Slow SFTP transfer speeds on local 1Gbps network

[udonetsm]

I am experiencing very slow file transfer speeds over SFTP, capped at approximately 1 MB/s, despite being on a 1 Gbps local network. For comparison, other protocols like SCP and rsync utilize the full network bandwidth in the same environment.

I have attempted to resolve this by increasing the buffer and window sizes in the SFTP client implementation, but the speed remains bottlenecked.

I am attaching a patch showing my attempts to fix this. Could you please review it or suggest a way to optimize the throughput?

my_changes.patch

I suspect we should make the transfer implementation asynchronous.