/*
    * Copyright (C) 2008, 2020 Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.transport;
  
  import static java.util.Collections.unmodifiableMap;
  import static java.util.Objects.requireNonNull;
  import static org.eclipse.jgit.lib.Constants.R_TAGS;
  import static org.eclipse.jgit.transport.GitProtocolConstants.CAPABILITY_REF_IN_WANT;
  import static org.eclipse.jgit.transport.GitProtocolConstants.CAPABILITY_SERVER_OPTION;
  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_SIDEBAND_ALL;
  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 static org.eclipse.jgit.transport.GitProtocolConstants.VERSION_2_REQUEST;
  import static org.eclipse.jgit.util.RefMap.toRefMap;
  
  import java.io.ByteArrayOutputStream;
  import java.io.EOFException;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.io.UncheckedIOException;
  import java.text.MessageFormat;
  import java.time.Duration;
  import java.time.Instant;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Optional;
  import java.util.Set;
  import java.util.TreeMap;
  import java.util.function.Predicate;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  
  import org.eclipse.jgit.annotations.NonNull;
  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.CachedPackUriProvider;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.internal.transport.parser.FirstWant;
  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.RefDatabase;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.revwalk.AsyncRevObjectQueue;
  import org.eclipse.jgit.revwalk.DepthWalk;
  import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
  import org.eclipse.jgit.revwalk.ObjectWalk;
  import org.eclipse.jgit.revwalk.ReachabilityChecker;
  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 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 want-list, the line itself plus options.
 	 *
 	 * @deprecated Use {@link FirstWant} instead
 	 */
 	@Deprecated
 	public static class FirstLine {
 
 		private final FirstWant firstWant;
 
 		/**
 		 * @param line
 		 *            line from the client.
 		 */
 		public FirstLine(String line) {
 			try {
 				firstWant = FirstWant.fromLine(line);
 			} catch (PackProtocolException e) {
 				throw new UncheckedIOException(e);
 			}
 		}
 
 		/** @return non-capabilities part of the line. */
 		public String getLine() {
 			return firstWant.getLine();
 		}
 
 		/** @return capabilities parsed from the line. */
 		public Set<String> getOptions() {
 			if (firstWant.getAgent() != null) {
 				Set<String> caps = new HashSet<>(firstWant.getCapabilities());
 				caps.add(OPTION_AGENT + '=' + firstWant.getAgent());
 				return caps;
 			}
 			return firstWant.getCapabilities();
 		}
 	}
 
 	/*
 	 * {@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 OutputStream msgOut = NullOutputStream.INSTANCE;
 
 	private ErrorWriter errOut = new PackProtocolErrorWriter();
 
 	/**
 	 * Refs eligible for advertising to the client, set using
 	 * {@link #setAdvertisedRefs}.
 	 */
 	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;
 
 	/** Whether the {@link #advertiseRefsHook} has been invoked. */
 	private boolean advertiseRefsHookCalled;
 
 	/** 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;
 
 	/** Caller user agent */
 	String userAgent;
 
 	/** Raw ObjectIds the client has asked for, before validating them. */
 	private 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<>();
 
 	/** 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. */
 	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;
 
 	/**
 	 * Request this instance is handling.
 	 *
 	 * We need to keep a reference to it for {@link PreUploadHook pre upload
 	 * hooks}. They receive a reference this instance and invoke methods like
 	 * getDepth() to get information about the request.
 	 */
 	private FetchRequest currentRequest;
 
 	private CachedPackUriProvider cachedPackUriProvider;
 
 	/**
 	 * 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. Only valid during
 	 *         the negotiation phase. Will return {@code null} if
 	 *         {@link #setAdvertisedRefs(Map)} has not been called yet or if
 	 *         {@code #sendPack()} has been called.
 	 */
 	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(@Nullable 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(@Nullable 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(
 			@Nullable AdvertiseRefsHook advertiseRefsHook) {
 		this.advertiseRefsHook = advertiseRefsHook != null ? advertiseRefsHook
 				: AdvertiseRefsHook.DEFAULT;
 	}
 
 	/**
 	 * Set the protocol V2 hook.
 	 *
 	 * @param hook
 	 *            the hook; if null no special actions are taken.
 	 * @since 5.1
 	 */
 	public void setProtocolV2Hook(@Nullable ProtocolV2Hook hook) {
 		this.protocolV2Hook = hook != null ? hook : ProtocolV2Hook.DEFAULT;
 	}
 
 	/**
 	 * Get the currently installed protocol v2 hook.
 	 *
 	 * @return the hook or a default implementation if none installed.
 	 *
 	 * @since 5.5
 	 */
 	public ProtocolV2Hook getProtocolV2Hook() {
 		return this.protocolV2Hook != null ? this.protocolV2Hook
 				: ProtocolV2Hook.DEFAULT;
 	}
 
