/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  package org.eclipse.aether;
  
  import java.io.Closeable;
  import java.nio.file.Path;
  import java.util.Collection;
  import java.util.Map;
  import java.util.function.Supplier;
  
  import org.eclipse.aether.artifact.ArtifactTypeRegistry;
  import org.eclipse.aether.collection.DependencyGraphTransformer;
  import org.eclipse.aether.collection.DependencyManager;
  import org.eclipse.aether.collection.DependencySelector;
  import org.eclipse.aether.collection.DependencyTraverser;
  import org.eclipse.aether.collection.VersionFilter;
  import org.eclipse.aether.repository.AuthenticationSelector;
  import org.eclipse.aether.repository.LocalRepository;
  import org.eclipse.aether.repository.LocalRepositoryManager;
  import org.eclipse.aether.repository.MirrorSelector;
  import org.eclipse.aether.repository.ProxySelector;
  import org.eclipse.aether.repository.RemoteRepository;
  import org.eclipse.aether.repository.RepositoryPolicy;
  import org.eclipse.aether.repository.WorkspaceReader;
  import org.eclipse.aether.resolution.ArtifactDescriptorPolicy;
  import org.eclipse.aether.resolution.ResolutionErrorPolicy;
  import org.eclipse.aether.scope.ScopeManager;
  import org.eclipse.aether.scope.SystemDependencyScope;
  import org.eclipse.aether.transfer.TransferListener;
  
  /**
   * Defines settings and components that control the repository system. Once initialized, the session object itself is
   * supposed to be immutable and hence can safely be shared across an entire application and any concurrent threads
   * reading it. Components that wish to tweak some aspects of an existing session should use the copy constructor of
   * {@link DefaultRepositorySystemSession} and its mutators to derive a custom session.
   *
   * @noimplement This interface is not intended to be implemented by clients.
   * @noextend This interface is not intended to be extended by clients.
   */
  public interface RepositorySystemSession {
  
      /**
       * Immutable session that is closeable, should be handled as a resource. These session instances can be
       * created with {@link SessionBuilder}.
       *
       * @noimplement This interface is not intended to be implemented by clients.
       * @noextend This interface is not intended to be extended by clients.
       *
       * @since 2.0.0
       */
      interface CloseableSession extends RepositorySystemSession, Closeable {
          /**
           * Returns the ID of this closeable session instance. Each closeable session has different ID, unique within
           * repository system they were created with.
           *
           * @return The session ID that is never {@code null}.
           */
          String sessionId();
  
          /**
           * Closes the session. The session should be closed by its creator. A closed session should not be used anymore.
           * This method may be invoked multiple times, but close will act only once (first time).
           */
          @Override
          void close();
      }
  
      /**
       * Builder for building {@link CloseableSession} instances. Builder instances can be created with
       * {@link RepositorySystem#createSessionBuilder()} method. Instances are not thread-safe nor immutable.
       * <p>
       * Important: if you set a stateful member on builder (for example {@link SessionData} or {@link RepositoryCache}),
       * the builder will create session instances using same provided stateful members, that may lead to unexpected side
       * effects. Solution for these cases is to not reuse builder instances, or, keep reconfiguring it, or ultimately
       * provide suppliers that create new instance per each call.
       *
       * @noimplement This interface is not intended to be implemented by clients.
       * @noextend This interface is not intended to be extended by clients.
       *
       * @since 2.0.0
       */
      interface SessionBuilder {
          /**
          * Controls whether the repository system operates in offline mode and avoids/refuses any access to remote
          * repositories.
          *
          * @param offline {@code true} if the repository system is in offline mode, {@code false} otherwise.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setOffline(boolean offline);
 
         /**
          * Controls whether repositories declared in artifact descriptors should be ignored during transitive dependency
          * collection. If enabled, only the repositories originally provided with the collect request will be considered.
          *
          * @param ignoreArtifactDescriptorRepositories {@code true} to ignore additional repositories from artifact
          *                                             descriptors, {@code false} to merge those with the originally
          *                                             specified repositories.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setIgnoreArtifactDescriptorRepositories(boolean ignoreArtifactDescriptorRepositories);
 
