/*
    * Copyright (C) 2008-2010, Google Inc.
    * 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 java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.text.MessageFormat;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Date;
  import java.util.Set;
  
  import org.eclipse.jgit.errors.PackProtocolException;
  import org.eclipse.jgit.errors.TransportException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.file.PackLock;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.MutableObjectId;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectInserter;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevCommitList;
  import org.eclipse.jgit.revwalk.RevFlag;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevSort;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.revwalk.filter.CommitTimeRevFilter;
  import org.eclipse.jgit.revwalk.filter.RevFilter;
  import org.eclipse.jgit.transport.GitProtocolConstants.MultiAck;
  import org.eclipse.jgit.transport.PacketLineIn.AckNackResult;
  import org.eclipse.jgit.util.TemporaryBuffer;
  
  /**
   * Fetch implementation using the native Git pack transfer service.
   * <p>
   * This is the canonical implementation for transferring objects from the remote
   * repository to the local repository by talking to the 'git-upload-pack'
   * service. Objects are packed on the remote side into a pack file and then sent
   * down the pipe to us.
   * <p>
   * This connection requires only a bi-directional pipe or socket, and thus is
   * easily wrapped up into a local process pipe, anonymous TCP socket, or a
   * command executed through an SSH tunnel.
   * <p>
   * If {@link org.eclipse.jgit.transport.BasePackConnection#statelessRPC} is
   * {@code true}, this connection can be tunneled over a request-response style
   * RPC system like HTTP. The RPC call boundary is determined by this class
   * switching from writing to the OutputStream to reading from the InputStream.
   * <p>
   * Concrete implementations should just call
  * {@link #init(java.io.InputStream, java.io.OutputStream)} and
  * {@link #readAdvertisedRefs()} methods in constructor or before any use. They
  * should also handle resources releasing in {@link #close()} method if needed.
  */
 public abstract class BasePackFetchConnection extends BasePackConnection
 		implements FetchConnection {
 	/**
 	 * Maximum number of 'have' lines to send before giving up.
 	 * <p>
 	 * During {@link #negotiate(ProgressMonitor)} we send at most this many
 	 * commits to the remote peer as 'have' lines without an ACK response before
 	 * we give up.
 	 */
 	private static final int MAX_HAVES = 256;
 
 	/**
 	 * Amount of data the client sends before starting to read.
 	 * <p>
 	 * Any output stream given to the client must be able to buffer this many
 	 * bytes before the client will stop writing and start reading from the
 	 * input stream. If the output stream blocks before this many bytes are in
 	 * the send queue, the system will deadlock.
 	 */
 	protected static final int MIN_CLIENT_BUFFER = 2 * 32 * 46 + 8;
 
 	/**
 	 * Include tags if we are also including the referenced objects.
 	 * @since 2.0
 	 */
 	public static final String OPTION_INCLUDE_TAG = GitProtocolConstants.OPTION_INCLUDE_TAG;
 
 	/**
 	 * Mutli-ACK support for improved negotiation.
 	 * @since 2.0
 	 */
 	public static final String OPTION_MULTI_ACK = GitProtocolConstants.OPTION_MULTI_ACK;
 
 	/**
 	 * Mutli-ACK detailed support for improved negotiation.
 	 * @since 2.0
 	 */
 	public static final String OPTION_MULTI_ACK_DETAILED = GitProtocolConstants.OPTION_MULTI_ACK_DETAILED;
 
 	/**
 	 * The client supports packs with deltas but not their bases.
 	 * @since 2.0
 	 */
 	public static final String OPTION_THIN_PACK = GitProtocolConstants.OPTION_THIN_PACK;
 
 	/**
 	 * The client supports using the side-band for progress messages.
 	 * @since 2.0
 	 */
 	public static final String OPTION_SIDE_BAND = GitProtocolConstants.OPTION_SIDE_BAND;
 
 	/**
 	 * The client supports using the 64K side-band for progress messages.
 	 * @since 2.0
 	 */
 	public static final String OPTION_SIDE_BAND_64K = GitProtocolConstants.OPTION_SIDE_BAND_64K;
 
 	/**
 	 * The client supports packs with OFS deltas.
 	 * @since 2.0
 	 */
 	public static final String OPTION_OFS_DELTA = GitProtocolConstants.OPTION_OFS_DELTA;
 
