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();
         }