jgit/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

/*
 * Copyright (C) 2008-2010, Google Inc.
 * 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.Constants.R_TAGS;
import static org.eclipse.jgit.lib.RefDatabase.ALL;
import static org.eclipse.jgit.transport.GitProtocolConstants.CAPABILITY_REF_IN_WANT;
import static org.eclipse.jgit.transport.GitProtocolConstants.COMMAND_FETCH;
import static org.eclipse.jgit.transport.GitProtocolConstants.COMMAND_LS_REFS;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_AGENT;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_ALLOW_REACHABLE_SHA1_IN_WANT;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_ALLOW_TIP_SHA1_IN_WANT;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_DEEPEN_RELATIVE;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_FILTER;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_INCLUDE_TAG;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_MULTI_ACK;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_MULTI_ACK_DETAILED;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_NO_DONE;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_NO_PROGRESS;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_OFS_DELTA;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SHALLOW;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SIDE_BAND;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_SIDE_BAND_64K;
import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_THIN_PACK;

import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.eclipse.jgit.annotations.Nullable;
import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.PackProtocolException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.internal.storage.pack.PackWriter;
import org.eclipse.jgit.lib.BitmapIndex;
import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.NullProgressMonitor;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.AsyncRevObjectQueue;
import org.eclipse.jgit.revwalk.BitmapWalker;
import org.eclipse.jgit.revwalk.DepthWalk;
import org.eclipse.jgit.revwalk.ObjectWalk;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevFlag;
import org.eclipse.jgit.revwalk.RevFlagSet;
import org.eclipse.jgit.revwalk.RevObject;
import org.eclipse.jgit.revwalk.RevTag;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.revwalk.filter.CommitTimeRevFilter;
import org.eclipse.jgit.storage.pack.PackConfig;
import org.eclipse.jgit.storage.pack.PackStatistics;
import org.eclipse.jgit.transport.GitProtocolConstants.MultiAck;
import org.eclipse.jgit.transport.RefAdvertiser.PacketLineOutRefAdvertiser;
import org.eclipse.jgit.transport.TransferConfig.ProtocolVersion;
import org.eclipse.jgit.util.io.InterruptTimer;
import org.eclipse.jgit.util.io.NullOutputStream;
import org.eclipse.jgit.util.io.TimeoutInputStream;
import org.eclipse.jgit.util.io.TimeoutOutputStream;

/**
 * Implements the server side of a fetch connection, transmitting objects.
 */
public class UploadPack {
	/** Policy the server uses to validate client requests */
	public static enum RequestPolicy {
		/** Client may only ask for objects the server advertised a reference for. */
		ADVERTISED,

		/**
		 * Client may ask for any commit reachable from a reference advertised by
		 * the server.
		 */
		REACHABLE_COMMIT,

		/**
		 * Client may ask for objects that are the tip of any reference, even if not
		 * advertised.
		 * <p>
		 * This may happen, for example, when a custom {@link RefFilter} is set.
		 *
		 * @since 3.1
		 */
		TIP,

		/**
		 * Client may ask for any commit reachable from any reference, even if that
		 * reference wasn't advertised.
		 *
		 * @since 3.1
		 */
		REACHABLE_COMMIT_TIP,

		/** Client may ask for any SHA-1 in the repository. */
		ANY;
	}

	/**
	 * Validator for client requests.
	 *
	 * @since 3.1
	 */
	public interface RequestValidator {
		/**
		 * Check a list of client wants against the request policy.
		 *
		 * @param up
		 *            {@link UploadPack} instance.
		 * @param wants
		 *            objects the client requested that were not advertised.
		 *
		 * @throws PackProtocolException
		 *            if one or more wants is not valid.
		 * @throws IOException
		 *            if a low-level exception occurred.
		 * @since 3.1
		 */
		void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException;
	}

	/** Data in the first line of a request, the line itself plus options. */
	public static class FirstLine {
		private final String line;
		private final Set<String> options;

		/**
		 * Parse the first line of a receive-pack request.
		 *
		 * @param line
		 *            line from the client.
		 */
		public FirstLine(String line) {
			if (line.length() > 45) {
				final HashSet<String> opts = new HashSet<>();
				String opt = line.substring(45);
				if (opt.startsWith(" ")) //$NON-NLS-1$
					opt = opt.substring(1);
				for (String c : opt.split(" ")) //$NON-NLS-1$
					opts.add(c);
				this.line = line.substring(0, 45);
				this.options = Collections.unmodifiableSet(opts);
			} else {
				this.line = line;
				this.options = Collections.emptySet();
			}
		}

		/** @return non-capabilities part of the line. */
		public String getLine() {
			return line;
		}

		/** @return options parsed from the line. */
		public Set<String> getOptions() {
			return options;
		}
	}

	/*
	 * {@link java.util.function.Consumer} doesn't allow throwing checked
	 * exceptions. Define our own to propagate IOExceptions.
	 */
	@FunctionalInterface
	private static interface IOConsumer<R> {
		void accept(R t) throws IOException;
	}

	/** Database we read the objects from. */
	private final Repository db;

	/** Revision traversal support over {@link #db}. */
	private final RevWalk walk;

	/** Configuration to pass into the PackWriter. */
	private PackConfig packConfig;

	/** Configuration for various transfer options. */
	private TransferConfig transferConfig;

	/** Timeout in seconds to wait for client interaction. */
	private int timeout;

	/**
	 * Is the client connection a bi-directional socket or pipe?
	 * <p>
	 * If true, this class assumes it can perform multiple read and write cycles
	 * with the client over the input and output streams. This matches the
	 * functionality available with a standard TCP/IP connection, or a local
	 * operating system or in-memory pipe.
	 * <p>
	 * If false, this class runs in a read everything then output results mode,
	 * making it suitable for single round-trip systems RPCs such as HTTP.
	 */
	private boolean biDirectionalPipe = true;

	/** Timer to manage {@link #timeout}. */
	private InterruptTimer timer;

	/**
	 * Whether the client requested to use protocol V2 through a side
	 * channel (such as the Git-Protocol HTTP header).
	 */
	private boolean clientRequestedV2;

	private InputStream rawIn;

	private ResponseBufferedOutputStream rawOut;

	private PacketLineIn pckIn;

	private PacketLineOut pckOut;

	private OutputStream msgOut = NullOutputStream.INSTANCE;

	/** The refs we advertised as existing at the start of the connection. */
	private Map<String, Ref> refs;

	/** Hook used while processing Git protocol v2 requests. */
	private ProtocolV2Hook protocolV2Hook = ProtocolV2Hook.DEFAULT;

	/** Hook used while advertising the refs to the client. */
	private AdvertiseRefsHook advertiseRefsHook = AdvertiseRefsHook.DEFAULT;

	/** Filter used while advertising the refs to the client. */
	private RefFilter refFilter = RefFilter.DEFAULT;

	/** Hook handling the various upload phases. */
	private PreUploadHook preUploadHook = PreUploadHook.NULL;

	/** Hook for taking post upload actions. */
	private PostUploadHook postUploadHook = PostUploadHook.NULL;

	/** Capabilities requested by the client. */
	private Set<String> options;
	String userAgent;

	/** Raw ObjectIds the client has asked for, before validating them. */
	private final Set<ObjectId> wantIds = new HashSet<>();

	/** Objects the client wants to obtain. */
	private final Set<RevObject> wantAll = new HashSet<>();

	/** Objects on both sides, these don't have to be sent. */
	private final Set<RevObject> commonBase = new HashSet<>();

	/** Shallow commits the client already has. */
	private Set<ObjectId> clientShallowCommits = new HashSet<>();

	/** Desired depth from the client on a shallow request. */
	private int depth;

	/**
	 * Commit time of the newest objects the client has asked us using
	 * --shallow-since not to send. Cannot be nonzero if depth is nonzero.
	 */
	private int shallowSince;

	/**
	 * (Possibly short) ref names, ancestors of which the client has asked us
	 * not to send using --shallow-exclude. Cannot be non-empty if depth is
	 * nonzero.
	 */
	private List<String> deepenNotRefs = new ArrayList<>();

	/** Commit time of the oldest common commit, in seconds. */
	private int oldestTime;

	/** null if {@link #commonBase} should be examined again. */
	private Boolean okToGiveUp;

	private boolean sentReady;