         /**
          * Sets the policy which controls whether resolutions errors from remote repositories should be cached.
          *
          * @param resolutionErrorPolicy The resolution error policy for this session, may be {@code null} if resolution
          *                              errors should generally not be cached.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setResolutionErrorPolicy(ResolutionErrorPolicy resolutionErrorPolicy);
 
         /**
          * Sets the policy which controls how errors related to reading artifact descriptors should be handled.
          *
          * @param artifactDescriptorPolicy The descriptor error policy for this session, may be {@code null} if descriptor
          *                                 errors should generally not be tolerated.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setArtifactDescriptorPolicy(ArtifactDescriptorPolicy artifactDescriptorPolicy);
 
         /**
          * Sets the global checksum policy. If set, the global checksum policy overrides the checksum policies of the remote
          * repositories being used for resolution.
          *
          * @param checksumPolicy The global checksum policy, may be {@code null}/empty to apply the per-repository policies.
          * @return This session for chaining, never {@code null}.
          * @see RepositoryPolicy#CHECKSUM_POLICY_FAIL
          * @see RepositoryPolicy#CHECKSUM_POLICY_IGNORE
          * @see RepositoryPolicy#CHECKSUM_POLICY_WARN
          */
         SessionBuilder setChecksumPolicy(String checksumPolicy);
 
         /**
          * Sets the global update policy. If set, the global update policy overrides the update policies of the remote
          * repositories being used for resolution.
          * <p>
          * This method is meant for code that does not want to distinguish between artifact and metadata policies.
          * Note: applications should either use get/set updatePolicy (this method and
          * {@link RepositorySystemSession#getUpdatePolicy()}) or also distinguish between artifact and
          * metadata update policies (and use other methods), but <em>should not mix the two!</em>
          *
          * @param updatePolicy The global update policy, may be {@code null}/empty to apply the per-repository policies.
          * @return This session for chaining, never {@code null}.
          * @see RepositoryPolicy#UPDATE_POLICY_ALWAYS
          * @see RepositoryPolicy#UPDATE_POLICY_DAILY
          * @see RepositoryPolicy#UPDATE_POLICY_NEVER
          * @see #setArtifactUpdatePolicy(String)
          * @see #setMetadataUpdatePolicy(String)
          */
         SessionBuilder setUpdatePolicy(String updatePolicy);
 
         /**
          * Sets the global artifact update policy. If set, the global update policy overrides the artifact update policies
          * of the remote repositories being used for resolution.
          *
          * @param artifactUpdatePolicy The global update policy, may be {@code null}/empty to apply the per-repository policies.
          * @return This session for chaining, never {@code null}.
          * @see RepositoryPolicy#UPDATE_POLICY_ALWAYS
          * @see RepositoryPolicy#UPDATE_POLICY_DAILY
          * @see RepositoryPolicy#UPDATE_POLICY_NEVER
          * @since 2.0.0
          */
         SessionBuilder setArtifactUpdatePolicy(String artifactUpdatePolicy);
 
         /**
          * Sets the global metadata update policy. If set, the global update policy overrides the metadata update policies
          * of the remote repositories being used for resolution.
          *
          * @param metadataUpdatePolicy The global update policy, may be {@code null}/empty to apply the per-repository policies.
          * @return This session for chaining, never {@code null}.
          * @see RepositoryPolicy#UPDATE_POLICY_ALWAYS
          * @see RepositoryPolicy#UPDATE_POLICY_DAILY
          * @see RepositoryPolicy#UPDATE_POLICY_NEVER
          * @since 2.0.0
          */
         SessionBuilder setMetadataUpdatePolicy(String metadataUpdatePolicy);
 
         /**
          * Sets the local repository manager used during this session. <em>Note:</em> Eventually, a valid session must have
          * a local repository manager set.
          *
          * @param localRepositoryManager The local repository manager used during this session, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setLocalRepositoryManager(LocalRepositoryManager localRepositoryManager);
 
