# -*- mode:python; coding:utf-8 -*-
# Copyright (c) 2020 IBM Corp. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Compliance evidence management automation module."""
import inspect
import json
from collections import namedtuple
from functools import wraps
from pathlib import PurePath
from compliance.check import ComplianceCheck
from compliance.config import get_config
from compliance.utils.data_parse import format_json, parse_dot_key
from compliance.utils.exceptions import (
DependencyFetcherNotFoundError,
DependencyUnavailableError,
EvidenceNotFoundError,
StaleEvidenceError
)
from compliance.utils.path import FETCH_PREFIX, substitute_config
from deprecated import deprecated
HOUR = 60 * 60
DAY = HOUR * 24
YEAR = DAY * 365
LazyLoader = namedtuple('LazyLoader', 'path ev_class')
class _BaseEvidence(object):
"""
The evidence base class.
:param name: the name of the evidence (e.g. 'users.csv', or
'{org[name]}-backups.json'). Note that this parameter can be a string
template where config values can be used.
:param category: the category or service where this category will be
classified (e.g. 'dbs', 'github', etc.). This is useful for grouping
evidence that are considered of the same type or that belong to a
specific type of source.
:param ttl: the time (in seconds) after which the evidence will be
considered as stale/invalid.
:param description: a string containing a longer description about
the evidence.
"""
def __init__(self, name, category, ttl=DAY, description='', **kwargs):
self._name = name
self.category = category
self.ttl = ttl
self.description = description
self._content = None
@classmethod
def from_evidence(cls, evidence):
new_evidence = cls(
evidence.name,
evidence.category,
evidence.ttl,
evidence.description
)
if evidence.content:
new_evidence.set_content(evidence.content)
return new_evidence
@classmethod
def lazy_load(cls, path):
return LazyLoader(path, cls)
@classmethod
def from_locker(cls, path, locker):
path = substitute_config(path)
return cls(locker.get_evidence(path))
@property
def rootdir(self):
raise NotImplementedError('The root directory is not set.')
@property
def dir_path(self):
return str(PurePath(self.rootdir).joinpath(self.category))
@property
def name(self):
return substitute_config(self._name)
@property
def path(self):
return str(PurePath(self.dir_path).joinpath(self.name))
@property
def extension(self):
return PurePath(self.name).suffix.lstrip('.')
@property
def content(self):
return self._content
@property
def content_as_json(self):
if self.extension != 'json':
raise ValueError(f'{self.name} does not have JSON content.')
if not hasattr(self, '_content_as_json'):
self._content_as_json = json.loads(self.content)
return self._content_as_json
def set_content(self, str_content):
self._content = str_content
if self.extension == 'json':
self._content = format_json(json.loads(str_content))
[docs]class RawEvidence(_BaseEvidence):
"""
The raw evidence class.
Raw evidence is partition-able if the content is JSON and by providing a
list of partition fields along with an optional partition root. The
evidence partitioning can be defined in configuration JSON or directly upon
construction of a RawEvidence object. The constructor route overrides the
configuration settings, if both are provided.
"""
def __init__(self, *args, **kwargs):
"""Construct and initialize the raw evidence object."""
super().__init__(*args, **kwargs)
lp_config = get_config().get('locker.partitions', {})
partition = kwargs.get(
'partition', lp_config.get(f'{self.category}/{self.name}', {})
)
self.part_fields = partition.get('fields')
self.part_root = partition.get('root')
self.binary_content = kwargs.get('binary_content', False)
@property
def rootdir(self):
"""Root directory for raw evidence."""
return 'raw'
@property
def is_partitioned(self):
"""Raw evidence partitioned status."""
return self.part_fields is not None and self.extension == 'json'
@property
def partition_keys(self):
"""
All partition keys for this evidence object.
Return all key values based on evidence content and the
key fields provided during evidence instantiation. Key values are
relative to the root partition provided during evidence instantiation.
:returns: A list of key values where the key values are lists as well.
"""
if getattr(self, '_partition_keys', None) is None:
keys = set()
if self.part_root:
root = parse_dot_key(json.loads(self._content), self.part_root)
else:
root = json.loads(self._content)
for data in root:
key_values = []
for field in self.part_fields:
key_value = data
key_values.append(parse_dot_key(key_value, field))
keys.add(tuple(key_values))
self._partition_keys = [list(k) for k in keys]
return self._partition_keys
[docs] def get_partition(self, key):
"""
Provide a slice of content based on the supplied partition key.
