bundles/org.eclipse.equinox.p2.repository/src/org/eclipse/equinox/internal/p2/repository/CacheManager.java - equinox/rt.equinox.p2 - Git at Google

 /*******************************************************************************
  * Copyright (c) 2008, 2012 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  *     IBM Corporation - initial API and implementation
  *     Cloudsmith Inc - additional implementation
  *     Sonatype Inc - additional implementation
  *******************************************************************************/
 package org.eclipse.equinox.internal.p2.repository;

 import java.io.*;
 import java.net.*;
 import java.util.EventObject;
 import java.util.HashSet;
 import org.eclipse.core.runtime.*;
 import org.eclipse.equinox.internal.p2.core.helpers.LogHelper;
 import org.eclipse.equinox.internal.provisional.p2.core.eventbus.IProvisioningEventBus;
 import org.eclipse.equinox.internal.provisional.p2.core.eventbus.SynchronousProvisioningListener;
 import org.eclipse.equinox.internal.provisional.p2.repository.IStateful;
 import org.eclipse.equinox.internal.provisional.p2.repository.RepositoryEvent;
 import org.eclipse.equinox.p2.core.IAgentLocation;
 import org.eclipse.equinox.p2.core.ProvisionException;
 import org.eclipse.equinox.p2.repository.IRepository;
 import org.eclipse.osgi.util.NLS;

 /**
  * A class to manage metadata cache files. Creating the cache files will place
  * the file in the AgentData location in a cache directory.
  *
  * Using the bus listeners will allow the manager to listen for repository
  * events. When a repository is removed, it will remove the cache file if one
  * was created for the repository.
  */
 public class CacheManager {
 	/**
 	 * Service name for the internal cache manager service.
 	 */
 	public static final String SERVICE_NAME = CacheManager.class.getName();

 	private final IAgentLocation agentLocation;

 	private final Transport transport;

 	/**
 	 * IStateful implementation of BufferedOutputStream. Class is used to get the status from
 	 * a download operation.
 	 */
 	private static class StatefulStream extends BufferedOutputStream implements IStateful {
 		private IStatus status;

 		public StatefulStream(OutputStream stream) {
 			super(stream);
 		}

 		public IStatus getStatus() {

 			return status;
 		}

 		public void setStatus(IStatus aStatus) {
 			status = aStatus;
 		}

 	}

 	public CacheManager(IAgentLocation agentLocation, Transport transport) {
 		this.agentLocation = agentLocation;
 		this.transport = transport;
 	}

 	private static SynchronousProvisioningListener busListener;
 	private static final String DOWNLOADING = "downloading"; //$NON-NLS-1$
 	private static final String JAR_EXTENSION = ".jar"; //$NON-NLS-1$
 	private static final String XML_EXTENSION = ".xml"; //$NON-NLS-1$

 	private final HashSet<String> knownPrefixes = new HashSet<String>(5);

 	/**
 	 * Returns a hash of the repository location.
 	 */
 	private int computeHash(URI repositoryLocation) {
 		return repositoryLocation.hashCode();
 	}

 	public File createCacheFromFile(URI remoteFile, IProgressMonitor monitor) throws ProvisionException, IOException {
 		if (!isURL(remoteFile)) {
 			throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_CannotLoadNonUrlLocation, remoteFile), null));
 		}

 		SubMonitor submonitor = SubMonitor.convert(monitor, 1000);
 		try {
 			File cacheFile = getCacheFile(remoteFile);

 			boolean stale = true;
 			long lastModified = cacheFile.lastModified();
 			long lastModifiedRemote = 0L;

 			// bug 269588 - server may return 0 when file exists, so extra flag is needed
 			try {
 				lastModifiedRemote = transport.getLastModified(remoteFile, submonitor.newChild(1));
 				if (lastModifiedRemote <= 0)
 					LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + remoteFile)); //$NON-NLS-1$
 			} catch (AuthenticationFailedException e) {
 				// it is not meaningful to continue - the credentials are for the server
 				// do not pass the exception - it gives no additional meaningful user information
 				throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, remoteFile), null));
 			} catch (CoreException e) {
 				// give up on a timeout - if we did not get a 404 on the jar, we will just prolong the pain
 				// by (almost certainly) also timing out on the xml.
 				if (e.getStatus() != null && e.getStatus().getException() != null) {
 					Throwable ex = e.getStatus().getException();
 					if (ex.getClass() == java.net.SocketTimeoutException.class)
 						throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_READ, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, remoteFile), ex));
 				}
 			} catch (OperationCanceledException e) {
 				// must pass this on
 				throw e;
 			} catch (Exception e) {
 				// not ideal, just skip the jar on error, and try the xml instead - report errors for
 				// the xml.
 			}

 			stale = lastModifiedRemote != lastModified;
 			if (!stale)
 				return cacheFile;

