fix(fullstack): Streaming::into_inner() returning empty stream (#4961)

* fix(fullstack): Streaming::into_inner() returning empty stream

The Streaming struct previously maintained separate input_stream and
output_stream fields, but into_inner() always returned input_stream.
This caused it to return an empty stream on both client and server sides
where data was placed in output_stream.

Consolidate to a single stream field that properly returns the actual
stream data when into_inner() is called.

Also add examples demonstrating bidirectional streaming:
- echo_stream: passes client stream through server unchanged
- transform_stream: transforms client stream on server using filter_map
- Use stream::unfold for cleaner client-side stream generation

Reviewed-by: Claude <noreply@anthropic.com>
Commit-message-by: Claude <noreply@anthropic.com>

* fmt

examples/07-fullstack/streaming.rs

@@ -21,6 +21,7 @@ use dioxus::{
     fullstack::{JsonEncoding, Streaming, TextStream},
     prelude::*,
 };
+use futures::{StreamExt as _, TryStreamExt};
 
 fn main() {
     dioxus::launch(app)
@@ -29,6 +30,8 @@ fn main() {
 fn app() -> Element {
     let mut text_responses = use_signal(String::new);
     let mut json_responses = use_signal(Vec::new);
+    let mut echo_responses = use_signal(Vec::new);
+    let mut transform_responses = use_signal(Vec::new);
 
     let mut start_text_stream = use_action(move || async move {
         text_responses.clear();
@@ -53,6 +56,64 @@ fn app() -> Element {
         dioxus::Ok(())
     });
 
+    let mut continue_echo_stream = use_signal_sync(|| false);
+    let mut start_echo_stream = use_action(move || async move {
+        continue_echo_stream.set(true);
+        echo_responses.clear();
+        let stream = echo_stream(Streaming::new(futures::stream::unfold(
+            0,
+            move |index| async move {
+                if !continue_echo_stream() {
+                    return None;
+                }
+                tokio::time::sleep(tokio::time::Duration::from_millis(500)).await;
+                let dog = Dog {
+                    name: format!("Dog {}", index),
+                    age: (index % 10) as u8,
+                };
+                Some((dog, index + 1))
+            },
+        )))
+        .await?;
+        stream
+            .into_inner()
+            .try_for_each(move |dog| async move {
+                echo_responses.push(dog);
+                Ok(())
+            })
+            .await?;
+        dioxus::Ok(())
+    });
+
+    let mut continue_transform_stream = use_signal_sync(|| false);
+    let mut start_transform_stream = use_action(move || async move {
+        continue_transform_stream.set(true);
+        transform_responses.clear();
+        let stream = transform_stream(Streaming::new(futures::stream::unfold(
+            0,
+            move |index| async move {
+                if !continue_transform_stream() {
+                    return None;
+                }
+                tokio::time::sleep(tokio::time::Duration::from_millis(500)).await;
+                let dog = Dog {
+                    name: format!("Dog {}", index),
+                    age: (index % 10) as u8,
+                };
+                Some((dog, index + 1))
+            },
+        )))
+        .await?;
+        stream
+            .into_inner()
+            .try_for_each(move |text| async move {
+                transform_responses.push(text);
+                Ok(())
+            })
+            .await?;
+        dioxus::Ok(())
+    });
+
     rsx! {
         div {
             button { onclick: move |_| start_text_stream.call(), "Start text stream" }
@@ -66,6 +127,20 @@ fn app() -> Element {
                 pre { "{dog:?}" }
             }
         }
+        div {
+            button { onclick: move |_| start_echo_stream.call(), "Start echo stream" }
+            button { onclick: move |_| continue_echo_stream.set(false), "Stop echo stream" }
+            for dog in echo_responses.read().iter() {
+                pre { "{dog:?}" }
+            }
+        }
+        div {
+            button { onclick: move |_| start_transform_stream.call(), "Start transform stream" }
+            button { onclick: move |_| continue_transform_stream.set(false), "Stop transform stream" }
+            for text in transform_responses.read().iter() {
+                pre { "{text}" }
+            }
+        }
     }
 }
 
