5 files changed, 186 insertions, 0 deletions
diff --git a/swaystatus-plugin/.cargo/config b/swaystatus-plugin/.cargo/config
new file mode 100644
index 0000000..d046680
--- /dev/null
+++ b/swaystatus-plugin/.cargo/config
@@ -0,0 +1,2 @@
+[build]
+rustflags = ["-C", "prefer-dynamic"]
diff --git a/swaystatus-plugin/.gitignore b/swaystatus-plugin/.gitignore
new file mode 100644
index 0000000..d4790ef
--- /dev/null
+++ b/swaystatus-plugin/.gitignore
@@ -0,0 +1,4 @@
+/target
+*~
+*.swp
+Cargo.lock
diff --git a/swaystatus-plugin/Cargo.toml b/swaystatus-plugin/Cargo.toml
new file mode 100644
index 0000000..c521baa
--- /dev/null
+++ b/swaystatus-plugin/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "swaystatus-plugin"
+version = "0.1.0"
+authors = ["Andreas Grois <andi@grois.info>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+erased-serde = "0.3"
+
+[build-dependencies]
+rustc_version = "0.2.3"
diff --git a/swaystatus-plugin/build.rs b/swaystatus-plugin/build.rs
new file mode 100644
index 0000000..a38022f
--- /dev/null
+++ b/swaystatus-plugin/build.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let version = rustc_version::version().unwrap();
+    println!("cargo:rustc-env=RUSTC_VERSION={}", version);
+}
diff --git a/swaystatus-plugin/src/lib.rs b/swaystatus-plugin/src/lib.rs
new file mode 100644
index 0000000..3e27d19
--- /dev/null
+++ b/swaystatus-plugin/src/lib.rs
@@ -0,0 +1,163 @@
+#![warn(missing_docs)]
+//! Interface definitions for swaystatus plugins.
+//!
+//! A plugin is a shared library that provides the following types:
+//! - `SwayStatusModule`, the main entry point of the module, used to create SwayStatusModuleInstance 
+//! - `SwayStatusModuleInstance`, one instance of the module. Gets initialized with settings and creates SwayStatusModuleRunnable.
+//! - `SwayStatusModuleRunnable`, created by SwayStatusModuleInstance, the plugin's main loop
+//!
+//! In addition the plugin must have a constructor function that returns a valid SwayStatusModule.
+//! This can then be exported using the `declare_swaystatus_module()` macro.
+//!
+//! The swaystatus main program will call methods on your `SwayStatusModule` during initialization.
+//! All calls to this interface will come from the main thread.
+//!
+//! The `make_runnable()` method should prepare a runnable object, which will then be run in a
+//! separate worker thread. You have full control over that thread, meaning you can just sleep
+//! until an update is required. The make_runnable() is still called from the main thread.
+//! However the runnable's run() method is called from a worker thread.
+//!
+//! Communication between plugin and main module is routed through special trait objects instead
+//! of directly moving channel endpoints. This is done for two reasons. The first is that it allows
+//! to abstract away the need to use a given synchronization framework. That way for instance the
+//! communication from main to plugin could use crossbeam, while the answers from the plugin are
+//! sent using the standard library's mpsc channels.
+//! The second, and more important reason is that (at least crossbeam's) channels use thread-local
+//! storage, which would only work properly between different dynamic libraries, if they also
+//! dynamically link against the library that supplies the channel implementation. Since linkage
+//! with Cargo is defined by the dependency, not by the user, that's not really an option...
+//!
+//! ## Note on lifetimes:
+//! There are relatively strict lifetimes imposed. No created trait object may outlive its creator.
+//! This is because loading plugins is by definition unsafe, and we need to make sure that nothing
+//! can exist beyond the symbols from the dynamic library.
+//!
+//! ## Note on linkage:
+//! While you can't easily change how dependencies are linked into your plugin, you can choose to
+//! dynamically link against the Rust standard library. For memory reasons I'd strongly recommend
+//! to do so. The easiest way is to set rustc compiler flags using .cargo/config in the project.
+
+use erased_serde::serialize_trait_object;
+
+#[doc(hidden)]
+pub static RUSTC_VERSION : &str = env!("RUSTC_VERSION");
+#[doc(hidden)]
+pub static MODULE_VERSION : &str = env!("CARGO_PKG_VERSION");
+
+/// Declares a public export C function that creates your plugin's main object.
+/// parameters are: The plugin's concrete type, and the constructor function for it.
+/// This is blatantly stolen from
+/// https://michael-f-bryan.github.io/rust-ffi-guide/dynamic_loading.html
+#[macro_export]
+macro_rules! declare_swaystatus_module {
+    ($plugin_type:ty, $constructor:path) => {
+        #[no_mangle]
+        pub extern "C" fn _swaystatus_module_create() -> *mut dyn $crate::SwayStatusModule {
+            // make sure the constructor is the correct type.