	/** Objects we sent in our advertisement list, clients can ask for these. */
	private Set<ObjectId> advertised;

	/** Marked on objects the client has asked us to give them. */
	private final RevFlag WANT;

	/** Marked on objects both we and the client have. */
	private final RevFlag PEER_HAS;

	/** Marked on objects in {@link #commonBase}. */
	private final RevFlag COMMON;

	/** Objects where we found a path from the want list to a common base. */
	private final RevFlag SATISFIED;

	private final RevFlagSet SAVE;

	private RequestValidator requestValidator = new AdvertisedRequestValidator();

	private MultiAck multiAck = MultiAck.OFF;

	private boolean noDone;

	private PackStatistics statistics;

	private long filterBlobLimit = -1;

	/**
	 * Create a new pack upload for an open repository.
	 *
	 * @param copyFrom
	 *            the source repository.
	 */
	public UploadPack(Repository copyFrom) {
		db = copyFrom;
		walk = new RevWalk(db);
		walk.setRetainBody(false);

		WANT = walk.newFlag("WANT"); //$NON-NLS-1$
		PEER_HAS = walk.newFlag("PEER_HAS"); //$NON-NLS-1$
		COMMON = walk.newFlag("COMMON"); //$NON-NLS-1$
		SATISFIED = walk.newFlag("SATISFIED"); //$NON-NLS-1$
		walk.carry(PEER_HAS);

		SAVE = new RevFlagSet();
		SAVE.add(WANT);
		SAVE.add(PEER_HAS);
		SAVE.add(COMMON);
		SAVE.add(SATISFIED);

		setTransferConfig(null);
	}

	/**
	 * Get the repository this upload is reading from.
	 *
	 * @return the repository this upload is reading from.
	 */
	public final Repository getRepository() {
		return db;
	}

	/**
	 * Get the RevWalk instance used by this connection.
	 *
	 * @return the RevWalk instance used by this connection.
	 */
	public final RevWalk getRevWalk() {
		return walk;
	}

	/**
	 * Get refs which were advertised to the client.
	 *
	 * @return all refs which were advertised to the client, or null if
	 *         {@link #setAdvertisedRefs(Map)} has not been called yet.
	 */
	public final Map<String, Ref> getAdvertisedRefs() {
		return refs;
	}

	/**
	 * Set the refs advertised by this UploadPack.
	 * <p>
	 * Intended to be called from a
	 * {@link org.eclipse.jgit.transport.PreUploadHook}.
	 *
	 * @param allRefs
	 *            explicit set of references to claim as advertised by this
	 *            UploadPack instance. This overrides any references that may
	 *            exist in the source repository. The map is passed to the
	 *            configured {@link #getRefFilter()}. If null, assumes all refs
	 *            were advertised.
	 */
	public void setAdvertisedRefs(Map<String, Ref> allRefs) {
		if (allRefs != null)
			refs = allRefs;
		else
			refs = db.getAllRefs();
		if (refFilter == RefFilter.DEFAULT)
			refs = transferConfig.getRefFilter().filter(refs);
		else
			refs = refFilter.filter(refs);
	}

	/**
	 * Get timeout (in seconds) before aborting an IO operation.
	 *
	 * @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 the
	 *            connected client.
	 */
	public void setTimeout(int seconds) {
		timeout = seconds;
	}

	/**
	 * Whether this class expects a bi-directional pipe opened between the
	 * client and itself.
	 *
	 * @return true if this class expects a bi-directional pipe opened between
	 *         the client and itself. The default is true.
	 */
	public boolean isBiDirectionalPipe() {
		return biDirectionalPipe;
	}

	/**
	 * Set whether this class will assume the socket is a fully bidirectional
	 * pipe between the two peers
	 *
	 * @param twoWay
	 *            if true, this class will assume the socket is a fully
	 *            bidirectional pipe between the two peers and takes advantage
	 *            of that by first transmitting the known refs, then waiting to
	 *            read commands. If false, this class assumes it must read the
	 *            commands before writing output and does not perform the
	 *            initial advertising.
	 */
	public void setBiDirectionalPipe(boolean twoWay) {
		biDirectionalPipe = twoWay;
	}

	/**
	 * Get policy used by the service to validate client requests
	 *
	 * @return policy used by the service to validate client requests, or null
	 *         for a custom request validator.
	 */
	public RequestPolicy getRequestPolicy() {
		if (requestValidator instanceof AdvertisedRequestValidator)
			return RequestPolicy.ADVERTISED;
		if (requestValidator instanceof ReachableCommitRequestValidator)
			return RequestPolicy.REACHABLE_COMMIT;
		if (requestValidator instanceof TipRequestValidator)
			return RequestPolicy.TIP;
		if (requestValidator instanceof ReachableCommitTipRequestValidator)
			return RequestPolicy.REACHABLE_COMMIT_TIP;
		if (requestValidator instanceof AnyRequestValidator)
			return RequestPolicy.ANY;
		return null;
	}

	/**
	 * Set the policy used to enforce validation of a client's want list.
	 *
	 * @param policy
	 *            the policy used to enforce validation of a client's want list.
	 *            By default the policy is
	 *            {@link org.eclipse.jgit.transport.UploadPack.RequestPolicy#ADVERTISED},
	 *            which is the Git default requiring clients to only ask for an
	 *            object that a reference directly points to. This may be
	 *            relaxed to
	 *            {@link org.eclipse.jgit.transport.UploadPack.RequestPolicy#REACHABLE_COMMIT}
	 *            or
	 *            {@link org.eclipse.jgit.transport.UploadPack.RequestPolicy#REACHABLE_COMMIT_TIP}
	 *            when callers have {@link #setBiDirectionalPipe(boolean)} set
	 *            to false. Overrides any policy specified in a
	 *            {@link org.eclipse.jgit.transport.TransferConfig}.
	 */
	public void setRequestPolicy(RequestPolicy policy) {
		switch (policy) {
			case ADVERTISED:
			default:
				requestValidator = new AdvertisedRequestValidator();
				break;
			case REACHABLE_COMMIT:
				requestValidator = new ReachableCommitRequestValidator();
				break;
			case TIP:
				requestValidator = new TipRequestValidator();
				break;
			case REACHABLE_COMMIT_TIP:
				requestValidator = new ReachableCommitTipRequestValidator();
				break;
			case ANY:
				requestValidator = new AnyRequestValidator();
				break;
		}
	}

	/**
	 * Set custom validator for client want list.
	 *
	 * @param validator
	 *            custom validator for client want list.
	 * @since 3.1
	 */
	public void setRequestValidator(RequestValidator validator) {
		requestValidator = validator != null ? validator
				: new AdvertisedRequestValidator();
	}

	/**
	 * Get the hook used while advertising the refs to the client.
	 *
	 * @return the hook used while advertising the refs to the client.
	 */
	public AdvertiseRefsHook getAdvertiseRefsHook() {
		return advertiseRefsHook;
	}

	/**
	 * Get the filter used while advertising the refs to the client.
	 *
	 * @return the filter used while advertising the refs to the client.
	 */
	public RefFilter getRefFilter() {
		return refFilter;
	}

	/**
	 * Set the hook used while advertising the refs to the client.
	 * <p>
	 * If the {@link org.eclipse.jgit.transport.AdvertiseRefsHook} chooses to
	 * call {@link #setAdvertisedRefs(Map)}, only refs set by this hook
	 * <em>and</em> selected by the {@link org.eclipse.jgit.transport.RefFilter}
	 * will be shown to the client.
	 *
	 * @param advertiseRefsHook
	 *            the hook; may be null to show all refs.
	 */
	public void setAdvertiseRefsHook(AdvertiseRefsHook advertiseRefsHook) {
		if (advertiseRefsHook != null)
			this.advertiseRefsHook = advertiseRefsHook;
		else
			this.advertiseRefsHook = AdvertiseRefsHook.DEFAULT;
	}

	/**
	 * Set the protocol V2 hook.
	 *
	 * @param hook
	 * @since 5.1
	 */
	public void setProtocolV2Hook(ProtocolV2Hook hook) {
		this.protocolV2Hook = hook;
	}

