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Address issue #163.

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Changed behavior:
Write metadata only if the uncompressed version has not been written, has changed, or if
compressed versions are missing (if requested).  Not only is re-saving unmodified metadata not ideal, it also forces a new version of the release file if compressed metadata is rewritten.  gzip attaches a timestamp to compressed files, which may cause compressed content to generate different digests if independently written.

Update libtuf.py comments.
Minor edit to docstrings of previous commit that addressed interposition issues.
This commit is contained in:
Vladimir Diaz 2014-01-13 09:34:21 -05:00
parent 08f894f741
commit 04221d3f0d
4 changed files with 119 additions and 55 deletions
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1
tuf/formats.py
View file

@ -383,6 +383,7 @@
object_name = 'ROOT_SCHEMA',
_type = SCHEMA.String('Root'),
version = METADATAVERSION_SCHEMA,
#consistent_snapshots = BOOLEAN_SCHEMA,
expires = TIME_SCHEMA,
keys = KEYDICT_SCHEMA,
roles = ROLEDICT_SCHEMA)

2
tuf/interposition/__init__.py
View file

@ -288,7 +288,7 @@ def configure(filename="tuf.interposition.json",
def refresh(configurations):
"""Refresh the top-level metadata for previously read configurations."""
# Get the updater and refresh its top-level metadata. In the majority
# Get the updater and refresh its top-level metadata. In the majority of
# integrations, a software updater integrating TUF with interposition will
# usually only require an initial refresh() (i.e., when configure() is
# called). A series of target file requests may then occur, which are all

2
tuf/interposition/updater.py
View file

@ -288,7 +288,7 @@ def refresh(self, configuration):
assert configuration.hostname in self.__updaters
assert repository_mirror_hostnames.issubset(self.__repository_mirror_hostnames)
# Get the updater and refresh its top-level metadata. In the majority
# Get the updater and refresh its top-level metadata. In the majority of
# integrations, a software updater integrating TUF with interposition will
# usually only require an initial refresh() (i.e., when configure() is
# called). A series of target file requests may then occur, which are all