 			// The cache is stale or missing, so we need to update it from the remote location
 			updateCache(cacheFile, remoteFile, lastModifiedRemote, submonitor);
 			return cacheFile;
 		} finally {
 			submonitor.done();
 		}

 	}

 	/**
 	 * Returns a local cache file with the contents of the given remote location,
 	 * or <code>null</code> if a local cache could not be created.
 	 *
 	 * @param repositoryLocation The remote location to be cached
 	 * @param prefix The prefix to use when creating the cache file
 	 * @param monitor a progress monitor
 	 * @return A {@link File} object pointing to the cache file or <code>null</code>
 	 * if the location is not a repository.
 	 * @throws FileNotFoundException if neither jar nor xml index file exists at given location
 	 * @throws AuthenticationFailedException if jar not available and xml causes authentication fail
 	 * @throws IOException on general IO errors
 	 * @throws ProvisionException on any error (e.g. user cancellation, unknown host, malformed address, connection refused, etc.)
 	 * @throws OperationCanceledException - if user canceled
 	 */
 	public File createCache(URI repositoryLocation, String prefix, IProgressMonitor monitor) throws IOException, ProvisionException {
 		if (!isURL(repositoryLocation)) {
 			throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_CannotLoadNonUrlLocation, repositoryLocation), null));
 		}

 		SubMonitor submonitor = SubMonitor.convert(monitor, 1000);
 		try {
 			knownPrefixes.add(prefix);
 			File cacheFile = getCache(repositoryLocation, prefix);
 			URI jarLocation = URIUtil.append(repositoryLocation, prefix + JAR_EXTENSION);
 			URI xmlLocation = URIUtil.append(repositoryLocation, prefix + XML_EXTENSION);
 			int hashCode = computeHash(repositoryLocation);

 			// Knowing if cache is stale is complicated by the fact that a jar could have been
 			// produced after an xml index (and vice versa), and by the need to capture any
 			// errors, as these needs to be reported to the user as something meaningful - instead of
 			// just a general "can't read repository".
 			// (Previous impl of stale checking ignored errors, and caused multiple round-trips)
 			boolean stale = true;
 			long lastModified = 0L;
 			String name = null;
 			String useExtension = JAR_EXTENSION;
 			URI remoteFile = jarLocation;

 			if (cacheFile != null) {
 				lastModified = cacheFile.lastModified();
 				name = cacheFile.getName();
 			}
 			// get last modified on jar
 			long lastModifiedRemote = 0L;
 			// bug 269588 - server may return 0 when file exists, so extra flag is needed
 			boolean useJar = true;
 			try {
 				lastModifiedRemote = transport.getLastModified(jarLocation, submonitor.newChild(1));
 				if (lastModifiedRemote <= 0)
 					LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + jarLocation)); //$NON-NLS-1$
 			} catch (AuthenticationFailedException e) {
 				// it is not meaningful to continue - the credentials are for the server
 				// do not pass the exception - it gives no additional meaningful user information
 				throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, repositoryLocation), null));
 			} catch (CoreException e) {
 				useJar = false;
 				// give up on a timeout - if we did not get a 404 on the jar, we will just prolong the pain
 				// by (almost certainly) also timing out on the xml.
 				if (e.getStatus() != null && e.getStatus().getException() != null) {
 					Throwable ex = e.getStatus().getException();
 					if (ex.getClass() == java.net.SocketTimeoutException.class)
 						throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_READ, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, repositoryLocation), ex));
 				}
 			} catch (OperationCanceledException e) {
 				// must pass this on
 				throw e;
 			} catch (Exception e) {
 				// not ideal, just skip the jar on error, and try the xml instead - report errors for
 				// the xml.
 				useJar = false;
 			}
 			if (submonitor.isCanceled())
 				throw new OperationCanceledException();