	/**
	 * Set the filter used while advertising the refs to the client.
	 * <p>
	 * Only refs allowed by this filter will be sent to the client. The filter
	 * is run against the refs specified by the
	 * {@link org.eclipse.jgit.transport.AdvertiseRefsHook} (if applicable). If
	 * null or not set, uses the filter implied by the
	 * {@link org.eclipse.jgit.transport.TransferConfig}.
	 *
	 * @param refFilter
	 *            the filter; may be null to show all refs.
	 */
	public void setRefFilter(RefFilter refFilter) {
		this.refFilter = refFilter != null ? refFilter : RefFilter.DEFAULT;
	}

	/**
	 * Get the configured pre upload hook.
	 *
	 * @return the configured pre upload hook.
	 */
	public PreUploadHook getPreUploadHook() {
		return preUploadHook;
	}

	/**
	 * Set the hook that controls how this instance will behave.
	 *
	 * @param hook
	 *            the hook; if null no special actions are taken.
	 */
	public void setPreUploadHook(PreUploadHook hook) {
		preUploadHook = hook != null ? hook : PreUploadHook.NULL;
	}

	/**
	 * Get the configured post upload hook.
	 *
	 * @return the configured post upload hook.
	 * @since 4.1
	 */
	public PostUploadHook getPostUploadHook() {
		return postUploadHook;
	}

	/**
	 * Set the hook for post upload actions (logging, repacking).
	 *
	 * @param hook
	 *            the hook; if null no special actions are taken.
	 * @since 4.1
	 */
	public void setPostUploadHook(PostUploadHook hook) {
		postUploadHook = hook != null ? hook : PostUploadHook.NULL;
	}

	/**
	 * 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) {
		this.packConfig = pc;
	}

	/**
	 * Set configuration controlling transfer options.
	 *
	 * @param tc
	 *            configuration controlling transfer options. If null the source
	 *            repository's settings will be used.
	 * @since 3.1
	 */
	public void setTransferConfig(TransferConfig tc) {
		this.transferConfig = tc != null ? tc : new TransferConfig(db);
		if (transferConfig.isAllowTipSha1InWant()) {
			setRequestPolicy(transferConfig.isAllowReachableSha1InWant()
				? RequestPolicy.REACHABLE_COMMIT_TIP : RequestPolicy.TIP);
		} else {
			setRequestPolicy(transferConfig.isAllowReachableSha1InWant()
				? RequestPolicy.REACHABLE_COMMIT : RequestPolicy.ADVERTISED);
		}
	}

	/**
	 * Check whether the client expects a side-band stream.
	 *
	 * @return true if the client has advertised a side-band capability, false
	 *     otherwise.
	 * @throws org.eclipse.jgit.transport.RequestNotYetReadException
	 *             if the client's request has not yet been read from the wire, so
	 *             we do not know if they expect side-band. Note that the client
	 *             may have already written the request, it just has not been
	 *             read.
	 */
	public boolean isSideBand() throws RequestNotYetReadException {
		if (options == null)
			throw new RequestNotYetReadException();
		return (options.contains(OPTION_SIDE_BAND)
				|| options.contains(OPTION_SIDE_BAND_64K));
	}

	/**
	 * Set the Extra Parameters provided by the client.
	 *
	 * <p>These are parameters passed by the client through a side channel
	 * such as the Git-Protocol HTTP header, to allow a client to request
	 * a newer response format while remaining compatible with older servers
	 * that do not understand different request formats.
	 *
	 * @param params
	 *            parameters supplied by the client, split at colons or NUL
	 *            bytes.
	 * @since 5.0
	 */
	public void setExtraParameters(Collection<String> params) {
		this.clientRequestedV2 = params.contains("version=2"); //$NON-NLS-1$
	}

	private boolean useProtocolV2() {
		return ProtocolVersion.V2.equals(transferConfig.protocolVersion)
				&& clientRequestedV2;
	}

	/**
	 * Execute the upload task on the socket.
	 *
	 * <p>If the client passed extra parameters (e.g., "version=2") through a
	 * side channel, the caller must call setExtraParameters first to supply
	 * them.
	 *
	 * @param input
	 *            raw input to read client commands from. Caller must ensure the
	 *            input is buffered, otherwise read performance may suffer.
	 * @param output
	 *            response back to the Git network client, to write the pack
	 *            data onto. Caller must ensure the output is buffered,
	 *            otherwise write performance may suffer.
	 * @param messages
	 *            secondary "notice" channel to send additional messages out
	 *            through. When run over SSH this should be tied back to the
	 *            standard error channel of the command execution. For most
	 *            other network connections this should be null.
	 * @throws java.io.IOException
	 */
	public void upload(final InputStream input, OutputStream output,
			final OutputStream messages) throws IOException {
		try {
			rawIn = input;
			if (messages != null)
				msgOut = messages;

			if (timeout > 0) {
				final Thread caller = Thread.currentThread();
				timer = new InterruptTimer(caller.getName() + "-Timer"); //$NON-NLS-1$
				TimeoutInputStream i = new TimeoutInputStream(rawIn, timer);
				@SuppressWarnings("resource")
				TimeoutOutputStream o = new TimeoutOutputStream(output, timer);
				i.setTimeout(timeout * 1000);
				o.setTimeout(timeout * 1000);
				rawIn = i;
				output = o;
			}

			rawOut = new ResponseBufferedOutputStream(output);
			if (biDirectionalPipe) {
				rawOut.stopBuffering();
			}

			pckIn = new PacketLineIn(rawIn);
			pckOut = new PacketLineOut(rawOut);
			if (useProtocolV2()) {
				serviceV2();
			} else {
				service();
			}
		} finally {
			msgOut = NullOutputStream.INSTANCE;
			walk.close();
			if (timer != null) {
				try {
					timer.terminate();
				} finally {
					timer = null;
				}
			}
		}
	}

	/**
	 * Get the PackWriter's statistics if a pack was sent to the client.
	 *
	 * @return statistics about pack output, if a pack was sent. Null if no pack
	 *         was sent, such as during the negotiation phase of a smart HTTP
	 *         connection, or if the client was already up-to-date.
	 * @since 4.1
	 */
	public PackStatistics getStatistics() {
		return statistics;
	}

	private Map<String, Ref> getAdvertisedOrDefaultRefs() throws IOException {
		if (refs == null)
			setAdvertisedRefs(db.getRefDatabase().getRefs(ALL));
		return refs;
	}

	private void service() throws IOException {
		boolean sendPack = false;
		// If it's a non-bidi request, we need to read the entire request before
		// writing a response. Buffer the response until then.
		PackStatistics.Accumulator accumulator = new PackStatistics.Accumulator();
		List<ObjectId> unshallowCommits = new ArrayList<>();
		try {
			if (biDirectionalPipe)
				sendAdvertisedRefs(new PacketLineOutRefAdvertiser(pckOut));
			else if (requestValidator instanceof AnyRequestValidator)
				advertised = Collections.emptySet();
			else
				advertised = refIdSet(getAdvertisedOrDefaultRefs().values());

			long negotiateStart = System.currentTimeMillis();
			accumulator.advertised = advertised.size();
			recvWants();
			if (wantIds.isEmpty()) {
				preUploadHook.onBeginNegotiateRound(this, wantIds, 0);
				preUploadHook.onEndNegotiateRound(this, wantIds, 0, 0, false);
				return;
			}
			accumulator.wants = wantIds.size();

			if (options.contains(OPTION_MULTI_ACK_DETAILED)) {
				multiAck = MultiAck.DETAILED;
				noDone = options.contains(OPTION_NO_DONE);
			} else if (options.contains(OPTION_MULTI_ACK))
				multiAck = MultiAck.CONTINUE;
			else
				multiAck = MultiAck.OFF;

			if (!clientShallowCommits.isEmpty())
				verifyClientShallow(clientShallowCommits);
			if (depth != 0) {
				computeShallowsAndUnshallows(wantIds, shallow -> {
					pckOut.writeString("shallow " + shallow.name() + '\n'); //$NON-NLS-1$
				}, unshallow -> {
					pckOut.writeString("unshallow " + unshallow.name() + '\n'); //$NON-NLS-1$
					unshallowCommits.add(unshallow);
				});
				pckOut.end();
			}
			if (!clientShallowCommits.isEmpty())
				walk.assumeShallow(clientShallowCommits);
			sendPack = negotiate(accumulator);
			accumulator.timeNegotiating += System.currentTimeMillis()
					- negotiateStart;

