/*
    * Copyright (C) 2008-2009, Google Inc.
    * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
    * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
    * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
   * accompanies this distribution, is reproduced below, and is
   * available at http://www.eclipse.org/org/documents/edl-v10.php
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.transport;
  
  import static org.eclipse.jgit.lib.RefDatabase.ALL;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.OutputStream;
  import java.io.PrintStream;
  import java.lang.ref.WeakReference;
  import java.lang.reflect.Field;
  import java.lang.reflect.Modifier;
  import java.net.URISyntaxException;
  import java.net.URL;
  import java.text.MessageFormat;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.Vector;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  import org.eclipse.jgit.api.errors.AbortedByHookException;
  import org.eclipse.jgit.errors.NotSupportedException;
  import org.eclipse.jgit.errors.TransportException;
  import org.eclipse.jgit.hooks.Hooks;
  import org.eclipse.jgit.hooks.PrePushHook;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectChecker;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.storage.pack.PackConfig;
  
  /**
   * Connects two Git repositories together and copies objects between them.
   * <p>
   * A transport can be used for either fetching (copying objects into the
   * caller's repository from the remote repository) or pushing (copying objects
   * into the remote repository from the caller's repository). Each transport
   * implementation is responsible for the details associated with establishing
   * the network connection(s) necessary for the copy, as well as actually
   * shuffling data back and forth.
   * <p>
   * Transport instances and the connections they create are not thread-safe.
  * Callers must ensure a transport is accessed by only one thread at a time.
  */
 public abstract class Transport implements AutoCloseable {
 	/** Type of operation a Transport is being opened for. */
 	public enum Operation {
 		/** Transport is to fetch objects locally. */
 		FETCH,
 		/** Transport is to push objects remotely. */
 		PUSH;
 	}
 
 	private static final List<WeakReference<TransportProtocol>> protocols =
 		new CopyOnWriteArrayList<>();
 
 	static {
 		// Registration goes backwards in order of priority.
 		register(TransportLocal.PROTO_LOCAL);
 		register(TransportBundleFile.PROTO_BUNDLE);
 		register(TransportAmazonS3.PROTO_S3);
 		register(TransportGitAnon.PROTO_GIT);
 		register(TransportSftp.PROTO_SFTP);
 		register(TransportHttp.PROTO_FTP);
 		register(TransportHttp.PROTO_HTTP);
 		register(TransportGitSsh.PROTO_SSH);
 
 		registerByService();
 	}
 
 	private static void registerByService() {
 		ClassLoader ldr = Thread.currentThread().getContextClassLoader();
 		if (ldr == null)
 			ldr = Transport.class.getClassLoader();
 		Enumeration<URL> catalogs = catalogs(ldr);
 		while (catalogs.hasMoreElements())
 			scan(ldr, catalogs.nextElement());
 	}
 
 	private static Enumeration<URL> catalogs(ClassLoader ldr) {
 		try {
 			String prefix = "META-INF/services/"; //$NON-NLS-1$
 			String name = prefix + Transport.class.getName();
 			return ldr.getResources(name);
 		} catch (IOException err) {
 			return new Vector<URL>().elements();
 		}
 	}
 
 	private static void scan(ClassLoader ldr, URL url) {
 		BufferedReader br;
 		try {
 			InputStream urlIn = url.openStream();
 			br = new BufferedReader(new InputStreamReader(urlIn, "UTF-8")); //$NON-NLS-1$
 		} catch (IOException err) {
 			// If we cannot read from the service list, go to the next.
 			//
 			return;
 		}
 
 		try {
 			String line;
 			while ((line = br.readLine()) != null) {
 				line = line.trim();
 				if (line.length() == 0)
 					continue;
 				int comment = line.indexOf('#');
 				if (comment == 0)
 					continue;
 				if (comment != -1)
 					line = line.substring(0, comment).trim();
 				load(ldr, line);
 			}
 		} catch (IOException err) {
 			// If we failed during a read, ignore the error.
 			//
 		} finally {
 			try {
 				br.close();
 			} catch (IOException e) {
 				// Ignore the close error; we are only reading.
 			}
 		}
 	}
 
 	private static void load(ClassLoader ldr, String cn) {
 		Class<?> clazz;
 		try {
 			clazz = Class.forName(cn, false, ldr);
 		} catch (ClassNotFoundException notBuiltin) {
 			// Doesn't exist, even though the service entry is present.
 			//
 			return;
 		}
 
 		for (Field f : clazz.getDeclaredFields()) {
 			if ((f.getModifiers() & Modifier.STATIC) == Modifier.STATIC
 					&& TransportProtocol.class.isAssignableFrom(f.getType())) {
 				TransportProtocol proto;
 				try {
 					proto = (TransportProtocol) f.get(null);
 				} catch (IllegalArgumentException e) {
 					// If we cannot access the field, don't.
 					continue;
 				} catch (IllegalAccessException e) {
 					// If we cannot access the field, don't.
 					continue;
 				}
 				if (proto != null)
 					register(proto);
 			}
 		}
 	}
 
 	/**
 	 * Register a TransportProtocol instance for use during open.
 	 * <p>
 	 * Protocol definitions are held by WeakReference, allowing them to be
 	 * garbage collected when the calling application drops all strongly held
 	 * references to the TransportProtocol. Therefore applications should use a
 	 * singleton pattern as described in {@link TransportProtocol}'s class
 	 * documentation to ensure their protocol does not get disabled by garbage
 	 * collection earlier than expected.
 	 * <p>
 	 * The new protocol is registered in front of all earlier protocols, giving
 	 * it higher priority than the built-in protocol definitions.
 	 *
 	 * @param proto
 	 *            the protocol definition. Must not be null.
 	 */
 	public static void register(TransportProtocol proto) {
 		protocols.add(0, new WeakReference<>(proto));
 	}
 
