from shutil import copy
from tempfile import mkstemp
from os import sysconf, fdopen, truncate, close, unlink, sendfile

page_size = sysconf('SC_PAGESIZE')
# this gives a file size equal to the default block size used in shutil, but
# any other multiple of page_size also triggers the bug for me
file_size = page_size * 2048

from_fd, from_name = mkstemp(dir='.')
to_fd, to_name = mkstemp(dir='.')

ff = fdopen(from_fd)
tf = fdopen(to_fd)

truncate(from_fd, file_size)

# Demonstrate that this is not a problem with sendfile, but with how we're
# calling it.
try:
    sent = 0
    while (sent < file_size):
        sent += sendfile(to_fd, from_fd, 0, file_size)
except Exception as e:
    print('Plain sendfile failed!')
    print(e)
finally:
    close(from_fd)
    close(to_fd)

# Demonstrate error in shutil
try:
    copy(from_name, to_name)
except Exception as e:
    print('Shutil Failed!')
    print(e)
finally:
    unlink(from_name)
    unlink(to_name)