1 WebPageReplay Rule Language 2 =========================== 3 4 WebPageReplay rules allows developers to customize record/replay handling. 5 6 Motiviation 7 ----------- 8 9 Web sites often require custom replay logic, e.g.: 10 11 1. The recording uploads various metrics/logs to: 12 13 http://example.com/gen_204?emsg=foo 14 15 but, during replay, it uploads different parameters: 16 17 http://example.com/gen_204?emsg=bar 18 19 so (as-is) our replay fails. We want "*/gen_204" to always respond 20 "HTTP 204 No Change". 21 22 2. The recording fetches data from one server: 23 24 http://mirrorA.example.com/stuff 25 26 but replay selects a different server: 27 28 http://mirrorB.example.com/stuff 29 30 which breaks replay. We want "mirror*.example.com/stuff" to be equivalent. 31 32 3. The recorded URL + response contains a UID, e.g.: 33 34 http://example.com?q=foo --> "you sent foo." 35 36 but the replay asks for: 37 38 http://example.com?q=bar --> replay error! 39 40 We want it to reply "you sent bar." 41 42 We could hack all the above rules into the code, but that can''t be (cleanly) extended or open sourced. 43 44 Instead, we want a simple config file of "predicate --> action" rules. 45 46 47 Format 48 ------ 49 50 The JSON-formatted rule file is specified on the command line: 51 52 replay.py ... --rules_path my_rules ... 53 54 The rules file must contain an array of single-item objects, e.g.: 55 56 [{"comment": "ignore me"}, 57 {"LogUrl": {"url": "example\\.com/logme.*"}}, 58 {"LogUrl": {"url": "example\\.com/someotherpath"}} 59 ] 60 61 All "comment" items are ignored and support arbitrary values, e.g., a string 62 or commented-out rule(s). 63 64 All other items must specify a string TYPE key and object ARGS value, e.g.: 65 66 {"LogUrl": {"url": "example\\.com/test", "stop": false}} 67 68 The default TYPE package is "rules" and the default rule_parser 69 "allowed_imports" is similarly restricted to only allow "rules" classes. 70 71 The TYPE implementation class must match the Rule API defined in 72 "rules/rule.py": 73 74 class Rule(object): 75 def IsType(self, rule_type_name): ... 76 def ApplyRule(self, return_value, request, response): ... 77 78 The ARGS must match the rule-specific constructor, e.g.: 79 80 class LogUrl(rule.Rule): 81 def __init__(self, url, stop=False): 82 self._url_re = re.compile(url) 83 self._stop = stop 84 ... 85 86 All rules of the same rule_type_name are chained together and applied in the 87 same order as they appear in the input JSON file. 88 89 90 Rules 91 ------- 92 93 ### rules.LogUrl: 94 95 If the url pattern matches then log the request URL. 96