 	/**
 	 * Unregister a TransportProtocol instance.
 	 * <p>
 	 * Unregistering a protocol usually isn't necessary, as protocols are held
 	 * by weak references and will automatically clear when they are garbage
 	 * collected by the JVM. Matching is handled by reference equality, so the
 	 * exact reference given to {@link #register(TransportProtocol)} must be
 	 * used.
 	 *
 	 * @param proto
 	 *            the exact object previously given to register.
 	 */
 	public static void unregister(TransportProtocol proto) {
 		for (WeakReference<TransportProtocol> ref : protocols) {
 			TransportProtocol refProto = ref.get();
 			if (refProto == null || refProto == proto)
 				protocols.remove(ref);
 		}
 	}
 
 	/**
 	 * Obtain a copy of the registered protocols.
 	 *
 	 * @return an immutable copy of the currently registered protocols.
 	 */
 	public static List<TransportProtocol> getTransportProtocols() {
 		int cnt = protocols.size();
 		List<TransportProtocol> res = new ArrayList<>(cnt);
 		for (WeakReference<TransportProtocol> ref : protocols) {
 			TransportProtocol proto = ref.get();
 			if (proto != null)
 				res.add(proto);
 			else
 				protocols.remove(ref);
 		}
 		return Collections.unmodifiableList(res);
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 * <p>
 	 * This method assumes {@link Operation#FETCH}.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param remote
 	 *            location of the remote repository - may be URI or remote
 	 *            configuration name.
 	 * @return the new transport instance. Never null. In case of multiple URIs
 	 *         in remote configuration, only the first is chosen.
 	 * @throws URISyntaxException
 	 *             the location is not a remote defined in the configuration
 	 *             file and is not a well-formed URL.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static Transport open(final Repository local, final String remote)
 			throws NotSupportedException, URISyntaxException,
 			TransportException {
 		return open(local, remote, Operation.FETCH);
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param remote
 	 *            location of the remote repository - may be URI or remote
 	 *            configuration name.
 	 * @param op
 	 *            planned use of the returned Transport; the URI may differ
 	 *            based on the type of connection desired.
 	 * @return the new transport instance. Never null. In case of multiple URIs
 	 *         in remote configuration, only the first is chosen.
 	 * @throws URISyntaxException
 	 *             the location is not a remote defined in the configuration
 	 *             file and is not a well-formed URL.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static Transport open(final Repository local, final String remote,
 			final Operation op) throws NotSupportedException,
 			URISyntaxException, TransportException {
 		if (local != null) {
 			final RemoteConfig cfg = new RemoteConfig(local.getConfig(), remote);
 			if (doesNotExist(cfg))
 				return open(local, new URIish(remote), null);
 			return open(local, cfg, op);
 		} else
 			return open(new URIish(remote));
 
 	}
 
 	/**
 	 * Open new transport instances to connect two repositories.
 	 * <p>
 	 * This method assumes {@link Operation#FETCH}.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param remote
 	 *            location of the remote repository - may be URI or remote
 	 *            configuration name.
 	 * @return the list of new transport instances for every URI in remote
 	 *         configuration.
 	 * @throws URISyntaxException
 	 *             the location is not a remote defined in the configuration
 	 *             file and is not a well-formed URL.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static List<Transport> openAll(final Repository local,
 			final String remote) throws NotSupportedException,
 			URISyntaxException, TransportException {
 		return openAll(local, remote, Operation.FETCH);
 	}
 
 	/**
 	 * Open new transport instances to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param remote
 	 *            location of the remote repository - may be URI or remote
 	 *            configuration name.
 	 * @param op
 	 *            planned use of the returned Transport; the URI may differ
 	 *            based on the type of connection desired.
 	 * @return the list of new transport instances for every URI in remote
 	 *         configuration.
 	 * @throws URISyntaxException
 	 *             the location is not a remote defined in the configuration
 	 *             file and is not a well-formed URL.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static List<Transport> openAll(final Repository local,
 			final String remote, final Operation op)
 			throws NotSupportedException, URISyntaxException,
 			TransportException {
 		final RemoteConfig cfg = new RemoteConfig(local.getConfig(), remote);
 		if (doesNotExist(cfg)) {
 			final ArrayList<Transport> transports = new ArrayList<>(1);
 			transports.add(open(local, new URIish(remote), null));
 			return transports;
 		}
 		return openAll(local, cfg, op);
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 * <p>
 	 * This method assumes {@link Operation#FETCH}.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param cfg
 	 *            configuration describing how to connect to the remote
 	 *            repository.
 	 * @return the new transport instance. Never null. In case of multiple URIs
 	 *         in remote configuration, only the first is chosen.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 * @throws IllegalArgumentException
 	 *             if provided remote configuration doesn't have any URI
 	 *             associated.
 	 */
 	public static Transport open(final Repository local, final RemoteConfig cfg)
 			throws NotSupportedException, TransportException {
 		return open(local, cfg, Operation.FETCH);
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param cfg
 	 *            configuration describing how to connect to the remote
 	 *            repository.
 	 * @param op
 	 *            planned use of the returned Transport; the URI may differ
 	 *            based on the type of connection desired.
 	 * @return the new transport instance. Never null. In case of multiple URIs
 	 *         in remote configuration, only the first is chosen.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 * @throws IllegalArgumentException
 	 *             if provided remote configuration doesn't have any URI
 	 *             associated.
 	 */
 	public static Transport open(final Repository local,
 			final RemoteConfig cfg, final Operation op)
 			throws NotSupportedException, TransportException {
 		final List<URIish> uris = getURIs(cfg, op);
 		if (uris.isEmpty())
 			throw new IllegalArgumentException(MessageFormat.format(
 					JGitText.get().remoteConfigHasNoURIAssociated, cfg.getName()));
 		final Transport tn = open(local, uris.get(0), cfg.getName());
 		tn.applyConfig(cfg);
 		return tn;
 	}
 