 	/**
 	 * 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(@Nullable 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(@Nullable 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(@Nullable 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(@Nullable 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(@Nullable 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 (currentRequest == null) {
 			throw new RequestNotYetReadException();
 		}
 		Set<String> caps = currentRequest.getClientCapabilities();
 		return caps.contains(OPTION_SIDE_BAND)
 				|| caps.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_REQUEST);
 	}
 
 	/**
 	 * @param p provider of URIs corresponding to cached packs (to support
 	 *     the packfile URIs feature)
 	 * @since 5.5
 	 */
 	public void setCachedPackUriProvider(@Nullable CachedPackUriProvider p) {
 		cachedPackUriProvider = p;
 	}
 
 	private boolean useProtocolV2() {
 		return (transferConfig.protocolVersion == null
 			|| ProtocolVersion.V2.equals(transferConfig.protocolVersion))
 				&& clientRequestedV2;
 	}
 
 	/**
 	 * Execute the upload task on the socket.
 	 *
 	 * <p>
 	 * Same as {@link #uploadWithExceptionPropagation} except that the thrown
 	 * exceptions are handled in the method, and the error messages are sent to
 	 * the clients.
 	 *
 	 * <p>
 	 * Call this method if the caller does not have an error handling mechanism.
 	 * Call {@link #uploadWithExceptionPropagation} if the caller wants to have
 	 * its own error handling mechanism.
 	 *
 	 * @param input
 	 * @param output
 	 * @param messages
 	 * @throws java.io.IOException
 	 */
 	public void upload(InputStream input, OutputStream output,
 			@Nullable OutputStream messages) throws IOException {
 		try {
 			uploadWithExceptionPropagation(input, output, messages);
 		} catch (ServiceMayNotContinueException err) {
 			if (!err.isOutput() && err.getMessage() != null) {
 				try {
 					errOut.writeError(err.getMessage());
 				} catch (IOException e) {
 					err.addSuppressed(e);
 					throw err;
 				}
 				err.setOutput();
 			}
 			throw err;
 		} catch (IOException | RuntimeException | Error err) {
 			if (rawOut != null) {
 				String msg = err instanceof PackProtocolException
 						? err.getMessage()
 						: JGitText.get().internalServerError;
 				try {
 					errOut.writeError(msg);
 				} catch (IOException e) {
 					err.addSuppressed(e);
 					throw err;
 				}
 				throw new UploadPackInternalServerErrorException(err);
 			}
 			throw err;
 		}
 	}
 
 	/**
 	 * 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 ServiceMayNotContinueException
 	 *             thrown if one of the hooks throws this.
 	 * @throws IOException
 	 *             thrown if the server or the client I/O fails, or there's an
 	 *             internal server error.
 	 * @since 5.6
 	 */
 	public void uploadWithExceptionPropagation(InputStream input,
 			OutputStream output, @Nullable OutputStream messages)
 			throws ServiceMayNotContinueException, 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);
 			PacketLineOut pckOut = new PacketLineOut(rawOut);
 			if (useProtocolV2()) {
 				serviceV2(pckOut);
 			} else {
 				service(pckOut);
 			}
 		} 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) {
 			return refs;
 		}
 
 		if (!advertiseRefsHookCalled) {
 			advertiseRefsHook.advertiseRefs(this);
 			advertiseRefsHookCalled = true;
 		}
 		if (refs == null) {
 			// Fall back to all refs.
 			setAdvertisedRefs(
 					db.getRefDatabase().getRefs().stream()
 							.collect(toRefMap((a, b) -> b)));
 		}
 		return refs;
 	}
 
 	private Map<String, Ref> getFilteredRefs(Collection<String> refPrefixes)
 					throws IOException {
 		if (refPrefixes.isEmpty()) {
 			return getAdvertisedOrDefaultRefs();
 		}
 		if (refs == null && !advertiseRefsHookCalled) {
 			advertiseRefsHook.advertiseRefs(this);
 			advertiseRefsHookCalled = true;
 		}
 		if (refs == null) {
 			// Fast path: the advertised refs hook did not set advertised refs.
 			String[] prefixes = refPrefixes.toArray(new String[0]);
 			Map<String, Ref> rs =
 					db.getRefDatabase().getRefsByPrefix(prefixes).stream()
 							.collect(toRefMap((a, b) -> b));
 			if (refFilter != RefFilter.DEFAULT) {
 				return refFilter.filter(rs);
 			}
 			return transferConfig.getRefFilter().filter(rs);
 		}
 