 	/**
 	 * The client supports shallow fetches.
 	 * @since 2.0
 	 */
 	public static final String OPTION_SHALLOW = GitProtocolConstants.OPTION_SHALLOW;
 
 	/**
 	 * The client does not want progress messages and will ignore them.
 	 * @since 2.0
 	 */
 	public static final String OPTION_NO_PROGRESS = GitProtocolConstants.OPTION_NO_PROGRESS;
 
 	/**
 	 * The client supports receiving a pack before it has sent "done".
 	 * @since 2.0
 	 */
 	public static final String OPTION_NO_DONE = GitProtocolConstants.OPTION_NO_DONE;
 
 	/**
 	 * The client supports fetching objects at the tip of any ref, even if not
 	 * advertised.
 	 * @since 3.1
 	 */
 	public static final String OPTION_ALLOW_TIP_SHA1_IN_WANT = GitProtocolConstants.OPTION_ALLOW_TIP_SHA1_IN_WANT;
 
 	/**
 	 * The client supports fetching objects that are reachable from a tip of a
 	 * ref that is allowed to fetch.
 	 * @since 4.1
 	 */
 	public static final String OPTION_ALLOW_REACHABLE_SHA1_IN_WANT = GitProtocolConstants.OPTION_ALLOW_REACHABLE_SHA1_IN_WANT;
 
 	/**
 	 * The client specified a filter expression.
 	 *
 	 * @since 5.0
 	 */
 	public static final String OPTION_FILTER = GitProtocolConstants.OPTION_FILTER;
 
 	private final RevWalk walk;
 
 	/** All commits that are immediately reachable by a local ref. */
 	private RevCommitList<RevCommit> reachableCommits;
 
 	/** Marks an object as having all its dependencies. */
 	final RevFlag REACHABLE;
 
 	/** Marks a commit known to both sides of the connection. */
 	final RevFlag COMMON;
 
 	/** Like {@link #COMMON} but means its also in {@link #pckState}. */
 	private final RevFlag STATE;
 
 	/** Marks a commit listed in the advertised refs. */
 	final RevFlag ADVERTISED;
 
 	private MultiAck multiAck = MultiAck.OFF;
 
 	private boolean thinPack;
 
 	private boolean sideband;
 
 	private boolean includeTags;
 
 	private boolean allowOfsDelta;
 
 	private boolean noDone;
 
 	private boolean noProgress;
 
 	private String lockMessage;
 
 	private PackLock packLock;
 
 	private int maxHaves;
 
 	/** RPC state, if {@link BasePackConnection#statelessRPC} is true. */
 	private TemporaryBuffer.Heap state;
 
 	private PacketLineOut pckState;
 
 	/** If not -1, the maximum blob size to be sent to the server. */
 	private final long filterBlobLimit;
 
 	/**
 	 * Create a new connection to fetch using the native git transport.
 	 *
 	 * @param packTransport
 	 *            the transport.
 	 */
 	public BasePackFetchConnection(PackTransport packTransport) {
 		super(packTransport);
 
 		if (local != null) {
 			final FetchConfig cfg = getFetchConfig();
 			allowOfsDelta = cfg.allowOfsDelta;
 			maxHaves = cfg.maxHaves;
 		} else {
 			allowOfsDelta = true;
 			maxHaves = Integer.MAX_VALUE;
 		}
 
 		includeTags = transport.getTagOpt() != TagOpt.NO_TAGS;
 		thinPack = transport.isFetchThin();
 		filterBlobLimit = transport.getFilterBlobLimit();
 
 		if (local != null) {
 			walk = new RevWalk(local);
 			reachableCommits = new RevCommitList<>();
 			REACHABLE = walk.newFlag("REACHABLE"); //$NON-NLS-1$
 			COMMON = walk.newFlag("COMMON"); //$NON-NLS-1$
 			STATE = walk.newFlag("STATE"); //$NON-NLS-1$
 			ADVERTISED = walk.newFlag("ADVERTISED"); //$NON-NLS-1$
 
 			walk.carry(COMMON);
 			walk.carry(REACHABLE);
 			walk.carry(ADVERTISED);
 		} else {
 			walk = null;
 			REACHABLE = null;
 			COMMON = null;
 			STATE = null;
 			ADVERTISED = null;
 		}
 	}
 
 	static class FetchConfig {
 		final boolean allowOfsDelta;
 
 		final int maxHaves;
 