 	/**
 	 * Open new transport instances to connect two repositories.
 	 * <p>
 	 * This method assumes {@link Operation#FETCH}.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param cfg
 	 *            configuration describing how to connect to the remote
 	 *            repository.
 	 * @return the list of new transport instances for every URI in remote
 	 *         configuration.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static List<Transport> openAll(final Repository local,
 			final RemoteConfig cfg) throws NotSupportedException,
 			TransportException {
 		return openAll(local, cfg, Operation.FETCH);
 	}
 
 	/**
 	 * Open new transport instances to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param cfg
 	 *            configuration describing how to connect to the remote
 	 *            repository.
 	 * @param op
 	 *            planned use of the returned Transport; the URI may differ
 	 *            based on the type of connection desired.
 	 * @return the list of new transport instances for every URI in remote
 	 *         configuration.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static List<Transport> openAll(final Repository local,
 			final RemoteConfig cfg, final Operation op)
 			throws NotSupportedException, TransportException {
 		final List<URIish> uris = getURIs(cfg, op);
 		final List<Transport> transports = new ArrayList<>(uris.size());
 		for (final URIish uri : uris) {
 			final Transport tn = open(local, uri, cfg.getName());
 			tn.applyConfig(cfg);
 			transports.add(tn);
 		}
 		return transports;
 	}
 
 	private static List<URIish> getURIs(final RemoteConfig cfg,
 			final Operation op) {
 		switch (op) {
 		case FETCH:
 			return cfg.getURIs();
 		case PUSH: {
 			List<URIish> uris = cfg.getPushURIs();
 			if (uris.isEmpty())
 				uris = cfg.getURIs();
 			return uris;
 		}
 		default:
 			throw new IllegalArgumentException(op.toString());
 		}
 	}
 
 	private static boolean doesNotExist(final RemoteConfig cfg) {
 		return cfg.getURIs().isEmpty() && cfg.getPushURIs().isEmpty();
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param uri
 	 *            location of the remote repository.
 	 * @return the new transport instance. Never null.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static Transport open(final Repository local, final URIish uri)
 			throws NotSupportedException, TransportException {
 		return open(local, uri, null);
 	}
 
 	/**
 	 * Open a new transport instance to connect two repositories.
 	 *
 	 * @param local
 	 *            existing local repository.
 	 * @param uri
 	 *            location of the remote repository.
 	 * @param remoteName
 	 *            name of the remote, if the remote as configured in
 	 *            {@code local}; otherwise null.
 	 * @return the new transport instance. Never null.
 	 * @throws NotSupportedException
 	 *             the protocol specified is not supported.
 	 * @throws TransportException
 	 *             the transport cannot open this URI.
 	 */
 	public static Transport open(Repository local, URIish uri, String remoteName)
 			throws NotSupportedException, TransportException {
 		for (WeakReference<TransportProtocol> ref : protocols) {
 			TransportProtocol proto = ref.get();
 			if (proto == null) {
 				protocols.remove(ref);
 				continue;
 			}
 
 			if (proto.canHandle(uri, local, remoteName)) {
 				Transport tn = proto.open(uri, local, remoteName);
 				tn.prePush = Hooks.prePush(local, tn.hookOutRedirect);
 				tn.prePush.setRemoteLocation(uri.toString());
 				tn.prePush.setRemoteName(remoteName);
 				return tn;
 			}
 		}
 
 		throw new NotSupportedException(MessageFormat.format(JGitText.get().URINotSupported, uri));
 	}
 
 	/**
 	 * Open a new transport with no local repository.
 	 * <p>
 	 * Note that the resulting transport instance can not be used for fetching
 	 * or pushing, but only for reading remote refs.
 	 *
 	 * @param uri
 	 * @return new Transport instance
 	 * @throws NotSupportedException
 	 * @throws TransportException
 	 */
 	public static Transport open(URIish uri) throws NotSupportedException, TransportException {
 		for (WeakReference<TransportProtocol> ref : protocols) {
 			TransportProtocol proto = ref.get();
 			if (proto == null) {
 				protocols.remove(ref);
 				continue;
 			}
 
 			if (proto.canHandle(uri, null, null))
 				return proto.open(uri);
 		}
 
 		throw new NotSupportedException(MessageFormat.format(JGitText.get().URINotSupported, uri));
 	}
 
 	/**
 	 * Convert push remote refs update specification from {@link RefSpec} form
 	 * to {@link RemoteRefUpdate}. Conversion expands wildcards by matching
 	 * source part to local refs. expectedOldObjectId in RemoteRefUpdate is
 	 * set when specified in leases. Tracking branch is configured if RefSpec
 	 * destination matches source of any fetch ref spec for this transport
 	 * remote configuration.
 	 *
 	 * @param db
 	 *            local database.
 	 * @param specs
 	 *            collection of RefSpec to convert.
 	 * @param leases
 	 *            map from ref to lease (containing expected old object id)
 	 * @param fetchSpecs
 	 *            fetch specifications used for finding localtracking refs. May
 	 *            be null or empty collection.
 	 * @return collection of set up {@link RemoteRefUpdate}.
 	 * @throws IOException
 	 *             when problem occurred during conversion or specification set
 	 *             up: most probably, missing objects or refs.
 	 * @since 4.7
 	 */
 	public static Collection<RemoteRefUpdate> findRemoteRefUpdatesFor(
 			final Repository db, final Collection<RefSpec> specs,
 			final Map<String, RefLeaseSpec> leases,
 			Collection<RefSpec> fetchSpecs) throws IOException {
 		if (fetchSpecs == null)
 			fetchSpecs = Collections.emptyList();
 		final List<RemoteRefUpdate> result = new LinkedList<>();
 		final Collection<RefSpec> procRefs = expandPushWildcardsFor(db, specs);
 
 		for (final RefSpec spec : procRefs) {
 			String srcSpec = spec.getSource();
 			final Ref srcRef = db.findRef(srcSpec);
 			if (srcRef != null)
 				srcSpec = srcRef.getName();
 