         /**
          * Sets the workspace reader used during this session. If set, the workspace reader will usually be consulted first
          * to resolve artifacts.
          *
          * @param workspaceReader The workspace reader for this session, may be {@code null} if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setWorkspaceReader(WorkspaceReader workspaceReader);
 
         /**
          * Sets the listener being notified of actions in the repository system.
          *
          * @param repositoryListener The repository listener, may be {@code null} if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setRepositoryListener(RepositoryListener repositoryListener);
 
         /**
          * Sets the listener being notified of uploads/downloads by the repository system.
          *
          * @param transferListener The transfer listener, may be {@code null} if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setTransferListener(TransferListener transferListener);
 
         /**
          * Sets the system properties to use, e.g. for processing of artifact descriptors. System properties are usually
          * collected from the runtime environment like {@link System#getProperties()} and environment variables.
          * <p>
          * <em>Note:</em> System properties are of type {@code Map<String, String>} and any key-value pair in the input map
          * that doesn't match this type will be silently ignored.
          *
          * @param systemProperties The system properties, may be {@code null} or empty if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setSystemProperties(Map<?, ?> systemProperties);
 
         /**
          * Sets the specified system property.
          *
          * @param key   The property key, must not be {@code null}.
          * @param value The property value, may be {@code null} to remove/unset the property.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setSystemProperty(String key, String value);
 
         /**
          * Sets the user properties to use, e.g. for processing of artifact descriptors. User properties are similar to
          * system properties but are set on the discretion of the user and hence are considered of higher priority than
          * system properties in case of conflicts.
          * <p>
          * <em>Note:</em> User properties are of type {@code Map<String, String>} and any key-value pair in the input map
          * that doesn't match this type will be silently ignored.
          *
          * @param userProperties The user properties, may be {@code null} or empty if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setUserProperties(Map<?, ?> userProperties);
 
         /**
          * Sets the specified user property.
          *
          * @param key   The property key, must not be {@code null}.
          * @param value The property value, may be {@code null} to remove/unset the property.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setUserProperty(String key, String value);
 
         /**
          * Sets the configuration properties used to tweak internal aspects of the repository system (e.g. thread pooling,
          * connector-specific behavior, etc.).
          * <p>
          * <em>Note:</em> Configuration properties are of type {@code Map<String, Object>} and any key-value pair in the
          * input map that doesn't match this type will be silently ignored.
          *
          * @param configProperties The configuration properties, may be {@code null} or empty if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setConfigProperties(Map<?, ?> configProperties);
 
         /**
          * Sets the specified configuration property.
          *
          * @param key   The property key, must not be {@code null}.
          * @param value The property value, may be {@code null} to remove/unset the property.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setConfigProperty(String key, Object value);
 
         /**
          * Sets the mirror selector to use for repositories discovered in artifact descriptors. Note that this selector is
          * not used for remote repositories which are passed as request parameters to the repository system, those
          * repositories are supposed to denote the effective repositories.
          *
          * @param mirrorSelector The mirror selector to use, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setMirrorSelector(MirrorSelector mirrorSelector);
 
         /**
          * Sets the proxy selector to use for repositories discovered in artifact descriptors. Note that this selector is
          * not used for remote repositories which are passed as request parameters to the repository system, those
          * repositories are supposed to have their proxy (if any) already set.
          *
          * @param proxySelector The proxy selector to use, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          * @see RemoteRepository#getProxy()
          */
         SessionBuilder setProxySelector(ProxySelector proxySelector);
 
         /**
          * Sets the authentication selector to use for repositories discovered in artifact descriptors. Note that this
          * selector is not used for remote repositories which are passed as request parameters to the repository system,
          * those repositories are supposed to have their authentication (if any) already set.
          *
          * @param authenticationSelector The authentication selector to use, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          * @see RemoteRepository#getAuthentication()
          */
         SessionBuilder setAuthenticationSelector(AuthenticationSelector authenticationSelector);
 
