import os
import tarfile
import copy
from abc import ABCMeta, abstractmethod
from collections import defaultdict
from six import add_metaclass
from util.abchelpers import nooper
class TarLayerReadException(Exception):
""" Exception raised when reading a layer has failed. """
pass
# 9MB (+ padding below) so that it matches the 10MB expected by Gzip.
CHUNK_SIZE = 1024 * 1024 * 9
@add_metaclass(ABCMeta)
class TarLayerFormatterReporter(object):
@abstractmethod
def report_pass(self, stream_count):
""" Reports a formatting pass. """
pass
@nooper
class NoopReporter(TarLayerFormatterReporter):
pass
@add_metaclass(ABCMeta)
class TarLayerFormat(object):
""" Class which creates a generator of the combined TAR data. """
def __init__(self, tar_stream_getter_iterator, path_prefix=None, reporter=None):
self.tar_stream_getter_iterator = tar_stream_getter_iterator
self.path_prefix = path_prefix or ''
self.reporter = reporter or NoopReporter()
def get_generator(self):
for stream_getter in self.tar_stream_getter_iterator():
current_tar_stream = stream_getter()
# Read the current TAR. If it is empty, we just continue
# to the next one.
tar_file = TarLayerFormat._tar_file_from_stream(current_tar_stream)
if not tar_file:
continue
# For each of the tar entries, yield them IF and ONLY IF we have not
# encountered the path before.
dangling_hard_links = defaultdict(list)
for tar_info in tar_file:
if not self.should_append_file(tar_info.name):
continue
# Note: We use a copy here because we need to make sure we copy over all the internal
# data of the tar header. We cannot use frombuf(tobuf()), however, because it doesn't
# properly handle large filenames.
clone = copy.deepcopy(tar_info)
clone.name = os.path.join(self.path_prefix, clone.name)
# If the entry is a *hard* link, then prefix it as well. Soft links are relative.
if clone.linkname and clone.type == tarfile.LNKTYPE:
# If the entry is a dangling hard link, we skip here. Dangling hard links will be handled
# in a second pass.
if self.is_skipped_file(tar_info.linkname):
dangling_hard_links[tar_info.linkname].append(tar_info)
continue
clone.linkname = os.path.join(self.path_prefix, clone.linkname)
# Yield the tar header.
yield clone.tobuf()
# Try to extract any file contents for the tar. If found, we yield them as well.
if tar_info.isreg():
for block in TarLayerFormat._emit_file(tar_file, tar_info):
yield block
# Close the layer stream now that we're done with it.
tar_file.close()
# If there are any dangling hard links, open a new stream and retarget the dangling hard
# links to a new copy of the contents, which will be placed under the *first* dangling hard
# link's name.
if len(dangling_hard_links) > 0:
tar_file = TarLayerFormat._tar_file_from_stream(stream_getter())
if not tar_file:
raise TarLayerReadException('Could not re-read tar layer')
for tar_info in tar_file:
# If we encounter a file that holds the data for a dangling link,
# emit it under the name of the first dangling hard link. All other
# dangling hard links will be retargeted to this first name.
if tar_info.name in dangling_hard_links:
first_dangling = dangling_hard_links[tar_info.name][0]
# Copy the first dangling hard link, change it to a normal file,
# and emit the deleted file's contents for it.
clone = copy.deepcopy(first_dangling)
clone.name = os.path.join(self.path_prefix, first_dangling.name)
clone.type = tar_info.type
clone.size = tar_info.size
clone.pax_headers = tar_info.pax_headers
yield clone.tobuf()
for block in TarLayerFormat._emit_file(tar_file, tar_info):
yield block
elif (tar_info.type == tarfile.LNKTYPE and
tar_info.linkname in dangling_hard_links and
not self.is_skipped_file(tar_info.name)):
# Retarget if necessary. All dangling hard links (but the first) will
# need to be retargeted.
first_dangling = dangling_hard_links[tar_info.linkname][0]
if tar_info.name == first_dangling.name:
# Skip; the first dangling is handled above.
continue
# Retarget the hard link to the first dangling hard link.
clone = copy.deepcopy(tar_info)
clone.name = os.path.join(self.path_prefix, clone.name)
clone.linkname = os.path.join(self.path_prefix, first_dangling.name)
yield clone.tobuf()
# Close the layer stream now that we're done with it.
tar_file.close()
# Conduct any post-tar work.
self.after_tar_layer()
self.reporter.report_pass(2 if len(dangling_hard_links) > 0 else 1)
# Last two records are empty in TAR spec.
yield '\0' * 512
yield '\0' * 512
@abstractmethod
def is_skipped_file(self, filename):
""" Returns true if the file with the given name will be skipped during append.
"""
pass
@abstractmethod
def should_append_file(self, filename):
""" Returns true if the file with the given name should be appended when producing
the new TAR.
"""
pass
@abstractmethod
def after_tar_layer(self):
""" Invoked after a TAR layer is added, to do any post-add work. """
pass
@staticmethod
def _tar_file_from_stream(stream):
tar_file = None
try:
tar_file = tarfile.open(mode='r|*', fileobj=stream)
except tarfile.ReadError as re:
if re.message != 'empty file':
raise TarLayerReadException('Could not read layer')
return tar_file
@staticmethod
def _emit_file(tar_file, tar_info):
file_stream = tar_file.extractfile(tar_info)
if file_stream is not None:
length = 0
while True:
current_block = file_stream.read(CHUNK_SIZE)
if not len(current_block):
break
yield current_block
length += len(current_block)
file_stream.close()
# Files must be padding to 512 byte multiples.
if length % 512 != 0:
yield '\0' * (512 - (length % 512))