 			String destSpec = spec.getDestination();
 			if (destSpec == null) {
 				// No destination (no-colon in ref-spec), DWIMery assumes src
 				//
 				destSpec = srcSpec;
 			}
 
 			if (srcRef != null && !destSpec.startsWith(Constants.R_REFS)) {
 				// Assume the same kind of ref at the destination, e.g.
 				// "refs/heads/foo:master", DWIMery assumes master is also
 				// under "refs/heads/".
 				//
 				final String n = srcRef.getName();
 				final int kindEnd = n.indexOf('/', Constants.R_REFS.length());
 				destSpec = n.substring(0, kindEnd + 1) + destSpec;
 			}
 
 			final boolean forceUpdate = spec.isForceUpdate();
 			final String localName = findTrackingRefName(destSpec, fetchSpecs);
 			final RefLeaseSpec leaseSpec = leases.get(destSpec);
 			final ObjectId expected = leaseSpec == null ? null :
 				db.resolve(leaseSpec.getExpected());
 			final RemoteRefUpdate rru = new RemoteRefUpdate(db, srcSpec,
 					destSpec, forceUpdate, localName, expected);
 			result.add(rru);
 		}
 		return result;
 	}
 
 	/**
 	 * Convert push remote refs update specification from {@link RefSpec} form
 	 * to {@link RemoteRefUpdate}. Conversion expands wildcards by matching
 	 * source part to local refs. expectedOldObjectId in RemoteRefUpdate is
 	 * always set as null. Tracking branch is configured if RefSpec destination
 	 * matches source of any fetch ref spec for this transport remote
 	 * configuration.
 	 *
 	 * @param db
 	 *            local database.
 	 * @param specs
 	 *            collection of RefSpec to convert.
 	 * @param fetchSpecs
 	 *            fetch specifications used for finding localtracking refs. May
 	 *            be null or empty collection.
 	 * @return collection of set up {@link RemoteRefUpdate}.
 	 * @throws IOException
 	 *             when problem occurred during conversion or specification set
 	 *             up: most probably, missing objects or refs.
 	 */
 	public static Collection<RemoteRefUpdate> findRemoteRefUpdatesFor(
 			final Repository db, final Collection<RefSpec> specs,
 			Collection<RefSpec> fetchSpecs) throws IOException {
 		return findRemoteRefUpdatesFor(db, specs, Collections.emptyMap(),
 					       fetchSpecs);
 	}
 
 	private static Collection<RefSpec> expandPushWildcardsFor(
 			final Repository db, final Collection<RefSpec> specs)
 			throws IOException {
 		final Map<String, Ref> localRefs = db.getRefDatabase().getRefs(ALL);
 		final Collection<RefSpec> procRefs = new HashSet<>();
 
 		for (final RefSpec spec : specs) {
 			if (spec.isWildcard()) {
 				for (final Ref localRef : localRefs.values()) {
 					if (spec.matchSource(localRef))
 						procRefs.add(spec.expandFromSource(localRef));
 				}
 			} else {
 				procRefs.add(spec);
 			}
 		}
 		return procRefs;
 	}
 
 	private static String findTrackingRefName(final String remoteName,
 			final Collection<RefSpec> fetchSpecs) {
 		// try to find matching tracking refs
 		for (final RefSpec fetchSpec : fetchSpecs) {
 			if (fetchSpec.matchSource(remoteName)) {
 				if (fetchSpec.isWildcard())
 					return fetchSpec.expandFromSource(remoteName)
 							.getDestination();
 				else
 					return fetchSpec.getDestination();
 			}
 		}
 		return null;
 	}
 
 	/**
 	 * Default setting for {@link #fetchThin} option.
 	 */
 	public static final boolean DEFAULT_FETCH_THIN = true;
 
 	/**
 	 * Default setting for {@link #pushThin} option.
 	 */
 	public static final boolean DEFAULT_PUSH_THIN = false;
 
 	/**
 	 * Specification for fetch or push operations, to fetch or push all tags.
 	 * Acts as --tags.
 	 */
 	public static final RefSpec REFSPEC_TAGS = new RefSpec(
 			"refs/tags/*:refs/tags/*"); //$NON-NLS-1$
 
 	/**
 	 * Specification for push operation, to push all refs under refs/heads. Acts
 	 * as --all.
 	 */
 	public static final RefSpec REFSPEC_PUSH_ALL = new RefSpec(
 			"refs/heads/*:refs/heads/*"); //$NON-NLS-1$
 
 	/** The repository this transport fetches into, or pushes out of. */
 	protected final Repository local;
 
 	/** The URI used to create this transport. */
 	protected final URIish uri;
 
 	/** Name of the upload pack program, if it must be executed. */
 	private String optionUploadPack = RemoteConfig.DEFAULT_UPLOAD_PACK;
 
 	/** Specifications to apply during fetch. */
 	private List<RefSpec> fetch = Collections.emptyList();
 
 	/**
 	 * How {@link #fetch(ProgressMonitor, Collection)} should handle tags.
 	 * <p>
 	 * We default to {@link TagOpt#NO_TAGS} so as to avoid fetching annotated
 	 * tags during one-shot fetches used for later merges. This prevents
 	 * dragging down tags from repositories that we do not have established
 	 * tracking branches for. If we do not track the source repository, we most
 	 * likely do not care about any tags it publishes.
 	 */
 	private TagOpt tagopt = TagOpt.NO_TAGS;
 
 	/** Should fetch request thin-pack if remote repository can produce it. */
 	private boolean fetchThin = DEFAULT_FETCH_THIN;
 
 	/** Name of the receive pack program, if it must be executed. */
 	private String optionReceivePack = RemoteConfig.DEFAULT_RECEIVE_PACK;
 