			if (sendPack && !biDirectionalPipe) {
				// Ensure the request was fully consumed. Any remaining input must
				// be a protocol error. If we aren't at EOF the implementation is broken.
				int eof = rawIn.read();
				if (0 <= eof) {
					sendPack = false;
					throw new CorruptObjectException(MessageFormat.format(
							JGitText.get().expectedEOFReceived,
							"\\x" + Integer.toHexString(eof))); //$NON-NLS-1$
				}
			}
		} catch (ServiceMayNotContinueException err) {
			if (!err.isOutput() && err.getMessage() != null) {
				try {
					pckOut.writeString("ERR " + err.getMessage() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
					err.setOutput();
				} catch (Throwable err2) {
					// Ignore this secondary failure (and not mark output).
				}
			}
			throw err;
		} catch (IOException | RuntimeException | Error err) {
			boolean output = false;
			try {
				String msg = err instanceof PackProtocolException
						? err.getMessage()
						: JGitText.get().internalServerError;
				pckOut.writeString("ERR " + msg + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
				output = true;
			} catch (Throwable err2) {
				// Ignore this secondary failure, leave output false.
			}
			if (output) {
				throw new UploadPackInternalServerErrorException(err);
			}
			throw err;
		} finally {
			if (!sendPack && !biDirectionalPipe) {
				while (0 < rawIn.skip(2048) || 0 <= rawIn.read()) {
					// Discard until EOF.
				}
			}
			rawOut.stopBuffering();
		}

		if (sendPack) {
			sendPack(accumulator, refs == null ? null : refs.values(), unshallowCommits);
		}
	}

	private void lsRefsV2() throws IOException {
		ProtocolV2Parser parser = new ProtocolV2Parser(transferConfig);
		LsRefsV2Request req = parser.parseLsRefsRequest(pckIn);
		protocolV2Hook.onLsRefs(req);

		rawOut.stopBuffering();
		PacketLineOutRefAdvertiser adv = new PacketLineOutRefAdvertiser(pckOut);
		adv.setUseProtocolV2(true);
		if (req.getPeel()) {
			adv.setDerefTags(true);
		}
		Map<String, Ref> refsToSend;
		if (req.getRefPrefixes().isEmpty()) {
			refsToSend = getAdvertisedOrDefaultRefs();
		} else {
			refsToSend = new HashMap<>();
			String[] prefixes = req.getRefPrefixes().toArray(new String[0]);
			for (Ref ref : db.getRefDatabase().getRefsByPrefix(prefixes)) {
				refsToSend.put(ref.getName(), ref);
			}
		}
		if (req.getSymrefs()) {
			findSymrefs(adv, refsToSend);
		}

		adv.send(refsToSend);
		adv.end();
	}

	private void fetchV2() throws IOException {
		// Depending on the requestValidator, #processHaveLines may
		// require that advertised be set. Set it only in the required
		// circumstances (to avoid a full ref lookup in the case that
		// we don't need it).
		if (requestValidator instanceof TipRequestValidator ||
				requestValidator instanceof ReachableCommitTipRequestValidator ||
				requestValidator instanceof AnyRequestValidator) {
			advertised = Collections.emptySet();
		} else {
			advertised = refIdSet(getAdvertisedOrDefaultRefs().values());
		}

		ProtocolV2Parser parser = new ProtocolV2Parser(transferConfig);
		FetchV2Request req = parser.parseFetchRequest(pckIn,
				db.getRefDatabase());
		rawOut.stopBuffering();

		protocolV2Hook.onFetch(req);

		// TODO(ifrade): Refactor to pass around the Request object, instead of
		// copying data back to class fields
		options = req.getOptions();
		wantIds.addAll(req.getWantsIds());
		clientShallowCommits = req.getClientShallowCommits();
		depth = req.getDepth();
		shallowSince = req.getDeepenSince();
		filterBlobLimit = req.getFilterBlobLimit();
		deepenNotRefs = req.getDeepenNotRefs();

		boolean sectionSent = false;
		boolean mayHaveShallow = req.getDepth() != 0
				|| req.getDeepenSince() != 0
				|| !req.getDeepenNotRefs().isEmpty();
		List<ObjectId> shallowCommits = new ArrayList<>();
		List<ObjectId> unshallowCommits = new ArrayList<>();

		if (!req.getClientShallowCommits().isEmpty()) {
			verifyClientShallow(req.getClientShallowCommits());
		}
		if (mayHaveShallow) {
			computeShallowsAndUnshallows(req.getWantsIds(),
					shallowCommit -> shallowCommits.add(shallowCommit),
					unshallowCommit -> unshallowCommits.add(unshallowCommit));
		}
		if (!req.getClientShallowCommits().isEmpty())
			walk.assumeShallow(req.getClientShallowCommits());

		if (req.wasDoneReceived()) {
			processHaveLines(req.getPeerHas(), ObjectId.zeroId(),
					new PacketLineOut(NullOutputStream.INSTANCE));
		} else {
			pckOut.writeString("acknowledgments\n"); //$NON-NLS-1$
			for (ObjectId id : req.getPeerHas()) {
				if (walk.getObjectReader().has(id)) {
					pckOut.writeString("ACK " + id.getName() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
				}
			}
			processHaveLines(req.getPeerHas(), ObjectId.zeroId(),
					new PacketLineOut(NullOutputStream.INSTANCE));
			if (okToGiveUp()) {
				pckOut.writeString("ready\n"); //$NON-NLS-1$
			} else if (commonBase.isEmpty()) {
				pckOut.writeString("NAK\n"); //$NON-NLS-1$
			}
			sectionSent = true;
		}

		if (req.wasDoneReceived() || okToGiveUp()) {
			if (mayHaveShallow) {
				if (sectionSent)
					pckOut.writeDelim();
				pckOut.writeString("shallow-info\n"); //$NON-NLS-1$
				for (ObjectId o : shallowCommits) {
					pckOut.writeString("shallow " + o.getName() + '\n'); //$NON-NLS-1$
				}
				for (ObjectId o : unshallowCommits) {
					pckOut.writeString("unshallow " + o.getName() + '\n'); //$NON-NLS-1$
				}
				sectionSent = true;
			}

			if (!req.getWantedRefs().isEmpty()) {
				if (sectionSent) {
					pckOut.writeDelim();
				}
				pckOut.writeString("wanted-refs\n"); //$NON-NLS-1$
				for (Map.Entry<String, ObjectId> entry : req.getWantedRefs()
						.entrySet()) {
					pckOut.writeString(entry.getValue().getName() + ' ' +
							entry.getKey() + '\n');
				}
				sectionSent = true;
			}

			if (sectionSent)
				pckOut.writeDelim();
			pckOut.writeString("packfile\n"); //$NON-NLS-1$
			sendPack(new PackStatistics.Accumulator(),
					req.getOptions().contains(OPTION_INCLUDE_TAG)
						? db.getRefDatabase().getRefsByPrefix(R_TAGS)
						: null,
					unshallowCommits);
			// sendPack invokes pckOut.end() for us, so we do not
			// need to invoke it here.
		} else {
			// Invoke pckOut.end() by ourselves.
			pckOut.end();
		}
	}