 			if (useJar) {
 				// There is a jar, and it should be used - cache is stale if it is xml based or
 				// if older (irrespective of jar or xml).
 				// Bug 269588 - also stale if remote reports 0
 				stale = lastModifiedRemote != lastModified || (name != null && name.endsWith(XML_EXTENSION) || lastModifiedRemote <= 0);
 			} else {
 				// Also need to check remote XML file, and handle cancel, and errors
 				// (Status is reported based on finding the XML file as giving up on certain errors
 				// when checking for the jar may not be correct).
 				try {
 					lastModifiedRemote = transport.getLastModified(xmlLocation, submonitor.newChild(1));
 					// if lastModifiedRemote is 0 - something is wrong in the communication stack, as
 					// a FileNotFound exception should have been thrown.
 					// bug 269588 - server may return 0 when file exists - site is not correctly configured
 					if (lastModifiedRemote <= 0)
 						LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + xmlLocation)); //$NON-NLS-1$

 				} catch (FileNotFoundException e) {
 					throw new FileNotFoundException(NLS.bind(Messages.CacheManager_Neither_0_nor_1_found, jarLocation, xmlLocation));
 				} catch (AuthenticationFailedException e) {
 					// do not pass the exception, it provides no additional meaningful user information
 					throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, repositoryLocation), null));
 				} catch (CoreException e) {
 					IStatus status = e.getStatus();
 					if (status == null)
 						throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, repositoryLocation), e));
 					else if (status.getException() instanceof FileNotFoundException)
 						throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, status.getMessage(), status.getException()));
 					throw new ProvisionException(status);

 				}
 				// There is an xml, and it should be used - cache is stale if it is jar based or
 				// if older (irrespective of jar or xml).
 				// bug 269588 - server may return 0 when file exists - assume it is stale
 				stale = lastModifiedRemote != lastModified || (name != null && name.endsWith(JAR_EXTENSION) || lastModifiedRemote <= 0);
 				useExtension = XML_EXTENSION;
 				remoteFile = xmlLocation;
 			}

 			if (!stale)
 				return cacheFile;

 			// The cache is stale or missing, so we need to update it from the remote location
 			cacheFile = new File(getCacheDirectory(), prefix + hashCode + useExtension);
 			updateCache(cacheFile, remoteFile, lastModifiedRemote, submonitor);
 			return cacheFile;
 		} finally {
 			submonitor.done();
 		}
 	}

 	/**
 	 * Deletes the local cache file(s) for the given repository
 	 * @param repositoryLocation
 	 */
 	void deleteCache(URI repositoryLocation) {
 		for (String prefix : knownPrefixes) {
 			File[] cacheFiles = getCacheFiles(repositoryLocation, prefix);
 			for (int i = 0; i < cacheFiles.length; i++) {
 				// delete the cache file if it exists
 				safeDelete(cacheFiles[i]);
 				// delete a resumable download if it exists
 				safeDelete(new File(new File(cacheFiles[i].getParentFile(), DOWNLOADING), cacheFiles[i].getName()));
 			}
 		}
 	}

 	/**
 	 * Determines the local file path of the repository's cache file.
 	 * @param repositoryLocation The location to compute the cache for
 	 * @param prefix The prefix to use for this location
 	 * @return A {@link File} pointing to the cache file or <code>null</code> if
 	 * the cache file does not exist.
 	 */
 	protected File getCache(URI repositoryLocation, String prefix) {
 		File[] files = getCacheFiles(repositoryLocation, prefix);
 		if (files[0].exists())
 			return files[0];
 		return files[1].exists() ? files[1] : null;
 	}

 	/**
 	 * Returns the file corresponding to the data area to be used by the cache manager.
 	 */
 	protected File getCacheDirectory() {
 		return URIUtil.toFile(agentLocation.getDataArea(Activator.ID + "/cache/")); //$NON-NLS-1$
 	}