 		FetchConfig(Config c) {
 			allowOfsDelta = c.getBoolean("repack", "usedeltabaseoffset", true); //$NON-NLS-1$ //$NON-NLS-2$
 			maxHaves = c.getInt("fetch", "maxhaves", Integer.MAX_VALUE); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 
 		FetchConfig(boolean allowOfsDelta, int maxHaves) {
 			this.allowOfsDelta = allowOfsDelta;
 			this.maxHaves = maxHaves;
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public final void fetch(final ProgressMonitor monitor,
 			final Collection<Ref> want, final Set<ObjectId> have)
 			throws TransportException {
 		fetch(monitor, want, have, null);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public final void fetch(final ProgressMonitor monitor,
 			final Collection<Ref> want, final Set<ObjectId> have,
 			OutputStream outputStream) throws TransportException {
 		markStartedOperation();
 		doFetch(monitor, want, have, outputStream);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean didFetchIncludeTags() {
 		return false;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean didFetchTestConnectivity() {
 		return false;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void setPackLockMessage(String message) {
 		lockMessage = message;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Collection<PackLock> getPackLocks() {
 		if (packLock != null)
 			return Collections.singleton(packLock);
 		return Collections.<PackLock> emptyList();
 	}
 
 	/**
 	 * Execute common ancestor negotiation and fetch the objects.
 	 *
 	 * @param monitor
 	 *            progress monitor to receive status updates. If the monitor is
 	 *            the {@link org.eclipse.jgit.lib.NullProgressMonitor#INSTANCE}, then the no-progress
 	 *            option enabled.
 	 * @param want
 	 *            the advertised remote references the caller wants to fetch.
 	 * @param have
 	 *            additional objects to assume that already exist locally. This
 	 *            will be added to the set of objects reachable from the
 	 *            destination repository's references.
 	 * @param outputStream
 	 *            ouputStream to write sideband messages to
 	 * @throws org.eclipse.jgit.errors.TransportException
 	 *             if any exception occurs.
 	 * @since 3.0
 	 */
 	protected void doFetch(final ProgressMonitor monitor,
 			final Collection<Ref> want, final Set<ObjectId> have,
 			OutputStream outputStream) throws TransportException {
 		try {
 			noProgress = monitor == NullProgressMonitor.INSTANCE;
 
 			markRefsAdvertised();
 			markReachable(have, maxTimeWanted(want));
 
 			if (statelessRPC) {
 				state = new TemporaryBuffer.Heap(Integer.MAX_VALUE);
 				pckState = new PacketLineOut(state);
 			}
 
 			if (sendWants(want)) {
 				negotiate(monitor);
 
 				walk.dispose();
 				reachableCommits = null;
 				state = null;
 				pckState = null;
 
 				receivePack(monitor, outputStream);
 			}
 		} catch (CancelledException ce) {
 			close();
 			return; // Caller should test (or just know) this themselves.
 		} catch (IOException err) {
 			close();
 			throw new TransportException(err.getMessage(), err);
 		} catch (RuntimeException err) {
 			close();
 			throw new TransportException(err.getMessage(), err);
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void close() {
 		if (walk != null)
 			walk.close();
 		super.close();
 	}
 
 	FetchConfig getFetchConfig() {
 		return local.getConfig().get(FetchConfig::new);
 	}
 
 	private int maxTimeWanted(Collection<Ref> wants) {
 		int maxTime = 0;
 		for (Ref r : wants) {
 			try {
 				final RevObject obj = walk.parseAny(r.getObjectId());
 				if (obj instanceof RevCommit) {
 					final int cTime = ((RevCommit) obj).getCommitTime();
 					if (maxTime < cTime)
 						maxTime = cTime;
 				}
 			} catch (IOException error) {
 				// We don't have it, but we want to fetch (thus fixing error).
 			}
 		}
 		return maxTime;
 	}
 
 	private void markReachable(Set<ObjectId> have, int maxTime)
 			throws IOException {
 		for (Ref r : local.getRefDatabase().getRefs()) {
 			ObjectId id = r.getPeeledObjectId();
 			if (id == null)
 				id = r.getObjectId();
 			if (id == null)
 				continue;
 			parseReachable(id);
 		}
 
