scanner: make plugin interface ffi-safe with handle-based registry

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I8e4790db3cc29f84f4e0d7d8eff36c2c6a6a6964

pscand-cli/Cargo.toml

@@ -26,6 +26,3 @@ ringbuf.workspace = true
 dirs.workspace = true
 sysinfo.workspace = true
 clap.workspace = true
-
-[profile.release]
-lto = true

pscand-cli/src/main.rs

@@ -1,3 +1,5 @@
+#![allow(improper_ctypes_definitions)]
+
 use clap::Parser;
 use libloading::Library;
 use pscand_core::logging::{LogLevel, RingBufferLogger};
@@ -10,7 +12,7 @@ use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
 use tokio::sync::RwLock;
 use tokio::time::interval;
 
-type ScannerCreator = unsafe extern "C" fn() -> Box<dyn Scanner>;
+type ScannerCreator = pscand_core::ScannerCreatorFfi;
 
 #[derive(Parser, Debug)]
 #[command(
@@ -452,7 +454,16 @@ async fn load_scanners(
                                 }
                             };
 
-                        let scanner = creator();
+                        let scanner = match pscand_core::get_scanner(creator()) {
+                            Some(s) => s,
+                            None => {
+                                log::error!(
+                                    "Failed to get scanner from library {}",
+                                    path.display()
+                                );
+                                continue;
+                            }
+                        };
                         let name = scanner.name().to_string();
 
                         let scanner_enabled = config.is_scanner_enabled(&name);

pscand-core/src/lib.rs

@@ -5,5 +5,7 @@ pub mod scanner;
 
 pub use config::Config;
 pub use logging::{DaemonLogEntry, LogLevel, RingBufferLogger};
-pub use scanner::{MetricValue, Scanner, ScannerError};
+pub use scanner::{
+    get_scanner, register_scanner, MetricValue, Scanner, ScannerCreatorFfi, ScannerError,
+};
 pub type Result<T> = std::result::Result<T, ScannerError>;

pscand-core/src/scanner.rs

@@ -1,10 +1,24 @@
 use std::collections::HashMap;
+use std::os::raw::c_void;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::LazyLock;
 use std::sync::Mutex;
 use std::time::Duration;
 
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
 
+pub type ScannerBox = Box<dyn Scanner>;
+pub type ScannerResult = Result<ScannerBox>;
+pub type ScannerMetrics = HashMap<String, MetricValue>;
+pub type ScannerCollectionResult = Result<ScannerMetrics>;
+pub type ScannerCollectFn = Box<dyn Fn() -> ScannerCollectionResult + Send + Sync>;
+pub type ScannerInitFnMut = Mutex<Box<dyn FnMut(&toml::Value) -> Result<()> + Send>>;
+pub type ScannerCleanupFnMut = Mutex<Box<dyn FnMut() -> Result<()> + Send>>;
+pub type ScannerCreatorFfi = unsafe extern "C" fn() -> *mut c_void;
+pub type ScannerInitFn = unsafe extern "C" fn() -> *mut c_void;
+pub type ScannerDropFn = unsafe extern "C" fn(*mut c_void);
+
 #[derive(Error, Debug)]
 pub enum ScannerError {
     #[error("IO error: {0}")]
@@ -43,7 +57,7 @@ impl MetricValue {
         MetricValue::Boolean(v)
     }
 
-    pub fn from_str(v: impl Into<String>) -> Self {
+    pub fn from_string(v: impl Into<String>) -> Self {
         MetricValue::String(v.into())
     }
 }
@@ -52,28 +66,56 @@ pub trait Scanner: Send + Sync {
     fn name(&self) -> &'static str;
     fn interval(&self) -> Duration;
     fn init(&mut self, config: &toml::Value) -> Result<()>;
-    fn collect(&self) -> Result<HashMap<String, MetricValue>>;
+    fn collect(&self) -> ScannerCollectionResult;
     fn cleanup(&mut self) -> Result<()>;
 }
 
