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1# Copyright 2018 Google LLC
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# https://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.
15import abc
17from google.protobuf import duration_pb2
18from google.protobuf import timestamp_pb2
19from google.protobuf import field_mask_pb2
20from google.protobuf import struct_pb2
21from google.protobuf import wrappers_pb2
23from proto.marshal import compat
24from proto.marshal.collections import MapComposite
25from proto.marshal.collections import Repeated
26from proto.marshal.collections import RepeatedComposite
28from proto.marshal.rules import bytes as pb_bytes
29from proto.marshal.rules import stringy_numbers
30from proto.marshal.rules import dates
31from proto.marshal.rules import struct
32from proto.marshal.rules import wrappers
33from proto.marshal.rules import field_mask
34from proto.primitives import ProtoType
37class Rule(abc.ABC):
38 """Abstract class definition for marshal rules."""
40 @classmethod
41 def __subclasshook__(cls, C):
42 if hasattr(C, "to_python") and hasattr(C, "to_proto"):
43 return True
44 return NotImplemented
47class BaseMarshal:
48 """The base class to translate between protobuf and Python classes.
50 Protocol buffers defines many common types (e.g. Timestamp, Duration)
51 which also exist in the Python standard library. The marshal essentially
52 translates between these: it keeps a registry of common protocol buffers
53 and their Python representations, and translates back and forth.
55 The protocol buffer class is always the "key" in this relationship; when
56 presenting a message, the declared field types are used to determine
57 whether a value should be transformed into another class. Similarly,
58 when accepting a Python value (when setting a field, for example),
59 the declared field type is still used. This means that, if appropriate,
60 multiple protocol buffer types may use the same Python type.
62 The primary implementation of this is :class:`Marshal`, which should
63 usually be used instead of this class directly.
64 """
66 def __init__(self):
67 self._rules = {}
68 self._noop = NoopRule()
69 self.reset()
71 def register(self, proto_type: type, rule: Rule = None):
72 """Register a rule against the given ``proto_type``.
74 This function expects a ``proto_type`` (the descriptor class) and
75 a ``rule``; an object with a ``to_python`` and ``to_proto`` method.
76 Each method should return the appropriate Python or protocol buffer
77 type, and be idempotent (e.g. accept either type as input).
79 This function can also be used as a decorator::
81 @marshal.register(timestamp_pb2.Timestamp)
82 class TimestampRule:
83 ...
85 In this case, the class will be initialized for you with zero
86 arguments.
88 Args:
89 proto_type (type): A protocol buffer message type.
90 rule: A marshal object
91 """
92 # If a rule was provided, register it and be done.
93 if rule:
94 # Ensure the rule implements Rule.
95 if not isinstance(rule, Rule):
96 raise TypeError(
97 "Marshal rule instances must implement "
98 "`to_proto` and `to_python` methods."
99 )
101 # Register the rule.
102 self._rules[proto_type] = rule
103 return
105 # Create an inner function that will register an instance of the
106 # marshal class to this object's registry, and return it.
107 def register_rule_class(rule_class: type):
108 # Ensure the rule class is a valid rule.
109 if not issubclass(rule_class, Rule):
110 raise TypeError(
111 "Marshal rule subclasses must implement "
112 "`to_proto` and `to_python` methods."
113 )
115 # Register the rule class.
116 self._rules[proto_type] = rule_class()
117 return rule_class
119 return register_rule_class
121 def reset(self):
122 """Reset the registry to its initial state."""
123 self._rules.clear()
125 # Register date and time wrappers.
126 self.register(timestamp_pb2.Timestamp, dates.TimestampRule())
127 self.register(duration_pb2.Duration, dates.DurationRule())
129 # Register FieldMask wrappers.
130 self.register(field_mask_pb2.FieldMask, field_mask.FieldMaskRule())
132 # Register nullable primitive wrappers.
133 self.register(wrappers_pb2.BoolValue, wrappers.BoolValueRule())
134 self.register(wrappers_pb2.BytesValue, wrappers.BytesValueRule())
135 self.register(wrappers_pb2.DoubleValue, wrappers.DoubleValueRule())
136 self.register(wrappers_pb2.FloatValue, wrappers.FloatValueRule())
137 self.register(wrappers_pb2.Int32Value, wrappers.Int32ValueRule())
138 self.register(wrappers_pb2.Int64Value, wrappers.Int64ValueRule())
139 self.register(wrappers_pb2.StringValue, wrappers.StringValueRule())
140 self.register(wrappers_pb2.UInt32Value, wrappers.UInt32ValueRule())
141 self.register(wrappers_pb2.UInt64Value, wrappers.UInt64ValueRule())
143 # Register the google.protobuf.Struct wrappers.
144 #
145 # These are aware of the marshal that created them, because they
146 # create RepeatedComposite and MapComposite instances directly and
147 # need to pass the marshal to them.
148 self.register(struct_pb2.Value, struct.ValueRule(marshal=self))
149 self.register(struct_pb2.ListValue, struct.ListValueRule(marshal=self))
150 self.register(struct_pb2.Struct, struct.StructRule(marshal=self))
152 # Special case for bytes to allow base64 encode/decode
153 self.register(ProtoType.BYTES, pb_bytes.BytesRule())
155 # Special case for int64 from strings because of dict round trip.
