RFC: Do not mutate user-supplied condition context.

nucypher/network/server.py

@@ -167,10 +167,6 @@ def _make_rest_app(this_node, log: Logger) -> Flask:
         # zip capsules with their respective conditions
         packets = zip(reenc_request.capsules, lingo)
 
-        # Populate default request context for decentralized nodes
-        if not this_node.federated_only:
-            context.update({'providers': this_node.condition_providers})
-
         # TODO: Detect if we are dealing with PRE or tDec here
         # TODO: This is for PRE only, relocate HRAC to RE.context
         hrac = reenc_request.hrac
@@ -217,15 +213,11 @@ def _make_rest_app(this_node, log: Logger) -> Flask:
             return Response(message, status=HTTPStatus.BAD_REQUEST)
 
         # Enforce Reencryption Conditions
+        providers = this_node.condition_providers if not this_node.federated_only else dict()
         capsules_to_process = list()
         for capsule, lingo in packets:
             # raises an exception or continues
-            evaluate_conditions_for_ursula(
-                lingo=lingo,
-                context=context,
-                log=log,
-                ursula=this_node
-            )
+            evaluate_conditions_for_ursula(lingo=lingo, providers=providers, context=context)
             capsules_to_process.append((lingo, capsule))
 
         # Strip away conditions that have already been evaluated

nucypher/policy/conditions/_utils.py

@@ -1,9 +1,10 @@
 import json
 from http import HTTPStatus
-from typing import Union, Type, Dict
+from typing import Union, Type, Dict, Optional
 
 from flask import Response
 from marshmallow import Schema, post_dump
+from web3.providers import BaseProvider
 
 from nucypher.policy.conditions.base import ReencryptionCondition
 from nucypher.policy.conditions.context import (
@@ -11,8 +12,10 @@ from nucypher.policy.conditions.context import (
     InvalidContextVariableData,
     RequiredContextVariable,
 )
+from nucypher.utilities.logging import Logger
 
 _ETH = 'eth_'
+__LOGGER = Logger('condition-eval')
 
 
 def to_camelcase(s):
@@ -78,13 +81,21 @@ def _deserialize_condition_lingo(data: Union[str, Dict[str, str]]) -> Union['Ope
     return instance
 
 
-def evaluate_conditions_for_ursula(lingo, context, log, ursula):
+def evaluate_conditions_for_ursula(lingo: 'ConditionLingo',
+                                   providers: Optional[Dict[str, BaseProvider]] = None,
+                                   context: Optional[Dict[Union[str, int], Union[str, int]]] = None,
+                                   log: Logger = __LOGGER,
+                                   ) -> Response:
+
+    # avoid using a mutable defaults and support federated mode
+    context = context or dict()
+    providers = providers or dict()
+
     if lingo is not None:
-        # TODO: Enforce policy expiration as a condition
         # TODO: Evaluate all conditions even if one fails and report the result
         try:
             log.info(f'Evaluating access conditions {lingo.id}')
-            _results = lingo.eval(**context)
+            _results = lingo.eval(providers=providers, **context)
         except ReencryptionCondition.InvalidCondition as e:
             message = f"Incorrect value provided for condition: {e}"
             error = (message, HTTPStatus.BAD_REQUEST)

nucypher/policy/conditions/evm.py

@@ -93,9 +93,11 @@ def _resolve_any_context_variables(
 
 def _validate_chain(chain: int):
     if not isinstance(chain, int):
-        raise ValueError(f'"chain" must be a the integer of a chain ID (got "{chain}").')
+        raise ValueError(f'"The chain" field of c a condition must be the '
+                         f'integer of a chain ID (got "{chain}").')
     if chain not in _CONDITION_CHAINS:
-        raise RPCCondition.InvalidCondition(f'chain ID {chain} is not a permitted blockchain for condition evaluation.')
+        raise RPCCondition.InvalidCondition(f'chain ID {chain} is not a permitted '
+                                            f'blockchain for condition evaluation.')
 
 
 class RPCCondition(ReencryptionCondition):

nucypher/policy/conditions/lingo.py

@@ -21,7 +21,7 @@ import base64
 import json
 import operator as pyoperator
 from hashlib import md5
-from typing import Any, Dict, List, Union, Iterator, Optional
+from typing import Any, Dict, List, Union, Iterator
 
 from marshmallow import fields, post_load
 

tests/acceptance/blockchain/conditions/test_conditions.py

@@ -412,7 +412,6 @@ def test_single_retrieve_with_onchain_conditions(enacted_blockchain_policy, bloc
              "value": "10000000000000"
          }
         }
-
     ]
     messages, message_kits = _make_message_kits(enacted_blockchain_policy.public_key, conditions)
     policy_info_kwargs = dict(