 		for (ObjectId id : local.getAdditionalHaves())
 			parseReachable(id);
 
 		for (ObjectId id : have)
 			parseReachable(id);
 
 		if (maxTime > 0) {
 			// Mark reachable commits until we reach maxTime. These may
 			// wind up later matching up against things we want and we
 			// can avoid asking for something we already happen to have.
 			//
 			final Date maxWhen = new Date(maxTime * 1000L);
 			walk.sort(RevSort.COMMIT_TIME_DESC);
 			walk.markStart(reachableCommits);
 			walk.setRevFilter(CommitTimeRevFilter.after(maxWhen));
 			for (;;) {
 				final RevCommit c = walk.next();
 				if (c == null)
 					break;
 				if (c.has(ADVERTISED) && !c.has(COMMON)) {
 					// This is actually going to be a common commit, but
 					// our peer doesn't know that fact yet.
 					//
 					c.add(COMMON);
 					c.carry(COMMON);
 					reachableCommits.add(c);
 				}
 			}
 		}
 	}
 
 	private void parseReachable(ObjectId id) {
 		try {
 			RevCommit o = walk.parseCommit(id);
 			if (!o.has(REACHABLE)) {
 				o.add(REACHABLE);
 				reachableCommits.add(o);
 			}
 		} catch (IOException readError) {
 			// If we cannot read the value of the ref skip it.
 		}
 	}
 
 	private boolean sendWants(Collection<Ref> want) throws IOException {
 		final PacketLineOut p = statelessRPC ? pckState : pckOut;
 		boolean first = true;
 		for (Ref r : want) {
 			ObjectId objectId = r.getObjectId();
 			if (objectId == null) {
 				continue;
 			}
 			try {
 				if (walk.parseAny(objectId).has(REACHABLE)) {
 					// We already have this object. Asking for it is
 					// not a very good idea.
 					//
 					continue;
 				}
 			} catch (IOException err) {
 				// Its OK, we don't have it, but we want to fix that
 				// by fetching the object from the other side.
 			}
 
 			final StringBuilder line = new StringBuilder(46);
 			line.append("want "); //$NON-NLS-1$
 			line.append(objectId.name());
 			if (first) {
 				line.append(enableCapabilities());
 				first = false;
 			}
 			line.append('\n');
 			p.writeString(line.toString());
 		}
 		if (first) {
 			return false;
 		}
 		if (filterBlobLimit == 0) {
 			p.writeString(OPTION_FILTER + " blob:none"); //$NON-NLS-1$
 		} else if (filterBlobLimit > 0) {
 			p.writeString(OPTION_FILTER + " blob:limit=" + filterBlobLimit); //$NON-NLS-1$
 		}
 		p.end();
 		outNeedsEnd = false;
 		return true;
 	}
 
 	private String enableCapabilities() throws TransportException {
 		final StringBuilder line = new StringBuilder();
 		if (noProgress)
 			wantCapability(line, OPTION_NO_PROGRESS);
 		if (includeTags)
 			includeTags = wantCapability(line, OPTION_INCLUDE_TAG);
 		if (allowOfsDelta)
 			wantCapability(line, OPTION_OFS_DELTA);
 
 		if (wantCapability(line, OPTION_MULTI_ACK_DETAILED)) {
 			multiAck = MultiAck.DETAILED;
 			if (statelessRPC)
 				noDone = wantCapability(line, OPTION_NO_DONE);
 		} else if (wantCapability(line, OPTION_MULTI_ACK))
 			multiAck = MultiAck.CONTINUE;
 		else
 			multiAck = MultiAck.OFF;
 
 		if (thinPack)
 			thinPack = wantCapability(line, OPTION_THIN_PACK);
 		if (wantCapability(line, OPTION_SIDE_BAND_64K))
 			sideband = true;
 		else if (wantCapability(line, OPTION_SIDE_BAND))
 			sideband = true;
 
 		if (statelessRPC && multiAck != MultiAck.DETAILED) {
 			// Our stateless RPC implementation relies upon the detailed
 			// ACK status to tell us common objects for reuse in future
 			// requests.  If its not enabled, we can't talk to the peer.
 			//
 			throw new PackProtocolException(uri, MessageFormat.format(
 					JGitText.get().statelessRPCRequiresOptionToBeEnabled,
 					OPTION_MULTI_ACK_DETAILED));
 		}
 