	/*
	 * Returns true if this is the last command and we should tear down the
	 * connection.
	 */
	private boolean serveOneCommandV2() throws IOException {
		String command;
		try {
			command = pckIn.readString();
		} catch (EOFException eof) {
			/* EOF when awaiting command is fine */
			return true;
		}
		if (command == PacketLineIn.END) {
			// A blank request is valid according
			// to the protocol; do nothing in this
			// case.
			return true;
		}
		if (command.equals("command=" + COMMAND_LS_REFS)) { //$NON-NLS-1$
			lsRefsV2();
			return false;
		}
		if (command.equals("command=" + COMMAND_FETCH)) { //$NON-NLS-1$
			fetchV2();
			return false;
		}
		throw new PackProtocolException(MessageFormat
				.format(JGitText.get().unknownTransportCommand, command));
	}

	private List<String> getV2CapabilityAdvertisement() {
		ArrayList<String> caps = new ArrayList<>();
		caps.add("version 2"); //$NON-NLS-1$
		caps.add(COMMAND_LS_REFS);
		boolean advertiseRefInWant = transferConfig.isAllowRefInWant() &&
				db.getConfig().getBoolean("uploadpack", null, //$NON-NLS-1$
						"advertiserefinwant", true); //$NON-NLS-1$
		caps.add(
				COMMAND_FETCH + '=' +
				(transferConfig.isAllowFilter() ? OPTION_FILTER + ' ' : "") + //$NON-NLS-1$
				(advertiseRefInWant ? CAPABILITY_REF_IN_WANT + ' ' : "") + //$NON-NLS-1$
				OPTION_SHALLOW);
		return caps;
	}

	private void serviceV2() throws IOException {
		if (biDirectionalPipe) {
			// Just like in service(), the capability advertisement
			// is sent only if this is a bidirectional pipe. (If
			// not, the client is expected to call
			// sendAdvertisedRefs() on its own.)
			protocolV2Hook
					.onCapabilities(CapabilitiesV2Request.builder().build());
			for (String s : getV2CapabilityAdvertisement()) {
				pckOut.writeString(s + "\n"); //$NON-NLS-1$
			}
			pckOut.end();

			while (!serveOneCommandV2()) {
				// Repeat until an empty command or EOF.
			}
			return;
		}

		try {
			serveOneCommandV2();
		} finally {
			while (0 < rawIn.skip(2048) || 0 <= rawIn.read()) {
				// Discard until EOF.
			}
			rawOut.stopBuffering();
		}
	}

	private static Set<ObjectId> refIdSet(Collection<Ref> refs) {
		Set<ObjectId> ids = new HashSet<>(refs.size());
		for (Ref ref : refs) {
			ObjectId id = ref.getObjectId();
			if (id != null) {
				ids.add(id);
			}
			id = ref.getPeeledObjectId();
			if (id != null) {
				ids.add(id);
			}
		}
		return ids;
	}

	/*
	 * Determines what object ids must be marked as shallow or unshallow for the
	 * client.
	 */
	private void computeShallowsAndUnshallows(Iterable<ObjectId> wants,
			IOConsumer<ObjectId> shallowFunc,
			IOConsumer<ObjectId> unshallowFunc)
			throws IOException {
		if (options.contains(OPTION_DEEPEN_RELATIVE) || shallowSince != 0
				|| !deepenNotRefs.isEmpty()) {
			// TODO(jonathantanmy): Implement deepen-relative, deepen-since,
			// and deepen-not.
			throw new UnsupportedOperationException();
		}

		int walkDepth = depth - 1;
		try (DepthWalk.RevWalk depthWalk = new DepthWalk.RevWalk(
				walk.getObjectReader(), walkDepth)) {

			// Find all the commits which will be shallow
			for (ObjectId o : wants) {
				try {
					depthWalk.markRoot(depthWalk.parseCommit(o));
				} catch (IncorrectObjectTypeException notCommit) {
					// Ignore non-commits in this loop.
				}
			}

			RevCommit o;
			while ((o = depthWalk.next()) != null) {
				DepthWalk.Commit c = (DepthWalk.Commit) o;

				// Commits at the boundary which aren't already shallow in
				// the client need to be marked as such
				if (c.getDepth() == walkDepth
						&& !clientShallowCommits.contains(c)) {
					shallowFunc.accept(c.copy());
				}

				// Commits not on the boundary which are shallow in the client
				// need to become unshallowed
				if (c.getDepth() < walkDepth
						&& clientShallowCommits.remove(c)) {
					unshallowFunc.accept(c.copy());
				}
			}
		}
	}

	/*
	 * Verify all shallow lines refer to commits
	 *
	 * It can mutate the input set (removing missing object ids from it)
	 */
	private void verifyClientShallow(Set<ObjectId> shallowCommits)
			throws IOException, PackProtocolException {
		AsyncRevObjectQueue q = walk.parseAny(shallowCommits, true);
		try {
			for (;;) {
				try {
					// Shallow objects named by the client must be commits.
					RevObject o = q.next();
					if (o == null) {
						break;
					}
					if (!(o instanceof RevCommit)) {
						throw new PackProtocolException(
							MessageFormat.format(
								JGitText.get().invalidShallowObject,
								o.name()));
					}
				} catch (MissingObjectException notCommit) {
					// shallow objects not known at the server are ignored
					// by git-core upload-pack, match that behavior.
					shallowCommits.remove(notCommit.getObjectId());
					continue;
				}
			}
		} finally {
			q.release();
		}
	}

	/**
	 * Generate an advertisement of available refs and capabilities.
	 *
	 * @param adv
	 *            the advertisement formatter.
	 * @throws java.io.IOException
	 *            the formatter failed to write an advertisement.
	 * @throws org.eclipse.jgit.transport.ServiceMayNotContinueException
	 *            the hook denied advertisement.
	 */
	public void sendAdvertisedRefs(RefAdvertiser adv) throws IOException,
			ServiceMayNotContinueException {
		sendAdvertisedRefs(adv, null);
	}

	/**
	 * Generate an advertisement of available refs and capabilities.
	 *
	 * @param adv
	 *            the advertisement formatter.
	 * @param serviceName
	 *            if not null, also output "# service=serviceName" followed by a
	 *            flush packet before the advertisement. This is required
	 *            in v0 of the HTTP protocol, described in Git's
	 *            Documentation/technical/http-protocol.txt.
	 * @throws java.io.IOException
	 *            the formatter failed to write an advertisement.
	 * @throws org.eclipse.jgit.transport.ServiceMayNotContinueException
	 *            the hook denied advertisement.
	 * @since 5.0
	 */
	public void sendAdvertisedRefs(RefAdvertiser adv,
			@Nullable String serviceName) throws IOException,
			ServiceMayNotContinueException {
		if (useProtocolV2()) {
			// The equivalent in v2 is only the capabilities
			// advertisement.
			protocolV2Hook
					.onCapabilities(CapabilitiesV2Request.builder().build());
			for (String s : getV2CapabilityAdvertisement()) {
				adv.writeOne(s);
			}
			adv.end();
			return;
		}

		try {
			advertiseRefsHook.advertiseRefs(this);
		} catch (ServiceMayNotContinueException fail) {
			if (fail.getMessage() != null) {
				adv.writeOne("ERR " + fail.getMessage()); //$NON-NLS-1$
				fail.setOutput();
			}
			throw fail;
		}

		if (serviceName != null) {
			adv.writeOne("# service=" + serviceName + '\n'); //$NON-NLS-1$
			adv.end();
		}
		adv.init(db);
		adv.advertiseCapability(OPTION_INCLUDE_TAG);
		adv.advertiseCapability(OPTION_MULTI_ACK_DETAILED);
		adv.advertiseCapability(OPTION_MULTI_ACK);
		adv.advertiseCapability(OPTION_OFS_DELTA);
		adv.advertiseCapability(OPTION_SIDE_BAND);
		adv.advertiseCapability(OPTION_SIDE_BAND_64K);
		adv.advertiseCapability(OPTION_THIN_PACK);
		adv.advertiseCapability(OPTION_NO_PROGRESS);
		adv.advertiseCapability(OPTION_SHALLOW);
		if (!biDirectionalPipe)
			adv.advertiseCapability(OPTION_NO_DONE);
		RequestPolicy policy = getRequestPolicy();
		if (policy == RequestPolicy.TIP
				|| policy == RequestPolicy.REACHABLE_COMMIT_TIP
				|| policy == null)
			adv.advertiseCapability(OPTION_ALLOW_TIP_SHA1_IN_WANT);
		if (policy == RequestPolicy.REACHABLE_COMMIT
				|| policy == RequestPolicy.REACHABLE_COMMIT_TIP
				|| policy == null)
			adv.advertiseCapability(OPTION_ALLOW_REACHABLE_SHA1_IN_WANT);
		adv.advertiseCapability(OPTION_AGENT, UserAgent.get());
		if (transferConfig.isAllowFilter()) {
			adv.advertiseCapability(OPTION_FILTER);
		}
		adv.setDerefTags(true);
		Map<String, Ref> advertisedOrDefaultRefs = getAdvertisedOrDefaultRefs();
		findSymrefs(adv, advertisedOrDefaultRefs);
		advertised = adv.send(advertisedOrDefaultRefs);
		if (adv.isEmpty())
			adv.advertiseId(ObjectId.zeroId(), "capabilities^{}"); //$NON-NLS-1$
		adv.end();
	}