169
tuf/libtuf.py
View file

@ -53,6 +53,8 @@
# are the recommended minimum and are good from the present through 2030.
DEFAULT_RSA_KEY_BITS = 3072
DEFAULT_HASH_ALGORITHM = 'sha256'
# The metadata filenames of the top-level roles.
ROOT_FILENAME = 'root.txt'
TARGETS_FILENAME = 'targets.txt'
@ -162,7 +164,7 @@ def __init__(self, repository_directory, metadata_directory, targets_directory):
def write(self, write_partial=False):
def write(self, write_partial=False, consistent_snapshots=False):
"""
<Purpose>
Write all the JSON Metadata objects to their corresponding files.
@ -177,6 +179,13 @@ def write(self, write_partial=False):
to independently sign and update role metadata. write() raises an
exception if a metadata role cannot be written due to not having enough
signatures.
consistent_snapshots:
A boolean indicating whether written metadata and target files should
include a digest in the filename (i.e., root.<digest>.txt,
targets.<digest>.txt.gz, README.<digest>.txt, where <digest> is the
file's SHA256 digest. Example:
'root.1f4e35a60c8f96d439e27e858ce2869c770c1cdd54e1ef76657ceaaf01da18a3.txt'
<Exceptions>
tuf.Error, if any of the top-level roles do not have a minimum
@ -194,6 +203,7 @@ def write(self, write_partial=False):
# types, and that all dict keys are properly named.
# Raise 'tuf.FormatError' if any are improperly formatted.
tuf.formats.BOOLEAN_SCHEMA.check_match(write_partial)
tuf.formats.BOOLEAN_SCHEMA.check_match(consistent_snapshots)
# At this point the tuf.keydb and tuf.roledb stores must be fully
# populated, otherwise write() throwns a 'tuf.Repository' exception if
@ -1250,8 +1260,9 @@ def __init__(self):
expiration = tuf.formats.format_time(time.time()+ROOT_EXPIRATION)
roleinfo = {'keyids': [], 'signing_keyids': [], 'threshold': 1,
'signatures': [], 'version': 0, 'compressions': [''],
'expires': expiration, 'partial_loaded': False}
'signatures': [], 'version': 0, 'consistent_snapshots': False,
'compressions': [''], 'expires': expiration,
'partial_loaded': False}
try:
tuf.roledb.add_role(self._rolename, roleinfo)
except tuf.RoleAlreadyExistsError, e:
@ -2109,8 +2120,8 @@ def _generate_and_write_metadata(rolename, filenames, write_partial,
if tuf.sig.verify(signable, rolename) or write_partial:
_remove_invalid_and_duplicate_signatures(signable)
for compression in roleinfo['compressions']:
write_metadata_file(signable, metadata_filename, compression)
compressions = roleinfo['compressions']
write_metadata_file(signable, metadata_filename, compressions)
return signable
@ -2352,11 +2363,28 @@ def _delete_obsolete_metadata(metadata_directory):
# metadata file is not actually deleted yet. Do it now.
if not tuf.roledb.role_exists(metadata_name):
os.remove(metadata_path)
def _get_written_metadata_and_digest(metadata_signable, hash_algorithm):
"""
Non-public function that returns the actual content of written metadata and
its digest.
"""
written_metadata_content = unicode(json.dumps(metadata_signable, indent=1,
sort_keys=True))
digest_object = tuf.hash.digest(hash_algorithm)
digest_object.update(written_metadata_content)
written_metadata_digest = digest_object.hexdigest()
return written_metadata_content, written_metadata_digest
def create_new_repository(repository_directory):
"""
<Purpose>
@ -3718,11 +3746,14 @@ def sign_metadata(metadata_object, keyids, filename):
def write_metadata_file(metadata, filename, compression=''):
def write_metadata_file(metadata, filename, compressions):
"""
<Purpose>
Write the 'metadata' signable object to 'filename', and the compressed
version of the metadata file if 'compression' is set.
If necessary, write the 'metadata' signable object to 'filename', and the
compressed version of the metadata file if 'compression' is set.
Note: Compression algorithms like gzip attach a timestamp to compressed
files, so a metadata file compressed multiple times may generate different
digests even though the uncompressed content has not changed.
<Arguments>
metadata:
@ -3731,12 +3762,12 @@ def write_metadata_file(metadata, filename, compression=''):
filename:
The filename of the metadata to be written (e.g., 'root.txt').
If 'compression' is set, the compressions extention is appended to
'filename'.
If a compression algorithm is specified in 'compressions', the
compression extention is appended to 'filename'.
compression:
Specify the algorithm, as a string, to compress the file; otherwise, the
file will be left uncompressed. Available options are 'gz' (gzip).
compressions:
Specify the algorithms, as a list of strings, used to compress the file;
The only currently available compression option is 'gz' (gzip).
<Exceptions>
tuf.FormatError, if the arguments are improperly formatted.
@ -3746,11 +3777,11 @@ def write_metadata_file(metadata, filename, compression=''):
Any other runtime (e.g., IO) exception.
<Side Effects>
The 'filename' (or the compressed filename) file is created or overwritten
The 'filename' (or the compressed filename) file is created, or overwritten
if it exists.
<Returns>
The file path of the written metadata.
None.
"""
# Do the arguments have the correct format?
@ -3759,52 +3790,85 @@ def write_metadata_file(metadata, filename, compression=''):
# Raise 'tuf.FormatError' if the check fails.
tuf.formats.SIGNABLE_SCHEMA.check_match(metadata)