         /**
          * Sets the registry of artifact types recognized by this session.
          *
          * @param artifactTypeRegistry The artifact type registry, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setArtifactTypeRegistry(ArtifactTypeRegistry artifactTypeRegistry);
 
         /**
          * Sets the dependency traverser to use for building dependency graphs.
          *
          * @param dependencyTraverser The dependency traverser to use for building dependency graphs, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setDependencyTraverser(DependencyTraverser dependencyTraverser);
 
         /**
          * Sets the dependency manager to use for building dependency graphs.
          *
          * @param dependencyManager The dependency manager to use for building dependency graphs, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setDependencyManager(DependencyManager dependencyManager);
 
         /**
          * Sets the dependency selector to use for building dependency graphs.
          *
          * @param dependencySelector The dependency selector to use for building dependency graphs, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setDependencySelector(DependencySelector dependencySelector);
 
         /**
          * Sets the version filter to use for building dependency graphs.
          *
          * @param versionFilter The version filter to use for building dependency graphs, may be {@code null} to not filter
          *                      versions.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setVersionFilter(VersionFilter versionFilter);
 
         /**
          * Sets the dependency graph transformer to use for building dependency graphs.
          *
          * @param dependencyGraphTransformer The dependency graph transformer to use for building dependency graphs, may be
          *                                   {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setDependencyGraphTransformer(DependencyGraphTransformer dependencyGraphTransformer);
 
         /**
          * Sets the custom data associated with this session.
          * Note: When this method used to set instance, same passed instance will be used for every built session out
          * of this builder instance, hence the built sessions will share these instances as well!
          *
          * @param data The session data, may be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setData(SessionData data);
 
         /**
          * Sets the cache the repository system may use to save data for future reuse during the session.
          * Note: When this method used to set instance, same passed instance will be used for every built session out
          * of this builder instance, hence the built sessions will share these instances as well!
          *
          * @param cache The repository cache, may be {@code null} if none.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setCache(RepositoryCache cache);
 
         /**
          * Sets the scope manager for session, may be {@code null}.
          *
          * @param scopeManager The scope manager, may be {@code null}.
          * @return The session for chaining, never {@code null}.
          */
         SessionBuilder setScopeManager(ScopeManager scopeManager);
 
         /**
          * Adds on session ended handler to be immediately registered when this builder creates session.
          *
          * @param handler The on session ended handler, may not be {@code null}.
          * @return The session for chaining, never {@code null}.
          */
         SessionBuilder addOnSessionEndedHandler(Runnable handler);
 
         /**
          * Sets the custom session data supplier associated with this session.
          * Note: The supplier will be used for every built session out of this builder instance, so if supplier supplies
          * <em>same instance</em> the built sessions will share these instances as well!
          *
          * @param dataSupplier The session data supplier, may not be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setSessionDataSupplier(Supplier<SessionData> dataSupplier);
 
         /**
          * Sets the cache supplier for the repository system may use to save data for future reuse during the session.
          * Note: The supplier will be used for every built session out of this builder instance, so if supplier supplies
          * <em>same instance</em> the built sessions will share these instances as well!
          *
          * @param cacheSupplier The repository cache supplier, may not be {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder setRepositoryCacheSupplier(Supplier<RepositoryCache> cacheSupplier);
 
         /**
          * Shortcut method to set up local repository manager directly onto builder. There must be at least one non-null
          * {@link Path} passed in this method. In case multiple files, session builder will use chained local repository
          * manager.
          *
          * @param baseDirectories The local repository base directories.
          * @return This session for chaining, never {@code null}.
          * @see #withLocalRepositories(LocalRepository...)
          */
         SessionBuilder withLocalRepositoryBaseDirectories(Path... baseDirectories);
 
         /**
          * Shortcut method to set up local repository manager directly onto builder. There must be at least one non-null
          * {@link Path} present in passed in list. In case multiple files, session builder will use chained local
          * repository manager.
          *
          * @param baseDirectories The local repository base directories.
          * @return This session for chaining, never {@code null}.
          * @see #withLocalRepositories(Collection)
          */
         SessionBuilder withLocalRepositoryBaseDirectories(Collection<Path> baseDirectories);
 
