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Move to/from_dict metadata API methods to util
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Add tuf.api.serialization.util module with functions to
convert between TUF metadata class model and the corresponding
dictionary representation. These functions replace the
corresponding to/from_dict classmethods.

Configure api/pylintrc to exempt '_type' from protected member
access warning, because the underscore prefix here is only used to
avoid name shadowing.

Signed-off-by: Lukas Puehringer <[email protected]>
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@lukpueh
lukpueh committed Feb 10, 2021
1 parent 19d96f3 commit b786bc0
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Showing 5 changed files with 166 additions and 148 deletions.
12 changes: 6 additions & 6 deletions tests/test_api.py
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ def setUpModule():
from tuf.api.serialization import (
DeserializationError
)
from tuf.api.serialization.util import metadata_to_dict
from tuf.api.serialization.json import (
JSONSerializer,
JSONDeserializer,
Expand Down Expand Up @@ -120,9 +121,9 @@ def test_generic_read(self):
self.assertTrue(
isinstance(metadata_obj2.signed, inner_metadata_cls))

# ... and return the same object (compared by dict representation)
self.assertDictEqual(
metadata_obj.to_dict(), metadata_obj2.to_dict())
# ... and are equal (compared by dict representation)
self.assertDictEqual(metadata_to_dict(metadata_obj),
metadata_to_dict(metadata_obj2))


# Assert that it chokes correctly on an unknown metadata type
Expand Down Expand Up @@ -154,9 +155,8 @@ def test_read_write_read_compare(self):
metadata_obj.to_file(path_2)
metadata_obj_2 = Metadata.from_file(path_2)

self.assertDictEqual(
metadata_obj.to_dict(),
metadata_obj_2.to_dict())
self.assertDictEqual(metadata_to_dict(metadata_obj),
metadata_to_dict(metadata_obj_2))

os.remove(path_2)

Expand Down
141 changes: 3 additions & 138 deletions tuf/api/metadata.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@
from datetime import datetime, timedelta
from typing import Any, Dict, Optional

import json
import tempfile

from securesystemslib.util import persist_temp_file
Expand All @@ -24,7 +23,6 @@
import tuf.exceptions



# Types
JsonDict = Dict[str, Any]

Expand Down Expand Up @@ -57,49 +55,6 @@ def __init__(self, signed: 'Signed', signatures: list) -> None:
self.signatures = signatures


# Deserialization (factories).
@classmethod
def from_dict(cls, metadata: JsonDict) -> 'Metadata':
"""Creates Metadata object from its JSON/dict representation.
Calls 'from_dict' for any complex metadata attribute represented by a
class also that has a 'from_dict' factory method. (Currently this is
only the signed attribute.)
Arguments:
metadata: TUF metadata in JSON/dict representation, as e.g.
returned by 'json.loads'.
Raises:
KeyError: The metadata dict format is invalid.
ValueError: The metadata has an unrecognized signed._type field.
Returns:
A TUF Metadata object.
"""
# Dispatch to contained metadata class on metadata _type field.
_type = metadata['signed']['_type']

if _type == 'targets':
inner_cls = Targets
elif _type == 'snapshot':
inner_cls = Snapshot
elif _type == 'timestamp':
inner_cls = Timestamp
elif _type == 'root':
inner_cls = Root
else:
raise ValueError(f'unrecognized metadata type "{_type}"')

# NOTE: If Signature becomes a class, we should iterate over
# metadata['signatures'], call Signature.from_dict for each item, and
# pass a list of Signature objects to the Metadata constructor intead.
return cls(
signed=inner_cls.from_dict(metadata['signed']),
signatures=metadata['signatures'])


@classmethod
def from_file(
cls, filename: str, deserializer: MetadataDeserializer = None,
Expand Down Expand Up @@ -140,24 +95,6 @@ def from_file(
return deserializer.deserialize(raw_data)


# Serialization.
def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
return {
'signatures': self.signatures,
'signed': self.signed.to_dict()
}


def to_json(self, compact: bool = False) -> None:
"""Returns the optionally compacted JSON representation of self. """
return json.dumps(
self.to_dict(),
indent=(None if compact else 1),
separators=((',', ':') if compact else (',', ': ')),
sort_keys=True)


def to_file(self, filename: str, serializer: MetadataSerializer = None,
storage_backend: StorageBackendInterface = None) -> None:
"""Writes TUF metadata to file storage.
Expand Down Expand Up @@ -313,39 +250,6 @@ def __init__(
self.version = version


# Deserialization (factories).
@classmethod
def from_dict(cls, signed_dict: JsonDict) -> 'Signed':
"""Creates Signed object from its JSON/dict representation. """

# Convert 'expires' TUF metadata string to a datetime object, which is
# what the constructor expects and what we store. The inverse operation
# is implemented in 'to_dict'.
signed_dict['expires'] = tuf.formats.expiry_string_to_datetime(
signed_dict['expires'])
# NOTE: We write the converted 'expires' back into 'signed_dict' above
# so that we can pass it to the constructor as '**signed_dict' below,
# along with other fields that belong to Signed subclasses.
# Any 'from_dict'(-like) conversions of fields that correspond to a
# subclass should be performed in the 'from_dict' method of that
# subclass and also be written back into 'signed_dict' before calling
# super().from_dict.

