Do not encode zero-sized response bodies (#3199)

* Do not encode zero-sized response bodies

* Test empty response remains empty after compression

actix-http/CHANGES.md

@@ -6,6 +6,10 @@
 
 - Updated `zstd` dependency to `0.13`.
 
+### Fixed
+
+- Do not encode zero-sized response bodies
+
 ## 3.4.0
 
 ### Added

actix-http/src/encoding/encoder.rs

@@ -52,7 +52,7 @@ impl<B: MessageBody> Encoder<B> {
 
     pub fn response(encoding: ContentEncoding, head: &mut ResponseHead, body: B) -> Self {
         // no need to compress an empty body
-        if matches!(body.size(), BodySize::None) {
+        if matches!(body.size(), BodySize::None | BodySize::Sized(0)) {
             return Self::none();
         }
 

actix-web/src/middleware/compress.rs

@@ -373,7 +373,7 @@ mod tests {
                 .default_service(web::to(move || {
                     HttpResponse::Ok()
                         .insert_header((header::VARY, "x-test"))
-                        .finish()
+                        .body(TEXT_DATA)
                 }))
         })
         .await;
@@ -429,4 +429,47 @@ mod tests {
         assert_successful_identity_res_with_content_type(&res, "image/jpeg");
         assert_eq!(test::read_body(res).await, TEXT_DATA.as_bytes());
     }
+
+    #[actix_rt::test]
+    async fn prevents_compression_empty() {
+        let app = test::init_service({
+            App::new()
+                .wrap(Compress::default())
+                .default_service(web::to(move || HttpResponse::Ok().finish()))
+        })
+        .await;
+
+        let req = test::TestRequest::default()
+            .insert_header((header::ACCEPT_ENCODING, "gzip"))
+            .to_request();
+        let res = test::call_service(&app, req).await;
+        assert_eq!(res.status(), StatusCode::OK);
+        assert!(!res.headers().contains_key(header::CONTENT_ENCODING));
+        assert!(test::read_body(res).await.is_empty());
+    }
+}
+
+#[cfg(feature = "compress-brotli")]
+#[cfg(test)]
+mod tests_brotli {
+    use super::*;
+    use crate::{test, web, App};
+
+    #[actix_rt::test]
+    async fn prevents_compression_empty() {
+        let app = test::init_service({
+            App::new()
+                .wrap(Compress::default())
+                .default_service(web::to(move || HttpResponse::Ok().finish()))
+        })
+        .await;
+
+        let req = test::TestRequest::default()
+            .insert_header((header::ACCEPT_ENCODING, "br"))
+            .to_request();
+        let res = test::call_service(&app, req).await;
+        assert_eq!(res.status(), StatusCode::OK);
+        assert!(!res.headers().contains_key(header::CONTENT_ENCODING));
+        assert!(test::read_body(res).await.is_empty());
+    }
 }