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1# Copyright 2015 Google Inc. All Rights Reserved.
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7#      http://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14
15r"""Rules parser.
16
17The input syntax is:
18  [{"comment": ignored_value},
19   {"rule_class_name1": {"arg1": value, "arg2": value, ...}},
20   {"rule_class_name2": {"arg1": value, "arg2": value, ...}},
21   ...]
22E.g.:
23  [{"comment": "this text is ignored"},
24   {"SendStatus": {"url": "example\\.com/ss.*", "status": 204}},
25   {"ModifyUrl": {"url": "(example\\.com)(/.*)", "new_url": "{1}"}}
26  ]
27"""
28
29import json
30import re
31
32
33class Error(Exception):
34  pass
35
36
37class Rules(object):
38
39  """A parsed sequence of Rule objects."""
40
41  def __init__(self, file_obj=None, allowed_imports=None):
42    """Initializes from the given file object.
43
44    Args:
45      file_obj: A file object.
46      allowed_imports: A set of strings, defaults to {'rules'}.
47        Use {'*'} to allow any import path.
48    """
49    if allowed_imports is None:
50      allowed_imports = {'rules'}
51    self._rules = [] if file_obj is None else _Load(file_obj, allowed_imports)
52
53  def Contains(self, rule_type_name):
54    """Returns true if any rule matches the given type name.
55
56    Args:
57      rule_type_name: a string.
58    Returns:
59      True if any rule matches, else False.
60    """
61    return any(rule for rule in self._rules if rule.IsType(rule_type_name))
62
63  def Find(self, rule_type_name):
64    """Returns a _Rule object containing all rules with the given type name.
65
66    Args:
67      rule_type_name: a string.
68    Returns:
69      A callable object that expects two arguments:
70        request: the httparchive ArchivedHttpRequest
71        response: the httparchive ArchivedHttpResponse
72      and returns the rule return_value of the first rule that returns
73      should_stop == True, or the last rule's return_value if all rules returns
74      should_stop == False.
75    """
76    matches = [rule for rule in self._rules if rule.IsType(rule_type_name)]
77    return _Rule(matches)
78
79  def __str__(self):
80    return _ToString(self._rules)
81
82  def __repr__(self):
83    return str(self)
84
85
86class _Rule(object):
87  """Calls a sequence of Rule objects until one returns should_stop."""
88
89  def __init__(self, rules):
90    self._rules = rules
91
92  def __call__(self, request, response):
93    """Calls the rules until one returns should_stop.
94
95    Args:
96      request: the httparchive ArchivedHttpRequest.
97      response: the httparchive ArchivedHttpResponse, which may be None.
98    Returns:
99      The rule return_value of the first rule that returns should_stop == True,
100      or the last rule's return_value if all rules return should_stop == False.
101    """
102    return_value = None
103    for rule in self._rules:
104      should_stop, return_value = rule.ApplyRule(
105          return_value, request, response)
106      if should_stop:
107        break
108    return return_value
109
110  def __str__(self):
111    return _ToString(self._rules)
112
113  def __repr__(self):
114    return str(self)
115
116
117def _ToString(rules):
118  """Formats a sequence of Rule objects into a string."""
119  return '[\n%s\n]' % '\n'.join('%s' % rule for rule in rules)
120
121
122def _Load(file_obj, allowed_imports):
123  """Parses and evaluates all rules in the given file.
124
125  Args:
126    file_obj: a file object.
127    allowed_imports: a sequence of strings, e.g.: {'rules'}.
128  Returns:
129    a list of rules.
130  """
131  rules = []
132  entries = json.load(file_obj)
133  if not isinstance(entries, list):
134    raise Error('Expecting a list, not %s', type(entries))
135  for i, entry in enumerate(entries):
136    if not isinstance(entry, dict):
137      raise Error('%s: Expecting a dict, not %s', i, type(entry))
138    if len(entry) != 1:
139      raise Error('%s: Expecting 1 item, not %d', i, len(entry))
140    name, args = next(entry.iteritems())
141    if not isinstance(name, basestring):
142      raise Error('%s: Expecting a string TYPE, not %s', i, type(name))
143    if not re.match(r'(\w+\.)*\w+$', name):
144      raise Error('%s: Expecting a classname TYPE, not %s', i, name)
145    if name == 'comment':
146      continue
147    if not isinstance(args, dict):
148      raise Error('%s: Expecting a dict ARGS, not %s', i, type(args))
149    fullname = str(name)
150    if '.' not in fullname:
151      fullname = 'rules.%s' % fullname
152
153    modulename, classname = fullname.rsplit('.', 1)
154    if '*' not in allowed_imports and modulename not in allowed_imports:
155      raise Error('%s: Package %r is not in allowed_imports', i, modulename)
156
157    module = __import__(modulename, fromlist=[classname])
158    clazz = getattr(module, classname)
159
160    missing = {s for s in ('IsType', 'ApplyRule') if not hasattr(clazz, s)}
161    if missing:
162      raise Error('%s: %s lacks %s', i, clazz.__name__, ' and '.join(missing))
163
164    rule = clazz(**args)
165
166    rules.append(rule)
167  return rules
168