@@ -145,3 +220,20 @@ async fn byte_stream() -> Result<Streaming<Bytes>> {
 
     Ok(Streaming::new(rx))
 }
+
+/// An example of echoing the stream back to the client.
+#[post("/api/echo_stream")]
+async fn echo_stream(stream: Streaming<Dog, JsonEncoding>) -> Result<Streaming<Dog, JsonEncoding>> {
+    Ok(stream)
+}
+
+/// An example of transforming the stream on the server.
+#[post("/api/transform_stream")]
+async fn transform_stream(stream: Streaming<Dog, JsonEncoding>) -> Result<TextStream> {
+    Ok(Streaming::new(stream.into_inner().filter_map(
+        |dog| async {
+            dog.ok()
+                .map(|dog| format!("name: {}, age: {}", dog.name, dog.age))
+        },
+    )))
+}

packages/fullstack/src/payloads/stream.rs

@@ -98,8 +98,7 @@ pub type ChunkedTextStream = Streaming<String, CborEncoding>;
 ///
 /// Also note that not all browsers support streaming bodies to servers.
 pub struct Streaming<T = String, E = ()> {
-    output_stream: Pin<Box<dyn Stream<Item = Result<T, StreamingError>> + Send>>,
-    input_stream: Pin<Box<dyn Stream<Item = Result<T, StreamingError>> + Send>>,
+    stream: Pin<Box<dyn Stream<Item = Result<T, StreamingError>> + Send>>,
     encoding: PhantomData<E>,
 }
 
@@ -123,9 +122,8 @@ impl<T: 'static + Send, E> Streaming<T, E> {
     pub fn new(value: impl Stream<Item = T> + Send + 'static) -> Self {
         // Box and pin the incoming stream and store as a trait object
         Self {
-            input_stream: Box::pin(value.map(|item| Ok(item)))
+            stream: Box::pin(value.map(|item| Ok(item)))
                 as Pin<Box<dyn Stream<Item = Result<T, StreamingError>> + Send>>,
-            output_stream: Box::pin(futures::stream::empty()) as _,
             encoding: PhantomData,
         }
     }
@@ -148,12 +146,12 @@ impl<T: 'static + Send, E> Streaming<T, E> {
 
     /// Returns the next item in the stream, or `None` if the stream has ended.
     pub async fn next(&mut self) -> Option<Result<T, StreamingError>> {
-        self.output_stream.as_mut().next().await
+        self.stream.as_mut().next().await
     }
 
     /// Consumes the wrapper, returning the inner stream.
     pub fn into_inner(self) -> impl Stream<Item = Result<T, StreamingError>> + Send {
-        self.input_stream
+        self.stream
     }
 
     /// Creates a streaming payload from an existing stream of bytes.
@@ -161,8 +159,7 @@ impl<T: 'static + Send, E> Streaming<T, E> {
     /// This uses the internal framing mechanism to decode the stream into items of type `T`.
     fn from_bytes(stream: impl Stream<Item = Result<T, StreamingError>> + Send + 'static) -> Self {
         Self {
-            input_stream: Box::pin(stream),
-            output_stream: Box::pin(futures::stream::empty()) as _,
+            stream: Box::pin(stream),
             encoding: PhantomData,
         }
     }
@@ -184,8 +181,7 @@ where
 {
     fn from(value: S) -> Self {
         Self {
-            input_stream: Box::pin(value.map(|data| data.map_err(|_| StreamingError::Failed))),
-            output_stream: Box::pin(futures::stream::empty()) as _,
+            stream: Box::pin(value.map(|data| data.map_err(|_| StreamingError::Failed))),
             encoding: PhantomData,
         }
     }
@@ -207,7 +203,7 @@ impl IntoResponse for Streaming<String> {
     fn into_response(self) -> axum_core::response::Response {
         axum::response::Response::builder()
             .header("Content-Type", "text/plain; charset=utf-8")
-            .body(axum::body::Body::from_stream(self.input_stream))
+            .body(axum::body::Body::from_stream(self.stream))
             .unwrap()
     }
 }
@@ -216,14 +212,14 @@ impl IntoResponse for Streaming<Bytes> {
     fn into_response(self) -> axum_core::response::Response {
         axum::response::Response::builder()
             .header("Content-Type", "application/octet-stream")
-            .body(axum::body::Body::from_stream(self.input_stream))
+            .body(axum::body::Body::from_stream(self.stream))
             .unwrap()
     }
 }
 
