Add max send buffer per stream option

src/client.rs

@@ -320,6 +320,9 @@ pub struct Builder {
     /// Initial target window size for new connections.
     initial_target_connection_window_size: Option<u32>,
 
+    /// Maximum amount of bytes to "buffer" for writing per stream.
+    max_send_buffer_size: usize,
+
     /// Maximum number of locally reset streams to keep at a time.
     reset_stream_max: usize,
 
@@ -628,6 +631,7 @@ impl Builder {
     /// ```
     pub fn new() -> Builder {
         Builder {
+            max_send_buffer_size: proto::DEFAULT_MAX_SEND_BUFFER_SIZE,
             reset_stream_duration: Duration::from_secs(proto::DEFAULT_RESET_STREAM_SECS),
             reset_stream_max: proto::DEFAULT_RESET_STREAM_MAX,
             initial_target_connection_window_size: None,
@@ -962,6 +966,24 @@ impl Builder {
         self
     }
 
+    /// Sets the maximum send buffer size per stream.
+    ///
+    /// Once a stream has buffered up to (or over) the maximum, the stream's
+    /// flow control will not "poll" additional capacity. Once bytes for the
+    /// stream have been written to the connection, the send buffer capacity
+    /// will be freed up again.
+    ///
+    /// The default is currently ~400MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `max` is larger than `u32::MAX`.
+    pub fn max_send_buffer_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.max_send_buffer_size = max;
+        self
+    }
+
     /// Enables or disables server push promises.
     ///
     /// This value is included in the initial SETTINGS handshake. When set, the
@@ -1184,6 +1206,7 @@ where
             proto::Config {
                 next_stream_id: builder.stream_id,
                 initial_max_send_streams: builder.initial_max_send_streams,
+                max_send_buffer_size: builder.max_send_buffer_size,
                 reset_stream_duration: builder.reset_stream_duration,
                 reset_stream_max: builder.reset_stream_max,
                 settings: builder.settings.clone(),

src/proto/connection.rs

@@ -77,6 +77,7 @@ struct DynConnection<'a, B: Buf = Bytes> {
 pub(crate) struct Config {
     pub next_stream_id: StreamId,
     pub initial_max_send_streams: usize,
+    pub max_send_buffer_size: usize,
     pub reset_stream_duration: Duration,
     pub reset_stream_max: usize,
     pub settings: frame::Settings,
@@ -108,6 +109,7 @@ where
                     .initial_window_size()
                     .unwrap_or(DEFAULT_INITIAL_WINDOW_SIZE),
                 initial_max_send_streams: config.initial_max_send_streams,
+                local_max_buffer_size: config.max_send_buffer_size,
                 local_next_stream_id: config.next_stream_id,
                 local_push_enabled: config.settings.is_push_enabled().unwrap_or(true),
                 extended_connect_protocol_enabled: config

src/proto/mod.rs

@@ -33,3 +33,4 @@ pub type WindowSize = u32;
 pub const MAX_WINDOW_SIZE: WindowSize = (1 << 31) - 1;
 pub const DEFAULT_RESET_STREAM_MAX: usize = 10;
 pub const DEFAULT_RESET_STREAM_SECS: u64 = 30;
+pub const DEFAULT_MAX_SEND_BUFFER_SIZE: usize = 1024 * 400;

src/proto/streams/mod.rs

@@ -41,6 +41,9 @@ pub struct Config {
     /// MAX_CONCURRENT_STREAMS specified in the frame.
     pub initial_max_send_streams: usize,
 
+    /// Max amount of DATA bytes to buffer per stream.
+    pub local_max_buffer_size: usize,
+
     /// The stream ID to start the next local stream with
     pub local_next_stream_id: StreamId,
 

src/proto/streams/send.rs

@@ -28,6 +28,9 @@ pub(super) struct Send {
     /// > the identified last stream.
     max_stream_id: StreamId,
 
+    /// The maximum amount of bytes a stream should buffer.
+    max_buffer_size: usize,
+
     /// Initial window size of locally initiated streams
     init_window_sz: WindowSize,
 
@@ -52,6 +55,7 @@ impl Send {
     pub fn new(config: &Config) -> Self {
         Send {
             init_window_sz: config.remote_init_window_sz,
+            max_buffer_size: config.local_max_buffer_size,
             max_stream_id: StreamId::MAX,
             next_stream_id: Ok(config.local_next_stream_id),
             prioritize: Prioritize::new(config),
@@ -333,14 +337,10 @@ impl Send {
 
