If you serve static content from a shared folder you might have run into a vboxsf file corruption bug. This hack disables the sendfile syscall for the go process which will force the standard library to fallback to userland buffered IO.

References:
Ticket #9069 shared folder doesn't seem to update
net: Add ability to disable sendfile

Save disable_sendfile_vbox_linux.go to somewhere in your go project. Or do

import (
	_ "github.com/wader/disable_sendfile_vbox_linux"
}

in a source file.

Public domain. Your free to do whatever you want.