|
| 1 | +""" |
| 2 | +Base for Parameter providers |
| 3 | +""" |
| 4 | + |
| 5 | +import base64 |
| 6 | +import json |
| 7 | +from abc import ABC, abstractmethod |
| 8 | +from collections import namedtuple |
| 9 | +from datetime import datetime, timedelta |
| 10 | +from typing import Dict, Optional, Union |
| 11 | + |
| 12 | +from .exceptions import GetParameterError, TransformParameterError |
| 13 | + |
| 14 | +DEFAULT_MAX_AGE_SECS = 5 |
| 15 | +ExpirableValue = namedtuple("ExpirableValue", ["value", "ttl"]) |
| 16 | +# These providers will be dynamically initialized on first use of the helper functions |
| 17 | +DEFAULT_PROVIDERS = {} |
| 18 | + |
| 19 | + |
| 20 | +class BaseProvider(ABC): |
| 21 | + """ |
| 22 | + Abstract Base Class for Parameter providers |
| 23 | + """ |
| 24 | + |
| 25 | + store = None |
| 26 | + |
| 27 | + def __init__(self): |
| 28 | + """ |
| 29 | + Initialize the base provider |
| 30 | + """ |
| 31 | + |
| 32 | + self.store = {} |
| 33 | + |
| 34 | + def get( |
| 35 | + self, name: str, max_age: int = DEFAULT_MAX_AGE_SECS, transform: Optional[str] = None, **sdk_options |
| 36 | + ) -> Union[str, list, dict, bytes]: |
| 37 | + """ |
| 38 | + Retrieve a parameter value or return the cached value |
| 39 | +
|
| 40 | + Parameters |
| 41 | + ---------- |
| 42 | + name: str |
| 43 | + Parameter name |
| 44 | + max_age: int |
| 45 | + Maximum age of the cached value |
| 46 | + transform: str |
| 47 | + Optional transformation of the parameter value. Supported values |
| 48 | + are "json" for JSON strings and "binary" for base 64 encoded |
| 49 | + values. |
| 50 | + sdk_options: dict, optional |
| 51 | + Arguments that will be passed directly to the underlying API call |
| 52 | +
|
| 53 | + Raises |
| 54 | + ------ |
| 55 | + GetParameterError |
| 56 | + When the parameter provider fails to retrieve a parameter value for |
| 57 | + a given name. |
| 58 | + TransformParameterError |
| 59 | + When the parameter provider fails to transform a parameter value. |
| 60 | + """ |
| 61 | + |
| 62 | + # If there are multiple calls to the same parameter but in a different |
| 63 | + # transform, they will be stored multiple times. This allows us to |
| 64 | + # optimize by transforming the data only once per retrieval, thus there |
| 65 | + # is no need to transform cached values multiple times. However, this |
| 66 | + # means that we need to make multiple calls to the underlying parameter |
| 67 | + # store if we need to return it in different transforms. Since the number |
| 68 | + # of supported transform is small and the probability that a given |
| 69 | + # parameter will always be used in a specific transform, this should be |
| 70 | + # an acceptable tradeoff. |
| 71 | + key = (name, transform) |
| 72 | + |
| 73 | + if key not in self.store or self.store[key].ttl < datetime.now(): |
| 74 | + try: |
| 75 | + value = self._get(name, **sdk_options) |
| 76 | + # Encapsulate all errors into a generic GetParameterError |
| 77 | + except Exception as exc: |
| 78 | + raise GetParameterError(str(exc)) |
| 79 | + |
| 80 | + if transform is not None: |
| 81 | + value = transform_value(value, transform) |
| 82 | + |
| 83 | + self.store[key] = ExpirableValue(value, datetime.now() + timedelta(seconds=max_age),) |
| 84 | + |
| 85 | + return self.store[key].value |
| 86 | + |
| 87 | + @abstractmethod |
| 88 | + def _get(self, name: str, **sdk_options) -> str: |
| 89 | + """ |
| 90 | + Retrieve paramater value from the underlying parameter store |
| 91 | + """ |
| 92 | + raise NotImplementedError() |
| 93 | + |
| 94 | + def get_multiple( |