	/**
	 * Send a message to the client, if it supports receiving them.
	 * <p>
	 * If the client doesn't support receiving messages, the message will be
	 * discarded, with no other indication to the caller or to the client.
	 *
	 * @param what
	 *            string describing the problem identified by the hook. The
	 *            string must not end with an LF, and must not contain an LF.
	 * @since 3.1
	 */
	public void sendMessage(String what) {
		try {
			msgOut.write(Constants.encode(what + "\n")); //$NON-NLS-1$
		} catch (IOException e) {
			// Ignore write failures.
		}
	}

	/**
	 * Get an underlying stream for sending messages to the client
	 *
	 * @return an underlying stream for sending messages to the client, or null.
	 * @since 3.1
	 */
	public OutputStream getMessageOutputStream() {
		return msgOut;
	}

	private void recvWants() throws IOException {
		boolean isFirst = true;
		boolean filterReceived = false;
		for (;;) {
			String line;
			try {
				line = pckIn.readString();
			} catch (EOFException eof) {
				if (isFirst)
					break;
				throw eof;
			}

			if (line == PacketLineIn.END)
				break;

			if (line.startsWith("deepen ")) { //$NON-NLS-1$
				depth = Integer.parseInt(line.substring(7));
				if (depth <= 0) {
					throw new PackProtocolException(
							MessageFormat.format(JGitText.get().invalidDepth,
									Integer.valueOf(depth)));
				}
				continue;
			}

			if (line.startsWith("shallow ")) { //$NON-NLS-1$
				clientShallowCommits.add(ObjectId.fromString(line.substring(8)));
				continue;
			}

			if (transferConfig.isAllowFilter()
					&& line.startsWith(OPTION_FILTER + " ")) { //$NON-NLS-1$
				String arg = line.substring(OPTION_FILTER.length() + 1);

				if (filterReceived) {
					throw new PackProtocolException(JGitText.get().tooManyFilters);
				}
				filterReceived = true;

				filterBlobLimit = ProtocolV2Parser.filterLine(arg);
				continue;
			}

			if (!line.startsWith("want ") || line.length() < 45) //$NON-NLS-1$
				throw new PackProtocolException(MessageFormat.format(JGitText.get().expectedGot, "want", line)); //$NON-NLS-1$

			if (isFirst) {
				if (line.length() > 45) {
					FirstLine firstLine = new FirstLine(line);
					options = firstLine.getOptions();
					line = firstLine.getLine();
				} else
					options = Collections.emptySet();
			}

			wantIds.add(ObjectId.fromString(line.substring(5)));
			isFirst = false;
		}
	}

	/**
	 * Returns the clone/fetch depth. Valid only after calling recvWants(). A
	 * depth of 1 means return only the wants.
	 *
	 * @return the depth requested by the client, or 0 if unbounded.
	 * @since 4.0
	 */
	public int getDepth() {
		if (options == null)
			throw new RequestNotYetReadException();
		return depth;
	}

	/**
	 * Get the user agent of the client.
	 * <p>
	 * If the client is new enough to use {@code agent=} capability that value
	 * will be returned. Older HTTP clients may also supply their version using
	 * the HTTP {@code User-Agent} header. The capability overrides the HTTP
	 * header if both are available.
	 * <p>
	 * When an HTTP request has been received this method returns the HTTP
	 * {@code User-Agent} header value until capabilities have been parsed.
	 *
	 * @return user agent supplied by the client. Available only if the client
	 *         is new enough to advertise its user agent.
	 * @since 4.0
	 */
	public String getPeerUserAgent() {
		return UserAgent.getAgent(options, userAgent);
	}

	private boolean negotiate(PackStatistics.Accumulator accumulator)
			throws IOException {
		okToGiveUp = Boolean.FALSE;

		ObjectId last = ObjectId.zeroId();
		List<ObjectId> peerHas = new ArrayList<>(64);
		for (;;) {
			String line;
			try {
				line = pckIn.readString();
			} catch (EOFException eof) {
				// EOF on stateless RPC (aka smart HTTP) and non-shallow request
				// means the client asked for the updated shallow/unshallow data,
				// disconnected, and will try another request with actual want/have.
				// Don't report the EOF here, its a bug in the protocol that the client
				// just disconnects without sending an END.
				if (!biDirectionalPipe && depth > 0)
					return false;
				throw eof;
			}

			if (line == PacketLineIn.END) {
				last = processHaveLines(peerHas, last, pckOut);
				if (commonBase.isEmpty() || multiAck != MultiAck.OFF)
					pckOut.writeString("NAK\n"); //$NON-NLS-1$
				if (noDone && sentReady) {
					pckOut.writeString("ACK " + last.name() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
					return true;
				}
				if (!biDirectionalPipe)
					return false;
				pckOut.flush();

			} else if (line.startsWith("have ") && line.length() == 45) { //$NON-NLS-1$
				peerHas.add(ObjectId.fromString(line.substring(5)));
				accumulator.haves++;
			} else if (line.equals("done")) { //$NON-NLS-1$
				last = processHaveLines(peerHas, last, pckOut);

				if (commonBase.isEmpty())
					pckOut.writeString("NAK\n"); //$NON-NLS-1$

				else if (multiAck != MultiAck.OFF)
					pckOut.writeString("ACK " + last.name() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$

				return true;

			} else {
				throw new PackProtocolException(MessageFormat.format(JGitText.get().expectedGot, "have", line)); //$NON-NLS-1$
			}
		}
	}

	private ObjectId processHaveLines(List<ObjectId> peerHas, ObjectId last, PacketLineOut out)
			throws IOException {
		preUploadHook.onBeginNegotiateRound(this, wantIds, peerHas.size());
		if (wantAll.isEmpty() && !wantIds.isEmpty())
			parseWants();
		if (peerHas.isEmpty())
			return last;

		sentReady = false;
		int haveCnt = 0;
		walk.getObjectReader().setAvoidUnreachableObjects(true);
		AsyncRevObjectQueue q = walk.parseAny(peerHas, false);
		try {
			for (;;) {
				RevObject obj;
				try {
					obj = q.next();
				} catch (MissingObjectException notFound) {
					continue;
				}
				if (obj == null)
					break;

				last = obj;
				haveCnt++;

				if (obj instanceof RevCommit) {
					RevCommit c = (RevCommit) obj;
					if (oldestTime == 0 || c.getCommitTime() < oldestTime)
						oldestTime = c.getCommitTime();
				}

				if (obj.has(PEER_HAS))
					continue;

				obj.add(PEER_HAS);
				if (obj instanceof RevCommit)
					((RevCommit) obj).carry(PEER_HAS);
				addCommonBase(obj);

				// If both sides have the same object; let the client know.
				//
				switch (multiAck) {
				case OFF:
					if (commonBase.size() == 1)
						out.writeString("ACK " + obj.name() + "\n"); //$NON-NLS-1$ //$NON-NLS-2$
					break;
				case CONTINUE:
					out.writeString("ACK " + obj.name() + " continue\n"); //$NON-NLS-1$ //$NON-NLS-2$
					break;
				case DETAILED:
					out.writeString("ACK " + obj.name() + " common\n"); //$NON-NLS-1$ //$NON-NLS-2$
					break;
				}
			}
		} finally {
			q.release();
			walk.getObjectReader().setAvoidUnreachableObjects(false);
		}

		int missCnt = peerHas.size() - haveCnt;

		// If we don't have one of the objects but we're also willing to
		// create a pack at this point, let the client know so it stops
		// telling us about its history.
		//
		boolean didOkToGiveUp = false;
		if (0 < missCnt) {
			for (int i = peerHas.size() - 1; i >= 0; i--) {
				ObjectId id = peerHas.get(i);
				if (walk.lookupOrNull(id) == null) {
					didOkToGiveUp = true;
					if (okToGiveUp()) {
						switch (multiAck) {
						case OFF:
							break;
						case CONTINUE:
							out.writeString("ACK " + id.name() + " continue\n"); //$NON-NLS-1$ //$NON-NLS-2$
							break;
						case DETAILED:
							out.writeString("ACK " + id.name() + " ready\n"); //$NON-NLS-1$ //$NON-NLS-2$
							sentReady = true;
							break;
						}
					}
					break;
				}
			}
		}

		if (multiAck == MultiAck.DETAILED && !didOkToGiveUp && okToGiveUp()) {
			ObjectId id = peerHas.get(peerHas.size() - 1);
			out.writeString("ACK " + id.name() + " ready\n"); //$NON-NLS-1$ //$NON-NLS-2$
			sentReady = true;
		}

		preUploadHook.onEndNegotiateRound(this, wantAll, haveCnt, missCnt, sentReady);
		peerHas.clear();
		return last;
	}

	private void parseWants() throws IOException {
		List<ObjectId> notAdvertisedWants = null;
		for (ObjectId obj : wantIds) {
			if (!advertised.contains(obj)) {
				if (notAdvertisedWants == null)
					notAdvertisedWants = new ArrayList<>();
				notAdvertisedWants.add(obj);
			}
		}
		if (notAdvertisedWants != null)
			requestValidator.checkWants(this, notAdvertisedWants);

