Strip body and content-length on 204, body on 304.

This works-around an issue where hyper incorrectly removes the body on
204 responses without removing the content-length or setting it to zero.

Resolves #2821.

core/lib/src/lifecycle.rs

@@ -134,12 +134,17 @@ impl Rocket<Orbit> {
         // Run the response fairings.
         self.fairings.handle_response(request, &mut response).await;
 
-        // Strip the body if this is a `HEAD` request.
-        if was_head_request {
+        // Strip the body if this is a `HEAD` request or a 304 response.
+        if was_head_request || response.status() == Status::NotModified {
             response.strip_body();
         }
 
-        if let Some(size) = response.body_mut().size().await {
+        // If the response status is 204, strip the body and its size (no
+        // content-length header). Otherwise, check if the body is sized and use
+        // that size to set the content-length headr appropriately.
+        if response.status() == Status::NoContent {
+            *response.body_mut() = crate::response::Body::unsized_none();
+        } else if let Some(size) = response.body_mut().size().await {
             response.set_raw_header("Content-Length", size.to_string());
         }
 

core/lib/src/response/body.rs

@@ -107,6 +107,14 @@ impl<'r> Body<'r> {
     /// The present value is `4096`.
     pub const DEFAULT_MAX_CHUNK: usize = 4096;
 
+    pub(crate) fn unsized_none() -> Self {
+        Body {
+            size: None,
+            inner: Inner::None,
+            max_chunk: Body::DEFAULT_MAX_CHUNK,
+        }
+    }
+
     pub(crate) fn with_sized<T>(body: T, preset_size: Option<usize>) -> Self
         where T: AsyncReadSeek + Send + 'r
     {

testbench/src/servers/mod.rs

@@ -7,3 +7,4 @@ pub mod mtls;
 pub mod sni_resolver;
 pub mod tracing;
 pub mod tls;
+pub mod no_content;

testbench/src/servers/no_content.rs

@@ -0,0 +1,30 @@
+//! Ensure that responses with a status of 204 or 304 do not have a body, and
+//! for the former, do not have a Content-Length header.
+
+use crate::prelude::*;
+
+use rocket::http::Status;
+
+#[get("/<code>")]
+fn status(code: u16) -> (Status, &'static [u8]) {
+    (Status::new(code), &[1, 2, 3, 4])
+}
+
+pub fn test_no_content() -> Result<()> {
+    let server = spawn!(Rocket::default().mount("/", routes![status]))?;
+
+    let client = Client::default();
+    let response = client.get(&server, "/204")?.send()?;
+    assert_eq!(response.status(), 204);
+    assert!(response.headers().get("Content-Length").is_none());
+    assert!(response.bytes()?.is_empty());
+
+    let response = client.get(&server, "/304")?.send()?;
+    assert_eq!(response.status(), 304);
+    assert_eq!(response.headers().get("Content-Length").unwrap(), "4");
+    assert!(response.bytes()?.is_empty());
+
+    Ok(())
+}
+
+register!(test_no_content);