Have SnowflakeClientConn implement io.WriterTo.

By forwarding the method to the inner smux.Stream. This is to prevent
io.Copy in the top-level proxy function from allocating a buffer per
client.

server/lib/snowflake.go

@@ -235,7 +235,7 @@ func (l *SnowflakeListener) acceptStreams(conn *kcp.UDPSession) error {
 			}
 			return err
 		}
-		l.queueConn(&SnowflakeClientConn{Conn: stream, address: addr})
+		l.queueConn(&SnowflakeClientConn{stream: stream, address: addr})
 	}
 }
 
@@ -283,15 +283,31 @@ func (l *SnowflakeListener) queueConn(conn net.Conn) error {
 	}
 }
 
-// SnowflakeClientConn is a wrapper for the underlying turbotunnel
-// conn. We need to reference our client address map to determine the
-// remote address
+// SnowflakeClientConn is a wrapper for the underlying turbotunnel conn
+// (smux.String). It implements the net.Conn and io.WriterTo interfaces. The
+// RemoteAddr method is overridden to refer to a real IP address, looked up from
+// the client address map, rather than an abstract client ID.
 type SnowflakeClientConn struct {
-	net.Conn
+	stream *smux.Stream
 	address net.Addr
 }
 
-// RemoteAddr returns the mapped client address of the Snowflake connection
+// Forward net.Conn methods, other than RemoteAddr, to the inner stream.
+func (conn *SnowflakeClientConn) Read(b []byte) (int, error) { return conn.stream.Read(b) }
+func (conn *SnowflakeClientConn) Write(b []byte) (int, error) { return conn.stream.Write(b) }
+func (conn *SnowflakeClientConn) Close() error { return conn.stream.Close() }
+func (conn *SnowflakeClientConn) LocalAddr() net.Addr { return conn.stream.LocalAddr() }
+func (conn *SnowflakeClientConn) SetDeadline(t time.Time) error { return conn.stream.SetDeadline(t) }
+func (conn *SnowflakeClientConn) SetReadDeadline(t time.Time) error { return conn.stream.SetReadDeadline(t) }
+func (conn *SnowflakeClientConn) SetWriteDeadline(t time.Time) error { return conn.stream.SetWriteDeadline(t) }
+
+// RemoteAddr returns the mapped client address of the Snowflake connection.
 func (conn *SnowflakeClientConn) RemoteAddr() net.Addr {
 	return conn.address
 }
+
+// WriteTo implements the io.WriterTo interface by passing the call to the
+// underlying smux.Stream.
+func (conn *SnowflakeClientConn) WriteTo(w io.Writer) (int64, error) {
+	return conn.stream.WriteTo(w)
+}