		AsyncRevObjectQueue q = walk.parseAny(wantIds, true);
		try {
			RevObject obj;
			while ((obj = q.next()) != null) {
				want(obj);

				if (!(obj instanceof RevCommit))
					obj.add(SATISFIED);
				if (obj instanceof RevTag) {
					obj = walk.peel(obj);
					if (obj instanceof RevCommit)
						want(obj);
				}
			}
			wantIds.clear();
		} catch (MissingObjectException notFound) {
			throw new WantNotValidException(notFound.getObjectId(), notFound);
		} finally {
			q.release();
		}
	}

	private void want(RevObject obj) {
		if (!obj.has(WANT)) {
			obj.add(WANT);
			wantAll.add(obj);
		}
	}

	/**
	 * Validator corresponding to {@link RequestPolicy#ADVERTISED}.
	 *
	 * @since 3.1
	 */
	public static final class AdvertisedRequestValidator
			implements RequestValidator {
		@Override
		public void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException {
			if (!up.isBiDirectionalPipe())
				new ReachableCommitRequestValidator().checkWants(up, wants);
			else if (!wants.isEmpty())
				throw new WantNotValidException(wants.iterator().next());
		}
	}

	/**
	 * Validator corresponding to {@link RequestPolicy#REACHABLE_COMMIT}.
	 *
	 * @since 3.1
	 */
	public static final class ReachableCommitRequestValidator
			implements RequestValidator {
		@Override
		public void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException {
			checkNotAdvertisedWants(up, wants,
					refIdSet(up.getAdvertisedRefs().values()));
		}
	}

	/**
	 * Validator corresponding to {@link RequestPolicy#TIP}.
	 *
	 * @since 3.1
	 */
	public static final class TipRequestValidator implements RequestValidator {
		@Override
		public void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException {
			if (!up.isBiDirectionalPipe())
				new ReachableCommitTipRequestValidator().checkWants(up, wants);
			else if (!wants.isEmpty()) {
				Set<ObjectId> refIds =
						refIdSet(up.getRepository().getRefDatabase().getRefs());
				for (ObjectId obj : wants) {
					if (!refIds.contains(obj))
						throw new WantNotValidException(obj);
				}
			}
		}
	}

	/**
	 * Validator corresponding to {@link RequestPolicy#REACHABLE_COMMIT_TIP}.
	 *
	 * @since 3.1
	 */
	public static final class ReachableCommitTipRequestValidator
			implements RequestValidator {
		@Override
		public void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException {
			checkNotAdvertisedWants(up, wants,
					refIdSet(up.getRepository().getRefDatabase().getRefs()));
		}
	}

	/**
	 * Validator corresponding to {@link RequestPolicy#ANY}.
	 *
	 * @since 3.1
	 */
	public static final class AnyRequestValidator implements RequestValidator {
		@Override
		public void checkWants(UploadPack up, List<ObjectId> wants)
				throws PackProtocolException, IOException {
			// All requests are valid.
		}
	}

	private static void checkNotAdvertisedWantsUsingBitmap(ObjectReader reader,
			BitmapIndex bitmapIndex, List<ObjectId> notAdvertisedWants,
			Set<ObjectId> reachableFrom) throws IOException {
		BitmapWalker bitmapWalker = new BitmapWalker(new ObjectWalk(reader), bitmapIndex, null);
		BitmapBuilder reachables = bitmapWalker.findObjects(reachableFrom, null, false);
		for (ObjectId oid : notAdvertisedWants) {
			if (!reachables.contains(oid)) {
				throw new WantNotValidException(oid);
			}
		}
	}

	private static void checkNotAdvertisedWants(UploadPack up,
			List<ObjectId> notAdvertisedWants, Set<ObjectId> reachableFrom)
			throws MissingObjectException, IncorrectObjectTypeException, IOException {
		// Walk the requested commits back to the provided set of commits. If any
		// commit exists, a branch was deleted or rewound and the repository owner
		// no longer exports that requested item. If the requested commit is merged
		// into an advertised branch it will be marked UNINTERESTING and no commits
		// return.

		ObjectReader reader = up.getRevWalk().getObjectReader();
		try (RevWalk walk = new RevWalk(reader)) {
			AsyncRevObjectQueue q = walk.parseAny(notAdvertisedWants, true);
			try {
				RevObject obj;
				while ((obj = q.next()) != null) {
					if (!(obj instanceof RevCommit)) {
						// If unadvertized non-commits are requested, use
						// bitmaps. If there are no bitmaps, instead of
						// incurring the expense of a manual walk, reject
						// the request.
						BitmapIndex bitmapIndex = reader.getBitmapIndex();
						if (bitmapIndex != null) {
							checkNotAdvertisedWantsUsingBitmap(
									reader,
									bitmapIndex,
									notAdvertisedWants,
									reachableFrom);
							return;
						}
						throw new WantNotValidException(obj);
					}
					walk.markStart((RevCommit) obj);
				}
			} catch (MissingObjectException notFound) {
				throw new WantNotValidException(notFound.getObjectId(),
						notFound);
			} finally {
				q.release();
			}
			for (ObjectId id : reachableFrom) {
				try {
					walk.markUninteresting(walk.parseCommit(id));
				} catch (IncorrectObjectTypeException notCommit) {
					continue;
				}
			}

			RevCommit bad = walk.next();
			if (bad != null) {
				throw new WantNotValidException(bad);
			}
		}
	}

	private void addCommonBase(RevObject o) {
		if (!o.has(COMMON)) {
			o.add(COMMON);
			commonBase.add(o);
			okToGiveUp = null;
		}
	}

	private boolean okToGiveUp() throws PackProtocolException {
		if (okToGiveUp == null)
			okToGiveUp = Boolean.valueOf(okToGiveUpImp());
		return okToGiveUp.booleanValue();
	}

	private boolean okToGiveUpImp() throws PackProtocolException {
		if (commonBase.isEmpty())
			return false;

		try {
			for (RevObject obj : wantAll) {
				if (!wantSatisfied(obj))
					return false;
			}
			return true;
		} catch (IOException e) {
			throw new PackProtocolException(JGitText.get().internalRevisionError, e);
		}
	}

	private boolean wantSatisfied(RevObject want) throws IOException {
		if (want.has(SATISFIED))
			return true;

		walk.resetRetain(SAVE);
		walk.markStart((RevCommit) want);
		if (oldestTime != 0)
			walk.setRevFilter(CommitTimeRevFilter.after(oldestTime * 1000L));
		for (;;) {
			final RevCommit c = walk.next();
			if (c == null)
				break;
			if (c.has(PEER_HAS)) {
				addCommonBase(c);
				want.add(SATISFIED);
				return true;
			}
		}
		return false;
	}