Return a JSON document that is a slice of the original evidence
content based on the list of key values provided. Key values are
expected to match the key fields provided during evidence
instantiation and are relative to the root partition provided during
evidence instantiation.
:param key: A list of key values to partition by
:returns: A JSON document filtered by the key values provided
"""
data = json.loads(self._content)
if not self.part_root:
data = self._partition(data, key)
else:
part = data
root = self.part_root.split('.')
for field in root[:-1]:
part = part[field]
part[root[-1]] = self._partition(part[root[-1]], key)
return format_json(data)
def _partition(self, data, key):
idx = 0
for field in self.part_fields:
data = list(
filter(lambda e: parse_dot_key(e, field) == key[idx], data)
)
idx += 1
return data
[docs]@deprecated(reason='Evidence class to be removed, use RawEvidence instead')
class DerivedEvidence(_BaseEvidence):
"""The derived evidence class."""
@property
def rootdir(self):
"""Root directory for derived evidence."""
return 'derived'
[docs]class ReportEvidence(_BaseEvidence):
"""The report evidence class."""
@property
def rootdir(self):
"""Root directory for report evidence."""
return 'reports'
[docs]@deprecated(reason='Evidence class to be removed')
class TmpEvidence(_BaseEvidence):
"""The temporary evidence class."""
@property
def rootdir(self):
"""Root directory for temporary evidence."""
return 'tmp'
[docs]class ExternalEvidence(_BaseEvidence):
"""The external evidence class."""
def __init__(self, name, category, ttl=YEAR, description='', **kwargs):
"""Construct and initialize the external evidence object."""
super().__init__(name, category, ttl, description, **kwargs)
@property
def rootdir(self):
"""Root directory for external evidence."""
return 'external'
class _EvidenceContextManager(object):
"""Base class for raw evidence context managers."""
def __init__(self, locker, evidence_path, evidence_type):
self.locker = locker
self.evidence_path = evidence_path
self.evidence_type = evidence_type
def __enter__(self):
path = self.evidence_path
if not path.startswith(f'{self.evidence_type}/'):
path = f'{self.evidence_type}/{path}'
self.evidence = get_evidence_by_path(path)
if self.locker.validate(self.evidence):
self.evidence = None
return self.evidence
def __exit__(self, typ, val, traceback):
if self.evidence and traceback is None:
self.locker.add_evidence(self.evidence)
[docs]class raw_evidence(_EvidenceContextManager): # noqa: N801
"""
Helper context manager for a typical ``fetch_`` method implementation.
Use when retrieving raw evidence by a fetcher and the name of the evidence
is dynamic. When the evidence name is static/known use the
@store_raw_evidence decorator instead.
If TTL has expired, the context manager yields the evidence object
specified by the ``evidence_path``. The context manager expects the
evidence content to be retrieved and set via ``set_content`` by the calling
``with`` block.
If TTL has not expired, the context manager yields ``None`` and expects the
calling ``with`` block to exit gracefully immediately.
"""
def __init__(self, locker, evidence_path):
"""
Construct and initialize the raw evidence context manager.
:param locker: The evidence locker object
:param evidence_path: The path to the raw evidence within the evidence
locker. For example, ``src/my_raw_evidence.json``.
"""
super().__init__(locker, evidence_path, 'raw')
[docs]@deprecated(reason='Context manager to be removed')
class tmp_evidence(_EvidenceContextManager): # noqa: N801
"""
Helper context manager for a typical ``fetch_`` method implementation.
Use when retrieving temporary evidence by a fetcher and the name of the
evidence is dynamic. When the evidence name is static/known use the
@store_tmp_evidence decorator instead.
If the evidence is not present, the context manager yields the evidence
object specified by the ``evidence_path``. The context manager expects the
evidence content to be retrieved and set via ``set_content`` by the calling
``with`` block.
If the evidence is present, the context manager yields ``None`` and expects
the calling ``with`` block to exit gracefully immediately.
"""
def __init__(self, locker, evidence_path):
"""
Construct and initialize the temporary evidence context manager.
