Increase smux and QueuePacketConn buffer sizes

This should increase the maximum amount of inflight data and hopefully
the performance of Snowflake, especially for clients geographically
distant from proxies and the server.

client/lib/snowflake.go

@@ -21,6 +21,9 @@ const (
 	SnowflakeTimeout = 20 * time.Second
 	// How long to wait for the OnOpen callback on a DataChannel.
 	DataChannelTimeout = 10 * time.Second
+
+	WindowSize = 65535
+	StreamSize = 1048576 //1MB
 )
 
 type dummyAddr struct{}
@@ -224,7 +227,7 @@ func newSession(snowflakes SnowflakeCollector) (net.PacketConn, *smux.Session, e
 	conn.SetStreamMode(true)
 	// Set the maximum send and receive window sizes to a high number
 	// Removes KCP bottlenecks: https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40026
-	conn.SetWindowSize(65535, 65535)
+	conn.SetWindowSize(WindowSize, WindowSize)
 	// Disable the dynamic congestion window (limit only by the
 	// maximum of local and remote static windows).
 	conn.SetNoDelay(
@@ -237,6 +240,8 @@ func newSession(snowflakes SnowflakeCollector) (net.PacketConn, *smux.Session, e
 	smuxConfig := smux.DefaultConfig()
 	smuxConfig.Version = 2
 	smuxConfig.KeepAliveTimeout = 10 * time.Minute
+	smuxConfig.MaxStreamBuffer = StreamSize
+
 	sess, err := smux.Client(conn, smuxConfig)
 	if err != nil {
 		conn.Close()