 	/**
 	 * Determines the local file paths of the repository's potential cache files.
 	 * @param repositoryLocation The location to compute the cache for
 	 * @param prefix The prefix to use for this location
 	 * @return A {@link File} array with the cache files for JAR and XML extensions.
 	 */
 	private File[] getCacheFiles(URI repositoryLocation, String prefix) {
 		File[] files = new File[2];
 		File dataAreaFile = getCacheDirectory();
 		int hashCode = computeHash(repositoryLocation);
 		files[0] = new File(dataAreaFile, prefix + hashCode + JAR_EXTENSION);
 		files[1] = new File(dataAreaFile, prefix + hashCode + XML_EXTENSION);
 		return files;
 	}

 	private File getCacheFile(URI url) {
 		File dataAreaFile = getCacheDirectory();
 		int hashCode = computeHash(url);
 		return new File(dataAreaFile, Integer.toString(hashCode));
 	}

 	private static boolean isURL(URI location) {
 		try {
 			new URL(location.toASCIIString());
 		} catch (MalformedURLException e) {
 			return false;
 		}
 		return true;
 	}

 	/**
 	 * Adds a {@link SynchronousProvisioningListener} to the event bus for
 	 * deleting cache files when the corresponding repository is deleted.
 	 */
 	private void registerRepoEventListener(IProvisioningEventBus eventBus) {
 		if (busListener == null) {
 			busListener = new SynchronousProvisioningListener() {
 				public void notify(EventObject o) {
 					if (o instanceof RepositoryEvent) {
 						RepositoryEvent event = (RepositoryEvent) o;
 						if (RepositoryEvent.REMOVED == event.getKind() && IRepository.TYPE_METADATA == event.getRepositoryType()) {
 							deleteCache(event.getRepositoryLocation());
 						}
 					}
 				}
 			};
 		}
 		// the bus could have disappeared and is now back again - so do this every time
 		eventBus.addListener(busListener);
 	}

 	private boolean safeDelete(File file) {
 		if (file.exists()) {
 			if (!file.delete()) {
 				file.deleteOnExit();
 				return true;
 			}
 		}
 		return false;
 	}

 	public void setEventBus(IProvisioningEventBus newBus) {
 		registerRepoEventListener(newBus);
 	}

 	public void unsetEventBus(IProvisioningEventBus oldBus) {
 		unregisterRepoEventListener(oldBus);
 	}

 	/**
 	 * Removes the {@link SynchronousProvisioningListener} that cleans up the
 	 * cache file from the event bus.
 	 */
 	private void unregisterRepoEventListener(IProvisioningEventBus bus) {
 		if (bus != null && busListener != null)
 			bus.removeListener(busListener);
 	}

 	protected void updateCache(File cacheFile, URI remoteFile, long lastModifiedRemote, SubMonitor submonitor) throws FileNotFoundException, IOException, ProvisionException {
 		cacheFile.getParentFile().mkdirs();
 		File downloadDir = new File(cacheFile.getParentFile(), DOWNLOADING);
 		if (!downloadDir.exists())
 			downloadDir.mkdir();
 		File tempFile = new File(downloadDir, cacheFile.getName());
 		// Ensure that the file from a previous download attempt is removed
 		if (tempFile.exists())
 			safeDelete(tempFile);

 		tempFile.createNewFile();

 		StatefulStream stream = null;
 		try {
 			stream = new StatefulStream(new FileOutputStream(tempFile));
 		} catch (Exception e) {
 			throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, e.getMessage(), e));
 		}
 		IStatus result = null;
 		try {
 			submonitor.setWorkRemaining(1000);
 			result = transport.download(remoteFile, stream, submonitor.newChild(1000));
 		} catch (OperationCanceledException e) {
 			// need to pick up the status - a new operation canceled exception is thrown at the end
 			// as status will be CANCEL.
 			result = stream.getStatus();
 		} finally {
 			stream.close();
 			// If there was any problem fetching the file, delete the temp file
 			if (result == null || !result.isOK())
 				safeDelete(tempFile);
 		}
 		if (result.isOK()) {
 			if (cacheFile.exists())
 				safeDelete(cacheFile);
 			if (tempFile.renameTo(cacheFile)) {
 				if (lastModifiedRemote != -1 && lastModifiedRemote != 0) {
 					//local cache file should have the same lastModified as the server's file. bug 324200
 					cacheFile.setLastModified(lastModifiedRemote);
 				}
 				return;
 			}
 			result = new Status(IStatus.ERROR, Activator.ID, NLS.bind(Messages.CacheManage_ErrorRenamingCache, new Object[] {remoteFile.toString(), tempFile.getAbsolutePath(), cacheFile.getAbsolutePath()}));
 		}