 impl<T: DeserializeOwned + Serialize + 'static, E: Encoding> IntoResponse for Streaming<T, E> {
     fn into_response(self) -> axum_core::response::Response {
-        let res = self.input_stream.map(|r| match r {
+        let res = self.stream.map(|r| match r {
             Ok(res) => match encode_stream_frame::<T, E>(res) {
                 Some(bytes) => Ok(bytes),
                 None => Err(StreamingError::Failed),
@@ -250,8 +246,7 @@ impl FromResponse for Streaming<String> {
             }));
 
             Ok(Self {
-                output_stream: client_stream,
-                input_stream: Box::pin(futures::stream::empty()),
+                stream: client_stream,
                 encoding: PhantomData,
             })
         })
@@ -269,8 +264,7 @@ impl FromResponse for Streaming<Bytes> {
             )));
 
             Ok(Self {
-                output_stream: client_stream,
-                input_stream: Box::pin(futures::stream::empty()),
+                stream: client_stream,
                 encoding: PhantomData,
             })
         }
@@ -293,8 +287,7 @@ impl<T: DeserializeOwned + Serialize + 'static + Send, E: Encoding> FromResponse
             )));
 
             Ok(Self {
-                output_stream: client_stream,
-                input_stream: Box::pin(futures::stream::empty()),
+                stream: client_stream,
                 encoding: PhantomData,
             })
         })
@@ -323,8 +316,7 @@ impl<S> FromRequest<S> for Streaming<String> {
             let stream = body.into_data_stream();
 
             Ok(Self {
-                input_stream: Box::pin(futures::stream::empty()),
-                output_stream: Box::pin(stream.map(|byte| match byte {
+                stream: Box::pin(stream.map(|byte| match byte {
                     Ok(bytes) => match String::from_utf8(bytes.to_vec()) {
                         Ok(string) => Ok(string),
                         Err(_) => Err(StreamingError::Decoding),
@@ -359,8 +351,7 @@ impl<S> FromRequest<S> for ByteStream {
             let stream = body.into_data_stream();
 
             Ok(Self {
-                input_stream: Box::pin(futures::stream::empty()),
-                output_stream: Box::pin(stream.map(|byte| match byte {
+                stream: Box::pin(stream.map(|byte| match byte {
                     Ok(bytes) => Ok(bytes),
                     Err(_) => Err(StreamingError::Failed),
                 })),
@@ -394,8 +385,7 @@ impl<T: DeserializeOwned + Serialize + 'static + Send, E: Encoding, S> FromReque
             let stream = body.into_data_stream();
 
             Ok(Self {
-                input_stream: Box::pin(futures::stream::empty()),
-                output_stream: Box::pin(stream.map(|byte| match byte {
+                stream: Box::pin(stream.map(|byte| match byte {
                     Ok(bytes) => match decode_stream_frame::<T, E>(bytes) {
                         Some(res) => Ok(res),
                         None => Err(StreamingError::Decoding),
@@ -416,7 +406,7 @@ impl IntoRequest for Streaming<String> {
         async move {
             builder
                 .header("Content-Type", "text/plain; charset=utf-8")?
-                .send_body_stream(self.input_stream.map(|e| e.map(Bytes::from)))
+                .send_body_stream(self.stream.map(|e| e.map(Bytes::from)))
                 .await
         }
     }
@@ -430,7 +420,7 @@ impl IntoRequest for ByteStream {
         async move {
             builder
                 .header(ContentType::name(), "application/octet-stream")?
-                .send_body_stream(self.input_stream)
+                .send_body_stream(self.stream)
                 .await
         }
     }
@@ -446,7 +436,7 @@ impl<T: DeserializeOwned + Serialize + 'static + Send, E: Encoding> IntoRequest
         async move {
             builder
                 .header("Content-Type", E::stream_content_type())?
-                .send_body_stream(self.input_stream.map(|r| {
+                .send_body_stream(self.stream.map(|r| {
                     r.and_then(|item| {
                         encode_stream_frame::<T, E>(item).ok_or(StreamingError::Failed)
                     })