 	/** Specifications to apply during push. */
 	private List<RefSpec> push = Collections.emptyList();
 
 	/** Should push produce thin-pack when sending objects to remote repository. */
 	private boolean pushThin = DEFAULT_PUSH_THIN;
 
 	/** Should push be all-or-nothing atomic behavior? */
 	private boolean pushAtomic;
 
 	/** Should push just check for operation result, not really push. */
 	private boolean dryRun;
 
 	/** Should an incoming (fetch) transfer validate objects? */
 	private ObjectChecker objectChecker;
 
 	/** Should refs no longer on the source be pruned from the destination? */
 	private boolean removeDeletedRefs;
 
 	/** Timeout in seconds to wait before aborting an IO read or write. */
 	private int timeout;
 
 	/** Pack configuration used by this transport to make pack file. */
 	private PackConfig packConfig;
 
 	/** Assists with authentication the connection. */
 	private CredentialsProvider credentialsProvider;
 
 	/** The option strings associated with the push operation. */
 	private List<String> pushOptions;
 
 	private PrintStream hookOutRedirect;
 
 	private PrePushHook prePush;
 	/**
 	 * Create a new transport instance.
 	 *
 	 * @param local
 	 *            the repository this instance will fetch into, or push out of.
 	 *            This must be the repository passed to
 	 *            {@link #open(Repository, URIish)}.
 	 * @param uri
 	 *            the URI used to access the remote repository. This must be the
 	 *            URI passed to {@link #open(Repository, URIish)}.
 	 */
 	protected Transport(final Repository local, final URIish uri) {
 		final TransferConfig tc = local.getConfig().get(TransferConfig.KEY);
 		this.local = local;
 		this.uri = uri;
 		this.objectChecker = tc.newObjectChecker();
 		this.credentialsProvider = CredentialsProvider.getDefault();
 		prePush = Hooks.prePush(local, hookOutRedirect);
 	}
 
 	/**
 	 * Create a minimal transport instance not tied to a single repository.
 	 *
 	 * @param uri
 	 */
 	protected Transport(final URIish uri) {
 		this.uri = uri;
 		this.local = null;
 		this.objectChecker = new ObjectChecker();
 		this.credentialsProvider = CredentialsProvider.getDefault();
 	}
 
 	/**
 	 * Get the URI this transport connects to.
 	 * <p>
 	 * Each transport instance connects to at most one URI at any point in time.
 	 *
 	 * @return the URI describing the location of the remote repository.
 	 */
 	public URIish getURI() {
 		return uri;
 	}
 
 	/**
 	 * Get the name of the remote executable providing upload-pack service.
 	 *
 	 * @return typically "git-upload-pack".
 	 */
 	public String getOptionUploadPack() {
 		return optionUploadPack;
 	}
 
 	/**
 	 * Set the name of the remote executable providing upload-pack services.
 	 *
 	 * @param where
 	 *            name of the executable.
 	 */
 	public void setOptionUploadPack(final String where) {
 		if (where != null && where.length() > 0)
 			optionUploadPack = where;
 		else
 			optionUploadPack = RemoteConfig.DEFAULT_UPLOAD_PACK;
 	}
 
 	/**
 	 * Get the description of how annotated tags should be treated during fetch.
 	 *
 	 * @return option indicating the behavior of annotated tags in fetch.
 	 */
 	public TagOpt getTagOpt() {
 		return tagopt;
 	}
 
 	/**
 	 * Set the description of how annotated tags should be treated on fetch.
 	 *
 	 * @param option
 	 *            method to use when handling annotated tags.
 	 */
 	public void setTagOpt(final TagOpt option) {
 		tagopt = option != null ? option : TagOpt.AUTO_FOLLOW;
 	}
 
 	/**
 	 * Default setting is: {@link #DEFAULT_FETCH_THIN}
 	 *
 	 * @return true if fetch should request thin-pack when possible; false
 	 *         otherwise
 	 * @see PackTransport
 	 */
 	public boolean isFetchThin() {
 		return fetchThin;
 	}
 
 	/**
 	 * Set the thin-pack preference for fetch operation. Default setting is:
 	 * {@link #DEFAULT_FETCH_THIN}
 	 *
 	 * @param fetchThin
 	 *            true when fetch should request thin-pack when possible; false
 	 *            when it shouldn't
 	 * @see PackTransport
 	 */
 	public void setFetchThin(final boolean fetchThin) {
 		this.fetchThin = fetchThin;
 	}
 
 	/**
 	 * @return true if fetch will verify received objects are formatted
 	 *         correctly. Validating objects requires more CPU time on the
 	 *         client side of the connection.
 	 */
 	public boolean isCheckFetchedObjects() {
 		return getObjectChecker() != null;
 	}
 
 	/**
 	 * @param check
 	 *            true to enable checking received objects; false to assume all
 	 *            received objects are valid.
 	 * @see #setObjectChecker(ObjectChecker)
 	 */
 	public void setCheckFetchedObjects(final boolean check) {
 		if (check && objectChecker == null)
 			setObjectChecker(new ObjectChecker());
 		else if (!check && objectChecker != null)
 			setObjectChecker(null);
 	}
 
 	/**
 	 * @return configured object checker for received objects, or null.
 	 * @since 3.6
 	 */
 	public ObjectChecker getObjectChecker() {
 		return objectChecker;
 	}
 
 	/**
 	 * @param impl
 	 *            if non-null the object checking instance to verify each
 	 *            received object with; null to disable object checking.
 	 * @since 3.6
 	 */
 	public void setObjectChecker(ObjectChecker impl) {
 		objectChecker = impl;
 	}
 
 	/**
 	 * Default setting is: {@link RemoteConfig#DEFAULT_RECEIVE_PACK}
 	 *
 	 * @return remote executable providing receive-pack service for pack
 	 *         transports.
 	 * @see PackTransport
 	 */
 	public String getOptionReceivePack() {
 		return optionReceivePack;
 	}
 