+static SCANNER_HANDLES: LazyLock<Mutex<HashMap<usize, ScannerBox>>> =
+    LazyLock::new(|| Mutex::new(HashMap::new()));
+static NEXT_HANDLE: AtomicUsize = AtomicUsize::new(1);
+
+#[inline]
+/// Register a scanner and return a handle.
+/// # Safety
+/// The handle must only be used with `get_scanner` from the same process.
+pub unsafe fn register_scanner(scanner: ScannerBox) -> usize {
+    let handle = NEXT_HANDLE.fetch_add(1, Ordering::SeqCst);
+    SCANNER_HANDLES.lock().unwrap().insert(handle, scanner);
+    handle
+}
+
+#[inline]
+/// Retrieve a scanner by handle, consuming the registration.
+/// # Safety
+/// The handle must have been obtained from `register_scanner` in this process,
+/// and the returned Box must be properly dropped.
+pub unsafe fn get_scanner(handle: *mut c_void) -> Option<ScannerBox> {
+    let handle = handle as usize;
+    if handle == 0 {
+        None
+    } else {
+        SCANNER_HANDLES.lock().unwrap().remove(&handle)
+    }
+}
+
 pub trait ScannerRegistry: Send + Sync {
     fn list_scanners(&self) -> Vec<&'static str>;
-    fn get_scanner(&self, name: &str) -> Option<Box<dyn Scanner>>;
+    fn get_scanner(&self, name: &str) -> Option<ScannerBox>;
 }
 
 pub struct DynamicScanner {
     name: &'static str,
     interval: Duration,
-    collect_fn: Box<dyn Fn() -> Result<HashMap<String, MetricValue>> + Send + Sync>,
-    init_fn: Mutex<Box<dyn FnMut(&toml::Value) -> Result<()> + Send>>,
-    cleanup_fn: Mutex<Box<dyn FnMut() -> Result<()> + Send>>,
+    collect_fn: ScannerCollectFn,
+    init_fn: ScannerInitFnMut,
+    cleanup_fn: ScannerCleanupFnMut,
 }
 
 impl DynamicScanner {
     pub fn new(
         name: &'static str,
         interval: Duration,
-        collect_fn: impl Fn() -> Result<HashMap<String, MetricValue>> + Send + Sync + 'static,
+        collect_fn: impl Fn() -> ScannerCollectionResult + Send + Sync + 'static,
         init_fn: impl FnMut(&toml::Value) -> Result<()> + Send + 'static,
         cleanup_fn: impl FnMut() -> Result<()> + Send + 'static,
     ) -> Self {
@@ -101,7 +143,7 @@ impl Scanner for DynamicScanner {
         (init_fn)(config)
     }
 
-    fn collect(&self) -> Result<HashMap<String, MetricValue>> {
+    fn collect(&self) -> ScannerCollectionResult {
         (self.collect_fn)()
     }
 

pscand-macros/src/lib.rs

@@ -12,7 +12,7 @@ pub fn scanner(name: TokenStream, input: TokenStream) -> TokenStream {
 
     let result = quote! {
         #[no_mangle]
-        pub extern "C" fn pscand_scanner() -> Box<dyn pscand_core::Scanner> {
+        pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
             struct ScannerImpl;
 
             impl pscand_core::Scanner for ScannerImpl {
@@ -37,7 +37,8 @@ pub fn scanner(name: TokenStream, input: TokenStream) -> TokenStream {
                 }
             }
 
-            Box::new(ScannerImpl)
+            let handle = unsafe { pscand_core::register_scanner(Box::new(ScannerImpl)) };
+            handle as *mut std::os::raw::c_void
         }
     };
 
@@ -53,8 +54,9 @@ pub fn register_scanner(input: TokenStream) -> TokenStream {
         #input
 
         #[no_mangle]
-        pub extern "C" fn pscand_scanner() -> Box<dyn pscand_core::Scanner> {
-            Box::new(#fn_name())
+        pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
+            let handle = unsafe { pscand_core::register_scanner(Box::new(#fn_name())) };
+            handle as *mut std::os::raw::c_void
         }
     };
 

scanners/scanner-power/src/lib.rs

@@ -1,4 +1,3 @@
-#![allow(improper_ctypes)]
 use pscand_core::helpers::PowerHelper;
 use pscand_core::scanner::{MetricValue, Scanner};
 use std::collections::HashMap;
@@ -6,9 +5,9 @@ use std::time::Duration;
 
 struct PowerScanner;
 