 		if (result.getSeverity() == IStatus.CANCEL || submonitor.isCanceled())
 			throw new OperationCanceledException();
 		throw new ProvisionException(result);
 	}
 }
	/*******************************************************************************
	* Copyright (c) 2008, 2012 IBM Corporation and others.
	* All rights reserved. This program and the accompanying materials
	* are made available under the terms of the Eclipse Public License v1.0
	* which accompanies this distribution, and is available at
	* http://www.eclipse.org/legal/epl-v10.html
	*
	* Contributors:
	* IBM Corporation - initial API and implementation
	* Cloudsmith Inc - additional implementation
	* Sonatype Inc - additional implementation
	*******************************************************************************/
	package org.eclipse.equinox.internal.p2.repository;

	import java.io.*;
	import java.net.*;
	import java.util.EventObject;
	import java.util.HashSet;
	import org.eclipse.core.runtime.*;
	import org.eclipse.equinox.internal.p2.core.helpers.LogHelper;
	import org.eclipse.equinox.internal.provisional.p2.core.eventbus.IProvisioningEventBus;
	import org.eclipse.equinox.internal.provisional.p2.core.eventbus.SynchronousProvisioningListener;
	import org.eclipse.equinox.internal.provisional.p2.repository.IStateful;
	import org.eclipse.equinox.internal.provisional.p2.repository.RepositoryEvent;
	import org.eclipse.equinox.p2.core.IAgentLocation;
	import org.eclipse.equinox.p2.core.ProvisionException;
	import org.eclipse.equinox.p2.repository.IRepository;
	import org.eclipse.osgi.util.NLS;

	/**
	* A class to manage metadata cache files. Creating the cache files will place
	* the file in the AgentData location in a cache directory.
	*
	* Using the bus listeners will allow the manager to listen for repository
	* events. When a repository is removed, it will remove the cache file if one
	* was created for the repository.
	*/
	public class CacheManager {
	/**
	* Service name for the internal cache manager service.
	*/
	public static final String SERVICE_NAME = CacheManager.class.getName();

	private final IAgentLocation agentLocation;

	private final Transport transport;

	/**
	* IStateful implementation of BufferedOutputStream. Class is used to get the status from
	* a download operation.
	*/
	private static class StatefulStream extends BufferedOutputStream implements IStateful {
	private IStatus status;

	public StatefulStream(OutputStream stream) {
	super(stream);
	}

	public IStatus getStatus() {

	return status;
	}

	public void setStatus(IStatus aStatus) {
	status = aStatus;
	}

	}

	public CacheManager(IAgentLocation agentLocation, Transport transport) {
	this.agentLocation = agentLocation;
	this.transport = transport;
	}

	private static SynchronousProvisioningListener busListener;
	private static final String DOWNLOADING = "downloading"; //$NON-NLS-1$
	private static final String JAR_EXTENSION = ".jar"; //$NON-NLS-1$
	private static final String XML_EXTENSION = ".xml"; //$NON-NLS-1$

	private final HashSet<String> knownPrefixes = new HashSet<String>(5);

	/**
	* Returns a hash of the repository location.
	*/
	private int computeHash(URI repositoryLocation) {
	return repositoryLocation.hashCode();
	}

	public File createCacheFromFile(URI remoteFile, IProgressMonitor monitor) throws ProvisionException, IOException {
	if (!isURL(remoteFile)) {
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_CannotLoadNonUrlLocation, remoteFile), null));
	}

	SubMonitor submonitor = SubMonitor.convert(monitor, 1000);
	try {
	File cacheFile = getCacheFile(remoteFile);

	boolean stale = true;
	long lastModified = cacheFile.lastModified();
	long lastModifiedRemote = 0L;