         /**
          * Shortcut method to set up local repository manager directly onto builder. There must be at least one non-null
          * {@link LocalRepository} passed in this method. In case multiple local repositories, session builder will
          * use chained local repository manager.
          *
          * @param localRepositories The local repositories.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withLocalRepositories(LocalRepository... localRepositories);
 
         /**
          * Shortcut method to set up local repository manager directly onto builder. There must be at least one non-null
          * {@link LocalRepository} present in passed in list. In case multiple local repositories, session builder will
          * use chained local repository manager.
          *
          * @param localRepositories The local repositories.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withLocalRepositories(Collection<LocalRepository> localRepositories);
 
         /**
          * Adds the listeners to be notified of actions in the repository system.
          *
          * @param repositoryListeners The repository listeners, never {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withRepositoryListener(RepositoryListener... repositoryListeners);
 
         /**
          * Adds the listeners to be notified of actions in the repository system.
          *
          * @param repositoryListeners The repository listeners, never {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withRepositoryListener(Collection<RepositoryListener> repositoryListeners);
 
         /**
          * Adds the listener to be notified of uploads/downloads by the repository system.
          *
          * @param transferListeners The transfer listeners, never {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withTransferListener(TransferListener... transferListeners);
 
         /**
          * Adds the listener to be notified of uploads/downloads by the repository system.
          *
          * @param transferListeners The transfer listeners, never {@code null}.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withTransferListener(Collection<TransferListener> transferListeners);
 
         /**
          * Shortcut method to shallow-copy passed in session into current builder.
          *
          * @param session The session to shallow-copy from.
          * @return This session for chaining, never {@code null}.
          */
         SessionBuilder withRepositorySystemSession(RepositorySystemSession session);
 
         /**
          * Creates immutable closeable session out this builder instance.
          *
          * @return Immutable closeable session, never {@code null}.
          */
         CloseableSession build();
     }
 
     /**
      * Indicates whether the repository system operates in offline mode and avoids/refuses any access to remote
      * repositories.
      *
      * @return {@code true} if the repository system is in offline mode, {@code false} otherwise.
      */
     boolean isOffline();
 
     /**
      * Indicates whether repositories declared in artifact descriptors should be ignored during transitive dependency
      * collection. If enabled, only the repositories originally provided with the collect request will be considered.
      *
      * @return {@code true} if additional repositories from artifact descriptors are ignored, {@code false} to merge
      *         those with the originally specified repositories.
      */
     boolean isIgnoreArtifactDescriptorRepositories();
 
     /**
      * Gets the policy which controls whether resolutions errors from remote repositories should be cached.
      *
      * @return The resolution error policy for this session or {@code null} if resolution errors should generally not be
      *         cached.
      */
     ResolutionErrorPolicy getResolutionErrorPolicy();
 
     /**
      * Gets the policy which controls how errors related to reading artifact descriptors should be handled.
      *
      * @return The descriptor error policy for this session or {@code null} if descriptor errors should generally not be
      *         tolerated.
      */
     ArtifactDescriptorPolicy getArtifactDescriptorPolicy();
 
     /**
      * Gets the global checksum policy. If set, the global checksum policy overrides the checksum policies of the remote
      * repositories being used for resolution.
      *
      * @return The global checksum policy or {@code null}/empty if not set and the per-repository policies apply.
      * @see RepositoryPolicy#CHECKSUM_POLICY_FAIL
      * @see RepositoryPolicy#CHECKSUM_POLICY_IGNORE
      * @see RepositoryPolicy#CHECKSUM_POLICY_WARN
      */
     String getChecksumPolicy();
 
     /**
      * Gets the global update policy, or {@code null} if not set.
      * <p>
      * This method is meant for code that does not want to distinguish between artifact and metadata policies.
      * Note: applications should either use get/set updatePolicy (this method and
      * {@link DefaultRepositorySystemSession#setUpdatePolicy(String)}) or also distinguish between artifact and
      * metadata update policies (and use other methods), but <em>should not mix the two!</em>
      *
      * @see #getArtifactUpdatePolicy()
      * @see #getMetadataUpdatePolicy()
      */
     String getUpdatePolicy();
 