 		// Slow path: filter the refs provided by the advertised refs hook.
 		// refFilter has already been applied to refs.
 		return refs.values().stream()
 				.filter(ref -> refPrefixes.stream()
 						.anyMatch(ref.getName()::startsWith))
 				.collect(toRefMap((a, b) -> b));
 	}
 
 	/**
 	 * Returns the specified references.
 	 * <p>
 	 * This produces an immutable map containing whatever subset of the
 	 * refs named by the caller are present in the supplied {@code refs}
 	 * map.
 	 *
 	 * @param refs
 	 *            Map to search for refs to return.
 	 * @param names
 	 *            which refs to search for in {@code refs}.
 	 * @return the requested Refs, omitting any that are null or missing.
 	 */
 	@NonNull
 	private static Map<String, Ref> mapRefs(
 			Map<String, Ref> refs, List<String> names) {
 		return unmodifiableMap(
 				names.stream()
 					.map(refs::get)
 					.filter(Objects::nonNull)
 						.collect(toRefMap((a, b) -> b)));
 	}
 
 	/**
 	 * Read refs on behalf of the client.
 	 * <p>
 	 * This checks whether the refs are present in the ref advertisement
 	 * since otherwise the client might not be supposed to be able to
 	 * read them.
 	 *
 	 * @param names
 	 *            unabbreviated names of references.
 	 * @return the requested Refs, omitting any that are not visible or
 	 *         do not exist.
 	 * @throws java.io.IOException
 	 *            on failure to read a ref or check it for visibility.
 	 */
 	@NonNull
 	private Map<String, Ref> exactRefs(List<String> names) throws IOException {
 		if (refs != null) {
 			return mapRefs(refs, names);
 		}
 		if (!advertiseRefsHookCalled) {
 			advertiseRefsHook.advertiseRefs(this);
 			advertiseRefsHookCalled = true;
 		}
 		if (refs == null &&
 				refFilter == RefFilter.DEFAULT &&
 				transferConfig.hasDefaultRefFilter()) {
 			// Fast path: no ref filtering is needed.
 			String[] ns = names.toArray(new String[0]);
 			return unmodifiableMap(db.getRefDatabase().exactRef(ns));
 		}
 		return mapRefs(getAdvertisedOrDefaultRefs(), names);
 	}
 
 	/**
 	 * Find a ref in the usual search path on behalf of the client.
 	 * <p>
 	 * This checks that the ref is present in the ref advertisement since
 	 * otherwise the client might not be supposed to be able to read it.
 	 *
 	 * @param name
 	 *            short name of the ref to find, e.g. "master" to find
 	 *            "refs/heads/master".
 	 * @return the requested Ref, or {@code null} if it is not visible or
 	 *         does not exist.
 	 * @throws java.io.IOException
 	 *            on failure to read the ref or check it for visibility.
 	 */
 	@Nullable
 	private Ref findRef(String name) throws IOException {
 		if (refs != null) {
 			return RefDatabase.findRef(refs, name);
 		}
 		if (!advertiseRefsHookCalled) {
 			advertiseRefsHook.advertiseRefs(this);
 			advertiseRefsHookCalled = true;
 		}
 		if (refs == null &&
 				refFilter == RefFilter.DEFAULT &&
 				transferConfig.hasDefaultRefFilter()) {
 			// Fast path: no ref filtering is needed.
 			return db.getRefDatabase().findRef(name);
 		}
 		return RefDatabase.findRef(getAdvertisedOrDefaultRefs(), name);
 	}
 
 	private void service(PacketLineOut pckOut) 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<>();
 		FetchRequest req;
 		try {
 			if (biDirectionalPipe)
 				sendAdvertisedRefs(new PacketLineOutRefAdvertiser(pckOut));
 			else if (requestValidator instanceof AnyRequestValidator)
 				advertised = Collections.emptySet();
 			else
 				advertised = refIdSet(getAdvertisedOrDefaultRefs().values());
 
 			Instant negotiateStart = Instant.now();
 			accumulator.advertised = advertised.size();
 
 			ProtocolV0Parser parser = new ProtocolV0Parser(transferConfig);
 			req = parser.recvWants(pckIn);
 			currentRequest = req;
 
 			wantIds = req.getWantIds();
 
 			if (req.getWantIds().isEmpty()) {
 				preUploadHook.onBeginNegotiateRound(this, req.getWantIds(), 0);
 				preUploadHook.onEndNegotiateRound(this, req.getWantIds(), 0, 0,
 						false);
 				return;
 			}
 			accumulator.wants = req.getWantIds().size();
 
 			if (req.getClientCapabilities().contains(OPTION_MULTI_ACK_DETAILED)) {
 				multiAck = MultiAck.DETAILED;
 				noDone = req.getClientCapabilities().contains(OPTION_NO_DONE);
 			} else if (req.getClientCapabilities().contains(OPTION_MULTI_ACK))
 				multiAck = MultiAck.CONTINUE;
 			else
 				multiAck = MultiAck.OFF;
 
