This is not possible for two reasons:

- on most POSIX systems, sendfile() works with mmap-like ("regular") files only, while HTTPConnection.send() accepts any file-like object as long as it provides a read() method

- after read()ing a chunk of data from the file and before send()ing it over the socket, the data can be subject to an intermediate conversion (datablock.encode("iso-8859-1")):
http://hg.python.org/cpython/file/87c6be1e393a/Lib/http/client.py#l839
...whereas sendfile() can only be used to send a binary file "as-is"

I think we can use sendfile() in ftplib.py though .
I'll open a ticket for that.