tuf.formats.PATH_SCHEMA.check_match(filename)
tuf.formats.COMPRESSION_SCHEMA.check_match(compression)
tuf.formats.COMPRESSIONS_SCHEMA.check_match(compressions)
# Verify the directory of 'filename', and convert 'filename' to its absolute
# path so that temporary files are moved to their expected destination.
_check_directory(os.path.dirname(filename))
filename = os.path.abspath(filename)
# Generate the actual metadata file content of 'metadata'. Metadata is
# saved as json and includes formatting, such as indentation and sorted
# objects. The new digest of 'metadata' is also calculated to help determine
# if re-saving is required.
file_content, new_digest = \
_get_written_metadata_and_digest(metadata, DEFAULT_HASH_ALGORITHM)
# The 'metadata' object is written to 'file_object', including compressed
# versions. To avoid partial metadata from being written, 'metadata' is first
# written to a temporary location (i.e., 'file_object') and then moved to
# 'filename'.
file_object = tuf.util.TempFile()
# Verify whether the uncompressed metadata needs to be written (i.e., has
# not been previously written or has changed.
write_uncompressed_metadata = False
# Has the uncompressed metadata changed? Does it exist? If so, set
# 'write_uncompressed_metadata' to True so that it is written.
# 'write_uncompressed_metadata' is also checked when writting compressed
# versions (compressed metadata should only be written if it does not exist
# or the uncompressed version has changed).
try:
file_length_junk, old_digest = tuf.util.get_file_details(filename)
old_digest = old_digest[DEFAULT_HASH_ALGORITHM]
if old_digest != new_digest:
write_uncompressed_metadata = True
# Generate the appropriate file content of 'file_object' (i.e., compressed or
# uncompressed metadata) and update the file extension of 'filename' if
# compression is used.
if not len(compression):
logger.info('No compression for '+repr(filename))
# 'tuf.Error' raised if 'filename' does not exist.
except tuf.Error, e:
write_uncompressed_metadata = True
# Generate the metadata files of 'metadata'. Sort 'compressions' so that
# the uncompressed version is written before the compressed.
for compression in sorted(compressions):
# The 'metadata' object is written to 'file_object', including compressed
# versions. To avoid partial metadata from being written, 'metadata' is
# first written to a temporary location (i.e., 'file_object') and then moved
# to 'filename'.
file_object = tuf.util.TempFile()
# Serialize 'metadata' to the file-like object and then write 'file_object'
# to disk. The dictionary keys of 'metadata' are sorted and indentation is
# used.
json.dump(metadata, file_object, indent=1, sort_keys=True)
file_object.write('\n')
elif compression == 'gz':
logger.info('gzip compression for '+str(filename))
filename = filename + '.gz'
# Instantiate a gzip object, but save compressed content to 'file_object'
# (i.e., GzipFile instance is based on its 'fileobj' argument).
with gzip.GzipFile(fileobj=file_object, mode='wb') as gzip_object:
json.dump(metadata, gzip_object, indent=1, sort_keys=True)
gzip_object.write('\n')
# Generate the appropriate file content of 'file_object' (i.e., compressed
# or uncompressed metadata) and update the file extension of 'filename' if
# compression is used.
if not len(compression):
if write_uncompressed_metadata:
logger.info('No compression for '+repr(filename))
# Serialize 'metadata' to the file-like object and then write
# 'file_object' to disk. The dictionary keys of 'metadata' are sorted
# and indentation is used.
file_object.write(file_content)
else:
continue
else:
raise tuf.FormatError('Unknown compression algorithm: '+str(compression))
elif compression == 'gz':
filename = filename + '.gz'
# The 'tuf.util.TempFile' file-like object is automically closed after the
# final move.
logger.info('Saving metadata to '+repr(filename))
file_object.move(filename)
# Save the compressed version if it does not exist or a new version
# of the uncompressed metadata has been written.
if not os.path.exists(filename) or write_uncompressed_metadata:
logger.info('gzip compression for '+str(filename))
# Instantiate a gzip object, but save compressed content to
# 'file_object' (i.e., GzipFile instance is based on its 'fileobj'
# argument).
with gzip.GzipFile(fileobj=file_object, mode='wb') as gzip_object:
gzip_object.write(file_content)
else:
continue
else:
raise tuf.FormatError('Unknown compression algorithm: '+repr(compression))
# The 'tuf.util.TempFile' file-like object is automically closed after the
# final move.
logger.info('Saving metadata to '+repr(filename))
file_object.move(filename)
# Return the written 'filename' if there are no exceptions.
return filename
@ -3932,8 +3996,7 @@ def write_delegated_metadata_file(repository_directory, targets_directory,
# If a non-partial version is written, ensure any signatures that may
# have been added with load_repository(), and now invalid, are discarded.
_remove_invalid_and_duplicate_signatures(signable)
for compression in compressions:
write_metadata_file(signable, metadata_filepath, compression)
write_metadata_file(signable, metadata_filepath, compressions)
else:
message = 'Not enough signatures for: '+repr(metadata_filepath)