[FELIX-6353] Constructor injection: activation with optional reference fails if service not available

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: scr-2.1.24
• Fix Version/s: scr-2.1.26
• Component/s: Declarative Services (SCR)
• Assignee: Tom Watson
• Reporter: Tobias Gunkel
• Created: 31/Oct/20 08:38
• Updated: 23/Feb/21 17:00
• Resolved: 04/Nov/20 22:04

Description

A service that uses constructor injection for an optional service will crash with an "activation failed" exception if the optional service is not available.
According to the OSGi R7 specification a "null" value should be injected instead.

Example:

@Activate
public SomeService(
  @Reference(cardinality = ReferenceCardinality.OPTIONAL)
  OptionalService optionalService)
{}

The above code works if an OptionalService instance is present but it fails and crashes if no OptionalService instance is present during activation time:

Error message in log:

ERROR : bundle optionalreferenceconstructor:0.1.0.. (1)[optionalreferenceconstructor.SomeService(0)] : Error during instantiation of the implementation object: Unable to get service for reference optionalService

Stack trace shown with scr:info:

State:        FAILED ACTIVATION
References:   (total 1)
  - optionalService: optionalreferenceconstructor.OptionalService SATISFIED 0..1 static
    target=(*) scope=bundle (no active bindings)
Failure:      java.lang.InstantiationException: Unable to get service for reference optionalService
java.lang.InstantiationException: Unable to get service for reference additionalSettingsStorage at org.apache.felix.scr.impl.inject.internal.ComponentConstructorImpl.newInstance(ComponentConstructorImpl.java:301) at org.apache.felix.scr.impl.manager.SingleComponentManager.createImplementationObject(SingleComponentManager.java:286) at org.apache.felix.scr.impl.manager.SingleComponentManager.createComponent(SingleComponentManager.java:115) at org.apache.felix.scr.impl.manager.SingleComponentManager.getService(SingleComponentManager.java:1000) at org.apache.felix.scr.impl.manager.SingleComponentManager.getServiceInternal(SingleComponentManager.java:973) at org.apache.felix.scr.impl.manager.AbstractComponentManager.activateInternal(AbstractComponentManager.java:785) at org.apache.felix.scr.impl.manager.DependencyManager$SingleStaticCustomizer.addedService(DependencyManager.java:1271) at org.apache.felix.scr.impl.manager.DependencyManager$SingleStaticCustomizer.addedService(DependencyManager.java:1222) at org.apache.felix.scr.impl.manager.ServiceTracker$Tracked.customizerAdded(ServiceTracker.java:1200) at org.apache.felix.scr.impl.manager.ServiceTracker$Tracked.customizerAdded(ServiceTracker.java:1121) at org.apache.felix.scr.impl.manager.ServiceTracker$AbstractTracked.trackAdding(ServiceTracker.java:928) at org.apache.felix.scr.impl.manager.ServiceTracker$AbstractTracked.track(ServiceTracker.java:864) at org.apache.felix.scr.impl.manager.ServiceTracker$Tracked.serviceChanged(ServiceTracker.java:1152) at org.apache.felix.scr.impl.BundleComponentActivator$ListenerInfo.serviceChanged(BundleComponentActivator.java:114) at org.apache.felix.framework.EventDispatcher.invokeServiceListenerCallback(EventDispatcher.java:990) at org.apache.felix.framework.EventDispatcher.fireEventImmediately(EventDispatcher.java:838) at org.apache.felix.framework.EventDispatcher.fireServiceEvent(EventDispatcher.java:545) at org.apache.felix.framework.Felix.fireServiceEvent(Felix.java:4833) at org.apache.felix.framework.Felix.registerService(Felix.java:3804) at org.apache.felix.framework.BundleContextImpl.registerService(BundleContextImpl.java:328) at
...

It seems that the ComponentConstructorImpl (line 301) does only check for multiple cardinality but not for optional cardinality.
Propably ComponentConstructorImpl.java (line 299) should be:

if ( !refMetadata.isMultiple())
{
	if ( !refMetadata.isOptional() && (ref == null) )
	{
		throw new InstantiationException("Unable to get service for reference " + refMetadata.getName());
	}
}

Instead of:

if ( !refMetadata.isMultiple())
{
	if ( ref == null )
	{
		throw new InstantiationException("Unable to get service for reference " + refMetadata.getName());
	}
}

The change is also attached a patch file. Please note that I did not have the opportunity to test the change. It might not fix the problem or cause other crashes.