 		if (filterBlobLimit >= 0 && !wantCapability(line, OPTION_FILTER)) {
 			throw new PackProtocolException(uri,
 					JGitText.get().filterRequiresCapability);
 		}
 
 		addUserAgentCapability(line);
 		return line.toString();
 	}
 
 	private void negotiate(ProgressMonitor monitor) throws IOException,
 			CancelledException {
 		final MutableObjectId ackId = new MutableObjectId();
 		int resultsPending = 0;
 		int havesSent = 0;
 		int havesSinceLastContinue = 0;
 		boolean receivedContinue = false;
 		boolean receivedAck = false;
 		boolean receivedReady = false;
 
 		if (statelessRPC) {
 			state.writeTo(out, null);
 		}
 
 		negotiateBegin();
 		SEND_HAVES: for (;;) {
 			final RevCommit c = walk.next();
 			if (c == null) {
 				break SEND_HAVES;
 			}
 
 			ObjectId o = c.getId();
 			pckOut.writeString("have " + o.name() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
 			havesSent++;
 			havesSinceLastContinue++;
 
 			if ((31 & havesSent) != 0) {
 				// We group the have lines into blocks of 32, each marked
 				// with a flush (aka end). This one is within a block so
 				// continue with another have line.
 				//
 				continue;
 			}
 
 			if (monitor.isCancelled()) {
 				throw new CancelledException();
 			}
 
 			pckOut.end();
 			resultsPending++; // Each end will cause a result to come back.
 
 			if (havesSent == 32 && !statelessRPC) {
 				// On the first block we race ahead and try to send
 				// more of the second block while waiting for the
 				// remote to respond to our first block request.
 				// This keeps us one block ahead of the peer.
 				//
 				continue;
 			}
 
 			READ_RESULT: for (;;) {
 				final AckNackResult anr = pckIn.readACK(ackId);
 				switch (anr) {
 				case NAK:
 					// More have lines are necessary to compute the
 					// pack on the remote side. Keep doing that.
 					//
 					resultsPending--;
 					break READ_RESULT;
 
 				case ACK:
 					// The remote side is happy and knows exactly what
 					// to send us. There is no further negotiation and
 					// we can break out immediately.
 					//
 					multiAck = MultiAck.OFF;
 					resultsPending = 0;
 					receivedAck = true;
 					if (statelessRPC) {
 						state.writeTo(out, null);
 					}
 					break SEND_HAVES;
 
 				case ACK_CONTINUE:
 				case ACK_COMMON:
 				case ACK_READY:
 					// The server knows this commit (ackId). We don't
 					// need to send any further along its ancestry, but
 					// we need to continue to talk about other parts of
 					// our local history.
 					//
 					markCommon(walk.parseAny(ackId), anr);
 					receivedAck = true;
 					receivedContinue = true;
 					havesSinceLastContinue = 0;
 					if (anr == AckNackResult.ACK_READY) {
 						receivedReady = true;
 					}
 					break;
 				}
 
 				if (monitor.isCancelled()) {
 					throw new CancelledException();
 				}
 			}
 
 			if (noDone & receivedReady) {
 				break SEND_HAVES;
 			}
 			if (statelessRPC) {
 				state.writeTo(out, null);
 			}
 
 			if (receivedContinue && havesSinceLastContinue > MAX_HAVES
 					|| havesSent >= maxHaves) {
 				// Our history must be really different from the remote's.
 				// We just sent a whole slew of have lines, and it did not
 				// recognize any of them. Avoid sending our entire history
 				// to them by giving up early.
 				//
 				break SEND_HAVES;
 			}
 		}
 
 		// Tell the remote side we have run out of things to talk about.
 		//
 		if (monitor.isCancelled()) {
 			throw new CancelledException();
 		}
 
 		if (!receivedReady || !noDone) {
 			// When statelessRPC is true we should always leave SEND_HAVES
 			// loop above while in the middle of a request. This allows us
 			// to just write done immediately.
 			//
 			pckOut.writeString("done\n"); //$NON-NLS-1$
 			pckOut.flush();
 		}
 
 		if (!receivedAck) {
 			// Apparently if we have never received an ACK earlier
 			// there is one more result expected from the done we
 			// just sent to the remote.
 			//
 			multiAck = MultiAck.OFF;
 			resultsPending++;
 		}
 