	// bug 269588 - server may return 0 when file exists, so extra flag is needed
	try {
	lastModifiedRemote = transport.getLastModified(remoteFile, submonitor.newChild(1));
	if (lastModifiedRemote <= 0)
	LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + remoteFile)); //$NON-NLS-1$
	} catch (AuthenticationFailedException e) {
	// it is not meaningful to continue - the credentials are for the server
	// do not pass the exception - it gives no additional meaningful user information
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, remoteFile), null));
	} catch (CoreException e) {
	// give up on a timeout - if we did not get a 404 on the jar, we will just prolong the pain
	// by (almost certainly) also timing out on the xml.
	if (e.getStatus() != null && e.getStatus().getException() != null) {
	Throwable ex = e.getStatus().getException();
	if (ex.getClass() == java.net.SocketTimeoutException.class)
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_READ, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, remoteFile), ex));
	}
	} catch (OperationCanceledException e) {
	// must pass this on
	throw e;
	} catch (Exception e) {
	// not ideal, just skip the jar on error, and try the xml instead - report errors for
	// the xml.
	}

	stale = lastModifiedRemote != lastModified;
	if (!stale)
	return cacheFile;

	// The cache is stale or missing, so we need to update it from the remote location
	updateCache(cacheFile, remoteFile, lastModifiedRemote, submonitor);
	return cacheFile;
	} finally {
	submonitor.done();
	}

	}

	/**
	* Returns a local cache file with the contents of the given remote location,
	* or <code>null</code> if a local cache could not be created.
	*
	* @param repositoryLocation The remote location to be cached
	* @param prefix The prefix to use when creating the cache file
	* @param monitor a progress monitor
	* @return A {@link File} object pointing to the cache file or <code>null</code>
	* if the location is not a repository.
	* @throws FileNotFoundException if neither jar nor xml index file exists at given location
	* @throws AuthenticationFailedException if jar not available and xml causes authentication fail
	* @throws IOException on general IO errors
	* @throws ProvisionException on any error (e.g. user cancellation, unknown host, malformed address, connection refused, etc.)
	* @throws OperationCanceledException - if user canceled
	*/
	public File createCache(URI repositoryLocation, String prefix, IProgressMonitor monitor) throws IOException, ProvisionException {
	if (!isURL(repositoryLocation)) {
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_CannotLoadNonUrlLocation, repositoryLocation), null));
	}

	SubMonitor submonitor = SubMonitor.convert(monitor, 1000);
	try {
	knownPrefixes.add(prefix);
	File cacheFile = getCache(repositoryLocation, prefix);
	URI jarLocation = URIUtil.append(repositoryLocation, prefix + JAR_EXTENSION);
	URI xmlLocation = URIUtil.append(repositoryLocation, prefix + XML_EXTENSION);
	int hashCode = computeHash(repositoryLocation);

	// Knowing if cache is stale is complicated by the fact that a jar could have been
	// produced after an xml index (and vice versa), and by the need to capture any
	// errors, as these needs to be reported to the user as something meaningful - instead of
	// just a general "can't read repository".
	// (Previous impl of stale checking ignored errors, and caused multiple round-trips)
	boolean stale = true;
	long lastModified = 0L;
	String name = null;
	String useExtension = JAR_EXTENSION;
	URI remoteFile = jarLocation;

	if (cacheFile != null) {
	lastModified = cacheFile.lastModified();
	name = cacheFile.getName();
	}
	// get last modified on jar
	long lastModifiedRemote = 0L;
	// bug 269588 - server may return 0 when file exists, so extra flag is needed
	boolean useJar = true;
	try {
	lastModifiedRemote = transport.getLastModified(jarLocation, submonitor.newChild(1));
	if (lastModifiedRemote <= 0)
	LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + jarLocation)); //$NON-NLS-1$
	} catch (AuthenticationFailedException e) {
	// it is not meaningful to continue - the credentials are for the server
	// do not pass the exception - it gives no additional meaningful user information
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, repositoryLocation), null));
	} catch (CoreException e) {
	useJar = false;
	// give up on a timeout - if we did not get a 404 on the jar, we will just prolong the pain
	// by (almost certainly) also timing out on the xml.
	if (e.getStatus() != null && e.getStatus().getException() != null) {
	Throwable ex = e.getStatus().getException();
	if (ex.getClass() == java.net.SocketTimeoutException.class)
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_READ, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, repositoryLocation), ex));
	}
	} catch (OperationCanceledException e) {
	// must pass this on
	throw e;
	} catch (Exception e) {
	// not ideal, just skip the jar on error, and try the xml instead - report errors for
	// the xml.
	useJar = false;
	}
	if (submonitor.isCanceled())
	throw new OperationCanceledException();

