Merge pull request hyperledger#3010 from dbluhm/feature/soft-binding

feat: soft binding for plugin flexibility

aries_cloudagent/askar/profile.py

@@ -114,7 +114,7 @@ def bind_providers(self):
                 "aries_cloudagent.indy.credx.issuer.IndyCredxIssuer", ref(self)
             ),
         )
-        injector.bind_provider(
+        injector.soft_bind_provider(
             VCHolder,
             ClassProvider(
                 "aries_cloudagent.storage.vc_holder.askar.AskarVCHolder",

aries_cloudagent/config/injector.py

@@ -1,6 +1,6 @@
 """Standard Injector implementation."""
 
-from typing import Mapping, Optional, Type
+from typing import Dict, Mapping, Optional, Type
 
 from .base import BaseProvider, BaseInjector, InjectionError, InjectType
 from .provider import InstanceProvider, CachedProvider
@@ -18,7 +18,7 @@ def __init__(
     ):
         """Initialize an `Injector`."""
         self.enforce_typing = enforce_typing
-        self._providers = {}
+        self._providers: Dict[Type, BaseProvider] = {}
         self._settings = Settings(settings)
 
     @property
@@ -45,6 +45,24 @@ def bind_provider(
             provider = CachedProvider(provider)
         self._providers[base_cls] = provider
 
+    def soft_bind_instance(self, base_cls: Type[InjectType], instance: InjectType):
+        """Add a static instance as a soft class binding.
+
+        The binding occurs only if a provider for the same type does not already exist.
+        """
+        if not self.get_provider(base_cls):
+            self.bind_instance(base_cls, instance)
+
+    def soft_bind_provider(
+        self, base_cls: Type[InjectType], provider: BaseProvider, *, cache: bool = False
+    ):
+        """Add a dynamic instance resolver as a soft class binding.
+
+        The binding occurs only if a provider for the same type does not already exist.
+        """
+        if not self.get_provider(base_cls):
+            self.bind_provider(base_cls, provider, cache=cache)
+
     def clear_binding(self, base_cls: Type[InjectType]):
         """Remove a previously-added binding."""
         if base_cls in self._providers:

aries_cloudagent/config/tests/test_injector.py

@@ -70,6 +70,39 @@ def test_inject_provider(self):
         assert mock_provider.settings[self.test_key] == override_settings[self.test_key]
         assert mock_provider.injector is self.test_instance
 
+    def test_inject_soft_provider_bindings(self):
+        """Test injecting providers with soft binding."""
+        provider = MockProvider(self.test_value)
+        override = MockProvider("Override")
+
+        self.test_instance.soft_bind_provider(str, provider)
+        assert self.test_instance.inject(str) == self.test_value
+
+        self.test_instance.clear_binding(str)
+        # Bound by a plugin on startup, for example
+        self.test_instance.bind_provider(str, override)
+
+        # Bound later in Profile.bind_providerse
+        self.test_instance.soft_bind_provider(str, provider)
+
+        # We want the plugin value, not the Profile bound value
+        assert self.test_instance.inject(str) == "Override"
+
+    def test_inject_soft_instance_bindings(self):
+        """Test injecting providers with soft binding."""
+        self.test_instance.soft_bind_instance(str, self.test_value)
+        assert self.test_instance.inject(str) == self.test_value
+
+        self.test_instance.clear_binding(str)
+        # Bound by a plugin on startup, for example
+        self.test_instance.bind_instance(str, "Override")
+
+        # Bound later in Profile.bind_providerse
+        self.test_instance.soft_bind_instance(str, self.test_value)
+
+        # We want the plugin value, not the Profile bound value
+        assert self.test_instance.inject(str) == "Override"
+
     def test_bad_provider(self):
         """Test empty and invalid provider results."""
         self.test_instance.bind_provider(str, MockProvider(None))