156 # See https://github.com/protocolbuffers/protobuf/issues/2679
157 for rule_class in stringy_numbers.STRINGY_NUMBER_RULES:
158 self.register(rule_class._proto_type, rule_class())
160 def get_rule(self, proto_type):
161 # Rules are needed to convert values between proto-plus and pb.
162 # Retrieve the rule for the specified proto type.
163 # The NoopRule will be used when a rule is not found.
164 rule = self._rules.get(proto_type, self._noop)
166 # If we don't find a rule, also check under `_instances`
167 # in case there is a rule in another package.
168 # See https://github.com/googleapis/proto-plus-python/issues/349
169 if rule == self._noop and hasattr(self, "_instances"):
170 for _, instance in self._instances.items():
171 rule = instance._rules.get(proto_type, self._noop)
172 if rule != self._noop:
173 break
174 return rule
176 def to_python(self, proto_type, value, *, absent: bool = None):
177 # Internal protobuf has its own special type for lists of values.
178 # Return a view around it that implements MutableSequence.
179 value_type = type(value) # Minor performance boost over isinstance
180 if value_type in compat.repeated_composite_types:
181 return RepeatedComposite(value, marshal=self)
182 if value_type in compat.repeated_scalar_types:
183 if isinstance(proto_type, type):
184 return RepeatedComposite(value, marshal=self, proto_type=proto_type)
185 else:
186 return Repeated(value, marshal=self)
188 # Same thing for maps of messages.
189 # See https://github.com/protocolbuffers/protobuf/issues/16596
190 # We need to look up the name of the type in compat.map_composite_type_names
191 # as class `MessageMapContainer` is no longer exposed
192 # This is done to avoid taking a breaking change in proto-plus.
193 if (
194 value_type in compat.map_composite_types
195 or value_type.__name__ in compat.map_composite_type_names
196 ):
197 return MapComposite(value, marshal=self)
198 return self.get_rule(proto_type=proto_type).to_python(value, absent=absent)
200 def to_proto(self, proto_type, value, *, strict: bool = False):
201 # The protos in google/protobuf/struct.proto are exceptional cases,
202 # because they can and should represent themselves as lists and dicts.
203 # These cases are handled in their rule classes.
204 if proto_type not in (
205 struct_pb2.Value,
206 struct_pb2.ListValue,
207 struct_pb2.Struct,
208 ):
209 # For our repeated and map view objects, simply return the
210 # underlying pb.
211 if isinstance(value, (Repeated, MapComposite)):
212 return value.pb
214 # Convert lists and tuples recursively.
215 if isinstance(value, (list, tuple)):
216 return type(value)(self.to_proto(proto_type, i) for i in value)
218 # Convert dictionaries recursively when the proto type is a map.
219 # This is slightly more complicated than converting a list or tuple
220 # because we have to step through the magic that protocol buffers does.
221 #
222 # Essentially, a type of map<string, Foo> will show up here as
223 # a FoosEntry with a `key` field, `value` field, and a `map_entry`
224 # annotation. We need to do the conversion based on the `value`
225 # field's type.
226 if isinstance(value, dict) and (
227 proto_type.DESCRIPTOR.has_options
228 and proto_type.DESCRIPTOR.GetOptions().map_entry
229 ):
230 recursive_type = type(proto_type().value)
231 return {k: self.to_proto(recursive_type, v) for k, v in value.items()}
233 pb_value = self.get_rule(proto_type=proto_type).to_proto(value)
235 # Sanity check: If we are in strict mode, did we get the value we want?
236 if strict and not isinstance(pb_value, proto_type):
237 raise TypeError(
238 "Parameter must be instance of the same class; "
239 "expected {expected}, got {got}".format(
240 expected=proto_type.__name__,
241 got=pb_value.__class__.__name__,
242 ),
243 )
244 # Return the final value.
245 return pb_value
248class Marshal(BaseMarshal):
249 """The translator between protocol buffer and Python instances.
251 The bulk of the implementation is in :class:`BaseMarshal`. This class
252 adds identity tracking: multiple instantiations of :class:`Marshal` with
253 the same name will provide the same instance.
254 """
256 _instances = {}
258 def __new__(cls, *, name: str):
259 """Create a marshal instance.
261 Args:
262 name (str): The name of the marshal. Instantiating multiple
263 marshals with the same ``name`` argument will provide the
264 same marshal each time.
265 """
266 klass = cls._instances.get(name)
267 if klass is None:
268 klass = cls._instances[name] = super().__new__(cls)
270 return klass
272 def __init__(self, *, name: str):
273 """Instantiate a marshal.
275 Args:
276 name (str): The name of the marshal. Instantiating multiple
277 marshals with the same ``name`` argument will provide the
278 same marshal each time.
279 """
280 self._name = name
281 if not hasattr(self, "_rules"):
282 super().__init__()
285class NoopRule:
286 """A catch-all rule that does nothing."""
288 def to_python(self, pb_value, *, absent: bool = None):
289 return pb_value
291 def to_proto(self, value):
292 return value
295__all__ = ("Marshal",)