 	/**
 	 * Set remote executable providing receive-pack service for pack transports.
 	 * Default setting is: {@link RemoteConfig#DEFAULT_RECEIVE_PACK}
 	 *
 	 * @param optionReceivePack
 	 *            remote executable, if null or empty default one is set;
 	 */
 	public void setOptionReceivePack(String optionReceivePack) {
 		if (optionReceivePack != null && optionReceivePack.length() > 0)
 			this.optionReceivePack = optionReceivePack;
 		else
 			this.optionReceivePack = RemoteConfig.DEFAULT_RECEIVE_PACK;
 	}
 
 	/**
 	 * Default setting is: {@value #DEFAULT_PUSH_THIN}
 	 *
 	 * @return true if push should produce thin-pack in pack transports
 	 * @see PackTransport
 	 */
 	public boolean isPushThin() {
 		return pushThin;
 	}
 
 	/**
 	 * Set thin-pack preference for push operation. Default setting is:
 	 * {@value #DEFAULT_PUSH_THIN}
 	 *
 	 * @param pushThin
 	 *            true when push should produce thin-pack in pack transports;
 	 *            false when it shouldn't
 	 * @see PackTransport
 	 */
 	public void setPushThin(final boolean pushThin) {
 		this.pushThin = pushThin;
 	}
 
 	/**
 	 * Default setting is false.
 	 *
 	 * @return true if push requires all-or-nothing atomic behavior.
 	 * @since 4.2
 	 */
 	public boolean isPushAtomic() {
 		return pushAtomic;
 	}
 
 	/**
 	 * Request atomic push (all references succeed, or none do).
 	 * <p>
 	 * Server must also support atomic push. If the server does not support the
 	 * feature the push will abort without making changes.
 	 *
 	 * @param atomic
 	 *            true when push should be an all-or-nothing operation.
 	 * @see PackTransport
 	 * @since 4.2
 	 */
 	public void setPushAtomic(final boolean atomic) {
 		this.pushAtomic = atomic;
 	}
 
 	/**
 	 * @return true if destination refs should be removed if they no longer
 	 *         exist at the source repository.
 	 */
 	public boolean isRemoveDeletedRefs() {
 		return removeDeletedRefs;
 	}
 
 	/**
 	 * Set whether or not to remove refs which no longer exist in the source.
 	 * <p>
 	 * If true, refs at the destination repository (local for fetch, remote for
 	 * push) are deleted if they no longer exist on the source side (remote for
 	 * fetch, local for push).
 	 * <p>
 	 * False by default, as this may cause data to become unreachable, and
 	 * eventually be deleted on the next GC.
 	 *
 	 * @param remove true to remove refs that no longer exist.
 	 */
 	public void setRemoveDeletedRefs(final boolean remove) {
 		removeDeletedRefs = remove;
 	}
 
 	/**
 	 * Apply provided remote configuration on this transport.
 	 *
 	 * @param cfg
 	 *            configuration to apply on this transport.
 	 */
 	public void applyConfig(final RemoteConfig cfg) {
 		setOptionUploadPack(cfg.getUploadPack());
 		setOptionReceivePack(cfg.getReceivePack());
 		setTagOpt(cfg.getTagOpt());
 		fetch = cfg.getFetchRefSpecs();
 		push = cfg.getPushRefSpecs();
 		timeout = cfg.getTimeout();
 	}
 
 	/**
 	 * @return true if push operation should just check for possible result and
 	 *         not really update remote refs, false otherwise - when push should
 	 *         act normally.
 	 */
 	public boolean isDryRun() {
 		return dryRun;
 	}
 
 	/**
 	 * Set dry run option for push operation.
 	 *
 	 * @param dryRun
 	 *            true if push operation should just check for possible result
 	 *            and not really update remote refs, false otherwise - when push
 	 *            should act normally.
 	 */
 	public void setDryRun(final boolean dryRun) {
 		this.dryRun = dryRun;
 	}
 
 	/** @return timeout (in seconds) before aborting an IO operation. */
 	public int getTimeout() {
 		return timeout;
 	}
 
 	/**
 	 * Set the timeout before willing to abort an IO call.
 	 *
 	 * @param seconds
 	 *            number of seconds to wait (with no data transfer occurring)
 	 *            before aborting an IO read or write operation with this
 	 *            remote.
 	 */
 	public void setTimeout(final int seconds) {
 		timeout = seconds;
 	}
 
 	/**
 	 * Get the configuration used by the pack generator to make packs.
 	 *
 	 * If {@link #setPackConfig(PackConfig)} was previously given null a new
 	 * PackConfig is created on demand by this method using the source
 	 * repository's settings.
 	 *
 	 * @return the pack configuration. Never null.
 	 */
 	public PackConfig getPackConfig() {
 		if (packConfig == null)
 			packConfig = new PackConfig(local);
 		return packConfig;
 	}
 
 	/**
 	 * Set the configuration used by the pack generator.
 	 *
 	 * @param pc
 	 *            configuration controlling packing parameters. If null the
 	 *            source repository's settings will be used.
 	 */
 	public void setPackConfig(PackConfig pc) {
 		packConfig = pc;
 	}
 
 	/**
 	 * A credentials provider to assist with authentication connections..
 	 *
 	 * @param credentialsProvider
 	 *            the credentials provider, or null if there is none
 	 */
 	public void setCredentialsProvider(CredentialsProvider credentialsProvider) {
 		this.credentialsProvider = credentialsProvider;
 	}
 
 	/**
 	 * The configured credentials provider.
 	 *
 	 * @return the credentials provider, or null if no credentials provider is
 	 *         associated with this transport.
 	 */
 	public CredentialsProvider getCredentialsProvider() {
 		return credentialsProvider;
 	}
 