 		READ_RESULT: while (resultsPending > 0 || multiAck != MultiAck.OFF) {
 			final AckNackResult anr = pckIn.readACK(ackId);
 			resultsPending--;
 			switch (anr) {
 			case NAK:
 				// A NAK is a response to an end we queued earlier
 				// we eat it and look for another ACK/NAK message.
 				//
 				break;
 
 			case ACK:
 				// A solitary ACK at this point means the remote won't
 				// speak anymore, but is going to send us a pack now.
 				//
 				break READ_RESULT;
 
 			case ACK_CONTINUE:
 			case ACK_COMMON:
 			case ACK_READY:
 				// We will expect a normal ACK to break out of the loop.
 				//
 				multiAck = MultiAck.CONTINUE;
 				break;
 			}
 
 			if (monitor.isCancelled()) {
 				throw new CancelledException();
 			}
 		}
 	}
 
 	private void negotiateBegin() throws IOException {
 		walk.resetRetain(REACHABLE, ADVERTISED);
 		walk.markStart(reachableCommits);
 		walk.sort(RevSort.COMMIT_TIME_DESC);
 		walk.setRevFilter(new RevFilter() {
 			@Override
 			public RevFilter clone() {
 				return this;
 			}
 
 			@Override
 			public boolean include(RevWalk walker, RevCommit c) {
 				final boolean remoteKnowsIsCommon = c.has(COMMON);
 				if (c.has(ADVERTISED)) {
 					// Remote advertised this, and we have it, hence common.
 					// Whether or not the remote knows that fact is tested
 					// before we added the flag. If the remote doesn't know
 					// we have to still send them this object.
 					//
 					c.add(COMMON);
 				}
 				return !remoteKnowsIsCommon;
 			}
 
 			@Override
 			public boolean requiresCommitBody() {
 				return false;
 			}
 		});
 	}
 
 	private void markRefsAdvertised() {
 		for (Ref r : getRefs()) {
 			markAdvertised(r.getObjectId());
 			if (r.getPeeledObjectId() != null)
 				markAdvertised(r.getPeeledObjectId());
 		}
 	}
 
 	private void markAdvertised(AnyObjectId id) {
 		try {
 			walk.parseAny(id).add(ADVERTISED);
 		} catch (IOException readError) {
 			// We probably just do not have this object locally.
 		}
 	}
 
 	private void markCommon(RevObject obj, AckNackResult anr)
 			throws IOException {
 		if (statelessRPC && anr == AckNackResult.ACK_COMMON && !obj.has(STATE)) {
 			StringBuilder s;
 
 			s = new StringBuilder(6 + Constants.OBJECT_ID_STRING_LENGTH);
 			s.append("have "); //$NON-NLS-1$
 			s.append(obj.name());
 			s.append('\n');
 			pckState.writeString(s.toString());
 			obj.add(STATE);
 		}
 		obj.add(COMMON);
 		if (obj instanceof RevCommit)
 			((RevCommit) obj).carry(COMMON);
 	}
 
 	private void receivePack(final ProgressMonitor monitor,
 			OutputStream outputStream) throws IOException {
 		onReceivePack();
 		InputStream input = in;
 		if (sideband)
 			input = new SideBandInputStream(input, monitor, getMessageWriter(),
 					outputStream);
 
 		try (ObjectInserter ins = local.newObjectInserter()) {
 			PackParser parser = ins.newPackParser(input);
 			parser.setAllowThin(thinPack);
 			parser.setObjectChecker(transport.getObjectChecker());
 			parser.setLockMessage(lockMessage);
 			packLock = parser.parse(monitor);
 			ins.flush();
 		}
 	}
 
 	/**
 	 * Notification event delivered just before the pack is received from the
 	 * network. This event can be used by RPC such as {@link org.eclipse.jgit.transport.TransportHttp} to
 	 * disable its request magic and ensure the pack stream is read correctly.
 	 *
 	 * @since 2.0
 	 */
 	protected void onReceivePack() {
 		// By default do nothing for TCP based protocols.
 	}
 
 	private static class CancelledException extends Exception {
 		private static final long serialVersionUID = 1L;
 	}
 }