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 15 r"""Rules parser. 16 17 The input syntax is: 18 [{"comment": ignored_value}, 19 {"rule_class_name1": {"arg1": value, "arg2": value, ...}}, 20 {"rule_class_name2": {"arg1": value, "arg2": value, ...}}, 21 ...] 22 E.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 29 import json 30 import re 31 32 33 class Error(Exception): 34 pass 35 36 37 class 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 86 class _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) 115 116 117 def _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) 120 121 122 def _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