 	/**
 	 * @return the option strings associated with the push operation
 	 * @since 4.5
 	 */
 	public List<String> getPushOptions() {
 		return pushOptions;
 	}
 
 	/**
 	 * Sets the option strings associated with the push operation.
 	 *
 	 * @param pushOptions
 	 *            null if push options are unsupported
 	 * @since 4.5
 	 */
 	public void setPushOptions(final List<String> pushOptions) {
 		this.pushOptions = pushOptions;
 	}
 
 	/**
 	 * Fetch objects and refs from the remote repository to the local one.
 	 * <p>
 	 * This is a utility function providing standard fetch behavior. Local
 	 * tracking refs associated with the remote repository are automatically
 	 * updated if this transport was created from a {@link RemoteConfig} with
 	 * fetch RefSpecs defined.
 	 *
 	 * @param monitor
 	 *            progress monitor to inform the user about our processing
 	 *            activity. Must not be null. Use {@link NullProgressMonitor} if
 	 *            progress updates are not interesting or necessary.
 	 * @param toFetch
 	 *            specification of refs to fetch locally. May be null or the
 	 *            empty collection to use the specifications from the
 	 *            RemoteConfig. Source for each RefSpec can't be null.
 	 * @return information describing the tracking refs updated.
 	 * @throws NotSupportedException
 	 *             this transport implementation does not support fetching
 	 *             objects.
 	 * @throws TransportException
 	 *             the remote connection could not be established or object
 	 *             copying (if necessary) failed or update specification was
 	 *             incorrect.
 	 */
 	public FetchResult fetch(final ProgressMonitor monitor,
 			Collection<RefSpec> toFetch) throws NotSupportedException,
 			TransportException {
 		if (toFetch == null || toFetch.isEmpty()) {
 			// If the caller did not ask for anything use the defaults.
 			//
 			if (fetch.isEmpty())
 				throw new TransportException(JGitText.get().nothingToFetch);
 			toFetch = fetch;
 		} else if (!fetch.isEmpty()) {
 			// If the caller asked for something specific without giving
 			// us the local tracking branch see if we can update any of
 			// the local tracking branches without incurring additional
 			// object transfer overheads.
 			//
 			final Collection<RefSpec> tmp = new ArrayList<>(toFetch);
 			for (final RefSpec requested : toFetch) {
 				final String reqSrc = requested.getSource();
 				for (final RefSpec configured : fetch) {
 					final String cfgSrc = configured.getSource();
 					final String cfgDst = configured.getDestination();
 					if (cfgSrc.equals(reqSrc) && cfgDst != null) {
 						tmp.add(configured);
 						break;
 					}
 				}
 			}
 			toFetch = tmp;
 		}
 
 		final FetchResult result = new FetchResult();
 		new FetchProcess(this, toFetch).execute(monitor, result);
 
 		local.autoGC(monitor);
 
 		return result;
 	}
 
 	/**
 	 * Push objects and refs from the local repository to the remote one.
 	 * <p>
 	 * This is a utility function providing standard push behavior. It updates
 	 * remote refs and send there necessary objects according to remote ref
 	 * update specification. After successful remote ref update, associated
 	 * locally stored tracking branch is updated if set up accordingly. Detailed
 	 * operation result is provided after execution.
 	 * <p>
 	 * For setting up remote ref update specification from ref spec, see helper
 	 * method {@link #findRemoteRefUpdatesFor(Collection)}, predefined refspecs
 	 * ({@link #REFSPEC_TAGS}, {@link #REFSPEC_PUSH_ALL}) or consider using
 	 * directly {@link RemoteRefUpdate} for more possibilities.
 	 * <p>
 	 * When {@link #isDryRun()} is true, result of this operation is just
 	 * estimation of real operation result, no real action is performed.
 	 *
 	 * @see RemoteRefUpdate
 	 *
 	 * @param monitor
 	 *            progress monitor to inform the user about our processing
 	 *            activity. Must not be null. Use {@link NullProgressMonitor} if
 	 *            progress updates are not interesting or necessary.
 	 * @param toPush
 	 *            specification of refs to push. May be null or the empty
 	 *            collection to use the specifications from the RemoteConfig
 	 *            converted by {@link #findRemoteRefUpdatesFor(Collection)}. No
 	 *            more than 1 RemoteRefUpdate with the same remoteName is
 	 *            allowed. These objects are modified during this call.
 	 * @param out
 	 *            output stream to write messages to
 	 * @return information about results of remote refs updates, tracking refs
 	 *         updates and refs advertised by remote repository.
 	 * @throws NotSupportedException
 	 *             this transport implementation does not support pushing
 	 *             objects.
 	 * @throws TransportException
 	 *             the remote connection could not be established or object
 	 *             copying (if necessary) failed at I/O or protocol level or
 	 *             update specification was incorrect.
 	 * @since 3.0
 	 */
 	public PushResult push(final ProgressMonitor monitor,
 			Collection<RemoteRefUpdate> toPush, OutputStream out)
 			throws NotSupportedException,
 			TransportException {
 		if (toPush == null || toPush.isEmpty()) {
 			// If the caller did not ask for anything use the defaults.
 			try {
 				toPush = findRemoteRefUpdatesFor(push);
 			} catch (final IOException e) {
 				throw new TransportException(MessageFormat.format(
 						JGitText.get().problemWithResolvingPushRefSpecsLocally, e.getMessage()), e);
 			}
 			if (toPush.isEmpty())
 				throw new TransportException(JGitText.get().nothingToPush);
 		}
 		if (prePush != null) {
 			try {
 				prePush.setRefs(toPush);
 				prePush.call();
 			} catch (AbortedByHookException | IOException e) {
 				throw new TransportException(e.getMessage(), e);
 			}
 		}
 
 		final PushProcess pushProcess = new PushProcess(this, toPush, out);
 		return pushProcess.execute(monitor);
 	}
 
