libchan | Like Go channels over the network | Socket library

It seems it is an attempted try to decode FIN ACK TCP packet coming from the client on exiting. The TCP connection is being closed, and at the server side we try to read this. We get EOF error because there is no more input to read. It seems to be a behaviour as specified in documentation:

EOF is the error returned by Read when no more input is available. Functions should return EOF only to signal a graceful end of input. If the EOF occurs unexpectedly in a structured data stream, the appropriate error is either ErrUnexpectedEOF or some other error giving more detail.

Under the hood, libchan spdy uses msgpack encoder and decoder (source code) that, in order to read this TCP packet will call bufio ReadByte() function (source code), that returns error when no more data is there to be read (and that's the case when TCP connection was closed).