src: Limit data frame payload size

src/connection/stream.rs

@@ -330,6 +330,7 @@ impl AsyncWrite for Stream {
                 return Poll::Pending
             }
             let k = std::cmp::min(shared.credit as usize, buf.len());
+            let k = std::cmp::min(k, crate::MAX_DATA_FRAME_PAYLOAD_SIZE);
             shared.credit = shared.credit.saturating_sub(k as u32);
             Vec::from(&buf[.. k])
         };

src/lib.rs

@@ -40,6 +40,21 @@ pub use crate::frame::{FrameDecodeError, header::{HeaderDecodeError, StreamId}};
 
 const DEFAULT_CREDIT: u32 = 256 * 1024; // as per yamux specification
 
+/// Maximum number of bytes a Yamux data frame might carry as its payload.
+///
+/// The data frame payload size is not restricted by the yamux specification.
+/// Still, this implementation restricts the size to:
+///
+/// 1. Reduce delays sending time-sensitive frames, e.g. window updates.
+/// 2. Minimize head-of-line blocking across streams.
+/// 3. Enable better interleaving of send and receive operations, as each is
+///    carried out atomically instead of concurrently with its respective
+///    counterpart.
+///
+/// For details on why this concrete value was chosen, see
+/// https://github.com/paritytech/yamux/issues/100.
+const MAX_DATA_FRAME_PAYLOAD_SIZE: usize = 16 * 1024;
+
 /// Specifies when window update frames are sent.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum WindowUpdateMode {