+            let constructor: fn() -> $plugin_type = $constructor;
+            let object = constructor();
+            let boxed: Box<$crate::SwayStatusModule> = Box::new(object);
+            Box::into_raw(boxed)
+        }
+        #[no_mangle]
+        pub extern "C" fn _swaystatus_module_version() -> *const str {
+            $crate::MODULE_VERSION
+        }
+        #[no_mangle]
+        pub extern "C" fn _swaystatus_rustc_version() -> *const str {
+            $crate::RUSTC_VERSION
+        }
+    };
+}
+
+/// You need to implement this trait, as creating a runnable needs to return this type as well.
+/// A typical implementation would be a thin wrapper around a channel's sender end.
+/// Please don't make this blocking to prevent deadlocks.
+pub trait MsgMainToModule {
+    /// Implement this in such a way, that when it's called from the main thread, your module will
+    /// soon-ish return from it's main function, after cleaning up it's resources and after joining
+    /// all threads it spawns.
+    fn send_quit(&self) -> Result<(),()>;
+
+    /// Implement this in such a way, that when it's called from the main thread, your module will
+    /// soon-ish send an updated text. The main module does not really wait for updates, so
+    /// ignoring this or implementing it empty is perfectly fine if you know that your module's
+    /// output cannot possibly change between updates it sends anyhow.
+    fn send_refresh(&self) -> Result<(),()>;
+}
+
+/// When communicating an error to the main program, this allows to choose an appropriate handling
+/// method. If the error does not prevent text updates, you likely just want to print it to stderr.
+/// If it makes further processing impossible but doesn't cause an outright crash, consider
+/// showing it instead of the usual text instead.
+#[derive(Debug)]
+pub enum PluginError {
+    /// Use this variant if your error is not critical for the plugin's operation, but should still
+    /// be communicated to the main program. The main program currently just calls eprintln! with
+    /// it, but this might change if it gets more features (like logging). If you want a
+    /// verbose/short type of error, send two errors, first one with this variant that holds the
+    /// verbose error, afterwards one with ShowInsteadOfText that just replaces the text with a
+    /// short error.
+    PrintToStdErr(String),
+    /// This notifies the main program that an error was encountered and no future text updates
+    /// from this plugin are expected. The main program will replace the last text output by this
+    /// error message. If you want to send both, a verbose error for the terminal/log and a short
+    /// one to be displayed in the status bar, first send a PrintToStdErr variant with a verbose
+    /// error, and then the short text as this variant.
+    ShowInsteadOfText(String)
+}
+impl std::error::Error for PluginError {}
+impl std::fmt::Display for PluginError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", match self {
+            PluginError::PrintToStdErr(x) => x,
+            PluginError::ShowInsteadOfText(x) => x
+        })
+    }
+}
+
+/// This is implemented by the main program and passed to your module when creating the runnable.
+/// Please note that the functions on this might eventually block until the main module finished
+/// processing them. 
+pub trait MsgModuleToMain : Send {
+    /// Invoke this to update your text. This triggers the main program to build a new line of
+    /// stdout output. While this can in theory return an error, that should practically never
+    /// happen. If this errors, you should probably clean up your resources and return from the
+    /// run() function. In other words, act as if main had sent you a quit command.
+    fn send_update(&self, text : Result<String, PluginError>) -> Result<(),()>;
+}
+
+/// Interface your module should implement. All functions of this will be called in the main thread.
+pub trait SwayStatusModule {
+    ///The plugin's name. Must be globally unique. Shown to users in the config file.
+    fn get_name(&self) -> &str;
+
+    ///Called by the main program with a deserializer that holds the config for an instance of this
+    ///module.
+    ///In almost all cases it's enough to just call `erased_serde::deserialize(deserializer)?` in
+    ///this function.
+    fn deserialize_config<'de, 'p>(&'p self, deserializer : &mut (dyn erased_serde::Deserializer + 'de)) -> Result<Box<dyn SwayStatusModuleInstance + 'p>,erased_serde::Error>;
+
+    ///This is used for the command line option to print a default configuration.
+    ///Let it return your config with all defaults (including optional fields).
+    fn get_default_config<'p>(&'p self) -> Box<dyn SwayStatusModuleInstance + 'p>;
+}
+
+///This is what `SwayStatusModuleInstance::make_runnable()` returns. The main function of your module.
+///Will be called in a worker thread.
+pub trait SwayStatusModuleRunnable : Send {
+    ///Starts executing this module.
+    fn run(&self); 
+}
+
+///Implement this trait on a struct that holds the configuration for a single instance of your
+///plugin. The make_runnable then creates a runnable that gets moved to a different thread.
+///In addition to making the runnable, the `make_runnable()` method also needs to return a
+///MsgMainToModule trait object.
+pub trait SwayStatusModuleInstance : erased_serde::Serialize { 
+    ///The main initialization function. Takes the 2 communication channels and a configuration.
+    ///The config is a trait object of the same type you provide in `get_default_config()` and 
+    ///`deserialize_config()`.
+    fn make_runnable<'p>(&'p self, to_main : Box<dyn MsgModuleToMain + 'p>) -> (Box<dyn SwayStatusModuleRunnable + 'p>, Box<dyn MsgMainToModule + 'p>);
+}
+serialize_trait_object!(SwayStatusModuleInstance);