-#[unsafe(no_mangle)]
-pub extern "C" fn pscand_scanner() -> Box<dyn Scanner> {
-    Box::new(PowerScanner)
+#[no_mangle]
+pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
+    Box::into_raw(Box::new(PowerScanner)) as *mut std::os::raw::c_void
 }
 
 impl Default for PowerScanner {
@@ -52,7 +51,7 @@ impl Scanner for PowerScanner {
             );
             metrics.insert(
                 "battery_status".to_string(),
-                MetricValue::from_str(&battery.status),
+                MetricValue::from_string(&battery.status),
             );
         }
 
@@ -61,7 +60,7 @@ impl Scanner for PowerScanner {
                 if let Some(status) = info.get("status") {
                     metrics.insert(
                         format!("supply_{}_status", name),
-                        MetricValue::from_str(status),
+                        MetricValue::from_string(status),
                     );
                 }
                 if let Some(online) = info.get("online") {
@@ -82,7 +81,10 @@ impl Scanner for PowerScanner {
         }
 
         if let Ok(state) = PowerHelper::suspend_state() {
-            metrics.insert("suspend_state".to_string(), MetricValue::from_str(&state));
+            metrics.insert(
+                "suspend_state".to_string(),
+                MetricValue::from_string(&state),
+            );
         }
 
         Ok(metrics)

scanners/scanner-proc/src/lib.rs

@@ -5,9 +5,9 @@ use std::time::Duration;
 
 struct ProcScanner;
 
-#[unsafe(no_mangle)]
-pub extern "C" fn pscand_scanner() -> Box<dyn Scanner> {
-    Box::new(ProcScanner)
+#[no_mangle]
+pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
+    Box::into_raw(Box::new(ProcScanner)) as *mut std::os::raw::c_void
 }
 
 impl Default for ProcScanner {
@@ -72,7 +72,7 @@ impl Scanner for ProcScanner {
                 }
                 metrics.insert(
                     "zombie_processes".to_string(),
-                    MetricValue::from_str(zombie_info.join(",")),
+                    MetricValue::from_string(zombie_info.join(",")),
                 );
             }
         }
@@ -81,7 +81,7 @@ impl Scanner for ProcScanner {
             for (i, proc) in top_mem.iter().enumerate() {
                 metrics.insert(
                     format!("top_mem_{}_name", i + 1),
-                    MetricValue::from_str(&proc.name),
+                    MetricValue::from_string(&proc.name),
                 );
                 metrics.insert(
                     format!("top_mem_{}_mb", i + 1),

scanners/scanner-sensor/src/lib.rs

@@ -1,4 +1,3 @@
-#![allow(improper_ctypes)]
 use pscand_core::helpers::SensorHelper;
 use pscand_core::scanner::{MetricValue, Scanner};
 use pscand_core::Result;
@@ -7,9 +6,9 @@ use std::time::Duration;
 
 struct SensorScanner;
 
-#[unsafe(no_mangle)]
-pub extern "C" fn pscand_scanner() -> Box<dyn Scanner> {
-    Box::new(SensorScanner)
+#[no_mangle]
+pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
+    Box::into_raw(Box::new(SensorScanner)) as *mut std::os::raw::c_void
 }
 
 impl Default for SensorScanner {

scanners/scanner-system/src/lib.rs

@@ -1,23 +1,17 @@
-#![allow(improper_ctypes)]
 use pscand_core::helpers::{ResourceHelper, SystemHelper};
 use pscand_core::scanner::{MetricValue, Scanner};
 use pscand_core::Result;
 use std::collections::HashMap;
 use std::time::Duration;
 
+#[derive(Default)]
 struct SystemScanner {
     _prev_cpu: Option<HashMap<String, f64>>,
 }
 
-impl Default for SystemScanner {
-    fn default() -> Self {
-        Self { _prev_cpu: None }
-    }
-}
-
-#[unsafe(no_mangle)]
-pub extern "C" fn pscand_scanner() -> Box<dyn Scanner> {
-    Box::new(SystemScanner::default())
+#[no_mangle]
+pub extern "C" fn pscand_scanner() -> *mut std::os::raw::c_void {
+    Box::into_raw(Box::new(SystemScanner::default())) as *mut std::os::raw::c_void
 }
 
 impl Scanner for SystemScanner {