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#!/usr/bin/env python
import errno
import os
import sys
SEEK_DATA = 3
SEEK_HOLE = 4
filename = sys.argv[1]
fd = os.open(filename, os.O_RDONLY)
pos = 0
DATA = 'data'
HOLE = 'hole'
EOF = 'eof'
def safe_lseek(fd, pos, whence):
try:
return os.lseek(fd, pos, whence)
except OSError as e:
if e.errno == errno.ENXIO:
return -1
raise
def current_data_or_pos(fd, pos):
length = safe_lseek(fd, 0, os.SEEK_END)
next_data = safe_lseek(fd, pos, SEEK_DATA)
next_hole = safe_lseek(fd, pos, SEEK_HOLE)
if pos == length:
return EOF, pos
elif pos == next_data:
return DATA, pos
elif pos == next_hole:
return HOLE, pos
else:
assert False, \
("Do not understand: pos=%d next_data=%d next_hole=%d" %
(pos, next_data, next_hole))
def next_data_or_hole(fd, pos):
length = safe_lseek(fd, 0, os.SEEK_END)
next_data = safe_lseek(fd, pos, SEEK_DATA)
next_hole = safe_lseek(fd, pos, SEEK_HOLE)
if pos == length:
return EOF, pos
elif pos == next_data:
# We are at data.
if next_hole == -1 or next_hole == length:
return EOF, length
else:
return HOLE, next_hole
elif pos == next_hole:
# We are at a hole.
if next_data == -1 or next_data == length:
return EOF, length
else:
return DATA, next_data
else:
assert False, \
("Do not understand: pos=%d next_data=%d next_hole=%d" %
(pos, next_data, next_hole))
def find_data_and_holes(fd):
pos = safe_lseek(fd, 0, os.SEEK_CUR)
kind, pos = current_data_or_pos(fd, pos)
while kind != EOF:
yield kind, pos
kind, pos = next_data_or_hole(fd, pos)
yield kind, pos
def make_xfer_instructions(fd):
prev_kind = None
prev_pos = None
for kind, pos in find_data_and_holes(fd):
if prev_kind == DATA:
yield (DATA, prev_pos, pos)
elif prev_kind == HOLE:
yield (HOLE, prev_pos, pos)
prev_kind = kind
prev_pos = pos
def copy_slice_from_file(to, fd, start, end):
safe_lseek(fd, start, os.SEEK_SET)
data = os.read(fd, end - start)
to.write(data)
for kind, start, end in make_xfer_instructions(fd):
if kind == HOLE:
sys.stdout.write('HOLE\n%d\n' % (end - start))
elif kind == DATA:
sys.stdout.write('DATA\n%d\n' % (end - start))
copy_slice_from_file(sys.stdout, fd, start, end)
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