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.
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.