Add max send buffer per stream option (#580)

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(