been implemented in the standalone targets. So if you're \
-         not hearing anything, then that's correct!"
-    );
+    match config.backend {
+        config::BackendType::Auto => match backend::Jack::new(config.clone()) {
+            Ok(backend) => run_wrapper::<P, _>(backend, config),
+            Err(_) => {
+                nih_log!("Could not initialize JACK, falling back to the dummy audio backend");
+                run_wrapper::<P, _>(backend::Dummy::new(config.clone()), config)
+            }
+        },
+        config::BackendType::Jack => match backend::Jack::new(config.clone()) {
+            Ok(backend) => run_wrapper::<P, _>(backend, config),
+            Err(err) => {
+                nih_log!("{:#}", err);
+                false
+            }
+        },
+        config::BackendType::Dummmy => {
+            run_wrapper::<P, _>(backend::Dummy::new(config.clone()), config)
+        }
+    }
+}
 
-    // TODO: We should try JACK first, then CPAL, and then fall back to the dummy backend. With a
-    //       command line option to override this behavior.
-    let backend = backend::Dummy::new(config.clone());
+fn run_wrapper<P: Plugin, B: Backend>(backend: B, config: WrapperConfig) -> bool {
     let wrapper = match Wrapper::<P, _>::new(backend, config.clone()) {
         Ok(wrapper) => wrapper,
         Err(err) => {

src/wrapper/standalone/backend.rs

@@ -1,3 +1,4 @@
+use anyhow::Result;
 use std::time::{Duration, Instant};
 
 use crate::buffer::Buffer;
@@ -15,10 +16,10 @@ pub trait Backend: 'static + Send + Sync {
     fn run(&mut self, cb: impl FnMut(&mut Buffer) -> bool);
 }
 
-// /// Uses JACK audio and MIDI.
-// pub struct Jack {
-//     // TODO
-// }
+/// Uses JACK audio and MIDI.
+pub struct Jack {
+    config: WrapperConfig,
+}
 
 /// This backend doesn't input or output any audio or MIDI. It only exists so the standalone
 /// application can continue to run even when there is no audio backend available. This can be
@@ -27,12 +28,11 @@ pub struct Dummy {
     config: WrapperConfig,
 }
 
-// TODO: Add a JACK backend
-// impl Backend for Jack {
-//     fn run(&mut self, cb: impl FnMut(&mut Buffer) -> bool) {
-//         todo!()
-//     }
-// }
+impl Backend for Jack {
+    fn run(&mut self, cb: impl FnMut(&mut Buffer) -> bool) {
+        todo!()
+    }
+}
 
 impl Backend for Dummy {
     fn run(&mut self, mut cb: impl FnMut(&mut Buffer) -> bool) {
@@ -73,6 +73,15 @@ impl Backend for Dummy {
     }
 }
 
+impl Jack {
+    /// Initialize the JACK backend. Returns an error if this failed for whatever reason.
+    pub fn new(config: WrapperConfig) -> Result<Self> {
+        // TODO: Actually implement the JACK backend
+        anyhow::bail!("Could not initialize JACK backend")
+        // Ok(Self { config })
+    }
+}
+
 impl Dummy {
     pub fn new(config: WrapperConfig) -> Self {
         Self { config }

src/wrapper/standalone/config.rs

@@ -51,6 +51,8 @@ pub enum BackendType {
     ///
     /// This defaults to JACK if JACK is available, and falls back to the dummy backend if not.
     Auto,
+    /// Use JACK for audio and MIDI.
+    Jack,
     /// Does not playback or receive any audio or MIDI.
     Dummmy,
 }