Add basic C FFI for chat plugins and corresponding plugin loader

rc_plugins/Cargo.toml

@@ -9,3 +9,4 @@ readme.workspace = true
 
 [dependencies]
 log.workspace = true
+libloading = "0.9"

rc_plugins/src/chat/c_binding.rs

@@ -0,0 +1,86 @@
+//! The foreign function interface implementation for writing ChatPlugins in different shared objects/libraries.
+//! This is sort of cursed, I'm sorry in advance.
+use std::ffi::{CString, c_char, CStr};
+
+const SET_SEND_MESSAGE_CALLBACK_SYMBOL_NAME: &[u8] = b"oj_rc_set_chat_send_message_callback";
+const SET_SEND_MESSAGE_CALLBACK_SYMBOL_NAME_STR: &str = "oj_rc_set_chat_send_message_callback";
+
+const ON_MESSAGE_SYMBOL_NAME: &[u8] = b"oj_rc_on_chat_message";
+const ON_MESSAGE_SYMBOL_NAME_STR: &str = "oj_rc_on_chat_message";
+
+pub struct ChatCPlugin {
+    dll: libloading::Library,
+    pretty_name: String,
+    provider: std::sync::Mutex<Option<std::sync::Arc<Box<dyn super::ChatProvider>>>>,
+}
+
+impl ChatCPlugin {
+    pub fn new(file: impl AsRef<std::path::Path>) -> Result<Self, libloading::Error> {
+        let dll = unsafe { libloading::Library::new(file.as_ref()) }?;
+        Ok(Self {
+            dll,
+            pretty_name: file.as_ref().to_string_lossy().to_string(),
+            provider: std::sync::Mutex::new(None),
+        })
+    }
+}
+
+struct ContextC {
+    provider: std::sync::Weak<Box<dyn super::ChatProvider>>,
+}
+
+impl super::ChatPlugin for ChatCPlugin {
+    fn set_provider(&self, provider: std::sync::Arc<Box<dyn super::ChatProvider>>) {
+        let func: libloading::Symbol<unsafe extern "C" fn(*const ContextC, unsafe extern "C" fn(*const ContextC, *const c_char, *const c_char, *const c_char))> = match unsafe { self.dll.get(SET_SEND_MESSAGE_CALLBACK_SYMBOL_NAME) } {
+            Ok(x) => x,
+            Err(e) => {
+                log::error!("Failed to find symbol {} in library {}: {}", SET_SEND_MESSAGE_CALLBACK_SYMBOL_NAME_STR, self.pretty_name, e);
+                return;
+            }
+        };
+        *self.provider.lock().unwrap() = Some(provider.clone());
+        let weak_provider = std::sync::Arc::downgrade(&provider);
+        let ctx = Box::new(ContextC {
+            provider: weak_provider,
+        });
+        extern "C" fn callback(ctx: *const ContextC, msg: *const c_char, chann: *const c_char, usern: *const c_char) {
+            let ctx = if let Some(ctx) = unsafe { ctx.as_ref() } { ctx } else { return };
+            let msg = unsafe { CStr::from_ptr(msg) };
+            let chann = unsafe { CStr::from_ptr(chann) };
+            let usern = unsafe { CStr::from_ptr(usern) };
+            if let Some(provider) = ctx.provider.upgrade() {
+                match (msg.to_str(), chann.to_str(), usern.to_str()) {
+                    (Ok(message), Ok(channel), Ok(username)) => {
+                        provider.send_message(message, channel, username);
+                    },
+                    _ => {
+                        log::warn!("{} called with invalid string parameter", SET_SEND_MESSAGE_CALLBACK_SYMBOL_NAME_STR);
+                    }
+                }
+            } else {
+                log::warn!("Chat provider callback invoked after it has been dropped");
+            }
+        }
+        unsafe {
+            func(&*ctx, callback)
+        }
+    }
+
+    fn on_message(&self, message: &str, channel: &str, username: &str) {
+        let func: libloading::Symbol<unsafe extern "C" fn(*const c_char, *const c_char, *const c_char)> = match unsafe { self.dll.get(ON_MESSAGE_SYMBOL_NAME) } {
+            Ok(x) => x,
+            Err(e) => {
+                log::error!("Failed to find symbol {} in library {}: {}", ON_MESSAGE_SYMBOL_NAME_STR, self.pretty_name, e);
+                return;
+            }
+        };
+        let message = CString::new(message).unwrap_or_default();
+        let channel = CString::new(channel).unwrap_or_default();
+        let username = CString::new(username).unwrap_or_default();
+        unsafe {
+            func(message.as_c_str().as_ptr(), channel.as_c_str().as_ptr(), username.as_c_str().as_ptr());
+        }
+    }
+}
+
+impl crate::Plugin for ChatCPlugin {}

rc_plugins/src/chat/mod.rs

@@ -1,2 +1,5 @@
 mod plugin;
 pub use plugin::{ChatProvider, ChatPlugin};
+
+mod c_binding;
+pub use c_binding::ChatCPlugin;