:param locker: The evidence locker object
:param evidence_path: The path to the raw evidence within the evidence
locker. For example, ``src/my_tmp_evidence.json``.
"""
super().__init__(locker, evidence_path, 'tmp')
[docs]@deprecated(reason='Context manager to be removed, use raw_evidence instead')
class derived_evidence(object): # noqa: N801
"""
Helper context manager for a typical ``fetch_`` method implementation.
Use when retrieving derived evidence by a fetcher and the name of the
evidence is dynamic. When the evidence name is static/known use the
@store_derived_evidence decorator instead.
If TTL has expired on the derived evidence, the context manager yields a
dictionary containing all of the source evidences as well as the derived
evidence objects specified in the ``sources`` and ``target`` arguments.
If TTL has not expired on the derived evidence, the context manager yields
``None`` and expects the calling ``with`` block to exit gracefully
immediately.
Inside the ``with`` block:
If ``sources`` are provided as a list then the source evidence is
accessible through the source path as the key for the yielded dictionary of
evidence.
If ``sources`` are provided as a dictionary where evidence short names are
keys and evidence source paths are the values then the evidence is
accessible through the evidence short name as the key for the yielded
dictionary of evidence.
If a single evidence source path is provided as a string then the source
evidence is accessible by using 'source' as the key for the yielded
dictionary of evidence.
The derived evidence object is always accessible by using 'derived' as the
key for the yielded dictionary of evidence.
The context manager expects the derived evidence content to be generated
and set via ``set_content`` by the calling ``with`` block.
"""
def __init__(self, locker, sources, target):
"""
Construct and initialize the derived evidence context manager.
:param locker: The evidence locker object
:param sources: The paths to the evidences within the evidence
locker that will make up the derived evidence. This can be a list,
a dict or a string.
For (list) example, ``['src/evidence.json', ...]``.
For (dict) example, ``{'evidence1': 'src/evidence.json', ...}.
For (str) example, ``'src/evidence.json'``.
:param target: The path to the derived evidence within the evidence
locker. For example, ``src/my_derived_evidence.json``.
"""
self.locker = locker
self.sources = sources
self.target = target
self.evidences = None
def __enter__(self):
"""Perform fetcher derived evidence pre-processing."""
target_path = self.target
if not target_path.startswith('derived/'):
target_path = f'derived/{target_path}'
target_evidence = get_evidence_by_path(target_path)
if self.locker.validate(target_evidence):
return
self.evidences = {'derived': target_evidence}
if isinstance(self.sources, list):
for src in self.sources:
self.evidences[src] = get_evidence_by_path(src, self.locker)
elif isinstance(self.sources, dict):
for src_name, src_path in self.sources.items():
self.evidences[src_name] = get_evidence_by_path(
src_path, self.locker
)
elif isinstance(self.sources, str):
self.evidences['source'] = get_evidence_by_path(
self.sources, self.locker
)
else:
self.evidences = None
return self.evidences
def __exit__(self, typ, val, traceback):
"""Perform fetcher derived evidence post-processing."""
if self.evidences and traceback is None:
self.locker.add_evidence(self.evidences['derived'])
[docs]class evidences(object): # noqa: N801
"""
Helper context manager for a typical ``test_`` method implementation.
Use when processing evidence by a check and the name(s) of the
evidence is/are dynamic. When the evidence names are static/known use the
@with_*_evidences decorators instead.
Inside the ``with`` block:
If ``evidence_paths`` are provided as a list then the evidence is
accessible through the evidence path as the key for the yielded dictionary
of evidence.
If ``evidence_paths`` are provided as a dictionary where evidence short
names are keys and evidence paths are the values then the evidence is
accessible through the evidence short name as the key for the yielded
dictionary of evidence.
If a single evidence path is provided as a string then the evidence object
is yielded by this context manager.
"""
def __init__(self, obj, from_evidences):
"""
Construct and initialize the evidences context manager.
:param obj: Either a check or locker object. Needed for backward
compatibility of evidences context manager.
