add semaphore module

2 files changed, 58 insertions, 0 deletions

diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 65e9666..71f60c9 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -34,6 +34,7 @@ mod ratelimit;
 mod redirect;
 mod switch;
 mod upgrade_insecure;
+mod semaphore;
 
 pub type NodeRequest = Request<BoxBody<Bytes, ServiceError>>;
 pub type NodeResponse = Response<BoxBody<Bytes, ServiceError>>;
@@ -63,6 +64,7 @@ pub static MODULES: &[&dyn NodeKind] = &[
     &delay::DelayKind,
     &ratelimit::RatelimitKind,
     &log::LogKind,
+    &semaphore::SemaphoreKind,
 ];
 
 pub struct NodeContext {
diff --git a/src/modules/semaphore.rs b/src/modules/semaphore.rs
new file mode 100644
index 0000000..b4f50b2
--- /dev/null
+++ b/src/modules/semaphore.rs
@@ -0,0 +1,56 @@
+/*
+    This file is part of gnix (https://codeberg.org/metamuffin/gnix)
+    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
+    Copyright (C) 2025 metamuffin <metamuffin.org>
+*/
+use super::{Node, NodeContext, NodeKind, NodeRequest, NodeResponse};
+use crate::{config::DynNode, error::ServiceError};
+use anyhow::Result;
+use serde::Deserialize;
+use serde_yml::Value;
+use std::{
+    future::Future,
+    pin::Pin,
+    sync::Arc,
+};
+use tokio::sync::Semaphore;
+
+pub struct SemaphoreKind;
+
+#[derive(Deserialize)]
+struct SemaphoreConfig {
+    permits: usize,
+    next: DynNode,
+}
+
+struct SemaphoreState {
+    config: SemaphoreConfig,
+    semaphore: Semaphore,
+}
+
+impl NodeKind for SemaphoreKind {
+    fn name(&self) -> &'static str {
+        "semaphore"
+    }
+    fn instanciate(&self, config: Value) -> Result<Arc<dyn Node>> {
+        let config = serde_yml::from_value::<SemaphoreConfig>(config)?;
+        Ok(Arc::new(SemaphoreState {
+            semaphore: Semaphore::new(config.permits),
+            config,
+        }))
+    }
+}
+impl Node for SemaphoreState {
+    fn handle<'a>(
+        &'a self,
+        context: &'a mut NodeContext,
+        request: NodeRequest,
+    ) -> Pin<Box<dyn Future<Output = Result<NodeResponse, ServiceError>> + Send + Sync + 'a>> {
+        Box::pin(async move {
+            let _permit = self.semaphore.acquire().await;
+            let resp = self.config.next.handle(context, request).await?;
+            drop(_permit);
+            Ok(resp)
+        })
+    }
+}