     /// Current available stream send capacity
     pub fn capacity(&self, stream: &mut store::Ptr) -> WindowSize {
-        let available = stream.send_flow.available().as_size();
+        let available = stream.send_flow.available().as_size() as usize;
         let buffered = stream.buffered_send_data;
 
-        if available as usize <= buffered {
-            0
-        } else {
-            available - buffered as WindowSize
-        }
+        available.min(self.max_buffer_size).saturating_sub(buffered) as WindowSize
     }
 
     pub fn poll_reset(

src/server.rs

@@ -245,6 +245,9 @@ pub struct Builder {
 
     /// Initial target window size for new connections.
     initial_target_connection_window_size: Option<u32>,
+
+    /// Maximum amount of bytes to "buffer" for writing per stream.
+    max_send_buffer_size: usize,
 }
 
 /// Send a response back to the client
@@ -633,6 +636,7 @@ impl Builder {
             reset_stream_max: proto::DEFAULT_RESET_STREAM_MAX,
             settings: Settings::default(),
             initial_target_connection_window_size: None,
+            max_send_buffer_size: proto::DEFAULT_MAX_SEND_BUFFER_SIZE,
         }
     }
 
@@ -870,6 +874,24 @@ impl Builder {
         self
     }
 
+    /// Sets the maximum send buffer size per stream.
+    ///
+    /// Once a stream has buffered up to (or over) the maximum, the stream's
+    /// flow control will not "poll" additional capacity. Once bytes for the
+    /// stream have been written to the connection, the send buffer capacity
+    /// will be freed up again.
+    ///
+    /// The default is currently ~400MB, but may change.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `max` is larger than `u32::MAX`.
+    pub fn max_send_buffer_size(&mut self, max: usize) -> &mut Self {
+        assert!(max <= std::u32::MAX as usize);
+        self.max_send_buffer_size = max;
+        self
+    }
+
     /// Sets the maximum number of concurrent locally reset streams.
     ///
     /// When a stream is explicitly reset by either calling
@@ -1290,6 +1312,7 @@ where
                     next_stream_id: 2.into(),
                     // Server does not need to locally initiate any streams
                     initial_max_send_streams: 0,
+                    max_send_buffer_size: self.builder.max_send_buffer_size,
                     reset_stream_duration: self.builder.reset_stream_duration,
                     reset_stream_max: self.builder.reset_stream_max,
                     settings: self.builder.settings.clone(),

tests/h2-tests/tests/flow_control.rs

@@ -1611,3 +1611,60 @@ async fn poll_capacity_after_send_data_and_reserve() {
 
     join(srv, h2).await;
 }
+
+#[tokio::test]
+async fn max_send_buffer_size_overflow() {
+    h2_support::trace_init!();
+    let (io, mut srv) = mock::new();
+
+    let srv = async move {
+        let settings = srv.assert_client_handshake().await;
+        assert_default_settings!(settings);
+        srv.recv_frame(frames::headers(1).request("POST", "https://www.example.com/"))
+            .await;
+        srv.send_frame(frames::headers(1).response(200).eos()).await;
+        srv.recv_frame(frames::data(1, &[0; 10][..])).await;
+        srv.recv_frame(frames::data(1, &[][..]).eos()).await;
+    };
+
+    let client = async move {
+        let (mut client, mut conn) = client::Builder::new()
+            .max_send_buffer_size(5)
+            .handshake::<_, Bytes>(io)
+            .await
+            .unwrap();
+        let request = Request::builder()
+            .method(Method::POST)
+            .uri("https://www.example.com/")
+            .body(())
+            .unwrap();
+
+        let (response, mut stream) = client.send_request(request, false).unwrap();
+
+        let response = conn.drive(response).await.unwrap();
+        assert_eq!(response.status(), StatusCode::OK);
+
+        assert_eq!(stream.capacity(), 0);
+        stream.reserve_capacity(10);
+        assert_eq!(
+            stream.capacity(),
+            5,
+            "polled capacity not over max buffer size"
+        );
+
+        stream.send_data([0; 10][..].into(), false).unwrap();
+
+        stream.reserve_capacity(15);
+        assert_eq!(
+            stream.capacity(),
+            0,
+            "now with buffered over the max, don't overflow"
+        );
+        stream.send_data([0; 0][..].into(), true).unwrap();
+
+        // Wait for the connection to close
+        conn.await.unwrap();
+    };
+
+    join(srv, client).await;
+}