:param from_evidences: The paths to evidences within the evidence
locker. It can be any of the following:
- A string path
- A LazyLoader namedtuple
- A list of string paths or LazyLoader namedtuples or a
combination of string paths and LazyLoader namedtuples
- A dictionary where a key is an evidence short name and a value
is either string path or a LazyLoader namedtuple
Using the LazyLoader namedtuple tells this context manager to cast
your evidence as a subclass of one of the framework's base evidence
classes.
"""
if isinstance(obj, ComplianceCheck):
self.check = obj
self.locker = self.check.locker
else:
self.locker = obj
self.from_evidences = from_evidences
def __enter__(self):
"""Perform check evidences pre-processing."""
evidence = {}
evidence_list = []
if isinstance(self.from_evidences, list):
for from_evidence in self.from_evidences:
path = from_evidence
if isinstance(from_evidence, LazyLoader):
# preserve original path to be used as key of evidence dict
path = from_evidence.path
ev = self._get_evidence(from_evidence)
evidence[path] = ev
evidence_list.append(ev.path)
elif isinstance(self.from_evidences, dict):
for evidence_name, from_evidence in self.from_evidences.items():
evidence[evidence_name] = self._get_evidence(from_evidence)
evidence_list.append(evidence[evidence_name].path)
else:
evidence = self._get_evidence(self.from_evidences)
evidence_list.append(evidence.path)
if hasattr(self, 'check'):
for ev_path in evidence_list:
self.check.add_evidence_metadata(ev_path)
return evidence
def __exit__(self, typ, val, traceback):
"""Perform check evidences post-processing."""
pass
def _get_evidence(self, from_evidence):
"""
Retrieve an evidence instance based on the from_evidence provided.
from_evidence can be either a path to the evidence in the locker as a
string or a LazyLoader namedtuple object that contains the path as a
string and an evidence class to cast the evidence as.
"""
path = from_evidence
ev_class = None
if isinstance(from_evidence, LazyLoader):
path = from_evidence.path
ev_class = from_evidence.ev_class
ev_types = get_evidence_types()
if not any(PurePath(path).parts[0] == et for et in ev_types):
for ev_type in ev_types:
base_evidence_class = get_evidence_class(ev_type)
if ev_class and issubclass(ev_class, base_evidence_class):
path = str(PurePath(ev_type, path))
break
evidence = get_evidence_by_path(path, self.locker)
if evidence.__class__ not in get_evidence_base_classes():
# Evidence returned from cache already cast
ev_class = evidence.__class__
base_evidence_class = get_evidence_class(evidence.rootdir)
if not ev_class or not issubclass(ev_class, base_evidence_class):
ev_class = base_evidence_class
return ev_class.from_evidence(evidence)
__init_map = {
'tmp': TmpEvidence,
'reports': ReportEvidence,
'derived': DerivedEvidence,
'raw': RawEvidence,
'external': ExternalEvidence
}
[docs]def get_evidence_class(evidence_type):
"""
Provide the appropriate evidence class based on the supplied type.
Returns the corresponding evidence class object based on the category
provided. If no match ``None`` is returned.
:param evidence_type: the type of evidence class desired as a string. Valid
values are ``reports``, ``raw``.
:returns: the appropriate evidence class.
"""
return __init_map.get(evidence_type)
[docs]def get_evidence_types():
"""Provide a list of all valid evidence types."""
return list(__init_map.keys())
[docs]def get_evidence_base_classes():
"""Provide a list of all valid base evidence class objects."""
return list(__init_map.values())
[docs]def get_evidence_by_path(path, locker=None):
"""
Provide an evidence object specified by the given path.
The following strategy is used:
* Return evidence if it is present in the evidence cache populating
content if necessary and possible.
* If evidence is not in the evidence cache but a locker is provided, then
the evidence will be retrieved from the locker.
* Otherwise, an evidence object is built with the default parameters.
:param path: relative path to the evidence within the Locker. For example,
``raw/source1/evidence.json``.
:returns: the evidence object.
"""
path = substitute_config(path)
evidence = get_config().get_evidence(path)
if evidence:
if locker and evidence.content is None:
evidence = locker.load_content(evidence)
return evidence
if locker:
try:
evidence = locker.get_evidence(path)
get_config().add_evidences([evidence])
return evidence
except ValueError:
pass
try:
rootdir, category, name = path.strip('/').split('/')
except ValueError:
raise ValueError(f'Invalid evidence path format "{path}"')
if rootdir not in __init_map:
raise ValueError(f'Unable to create evidence from root dir {rootdir}')
return __init_map[rootdir](name, category)
[docs]def get_evidence_dependency(path, locker, fetcher=None):
"""
Provide evidence to fetchers that depend on that other evidence to fetch.