# NOTE: cls might be a subclass of Signed, if 'from_dict' was called on
# that subclass (see e.g. Metadata.from_dict).
return cls(**signed_dict)


def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
return {
'_type': self._type,
'version': self.version,
'spec_version': self.spec_version,
'expires': self.expires.isoformat() + 'Z'
}


# Modification.
def bump_expiration(self, delta: timedelta = timedelta(days=1)) -> None:
"""Increments the expires attribute by the passed timedelta. """
Expand All @@ -357,6 +261,7 @@ def bump_version(self) -> None:
self.version += 1



class Root(Signed):
"""A container for the signed part of root metadata.
Expand Down Expand Up @@ -406,18 +311,6 @@ def __init__(
self.roles = roles


# Serialization.
def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
json_dict = super().to_dict()
json_dict.update({
'consistent_snapshot': self.consistent_snapshot,
'keys': self.keys,
'roles': self.roles
})
return json_dict


# Update key for a role.
def add_key(self, role: str, keyid: str, key_metadata: JsonDict) -> None:
"""Adds new key for 'role' and updates the key store. """
Expand All @@ -439,7 +332,6 @@ def remove_key(self, role: str, keyid: str) -> None:




class Timestamp(Signed):
"""A container for the signed part of timestamp metadata.
Expand Down Expand Up @@ -467,16 +359,6 @@ def __init__(
self.meta = meta


# Serialization.
def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
json_dict = super().to_dict()
json_dict.update({
'meta': self.meta
})
return json_dict


# Modification.
def update(self, version: int, length: int, hashes: JsonDict) -> None:
"""Assigns passed info about snapshot metadata to meta dict. """
Expand All @@ -487,6 +369,7 @@ def update(self, version: int, length: int, hashes: JsonDict) -> None:
}



class Snapshot(Signed):
"""A container for the signed part of snapshot metadata.
Expand Down Expand Up @@ -520,15 +403,6 @@ def __init__(
# TODO: Add class for meta
self.meta = meta

# Serialization.
def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
json_dict = super().to_dict()
json_dict.update({
'meta': self.meta
})
return json_dict


# Modification.
def update(
Expand All @@ -545,6 +419,7 @@ def update(
self.meta[metadata_fn]['hashes'] = hashes



class Targets(Signed):
"""A container for the signed part of targets metadata.
Expand Down Expand Up @@ -612,16 +487,6 @@ def __init__(
self.delegations = delegations


# Serialization.
def to_dict(self) -> JsonDict:
"""Returns the JSON-serializable dictionary representation of self. """
json_dict = super().to_dict()
json_dict.update({
'targets': self.targets,
'delegations': self.delegations,
})
return json_dict

# Modification.
def update(self, filename: str, fileinfo: JsonDict) -> None:
"""Assigns passed target file info to meta dict. """
Expand Down
3 changes: 3 additions & 0 deletions tuf/api/pylintrc
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Original file line number Diff line number Diff line change
Expand Up @@ -8,5 +8,8 @@ good-names=e
indent-string=" "
max-line-length=79

[CLASSES]
exclude-protected:_type

[DESIGN]
min-public-methods=0
9 changes: 5 additions & 4 deletions tuf/api/serialization/json.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,8 @@
MetadataDeserializer,
SignedSerializer,
SerializationError,
DeserializationError)
DeserializationError,
util)


class JSONDeserializer(MetadataDeserializer):
Expand All @@ -29,7 +30,7 @@ def deserialize(self, raw_data: bytes) -> Metadata:
"""Deserialize utf-8 encoded JSON bytes into Metadata object. """
try:
_dict = json.loads(raw_data.decode("utf-8"))
return Metadata.from_dict(_dict)
return util.metadata_from_dict(_dict)

except Exception as e: # pylint: disable=broad-except
six.raise_from(DeserializationError, e)
Expand All @@ -51,7 +52,7 @@ def serialize(self, metadata_obj: Metadata) -> bytes:
try:
indent = (None if self.compact else 1)
separators=((',', ':') if self.compact else (',', ': '))
return json.dumps(metadata_obj.to_dict(),
return json.dumps(util.metadata_to_dict(metadata_obj),
indent=indent,
separators=separators,
sort_keys=True).encode("utf-8")
Expand All @@ -66,7 +67,7 @@ class CanonicalJSONSerializer(SignedSerializer):
def serialize(self, signed_obj: Signed) -> bytes:
"""Serialize Signed object into utf-8 encoded Canonical JSON bytes. """
try:
signed_dict = signed_obj.to_dict()
signed_dict = util.signed_to_dict(signed_obj)
return encode_canonical(signed_dict).encode("utf-8")

except Exception as e: # pylint: disable=broad-except
Expand Down
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