	/**
	 * Send the requested objects to the client.
	 *
	 * @param accumulator
	 *                where to write statistics about the content of the pack.
	 * @param allTags
	 *                refs to search for annotated tags to include in the pack
	 *                if the {@link #OPTION_INCLUDE_TAG} capability was
	 *                requested.
	 * @param unshallowCommits
	 *                shallow commits on the client that are now becoming
	 *                unshallow
	 * @throws IOException
	 *                if an error occured while generating or writing the pack.
	 */
	private void sendPack(PackStatistics.Accumulator accumulator,
			@Nullable Collection<Ref> allTags,
			List<ObjectId> unshallowCommits) throws IOException {
		final boolean sideband = options.contains(OPTION_SIDE_BAND)
				|| options.contains(OPTION_SIDE_BAND_64K);
		if (sideband) {
			try {
				sendPack(true, accumulator, allTags, unshallowCommits);
			} catch (ServiceMayNotContinueException noPack) {
				// This was already reported on (below).
				throw noPack;
			} catch (IOException err) {
				if (reportInternalServerErrorOverSideband())
					throw new UploadPackInternalServerErrorException(err);
				else
					throw err;
			} catch (RuntimeException err) {
				if (reportInternalServerErrorOverSideband())
					throw new UploadPackInternalServerErrorException(err);
				else
					throw err;
			} catch (Error err) {
				if (reportInternalServerErrorOverSideband())
					throw new UploadPackInternalServerErrorException(err);
				else
					throw err;
			}
		} else {
			sendPack(false, accumulator, allTags, unshallowCommits);
		}
	}

	private boolean reportInternalServerErrorOverSideband() {
		try {
			@SuppressWarnings("resource" /* java 7 */)
			SideBandOutputStream err = new SideBandOutputStream(
					SideBandOutputStream.CH_ERROR,
					SideBandOutputStream.SMALL_BUF,
					rawOut);
			err.write(Constants.encode(JGitText.get().internalServerError));
			err.flush();
			return true;
		} catch (Throwable cannotReport) {
			// Ignore the reason. This is a secondary failure.
			return false;
		}
	}

	/**
	 * Send the requested objects to the client.
	 *
	 * @param sideband
	 *                whether to wrap the pack in side-band pkt-lines,
	 *                interleaved with progress messages and errors.
	 * @param accumulator
	 *                where to write statistics about the content of the pack.
	 * @param allTags
	 *                refs to search for annotated tags to include in the pack
	 *                if the {@link #OPTION_INCLUDE_TAG} capability was
	 *                requested.
	 * @param unshallowCommits
	 *                shallow commits on the client that are now becoming
	 *                unshallow
	 * @throws IOException
	 *                if an error occured while generating or writing the pack.
	 */
	private void sendPack(final boolean sideband,
			PackStatistics.Accumulator accumulator,
			@Nullable Collection<Ref> allTags,
			List<ObjectId> unshallowCommits) throws IOException {
		ProgressMonitor pm = NullProgressMonitor.INSTANCE;
		OutputStream packOut = rawOut;

		if (sideband) {
			int bufsz = SideBandOutputStream.SMALL_BUF;
			if (options.contains(OPTION_SIDE_BAND_64K))
				bufsz = SideBandOutputStream.MAX_BUF;

			packOut = new SideBandOutputStream(SideBandOutputStream.CH_DATA,
					bufsz, rawOut);
			if (!options.contains(OPTION_NO_PROGRESS)) {
				msgOut = new SideBandOutputStream(
						SideBandOutputStream.CH_PROGRESS, bufsz, rawOut);
				pm = new SideBandProgressMonitor(msgOut);
			}
		}

		try {
			if (wantAll.isEmpty()) {
				preUploadHook.onSendPack(this, wantIds, commonBase);
			} else {
				preUploadHook.onSendPack(this, wantAll, commonBase);
			}
			msgOut.flush();
		} catch (ServiceMayNotContinueException noPack) {
			if (sideband && noPack.getMessage() != null) {
				noPack.setOutput();
				@SuppressWarnings("resource" /* java 7 */)
				SideBandOutputStream err = new SideBandOutputStream(
						SideBandOutputStream.CH_ERROR,
						SideBandOutputStream.SMALL_BUF, rawOut);
				err.write(Constants.encode(noPack.getMessage()));
				err.flush();
			}
			throw noPack;
		}

		PackConfig cfg = packConfig;
		if (cfg == null)
			cfg = new PackConfig(db);
		@SuppressWarnings("resource") // PackWriter is referenced in the finally
										// block, and is closed there
		final PackWriter pw = new PackWriter(cfg, walk.getObjectReader(),
				accumulator);
		try {
			pw.setIndexDisabled(true);
			if (filterBlobLimit >= 0) {
				pw.setFilterBlobLimit(filterBlobLimit);
				pw.setUseCachedPacks(false);
			} else {
				pw.setUseCachedPacks(true);
			}
			pw.setUseBitmaps(depth == 0 && clientShallowCommits.isEmpty());
			pw.setClientShallowCommits(clientShallowCommits);
			pw.setReuseDeltaCommits(true);
			pw.setDeltaBaseAsOffset(options.contains(OPTION_OFS_DELTA));
			pw.setThin(options.contains(OPTION_THIN_PACK));
			pw.setReuseValidatingObjects(false);

			// Objects named directly by references go at the beginning
			// of the pack.
			if (commonBase.isEmpty() && refs != null) {
				Set<ObjectId> tagTargets = new HashSet<>();
				for (Ref ref : refs.values()) {
					if (ref.getPeeledObjectId() != null)
						tagTargets.add(ref.getPeeledObjectId());
					else if (ref.getObjectId() == null)
						continue;
					else if (ref.getName().startsWith(Constants.R_HEADS))
						tagTargets.add(ref.getObjectId());
				}
				pw.setTagTargets(tagTargets);
			}

			RevWalk rw = walk;
			if (depth > 0) {
				pw.setShallowPack(depth, unshallowCommits);
				rw = new DepthWalk.RevWalk(walk.getObjectReader(), depth - 1);
				rw.assumeShallow(clientShallowCommits);
			}

			if (wantAll.isEmpty()) {
				pw.preparePack(pm, wantIds, commonBase, clientShallowCommits);
			} else {
				walk.reset();

				ObjectWalk ow = rw.toObjectWalkWithSameObjects();
				pw.preparePack(pm, ow, wantAll, commonBase, PackWriter.NONE);
				rw = ow;
			}

			if (options.contains(OPTION_INCLUDE_TAG) && allTags != null) {
				for (Ref ref : allTags) {
					ObjectId objectId = ref.getObjectId();
					if (objectId == null) {
						// skip unborn branch
						continue;
					}

					// If the object was already requested, skip it.
					if (wantAll.isEmpty()) {
						if (wantIds.contains(objectId))
							continue;
					} else {
						RevObject obj = rw.lookupOrNull(objectId);
						if (obj != null && obj.has(WANT))
							continue;
					}

					if (!ref.isPeeled())
						ref = db.getRefDatabase().peel(ref);

					ObjectId peeledId = ref.getPeeledObjectId();
					objectId = ref.getObjectId();
					if (peeledId == null || objectId == null)
						continue;

					if (pw.willInclude(peeledId) && !pw.willInclude(objectId)) {
						pw.addObject(rw.parseAny(objectId));
					}
				}
			}

			pw.writePack(pm, NullProgressMonitor.INSTANCE, packOut);

			if (msgOut != NullOutputStream.INSTANCE) {
				String msg = pw.getStatistics().getMessage() + '\n';
				msgOut.write(Constants.encode(msg));
				msgOut.flush();
			}

		} finally {
			statistics = pw.getStatistics();
			if (statistics != null) {
				postUploadHook.onPostUpload(statistics);
			}
			pw.close();
		}

		if (sideband)
			pckOut.end();
	}

	private static void findSymrefs(
			final RefAdvertiser adv, final Map<String, Ref> refs) {
		Ref head = refs.get(Constants.HEAD);
		if (head != null && head.isSymbolic()) {
			adv.addSymref(Constants.HEAD, head.getLeaf().getName());
		}
	}

	private static class ResponseBufferedOutputStream extends OutputStream {
		private final OutputStream rawOut;

		private OutputStream out;

		ResponseBufferedOutputStream(OutputStream rawOut) {
			this.rawOut = rawOut;
			this.out = new ByteArrayOutputStream();
		}

		@Override
		public void write(int b) throws IOException {
			out.write(b);
		}

		@Override
		public void write(byte b[]) throws IOException {
			out.write(b);
		}

		@Override
		public void write(byte b[], int off, int len) throws IOException {
			out.write(b, off, len);
		}

		@Override
		public void flush() throws IOException {
			out.flush();
		}

		@Override
		public void close() throws IOException {
			out.close();
		}

		void stopBuffering() throws IOException {
			if (out != rawOut) {
				((ByteArrayOutputStream) out).writeTo(rawOut);
				out = rawOut;
			}
		}
	}
}