[MRESOLVER-19] DefaultRepositorySystem resolveDependencies() can yield a NullPointerException

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Maven Artifact Resolver 1.0.3
• Fix Version/s: Maven Artifact Resolver 1.1.0
• Component/s: Resolver
• Assignee: Christian Schulte
• Reporter: Laird Nelson
• Created: 17/Mar/17 18:14
• Updated: 17/Mar/17 21:15
• Resolved: 17/Mar/17 21:08

Description

If a transfer of an artifact fails, then a NullPointerException is thrown.

Starting from line 366:

ArtifactRequestBuilder builder = new ArtifactRequestBuilder( trace );
DependencyFilter filter = request.getFilter();
DependencyVisitor visitor = ( filter != null ) ? new FilteringDependencyVisitor( builder, filter ) : builder;
visitor = new TreeDependencyVisitor( visitor );
result.getRoot().accept( visitor ); // <-- if getRoot() is null: kaboom!
List<ArtifactRequest> requests = builder.getRequests();

This is the relevant section of my code that causes the error:

final CollectRequest collectRequest = new CollectRequest();
collectRequest.setRoot(new Dependency(artifact, JavaScopes.COMPILE));
collectRequest.setRepositories(Collections.singletonList(mavenCentral));

final DependencyRequest dependencyRequest = new DependencyRequest(collectRequest, classpathFilter);
final DependencyResult dependencyResult = repositorySystem.resolveDependencies(repositorySystemSession, dependencyRequest);

From looking inside DefaultRepositorySystem.java, it looks like the collection result never gets its root set. At line 340 and following you see this:

if ( request.getRoot() != null )
{
    result.setRoot( request.getRoot() );
}
else if ( request.getCollectRequest() != null )
{
    CollectResult collectResult;
    try
    {
        request.getCollectRequest().setTrace( trace );
        collectResult = dependencyCollector.collectDependencies( session, request.getCollectRequest() );
    }
    catch ( DependencyCollectionException e )
    {
        dce = e;
        collectResult = e.getResult();
    }
    result.setRoot( collectResult.getRoot() );
    result.setCycles( collectResult.getCycles() );
    result.setCollectExceptions( collectResult.getExceptions() );
}

Note in particular this line:

result.setRoot( collectResult.getRoot() );

Unless I'm missing something there's no guarantee that collectResult.getRoot() will be non-null if the collection request failed.