     /**
      * Gets the global artifact update policy. If set, the global update policy overrides the update policies of the
      * remote repositories being used for resolution.
      *
      * @return The global update policy or {@code null}/empty if not set and the per-repository policies apply.
      * @see RepositoryPolicy#UPDATE_POLICY_ALWAYS
      * @see RepositoryPolicy#UPDATE_POLICY_DAILY
      * @see RepositoryPolicy#UPDATE_POLICY_NEVER
      * @since 2.0.0
      */
     String getArtifactUpdatePolicy();
 
     /**
      * Gets the global metadata update policy. If set, the global update policy overrides the update policies of the remote
      * repositories being used for resolution.
      *
      * @return The global update policy or {@code null}/empty if not set and the per-repository policies apply.
      * @see RepositoryPolicy#UPDATE_POLICY_ALWAYS
      * @see RepositoryPolicy#UPDATE_POLICY_DAILY
      * @see RepositoryPolicy#UPDATE_POLICY_NEVER
      * @since 2.0.0
      */
     String getMetadataUpdatePolicy();
 
     /**
      * Gets the local repository used during this session. This is a convenience method for
      * {@link LocalRepositoryManager#getRepository()}.
      *
      * @return The local repository being during this session, never {@code null}.
      */
     LocalRepository getLocalRepository();
 
     /**
      * Gets the local repository manager used during this session.
      *
      * @return The local repository manager used during this session, never {@code null}.
      */
     LocalRepositoryManager getLocalRepositoryManager();
 
     /**
      * Gets the workspace reader used during this session. If set, the workspace reader will usually be consulted first
      * to resolve artifacts.
      *
      * @return The workspace reader for this session or {@code null} if none.
      */
     WorkspaceReader getWorkspaceReader();
 
     /**
      * Gets the listener being notified of actions in the repository system.
      *
      * @return The repository listener or {@code null} if none.
      */
     RepositoryListener getRepositoryListener();
 
     /**
      * Gets the listener being notified of uploads/downloads by the repository system.
      *
      * @return The transfer listener or {@code null} if none.
      */
     TransferListener getTransferListener();
 
     /**
      * Gets the system properties to use, e.g. for processing of artifact descriptors. System properties are usually
      * collected from the runtime environment like {@link System#getProperties()} and environment variables.
      *
      * @return The (read-only) system properties, never {@code null}.
      */
     Map<String, String> getSystemProperties();
 
     /**
      * Gets the user properties to use, e.g. for processing of artifact descriptors. User properties are similar to
      * system properties but are set on the discretion of the user and hence are considered of higher priority than
      * system properties.
      *
      * @return The (read-only) user properties, never {@code null}.
      */
     Map<String, String> getUserProperties();
 
     /**
      * Gets the configuration properties used to tweak internal aspects of the repository system (e.g. thread pooling,
      * connector-specific behavior, etc.)
      *
      * @return The (read-only) configuration properties, never {@code null}.
      * @see ConfigurationProperties
      */
     Map<String, Object> getConfigProperties();
 
     /**
      * Gets the mirror selector to use for repositories discovered in artifact descriptors. Note that this selector is
      * not used for remote repositories which are passed as request parameters to the repository system, those
      * repositories are supposed to denote the effective repositories.
      *
      * @return The mirror selector to use, never {@code null}.
      * @see RepositorySystem#newResolutionRepositories(RepositorySystemSession, java.util.List)
      */
     MirrorSelector getMirrorSelector();
 
     /**
      * Gets the proxy selector to use for repositories discovered in artifact descriptors. Note that this selector is
      * not used for remote repositories which are passed as request parameters to the repository system, those
      * repositories are supposed to have their proxy (if any) already set.
      *
      * @return The proxy selector to use, never {@code null}.
      * @see org.eclipse.aether.repository.RemoteRepository#getProxy()
      * @see RepositorySystem#newResolutionRepositories(RepositorySystemSession, java.util.List)
      */
     ProxySelector getProxySelector();
 
