Implement body size limit middleware with dynamic config reload

Add body_limit middleware that reads limit from ArcSwap<DynamicConfig>
on each request, enabling runtime config changes without restart.
Uses Content-Length header check for fast rejection and http_body_util::Limited
for streaming body enforcement. Default limit: 100 MB (104,857,600 bytes).
Returns 413 Payload Too Large when exceeded.

Cargo.lock

@@ -1585,6 +1585,7 @@ dependencies = [
  "axum",
  "clap",
  "futures",
+ "http-body-util",
  "hyper",
  "rcgen",
  "reqwest",

Cargo.toml

@@ -31,6 +31,7 @@ clap = { version = "=4.6.1", features = ["derive"] }
 signal-hook = "=0.3.18"
 anyhow = "=1.0.102"
 thiserror = "=2.0.18"
+http-body-util = "=0.1.3"
 futures = "=0.3.31"
 
 [dev-dependencies]

src/proxy/body_limit.rs

@@ -0,0 +1,51 @@
+use std::sync::Arc;
+
+use arc_swap::ArcSwap;
+use axum::body::Body;
+use axum::extract::State;
+use axum::http::StatusCode;
+use axum::response::IntoResponse;
+use http_body_util::Limited;
+
+use crate::config::DynamicConfig;
+
+pub const DEFAULT_BODY_LIMIT_BYTES: u64 = 104_857_600;
+
+pub async fn body_limit_middleware(
+    State(config): State<Arc<ArcSwap<DynamicConfig>>>,
+    request: axum::extract::Request,
+    next: axum::middleware::Next,
+) -> axum::response::Response {
+    let limit = config.load().body.limit_bytes;
+    let limit = if limit == 0 {
+        DEFAULT_BODY_LIMIT_BYTES
+    } else {
+        limit
+    };
+
+    if let Some(content_length) = request.headers().get("content-length") {
+        if let Ok(length_str) = content_length.to_str() {
+            if let Ok(length) = length_str.parse::<u64>() {
+                if length > limit {
+                    return (StatusCode::PAYLOAD_TOO_LARGE, "Payload Too Large").into_response();
+                }
+            }
+        }
+    }
+
+    let (parts, body) = request.into_parts();
+    let limited_body = Limited::new(body, limit as usize);
+    let request = axum::extract::Request::from_parts(parts, Body::new(limited_body));
+
+    next.run(request).await
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_body_limit_is_100mb() {
+        assert_eq!(DEFAULT_BODY_LIMIT_BYTES, 104_857_600);
+    }
+}

src/proxy/mod.rs

@@ -1,3 +1,20 @@
+pub mod body_limit;
 pub mod error;
 pub mod handler;
 pub mod headers;
+
+use std::sync::Arc;
+
+use arc_swap::ArcSwap;
+
+use crate::config::DynamicConfig;
+
+pub fn router_with_body_limit(
+    router: axum::Router,
+    config: Arc<ArcSwap<DynamicConfig>>,
+) -> axum::Router {
+    router.layer(axum::middleware::from_fn_with_state(
+        config,
+        body_limit::body_limit_middleware,
+    ))
+}

tests/integration_test.rs

@@ -1,5 +1,16 @@
 mod helpers;
 