	if (useJar) {
	// There is a jar, and it should be used - cache is stale if it is xml based or
	// if older (irrespective of jar or xml).
	// Bug 269588 - also stale if remote reports 0
	stale = lastModifiedRemote != lastModified \|\| (name != null && name.endsWith(XML_EXTENSION) \|\| lastModifiedRemote <= 0);
	} else {
	// Also need to check remote XML file, and handle cancel, and errors
	// (Status is reported based on finding the XML file as giving up on certain errors
	// when checking for the jar may not be correct).
	try {
	lastModifiedRemote = transport.getLastModified(xmlLocation, submonitor.newChild(1));
	// if lastModifiedRemote is 0 - something is wrong in the communication stack, as
	// a FileNotFound exception should have been thrown.
	// bug 269588 - server may return 0 when file exists - site is not correctly configured
	if (lastModifiedRemote <= 0)
	LogHelper.log(new Status(IStatus.WARNING, Activator.ID, "Server returned lastModified <= 0 for " + xmlLocation)); //$NON-NLS-1$

	} catch (FileNotFoundException e) {
	throw new FileNotFoundException(NLS.bind(Messages.CacheManager_Neither_0_nor_1_found, jarLocation, xmlLocation));
	} catch (AuthenticationFailedException e) {
	// do not pass the exception, it provides no additional meaningful user information
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_FAILED_AUTHENTICATION, NLS.bind(Messages.CacheManager_AuthenticationFaileFor_0, repositoryLocation), null));
	} catch (CoreException e) {
	IStatus status = e.getStatus();
	if (status == null)
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, NLS.bind(Messages.CacheManager_FailedCommunicationWithRepo_0, repositoryLocation), e));
	else if (status.getException() instanceof FileNotFoundException)
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, ProvisionException.REPOSITORY_NOT_FOUND, status.getMessage(), status.getException()));
	throw new ProvisionException(status);

	}
	// There is an xml, and it should be used - cache is stale if it is jar based or
	// if older (irrespective of jar or xml).
	// bug 269588 - server may return 0 when file exists - assume it is stale
	stale = lastModifiedRemote != lastModified \|\| (name != null && name.endsWith(JAR_EXTENSION) \|\| lastModifiedRemote <= 0);
	useExtension = XML_EXTENSION;
	remoteFile = xmlLocation;
	}

	if (!stale)
	return cacheFile;

	// The cache is stale or missing, so we need to update it from the remote location
	cacheFile = new File(getCacheDirectory(), prefix + hashCode + useExtension);
	updateCache(cacheFile, remoteFile, lastModifiedRemote, submonitor);
	return cacheFile;
	} finally {
	submonitor.done();
	}
	}

	/**
	* Deletes the local cache file(s) for the given repository
	* @param repositoryLocation
	*/
	void deleteCache(URI repositoryLocation) {
	for (String prefix : knownPrefixes) {
	File[] cacheFiles = getCacheFiles(repositoryLocation, prefix);
	for (int i = 0; i < cacheFiles.length; i++) {
	// delete the cache file if it exists
	safeDelete(cacheFiles[i]);
	// delete a resumable download if it exists
	safeDelete(new File(new File(cacheFiles[i].getParentFile(), DOWNLOADING), cacheFiles[i].getName()));
	}
	}
	}

	/**
	* Determines the local file path of the repository's cache file.
	* @param repositoryLocation The location to compute the cache for
	* @param prefix The prefix to use for this location
	* @return A {@link File} pointing to the cache file or <code>null</code> if
	* the cache file does not exist.
	*/
	protected File getCache(URI repositoryLocation, String prefix) {
	File[] files = getCacheFiles(repositoryLocation, prefix);
	if (files[0].exists())
	return files[0];
	return files[1].exists() ? files[1] : null;
	}

	/**
	* Returns the file corresponding to the data area to be used by the cache manager.
	*/
	protected File getCacheDirectory() {
	return URIUtil.toFile(agentLocation.getDataArea(Activator.ID + "/cache/")); //$NON-NLS-1$
	}