 	/**
 	 * Push objects and refs from the local repository to the remote one.
 	 * <p>
 	 * This is a utility function providing standard push behavior. It updates
 	 * remote refs and sends necessary objects according to remote ref update
 	 * specification. After successful remote ref update, associated locally
 	 * stored tracking branch is updated if set up accordingly. Detailed
 	 * operation result is provided after execution.
 	 * <p>
 	 * For setting up remote ref update specification from ref spec, see helper
 	 * method {@link #findRemoteRefUpdatesFor(Collection)}, predefined refspecs
 	 * ({@link #REFSPEC_TAGS}, {@link #REFSPEC_PUSH_ALL}) or consider using
 	 * directly {@link RemoteRefUpdate} for more possibilities.
 	 * <p>
 	 * When {@link #isDryRun()} is true, result of this operation is just
 	 * estimation of real operation result, no real action is performed.
 	 *
 	 * @see RemoteRefUpdate
 	 *
 	 * @param monitor
 	 *            progress monitor to inform the user about our processing
 	 *            activity. Must not be null. Use {@link NullProgressMonitor} if
 	 *            progress updates are not interesting or necessary.
 	 * @param toPush
 	 *            specification of refs to push. May be null or the empty
 	 *            collection to use the specifications from the RemoteConfig
 	 *            converted by {@link #findRemoteRefUpdatesFor(Collection)}. No
 	 *            more than 1 RemoteRefUpdate with the same remoteName is
 	 *            allowed. These objects are modified during this call.
 	 *
 	 * @return information about results of remote refs updates, tracking refs
 	 *         updates and refs advertised by remote repository.
 	 * @throws NotSupportedException
 	 *             this transport implementation does not support pushing
 	 *             objects.
 	 * @throws TransportException
 	 *             the remote connection could not be established or object
 	 *             copying (if necessary) failed at I/O or protocol level or
 	 *             update specification was incorrect.
 	 */
 	public PushResult push(final ProgressMonitor monitor,
 			Collection<RemoteRefUpdate> toPush) throws NotSupportedException,
 			TransportException {
 		return push(monitor, toPush, null);
 	}
 
 	/**
 	 * Convert push remote refs update specification from {@link RefSpec} form
 	 * to {@link RemoteRefUpdate}. Conversion expands wildcards by matching
 	 * source part to local refs. expectedOldObjectId in RemoteRefUpdate is
 	 * always set as null. Tracking branch is configured if RefSpec destination
 	 * matches source of any fetch ref spec for this transport remote
 	 * configuration.
 	 * <p>
 	 * Conversion is performed for context of this transport (database, fetch
 	 * specifications).
 	 *
 	 * @param specs
 	 *            collection of RefSpec to convert.
 	 * @return collection of set up {@link RemoteRefUpdate}.
 	 * @throws IOException
 	 *             when problem occurred during conversion or specification set
 	 *             up: most probably, missing objects or refs.
 	 */
 	public Collection<RemoteRefUpdate> findRemoteRefUpdatesFor(
 			final Collection<RefSpec> specs) throws IOException {
 		return findRemoteRefUpdatesFor(local, specs, Collections.emptyMap(),
 					       fetch);
 	}
 
 	/**
 	 * Convert push remote refs update specification from {@link RefSpec} form
 	 * to {@link RemoteRefUpdate}. Conversion expands wildcards by matching
 	 * source part to local refs. expectedOldObjectId in RemoteRefUpdate is
 	 * set according to leases. Tracking branch is configured if RefSpec destination
 	 * matches source of any fetch ref spec for this transport remote
 	 * configuration.
 	 * <p>
 	 * Conversion is performed for context of this transport (database, fetch
 	 * specifications).
 	 *
 	 * @param specs
 	 *            collection of RefSpec to convert.
 	 * @param leases
 	 *            map from ref to lease (containing expected old object id)
 	 * @return collection of set up {@link RemoteRefUpdate}.
 	 * @throws IOException
 	 *             when problem occurred during conversion or specification set
 	 *             up: most probably, missing objects or refs.
 	 * @since 4.7
 	 */
 	public Collection<RemoteRefUpdate> findRemoteRefUpdatesFor(
 			final Collection<RefSpec> specs,
 			final Map<String, RefLeaseSpec> leases) throws IOException {
 		return findRemoteRefUpdatesFor(local, specs, leases,
 					       fetch);
 	}
 
 	/**
 	 * Begins a new connection for fetching from the remote repository.
 	 * <p>
 	 * If the transport has no local repository, the fetch connection can only
 	 * be used for reading remote refs.
 	 *
 	 * @return a fresh connection to fetch from the remote repository.
 	 * @throws NotSupportedException
 	 *             the implementation does not support fetching.
 	 * @throws TransportException
 	 *             the remote connection could not be established.
 	 */
 	public abstract FetchConnection openFetch() throws NotSupportedException,
 			TransportException;
 
 	/**
 	 * Begins a new connection for pushing into the remote repository.
 	 *
 	 * @return a fresh connection to push into the remote repository.
 	 * @throws NotSupportedException
 	 *             the implementation does not support pushing.
 	 * @throws TransportException
 	 *             the remote connection could not be established
 	 */
 	public abstract PushConnection openPush() throws NotSupportedException,
 			TransportException;
 
 	/**
 	 * Close any resources used by this transport.
 	 * <p>
 	 * If the remote repository is contacted by a network socket this method
 	 * must close that network socket, disconnecting the two peers. If the
 	 * remote repository is actually local (same system) this method must close
 	 * any open file handles used to read the "remote" repository.
 	 * <p>
 	 * {@code AutoClosable.close()} declares that it throws {@link Exception}.
 	 * Implementers shouldn't throw checked exceptions. This override narrows
 	 * the signature to prevent them from doing so.
 	 */
 	@Override
 	public abstract void close();
 }