Add additive flag.

If present a received initial window update is intepreted as additive, i.e. the amount of credit is added to the default of 256 KiB.
libp2p · Aug 27, 2020 · eeebf9b · eeebf9b
1 parent 56a97af
commit eeebf9b
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Showing 2 changed files with 9 additions and 13 deletions.
diff --git a/src/connection.rs b/src/connection.rs
@@ -746,6 +746,7 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Connection<T> {
         }
 
         let is_finish = frame.header().flags().contains(header::FIN); // half-close
+        let is_additive = frame.header().flags().contains(header::ADD); // additive window update
 
         if frame.header().flags().contains(header::SYN) { // new stream
             if !self.is_valid_remote_id(stream_id, Tag::WindowUpdate) {
@@ -761,7 +762,7 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Connection<T> {
                 return Action::Terminate(Frame::protocol_error())
             }
             let stream = {
-                let credit = frame.header().credit();
+                let credit = frame.header().credit() + if is_additive { DEFAULT_CREDIT } else { 0 };
                 let config = self.config.clone();
                 let sender = self.stream_sender.clone();
                 let mut stream = Stream::new(stream_id, self.id, config, DEFAULT_CREDIT, credit, sender);

diff --git a/src/frame/header.rs b/src/frame/header.rs
@@ -332,8 +332,6 @@ impl Flags {
     }
 }
 
-const MAX_FLAG_VAL: u16 = 8;
-
 /// Indicates the start of a new stream.
 pub const SYN: Flags = Flags(1);
 
@@ -346,6 +344,10 @@ pub const FIN: Flags = Flags(4);
 /// Indicates an immediate stream reset.
 pub const RST: Flags = Flags(8);
 
+/// Temporary flag indicating that the initial window update is additive.
+/// (See https://github.com/paritytech/yamux/issues/92)
+pub const ADD: Flags = Flags(0x8000);
+
 /// The serialised header size in bytes.
 pub const HEADER_SIZE: usize = 12;
 
@@ -381,10 +383,6 @@ pub fn decode(buf: &[u8; HEADER_SIZE]) -> Result<Header<()>, HeaderDecodeError>
         _marker: std::marker::PhantomData
     };
 
-    if hdr.flags.0 > MAX_FLAG_VAL {
-        return Err(HeaderDecodeError::Flags(hdr.flags.0))
-    }
-
     Ok(hdr)
 }
 
@@ -395,17 +393,14 @@ pub enum HeaderDecodeError {
     /// Unknown version.
     Version(u8),
     /// An unknown frame type.
-    Type(u8),
-    /// Unknown flags.
-    Flags(u16)
+    Type(u8)
 }
 
 impl std::fmt::Display for HeaderDecodeError {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         match self {
             HeaderDecodeError::Version(v) => write!(f, "unknown version: {}", v),
-            HeaderDecodeError::Type(t) => write!(f, "unknown frame type: {}", t),
-            HeaderDecodeError::Flags(x) => write!(f, "unknown flags type: {}", x)
+            HeaderDecodeError::Type(t) => write!(f, "unknown frame type: {}", t)
         }
     }
 }
@@ -428,7 +423,7 @@ mod tests {
             Header {
                 version: Version(0),
                 tag,
-                flags: Flags(std::cmp::min(g.gen(), MAX_FLAG_VAL)),
+                flags: Flags(g.gen()),
                 stream_id: StreamId(g.gen()),
                 length: Len(g.gen()),
                 _marker: std::marker::PhantomData