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[monitorlib, mock_uss] Add idempotent handler decorator (#241)
* Add idempotent handler decorator * Replace magic values with constant
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,157 @@ | ||
| import base64 | ||
| import hashlib | ||
| from functools import wraps | ||
| import json | ||
| from typing import Callable, Optional, Dict | ||
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| import arrow | ||
| import flask | ||
| from loguru import logger | ||
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| from implicitdict import ImplicitDict, StringBasedDateTime | ||
| from monitoring.monitorlib.multiprocessing import SynchronizedValue | ||
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| _max_request_buffer_size = int(10e6) | ||
| """Number of bytes to dedicate to caching responses""" | ||
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| class Response(ImplicitDict): | ||
| """Information about a previously-returned response. | ||
| Note that this object is never actually used (in order to maximize performance); instead it serves as documentation | ||
| of the structure of the fields within a plain JSON dict/object.""" | ||
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| json: Optional[dict] | ||
| body: Optional[str] | ||
| code: int | ||
| timestamp: StringBasedDateTime | ||
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| def _get_responses(raw: bytes) -> Dict[str, Response]: | ||
| return json.loads(raw.decode("utf-8")) | ||
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| def _set_responses(responses: Dict[str, Response]) -> bytes: | ||
| while True: | ||
| s = json.dumps(responses) | ||
| if len(s) <= _max_request_buffer_size: | ||
| break | ||
|
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| # Remove oldest cached response | ||
| oldest_id = None | ||
| oldest_timestamp = None | ||
| for request_id, response in responses.items(): | ||
| t = arrow.get(response["timestamp"]) | ||
| if oldest_timestamp is None or t < oldest_timestamp: | ||
| oldest_id = request_id | ||
| oldest_timestamp = t | ||
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| del responses[oldest_id] | ||
| return s.encode("utf-8") | ||
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| _fulfilled_requests = SynchronizedValue( | ||
| {}, | ||
| decoder=_get_responses, | ||
| encoder=_set_responses, | ||
| capacity_bytes=_max_request_buffer_size, | ||
| ) | ||
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| def get_hashed_request_id() -> Optional[str]: | ||
| """Retrieves an identifier for the request by hashing key characteristics of the request.""" | ||
| characteristics = flask.request.method + flask.request.url | ||
| if flask.request.json: | ||
| characteristics += json.dumps(flask.request.json) | ||
| else: | ||
| characteristics += flask.request.data.decode("utf-8") | ||
| return base64.b64encode( | ||
| hashlib.sha512(characteristics.encode("utf-8")).digest() | ||
| ).decode("utf-8") | ||
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| def idempotent_request(get_request_id: Optional[Callable[[], Optional[str]]] = None): | ||
| """Decorator for idempotent Flask view handlers. | ||
| When subsequent requests are received with the same request identifier, this decorator will use a recent cached | ||
| response instead of invoking the underlying handler when possible. Note that there is no verification that the rest | ||
| of the request (apart from the request ID) is identical, so a request with different content but the same request ID | ||
| will receive the cached response from the first request. A developer could compute a request ID based on a hash of | ||
| important request characteristics to control this behavior. | ||
| Note that cached response characteristics are limited and the full original response is not produced verbatim. | ||
| """ | ||
| if get_request_id is None: | ||
| get_request_id = get_hashed_request_id | ||
|
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| def outer_wrapper(fn): | ||
| @wraps(fn) | ||
| def wrapper(*args, **kwargs): | ||
| request_id = get_request_id() | ||
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| cached_requests = _fulfilled_requests.value | ||
| if request_id in cached_requests: | ||
| endpoint = ( | ||
| flask.request.url_rule.rule | ||
| if flask.request.url_rule is not None | ||
| else "unknown endpoint" | ||
| ) | ||
| logger.warning( | ||
| "Fulfilling {} {} with cached response for request {}", | ||
| flask.request.method, | ||
| endpoint, | ||
| request_id, | ||
| ) | ||
| response = cached_requests[request_id] | ||
| if response["body"] is not None: | ||
| return response["body"], response["code"] | ||
| else: | ||
| return flask.jsonify(response["json"]), response["code"] | ||
|
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| result = fn(*args, **kwargs) | ||
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| response = { | ||
| "timestamp": arrow.utcnow().isoformat(), | ||
| "code": 200, | ||
| "body": None, | ||
| "json": None, | ||
| } | ||
| keep_code = False | ||
| if isinstance(result, tuple): | ||
| if len(result) == 2: | ||
| if not isinstance(result[1], int): | ||
| raise NotImplementedError( | ||
| f"Unable to cache Flask view handler result where the second 2-tuple element is a '{type(result[1]).__name__}'" | ||
| ) | ||
| response["code"] = result[1] | ||
| keep_code = True | ||
| result = result[0] | ||
| else: | ||
| raise NotImplementedError( | ||
| f"Unable to cache Flask view handler result which is a tuple of ({', '.join(type(v).__name__ for v in result)})" | ||
| ) | ||
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| if isinstance(result, str): | ||
| response["body"] = result | ||
| response["json"] = None | ||
| elif isinstance(result, flask.Response): | ||
| try: | ||
| response["json"] = result.get_json() | ||
| except ValueError: | ||
| response["body"] = result.get_data(as_text=True) | ||
| if not keep_code: | ||
| response["code"] = result.status_code | ||
| else: | ||
| raise NotImplementedError( | ||
| f"Unable to cache Flask view handler result of type '{type(result).__name__}'" | ||
| ) | ||
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| with _fulfilled_requests as cached_requests: | ||
| cached_requests[request_id] = response | ||
|
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| return result | ||
|
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| return wrapper | ||
|
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| return outer_wrapper |
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