fix(actix-web): improve streaming response behavior for Content-Length and Content-Type (#3737)

- Set default Content-Type to application/octet-stream for streaming responses
- Respect Content-Length header by automatically calling `no_chunking()` when set
- Resolves issue where Content-Length was ignored in streaming responses

Fixes #2306

---------

Co-authored-by: Yinuo Deng <i@dyn.im>

actix-web/CHANGES.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- `actix_web::response::builder::HttpResponseBuilder::streaming()` now sets `Content-Type` to `application/octet-stream` if `Content-Type` does not exist.
+- `actix_web::response::builder::HttpResponseBuilder::streaming()` now calls `actix_web::response::builder::HttpResponseBuilder::no_chunking()` if `Content-Length` is set by user.
+
 ## 4.11.0
 
 - Add `Logger::log_level()` method.

actix-web/src/response/builder.rs

@@ -318,12 +318,33 @@ impl HttpResponseBuilder {
     /// Set a streaming body and build the `HttpResponse`.
     ///
     /// `HttpResponseBuilder` can not be used after this call.
+    ///
+    /// If `Content-Type` is not set, then it is automatically set to `application/octet-stream`.
+    ///
+    /// If `Content-Length` is set, then [`no_chunking()`](Self::no_chunking) is automatically called.
     #[inline]
     pub fn streaming<S, E>(&mut self, stream: S) -> HttpResponse
     where
         S: Stream<Item = Result<Bytes, E>> + 'static,
         E: Into<BoxError> + 'static,
     {
+        // Set mime type to application/octet-stream if it is not set
+        if let Some(parts) = self.inner() {
+            if !parts.headers.contains_key(header::CONTENT_TYPE) {
+                self.insert_header((header::CONTENT_TYPE, mime::APPLICATION_OCTET_STREAM));
+            }
+        }
+
+        if let Some(parts) = self.inner() {
+            if let Some(length) = parts.headers.get(header::CONTENT_LENGTH) {
+                if let Ok(length) = length.to_str() {
+                    if let Ok(length) = length.parse::<u64>() {
+                        self.no_chunking(length);
+                    }
+                }
+            }
+        }
+
         self.body(BodyStream::new(stream))
     }
 

actix-web/tests/test_streaming_response.rs

@@ -0,0 +1,115 @@
+use std::{
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use actix_web::{
+    http::header::{self, HeaderValue},
+    HttpResponse,
+};
+use bytes::Bytes;
+use futures_core::Stream;
+
+struct FixedSizeStream {
+    data: Vec<u8>,
+    yielded: bool,
+}
+
+impl FixedSizeStream {
+    fn new(size: usize) -> Self {
+        Self {
+            data: vec![0u8; size],
+            yielded: false,
+        }
+    }
+}
+
+impl Stream for FixedSizeStream {
+    type Item = Result<Bytes, std::io::Error>;
+
+    fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        if self.yielded {
+            Poll::Ready(None)
+        } else {
+            self.yielded = true;
+            let data = std::mem::take(&mut self.data);
+            Poll::Ready(Some(Ok(Bytes::from(data))))
+        }
+    }
+}
+
+#[actix_rt::test]
+async fn test_streaming_response_with_content_length() {
+    let stream = FixedSizeStream::new(100);
+
+    let resp = HttpResponse::Ok()
+        .append_header((header::CONTENT_LENGTH, "100"))
+        .streaming(stream);
+
+    assert_eq!(
+        resp.headers().get(header::CONTENT_LENGTH),
+        Some(&HeaderValue::from_static("100")),
+        "Content-Length should be preserved when explicitly set"
+    );
+
+    let has_chunked = resp
+        .headers()
+        .get(header::TRANSFER_ENCODING)
+        .map(|v| v.to_str().unwrap_or(""))
+        .unwrap_or("")
+        .contains("chunked");
+
+    assert!(
+        !has_chunked,
+        "chunked should not be used when Content-Length is provided"
+    );
+
+    assert_eq!(
+        resp.headers().get(header::CONTENT_TYPE),
+        Some(&HeaderValue::from_static("application/octet-stream")),
+        "Content-Type should default to application/octet-stream"
+    );
+}
+
+#[actix_rt::test]
+async fn test_streaming_response_default_content_type() {
+    let stream = FixedSizeStream::new(50);
+
+    let resp = HttpResponse::Ok().streaming(stream);
+
+    assert_eq!(
+        resp.headers().get(header::CONTENT_TYPE),
+        Some(&HeaderValue::from_static("application/octet-stream")),
+        "Content-Type should default to application/octet-stream"
+    );
+}
+
+#[actix_rt::test]
+async fn test_streaming_response_user_defined_content_type() {
+    let stream = FixedSizeStream::new(25);
+
+    let resp = HttpResponse::Ok()
+        .insert_header((header::CONTENT_TYPE, "text/plain"))
+        .streaming(stream);
+
+    assert_eq!(
+        resp.headers().get(header::CONTENT_TYPE),
+        Some(&HeaderValue::from_static("text/plain")),
+        "User-defined Content-Type should be preserved"
+    );
+}
+
+#[actix_rt::test]
+async fn test_streaming_response_empty_stream() {
+    let stream = FixedSizeStream::new(0);
+
+    let resp = HttpResponse::Ok()
+        .append_header((header::CONTENT_LENGTH, "0"))
+        .streaming(stream);
+
+    assert_eq!(
+        resp.headers().get(header::CONTENT_LENGTH),
+        Some(&HeaderValue::from_static("0")),
+        "Content-Length 0 should be preserved for empty streams"
+    );
+}