+use std::sync::Arc;
+
+use arc_swap::ArcSwap;
+use axum::routing::post;
+use axum::Router;
+use reverse_proxy::config::dynamic_config::{
+    BodyConfig, DynamicConfig, RateLimitConfig, SiteConfig,
+};
+use reverse_proxy::proxy::body_limit::DEFAULT_BODY_LIMIT_BYTES;
+use reverse_proxy::proxy::router_with_body_limit;
+
 #[tokio::test]
 async fn test_upstream_spawn_and_connect() {
     let upstream = helpers::http_test_helper::TestUpstream::spawn_ok().await;
@@ -71,3 +82,207 @@ async fn test_health_check_disabled_when_port_zero() {
     assert_ne!(addr.port(), 0);
     handle.abort();
 }
+
+fn test_dynamic_config_with_limit(limit_bytes: u64) -> Arc<ArcSwap<DynamicConfig>> {
+    let config = DynamicConfig {
+        sites: vec![SiteConfig {
+            host: "test.local".to_string(),
+            upstream: "127.0.0.1:8080".to_string(),
+            upstream_scheme: "http".to_string(),
+            upstream_connect_timeout_secs: 5,
+            upstream_request_timeout_secs: 60,
+        }],
+        rate_limit: RateLimitConfig {
+            requests_per_second: 10,
+            burst: 20,
+        },
+        body: BodyConfig { limit_bytes },
+    };
+    Arc::new(ArcSwap::from_pointee(config))
+}
+
+async fn spawn_server_with_limit(limit_bytes: u64) -> helpers::http_test_helper::TestUpstream {
+    let config = test_dynamic_config_with_limit(limit_bytes);
+    helpers::http_test_helper::TestUpstream::spawn(|| {
+        let app = Router::new().route(
+            "/",
+            post(|body: axum::body::Body| async move {
+                let _ = body;
+                "ok"
+            }),
+        );
+        router_with_body_limit(app, config.clone())
+    })
+    .await
+}
+
+#[tokio::test]
+async fn test_body_limit_rejects_oversized_request() {
+    let server = spawn_server_with_limit(100).await;
+    let client = reqwest::Client::new();
+
+    let large_body = vec![0u8; 200];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(large_body)
+        .send()
+        .await
+        .unwrap();
+
+    assert_eq!(resp.status(), reqwest::StatusCode::PAYLOAD_TOO_LARGE);
+    let body = resp.text().await.unwrap();
+    assert_eq!(body, "Payload Too Large");
+
+    let _ = server.shutdown_tx.send(());
+}
+
+#[tokio::test]
+async fn test_body_limit_allows_request_within_limit() {
+    let server = spawn_server_with_limit(100).await;
+    let client = reqwest::Client::new();
+
+    let small_body = vec![0u8; 50];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(small_body)
+        .send()
+        .await
+        .unwrap();
+
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+
+    let _ = server.shutdown_tx.send(());
+}
+
+#[tokio::test]
+async fn test_body_limit_allows_request_at_exact_limit() {
+    let server = spawn_server_with_limit(100).await;
+    let client = reqwest::Client::new();
+
+    let exact_body = vec![0u8; 100];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(exact_body)
+        .send()
+        .await
+        .unwrap();
+
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+
+    let _ = server.shutdown_tx.send(());
+}
+
+#[tokio::test]
+async fn test_body_limit_content_length_header_rejection() {
+    let server = spawn_server_with_limit(100).await;
+    let client = reqwest::Client::new();
+
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .header("content-length", "200")
+        .body(vec![0u8; 200])
+        .send()
+        .await
+        .unwrap();
+
+    assert_eq!(resp.status(), reqwest::StatusCode::PAYLOAD_TOO_LARGE);
+    let body = resp.text().await.unwrap();
+    assert_eq!(body, "Payload Too Large");
+
+    let _ = server.shutdown_tx.send(());
+}
+
+#[tokio::test]
+async fn test_body_limit_default_is_100mb() {
+    assert_eq!(DEFAULT_BODY_LIMIT_BYTES, 104_857_600);
+}
+
+#[tokio::test]
+async fn test_body_limit_config_reload_changes_limit() {
+    let config = test_dynamic_config_with_limit(100);
+    let config_clone = config.clone();
+
+    let server = helpers::http_test_helper::TestUpstream::spawn(|| {
+        let app = Router::new().route(
+            "/",
+            post(|body: axum::body::Body| async move {
+                let _ = body;
+                "ok"
+            }),
+        );
+        router_with_body_limit(app, config_clone.clone())
+    })
+    .await;
+
+    let client = reqwest::Client::new();
+
+    let small_body = vec![0u8; 50];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(small_body.clone())
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+
+    let medium_body = vec![0u8; 150];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(medium_body.clone())
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), reqwest::StatusCode::PAYLOAD_TOO_LARGE);
+
+    let new_config = DynamicConfig {
+        sites: vec![SiteConfig {
+            host: "test.local".to_string(),
+            upstream: "127.0.0.1:8080".to_string(),
+            upstream_scheme: "http".to_string(),
+            upstream_connect_timeout_secs: 5,
+            upstream_request_timeout_secs: 60,
+        }],
+        rate_limit: RateLimitConfig {
+            requests_per_second: 10,
+            burst: 20,
+        },
+        body: BodyConfig { limit_bytes: 200 },
+    };
+    config.store(Arc::new(new_config));
+
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(medium_body)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+
+    let large_body = vec![0u8; 300];
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body(large_body)
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), reqwest::StatusCode::PAYLOAD_TOO_LARGE);
+
+    let _ = server.shutdown_tx.send(());
+}
+
+#[tokio::test]
+async fn test_body_limit_empty_body_request_succeeds() {
+    let server = spawn_server_with_limit(100).await;
+    let client = reqwest::Client::new();
+
+    let resp = client
+        .post(format!("http://127.0.0.1:{}/", server.addr.port()))
+        .body("")
+        .send()
+        .await
+        .unwrap();
+
+    assert_eq!(resp.status(), reqwest::StatusCode::OK);
+
+    let _ = server.shutdown_tx.send(());
+}