An extra character appears when using io.Copy

[da-tai]

Using io.copy (splice), the remote connection get a K (or other letters) infront of each message sent. Below is an exmaple and the config. How can I disable this?

K{"id":589,"jsonrpc":"2.0"}

&smux.Config{ Version: 1, KeepAliveDisabled: true, MaxFrameSize: 32768, MaxReceiveBuffer: 4194304, MaxStreamBuffer: 65536, }