There are certain modes where it simply cuts the connection when the server is done transmitting. There's no length header or end-of-transmission character or anything like that.
http://www.wumpus-cave.net/2013/10/27/why-gopher-is-awful/
Once I did a little research and wrote it all out, Gopher actually came out worse than I thought. Even if it were brought up to Gopher+ specifications (which haven't been implemented by anyone in 20 years), it would still be way behind HTTP/1.1 in terms of fixing design flaws.
And if the TCP sliding window is an issue for you, why not fix TCP?
Why should the server send any kind of header?
Doesn't TCP do checksums, already?
Fix sliding window? I don't think you understand TCP. This is an optimization to TCP to prevent the need to ACK every packet. It means fewer bytes on the wire and less CPU load for TCP processing, while also maintaining a respectable degree of reliability.
TCP checksums are not sufficient for data streams of more than a few kB.