| 95 | + self, |
| 96 | + path: str, |
| 97 | + max_age: int = DEFAULT_MAX_AGE_SECS, |
| 98 | + transform: Optional[str] = None, |
| 99 | + raise_on_transform_error: bool = False, |
| 100 | + **sdk_options, |
| 101 | + ) -> Union[Dict[str, str], Dict[str, dict], Dict[str, bytes]]: |
| 102 | + """ |
| 103 | + Retrieve multiple parameters based on a path prefix |
| 104 | +
|
| 105 | + Parameters |
| 106 | + ---------- |
| 107 | + path: str |
| 108 | + Parameter path used to retrieve multiple parameters |
| 109 | + max_age: int, optional |
| 110 | + Maximum age of the cached value |
| 111 | + transform: str, optional |
| 112 | + Optional transformation of the parameter value. Supported values |
| 113 | + are "json" for JSON strings and "binary" for base 64 encoded |
| 114 | + values. |
| 115 | + raise_on_transform_error: bool, optional |
| 116 | + Raises an exception if any transform fails, otherwise this will |
| 117 | + return a None value for each transform that failed |
| 118 | + sdk_options: dict, optional |
| 119 | + Arguments that will be passed directly to the underlying API call |
| 120 | +
|
| 121 | + Raises |
| 122 | + ------ |
| 123 | + GetParameterError |
| 124 | + When the parameter provider fails to retrieve parameter values for |
| 125 | + a given path. |
| 126 | + TransformParameterError |
| 127 | + When the parameter provider fails to transform a parameter value. |
| 128 | + """ |
| 129 | + |
| 130 | + key = (path, transform) |
| 131 | + |
| 132 | + if key not in self.store or self.store[key].ttl < datetime.now(): |
| 133 | + try: |
| 134 | + values = self._get_multiple(path, **sdk_options) |
| 135 | + # Encapsulate all errors into a generic GetParameterError |
| 136 | + except Exception as exc: |
| 137 | + raise GetParameterError(str(exc)) |
| 138 | + |
| 139 | + if transform is not None: |
| 140 | + new_values = {} |
| 141 | + for key, value in values.items(): |
| 142 | + try: |
| 143 | + new_values[key] = transform_value(value, transform) |
| 144 | + except Exception as exc: |
| 145 | + if raise_on_transform_error: |
| 146 | + raise exc |
| 147 | + else: |
| 148 | + new_values[key] = None |
| 149 | + |
| 150 | + values = new_values |
| 151 | + |
| 152 | + self.store[key] = ExpirableValue(values, datetime.now() + timedelta(seconds=max_age),) |
| 153 | + |
| 154 | + return self.store[key].value |
| 155 | + |
| 156 | + @abstractmethod |
| 157 | + def _get_multiple(self, path: str, **sdk_options) -> Dict[str, str]: |
| 158 | + """ |
| 159 | + Retrieve multiple parameter values from the underlying parameter store |
| 160 | + """ |
| 161 | + raise NotImplementedError() |
| 162 | + |
| 163 | + |
| 164 | +def transform_value(value: str, transform: str) -> Union[dict, bytes]: |
| 165 | + """ |
| 166 | + Apply a transform to a value |
| 167 | +
|
| 168 | + Parameters |
| 169 | + --------- |
| 170 | + value: str |
| 171 | + Parameter alue to transform |
| 172 | + transform: str |
| 173 | + Type of transform, supported values are "json" and "binary" |
| 174 | +
|
| 175 | + Raises |
| 176 | + ------ |
| 177 | + TransformParameterError: |
| 178 | + When the parameter value could not be transformed |
| 179 | + """ |
| 180 | + |
| 181 | + try: |
| 182 | + if transform == "json": |
| 183 | + return json.loads(value) |
| 184 | + elif transform == "binary": |
| 185 | + return base64.b64decode(value) |
| 186 | + else: |
| 187 | + raise ValueError(f"Invalid transform type '{transform}'") |
| 188 | + |
| 189 | + except Exception as exc: |
| 190 | + raise TransformParameterError(str(exc)) |
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