	/**
	* Determines the local file paths of the repository's potential cache files.
	* @param repositoryLocation The location to compute the cache for
	* @param prefix The prefix to use for this location
	* @return A {@link File} array with the cache files for JAR and XML extensions.
	*/
	private File[] getCacheFiles(URI repositoryLocation, String prefix) {
	File[] files = new File[2];
	File dataAreaFile = getCacheDirectory();
	int hashCode = computeHash(repositoryLocation);
	files[0] = new File(dataAreaFile, prefix + hashCode + JAR_EXTENSION);
	files[1] = new File(dataAreaFile, prefix + hashCode + XML_EXTENSION);
	return files;
	}

	private File getCacheFile(URI url) {
	File dataAreaFile = getCacheDirectory();
	int hashCode = computeHash(url);
	return new File(dataAreaFile, Integer.toString(hashCode));
	}

	private static boolean isURL(URI location) {
	try {
	new URL(location.toASCIIString());
	} catch (MalformedURLException e) {
	return false;
	}
	return true;
	}

	/**
	* Adds a {@link SynchronousProvisioningListener} to the event bus for
	* deleting cache files when the corresponding repository is deleted.
	*/
	private void registerRepoEventListener(IProvisioningEventBus eventBus) {
	if (busListener == null) {
	busListener = new SynchronousProvisioningListener() {
	public void notify(EventObject o) {
	if (o instanceof RepositoryEvent) {
	RepositoryEvent event = (RepositoryEvent) o;
	if (RepositoryEvent.REMOVED == event.getKind() && IRepository.TYPE_METADATA == event.getRepositoryType()) {
	deleteCache(event.getRepositoryLocation());
	}
	}
	}
	};
	}
	// the bus could have disappeared and is now back again - so do this every time
	eventBus.addListener(busListener);
	}

	private boolean safeDelete(File file) {
	if (file.exists()) {
	if (!file.delete()) {
	file.deleteOnExit();
	return true;
	}
	}
	return false;
	}

	public void setEventBus(IProvisioningEventBus newBus) {
	registerRepoEventListener(newBus);
	}

	public void unsetEventBus(IProvisioningEventBus oldBus) {
	unregisterRepoEventListener(oldBus);
	}

	/**
	* Removes the {@link SynchronousProvisioningListener} that cleans up the
	* cache file from the event bus.
	*/
	private void unregisterRepoEventListener(IProvisioningEventBus bus) {
	if (bus != null && busListener != null)
	bus.removeListener(busListener);
	}

	protected void updateCache(File cacheFile, URI remoteFile, long lastModifiedRemote, SubMonitor submonitor) throws FileNotFoundException, IOException, ProvisionException {
	cacheFile.getParentFile().mkdirs();
	File downloadDir = new File(cacheFile.getParentFile(), DOWNLOADING);
	if (!downloadDir.exists())
	downloadDir.mkdir();
	File tempFile = new File(downloadDir, cacheFile.getName());
	// Ensure that the file from a previous download attempt is removed
	if (tempFile.exists())
	safeDelete(tempFile);

	tempFile.createNewFile();

	StatefulStream stream = null;
	try {
	stream = new StatefulStream(new FileOutputStream(tempFile));
	} catch (Exception e) {
	throw new ProvisionException(new Status(IStatus.ERROR, Activator.ID, e.getMessage(), e));
	}
	IStatus result = null;
	try {
	submonitor.setWorkRemaining(1000);
	result = transport.download(remoteFile, stream, submonitor.newChild(1000));
	} catch (OperationCanceledException e) {
	// need to pick up the status - a new operation canceled exception is thrown at the end
	// as status will be CANCEL.
	result = stream.getStatus();
	} finally {
	stream.close();
	// If there was any problem fetching the file, delete the temp file
	if (result == null \|\| !result.isOK())
	safeDelete(tempFile);
	}
	if (result.isOK()) {
	if (cacheFile.exists())
	safeDelete(cacheFile);
	if (tempFile.renameTo(cacheFile)) {
	if (lastModifiedRemote != -1 && lastModifiedRemote != 0) {
	//local cache file should have the same lastModified as the server's file. bug 324200
	cacheFile.setLastModified(lastModifiedRemote);
	}
	return;
	}
	result = new Status(IStatus.ERROR, Activator.ID, NLS.bind(Messages.CacheManage_ErrorRenamingCache, new Object[] {remoteFile.toString(), tempFile.getAbsolutePath(), cacheFile.getAbsolutePath()}));
	}

	if (result.getSeverity() == IStatus.CANCEL \|\| submonitor.isCanceled())
	throw new OperationCanceledException();
	throw new ProvisionException(result);
	}
	}