Use when a fetcher needs evidence fetched by another fetcher in order to
complete its fetch process. The premise is that if the evidence is in the
evidence cache then return that because it was placed there by another
fetcher. If not then get the evidence directly from the locker without
putting that evidence into the evidence cache. When an evidence dependency
is not found the fetcher is queued up as a dependency rerun for subsequent
processing.
:param path: relative path to the evidence within the Locker. For example,
``raw/source1/evidence.json``.
:param locker: evidence Locker object.
:param fetcher: optional Python notation path to fetcher method. If
provided, this defines the fetcher that is added to the re-run list.
Otherwise the execution stack is traversed to find the fetcher caller.
:returns: the evidence object.
"""
path = substitute_config(path)
evidence = get_config().get_evidence(path)
if evidence is None or evidence.content is None:
try:
evidence = locker.get_evidence(path)
except (StaleEvidenceError, EvidenceNotFoundError):
rerun = None
if fetcher:
module, clss, method = fetcher.rsplit('.', 2)
rerun = {'module': module, 'class': clss, 'method': method}
else:
for frame_info in inspect.stack()[1:]:
if frame_info.function.startswith(FETCH_PREFIX):
frame = frame_info.frame
rerun = {
'module': inspect.getmodule(frame).__name__,
'class': frame.f_locals['self'].__class__.__name__,
'method': frame.f_code.co_name
}
break
if not rerun:
raise DependencyFetcherNotFoundError(
f'Cannot re-run, no fetcher found for evidence {path}.'
)
locker.dependency_rerun.append(rerun)
raise DependencyUnavailableError(
f'evidence dependency {path} is currently unavailable.'
)
return evidence
[docs]def store_raw_evidence(evidence_path):
"""
Decorate a typical ``fetcher_`` method fetching raw evidence.
Use when retrieving raw evidence by a fetcher and the name of the evidence
is static/known. When the evidence name is dynamic use the
raw_evidence context manager instead.
The decorator expects that the decorated method returns the content to be
stored in the locker. The storing of the evidence is also handled by this
decorator.
:param path: relative path to the evidence within the Locker. For example,
``source1/evidence.json``.
"""
def decorator(f):
@wraps(f) # required for preserving the function context
def wrapper(self, *args, **kwargs):
return _store_wrapper(self, evidence_path, f, 'raw')
return wrapper
return decorator
[docs]@deprecated(reason='Decorator to be removed')
def store_tmp_evidence(evidence_path):
"""
Decorate a typical ``fetcher_`` method fetching temporary evidence.
Use when retrieving temporary evidence by a fetcher and the name of the
evidence is static/known. When the evidence name is dynamic use the
tmp_evidence context manager instead.
:param path: relative path to the evidence within the Locker. For example,
``source1/evidence.json``.
"""
def decorator(f):
@wraps(f) # required for preserving the function context
def wrapper(self, *args, **kwargs):
return _store_wrapper(self, evidence_path, f, 'tmp')
return wrapper
return decorator
[docs]@deprecated(reason='Decorator to be removed, use store_raw_evidence instead')
def store_derived_evidence(evidences, target):
"""
Decorate a typical ``fetcher_`` method fetching derived evidence.
Use when retrieving derived evidence by a fetcher and the name of the
evidence is static/known. When the evidence name is dynamic use the
tmp_evidence context manager instead.
The decorator expects that the decorated method returns the content to be
stored in the locker. The storing of the evidence is also handled by this
decorator.
:param evidences: a list of relative paths to the evidences needed by
the fetcher. They will be passed to the method call.
For example, ``[raw/src/foo.json, derived/src/bar.json]``.
:param target: relative path to the evidence to be stored in the Locker.
For example, ``src/evidence.json``.