     /**
      * Gets the authentication selector to use for repositories discovered in artifact descriptors. Note that this
      * selector is not used for remote repositories which are passed as request parameters to the repository system,
      * those repositories are supposed to have their authentication (if any) already set.
      *
      * @return The authentication selector to use, never {@code null}.
      * @see org.eclipse.aether.repository.RemoteRepository#getAuthentication()
      * @see RepositorySystem#newResolutionRepositories(RepositorySystemSession, java.util.List)
      */
     AuthenticationSelector getAuthenticationSelector();
 
     /**
      * Gets the registry of artifact types recognized by this session, for instance when processing artifact
      * descriptors.
      *
      * @return The artifact type registry, never {@code null}.
      */
     ArtifactTypeRegistry getArtifactTypeRegistry();
 
     /**
      * Gets the dependency traverser to use for building dependency graphs.
      *
      * @return The dependency traverser to use for building dependency graphs or {@code null} if dependencies are
      *         unconditionally traversed.
      */
     DependencyTraverser getDependencyTraverser();
 
     /**
      * Gets the dependency manager to use for building dependency graphs.
      *
      * @return The dependency manager to use for building dependency graphs or {@code null} if dependency management is
      *         not performed.
      */
     DependencyManager getDependencyManager();
 
     /**
      * Gets the dependency selector to use for building dependency graphs.
      *
      * @return The dependency selector to use for building dependency graphs or {@code null} if dependencies are
      *         unconditionally included.
      */
     DependencySelector getDependencySelector();
 
     /**
      * Gets the version filter to use for building dependency graphs.
      *
      * @return The version filter to use for building dependency graphs or {@code null} if versions aren't filtered.
      */
     VersionFilter getVersionFilter();
 
     /**
      * Gets the dependency graph transformer to use for building dependency graphs.
      *
      * @return The dependency graph transformer to use for building dependency graphs or {@code null} if none.
      */
     DependencyGraphTransformer getDependencyGraphTransformer();
 
     /**
      * Gets the custom data associated with this session.
      *
      * @return The session data, never {@code null}.
      */
     SessionData getData();
 
     /**
      * Gets the cache the repository system may use to save data for future reuse during the session.
      *
      * @return The repository cache or {@code null} if none.
      */
     RepositoryCache getCache();
 
     /**
      * Returns the scope manager to be used in this session, may be {@code null} if not set.
      *
      * @return The scope manager or {@code null} if not set.
      * @since 2.0.0
      */
     ScopeManager getScopeManager();
 
     /**
      * Returns the system dependency scope.
      * <p>
      * Shorthand method for {@link ScopeManager#getSystemDependencyScope()}.
      * <p>
      * If {@link ScopeManager} is set, {@link #getScopeManager()} returns non-null value, the result of
      * {@link ScopeManager#getSystemDependencyScope()} is returned (that may be {@code null}). If no {@link ScopeManager}
      * if set, then {@link SystemDependencyScope#LEGACY} instance is returned, as lack of scope manager means that
      * resolver operates in "legacy" mode (Maven3 compatible mode).
      *
      * @return The system dependency scope or {@code null} if no such scope.
      * @since 2.0.0
      */
     SystemDependencyScope getSystemDependencyScope();
 
     /**
      * Registers a handler to execute when this session closed.
      * <p>
      * Note: Resolver 1.x sessions will not be able to register handlers. Migrate to Resolver 2.x way of handling
      * sessions to make full use of new features. New features (like HTTP/2 transport) depend on this functionality.
      * While they will function with Resolver 1.x sessions, they may produce resource leaks.
      *
      * @param handler the handler, never {@code null}.
      * @return {@code true} if handler successfully registered, {@code false} otherwise.
      * @since 2.0.0
      */
     boolean addOnSessionEndedHandler(Runnable handler);
 }