"""
def decorator(f):
@wraps(f) # required for preserving the function context
def wrapper(self, *args, **kwargs):
target_path = target
if not target_path.startswith('derived/'):
target_path = f'derived/{target_path}'
target_evidence = get_evidence_by_path(target_path)
if self.locker.validate(target_evidence):
return
depends = [get_evidence_by_path(e, self.locker) for e in evidences]
content = f(self, *depends)
target_evidence.set_content(content)
self.locker.add_evidence(target_evidence)
return wrapper
return decorator
[docs]def with_raw_evidences(*from_evidences):
"""
Decorate a typical ``test_`` check method processing raw evidences.
Use when processing raw evidence by a check and the name(s) of the
evidence is/are static/known. When the evidence names are dynamic use the
``evidences`` context manager instead.
:param from_evidences: relative paths to evidences as strings or
LazyLoader namedtuples that contain relative paths to evidences and
evidence classes required by the check.
"""
def decorator(f):
return _with_evidence_decorator(from_evidences, f, 'raw')
return decorator
[docs]def with_external_evidences(*from_evidences):
"""
Decorate a typical ``test_`` check method processing external evidences.
Use when processing external evidence by a check and the name(s) of the
evidence is/are static/known. When the evidence names are dynamic use the
``evidences`` context manager instead.
:param from_evidences: relative paths to evidences as strings or
LazyLoader namedtuples that contain relative paths to evidences and
evidence classes required by the check.
"""
def decorator(f):
return _with_evidence_decorator(from_evidences, f, 'external')
return decorator
[docs]@deprecated(reason='Decorator to be removed, use with_raw_evidences instead')
def with_derived_evidences(*from_evidences):
"""
Decorate a typical ``test_`` check method processing derived evidences.
Use when processing derived evidence by a check and the name(s) of the
evidence is/are static/known. When the evidence names are dynamic use the
``evidences`` context manager instead.
:param from_evidences: relative paths to evidences as strings or
LazyLoader namedtuples that contain relative paths to evidences and
evidence classes required by the check.
"""
def decorator(f):
return _with_evidence_decorator(from_evidences, f, 'derived')
return decorator
[docs]@deprecated(reason='Decorator to be removed')
def with_tmp_evidences(*from_evidences):
"""
Decorate a typical ``test_`` check method processing temporary evidences.
Use when processing temporary evidence by a check and the name(s) of the
evidence is/are static/known. When the evidence names are dynamic use the
``evidences`` context manager instead.
:param from_evidences: relative paths to evidences as strings or
LazyLoader namedtuples that contain relative paths to evidences and
evidence classes required by the check.
"""
def decorator(f):
return _with_evidence_decorator(from_evidences, f, 'tmp')
return decorator
def _store_wrapper(self, evidence_path, func, type_name):
path = evidence_path
if not path.startswith(f'{type_name}/'):
path = f'{type_name}/{path}'
evidence = get_evidence_by_path(path)
if self.locker.validate(evidence):
return
content = func(self)
evidence.set_content(content)
self.locker.add_evidence(evidence)
def _with_evidence_decorator(from_evidences, f, type_str):
from_evs = []
for from_ev in from_evidences:
path = from_ev
# Default the evidence class to evidence of type type_str.
# If from_ev is a LazyLoader and its evidence class is of the type
# type_str then set the evidence class to the from_ev evidence class.
ev_class = get_evidence_class(type_str)
if isinstance(from_ev, LazyLoader):
path = from_ev.path
if issubclass(from_ev.ev_class, ev_class):
ev_class = from_ev.ev_class
# Ensure path is the full relative path including the type root.
if PurePath(path).parts[0] != type_str:
path = str(PurePath(type_str, path))
from_evs.append(LazyLoader(path, ev_class))
if hasattr(f, 'args'):
f.args.extend(from_evs)
return f
@wraps(f) # required for preserving the function context
def wrapper(self, *args, **kwargs):
return _evidence_wrapper(self, wrapper.args, f)
wrapper.args = from_evs
return wrapper
def _evidence_wrapper(self, from_evidences, func):
evidences = []
for fe in from_evidences:
ev = get_evidence_by_path(fe.path, self.locker)
if ev.__class__ in get_evidence_base_classes():
# Only cast if evidence retrieved is a base evidence class object
ev = fe.ev_class.from_evidence(ev)
evidences.append(ev)
for evidence in evidences:
self.add_evidence_metadata(evidence.path)
return func(self, *evidences)