 			if (!req.getClientShallowCommits().isEmpty()) {
 				verifyClientShallow(req.getClientShallowCommits());
 			}
 
 			if (req.getDepth() != 0 || req.getDeepenSince() != 0) {
 				computeShallowsAndUnshallows(req, shallow -> {
 					pckOut.writeString("shallow " + shallow.name() + '\n'); //$NON-NLS-1$
 				}, unshallow -> {
 					pckOut.writeString("unshallow " + unshallow.name() + '\n'); //$NON-NLS-1$
 					unshallowCommits.add(unshallow);
 				}, Collections.emptyList());
 				pckOut.end();
 			}
 
 			if (!req.getClientShallowCommits().isEmpty())
 				walk.assumeShallow(req.getClientShallowCommits());
 			sendPack = negotiate(req, accumulator, pckOut);
 			accumulator.timeNegotiating = Duration
 					.between(negotiateStart, Instant.now()).toMillis();
 
 			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))); //$NON-NLS-1$
 				}
 			}
 		} finally {
 			if (!sendPack && !biDirectionalPipe) {
 				while (0 < rawIn.skip(2048) || 0 <= rawIn.read()) {
 					// Discard until EOF.
 				}
 			}
 			rawOut.stopBuffering();
 		}
 
 		if (sendPack) {
 			sendPack(accumulator, req, refs == null ? null : refs.values(),
 					unshallowCommits, Collections.emptyList(), pckOut);
 		}
 	}
 
 	private void lsRefsV2(PacketLineOut pckOut) 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 = getFilteredRefs(req.getRefPrefixes());
 		if (req.getSymrefs()) {
 			findSymrefs(adv, refsToSend);
 		}
 
 		adv.send(refsToSend.values());
 		adv.end();
 	}
 
 	// Resolves ref names from the request's want-ref lines to
 	// object ids, throwing PackProtocolException if any are missing.
 	private Map<String, ObjectId> wantedRefs(FetchV2Request req)
 			throws IOException {
 		Map<String, ObjectId> result = new TreeMap<>();
 
 		List<String> wanted = req.getWantedRefs();
 		Map<String, Ref> resolved = exactRefs(wanted);
 
 		for (String refName : wanted) {
 			Ref ref = resolved.get(refName);
 			if (ref == null) {
 				throw new PackProtocolException(MessageFormat
 						.format(JGitText.get().invalidRefName, refName));
 			}
 			ObjectId oid = ref.getObjectId();
 			if (oid == null) {
 				throw new PackProtocolException(MessageFormat
 						.format(JGitText.get().invalidRefName, refName));
 			}
 			result.put(refName, oid);
 		}
 		return result;
 	}
 
 	private void fetchV2(PacketLineOut pckOut) 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());
 		}
 
 		PackStatistics.Accumulator accumulator = new PackStatistics.Accumulator();
 		Instant negotiateStart = Instant.now();
 
 		ProtocolV2Parser parser = new ProtocolV2Parser(transferConfig);
 		FetchV2Request req = parser.parseFetchRequest(pckIn);
 		currentRequest = req;
 		rawOut.stopBuffering();
 
 		protocolV2Hook.onFetch(req);
 
 		if (req.getSidebandAll()) {
 			pckOut.setUsingSideband(true);
 		}
 
 		// TODO(ifrade): Refactor to pass around the Request object, instead of
 		// copying data back to class fields
 		List<ObjectId> deepenNots = new ArrayList<>();
 		for (String s : req.getDeepenNotRefs()) {
 			Ref ref = findRef(s);
 			if (ref == null) {
 				throw new PackProtocolException(MessageFormat
 						.format(JGitText.get().invalidRefName, s));
 			}
 			deepenNots.add(ref.getObjectId());
 		}
 
 		Map<String, ObjectId> wantedRefs = wantedRefs(req);
 		// TODO(ifrade): Avoid mutating the parsed request.
 		req.getWantIds().addAll(wantedRefs.values());
 		wantIds = req.getWantIds();
 
 		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,
 					shallowCommit -> shallowCommits.add(shallowCommit),
 					unshallowCommit -> unshallowCommits.add(unshallowCommit),
 					deepenNots);
 		}
 		if (!req.getClientShallowCommits().isEmpty())
 			walk.assumeShallow(req.getClientShallowCommits());
 
 		if (req.wasDoneReceived()) {
 			processHaveLines(req.getPeerHas(), ObjectId.zeroId(),
 					new PacketLineOut(NullOutputStream.INSTANCE, false),
 					accumulator);
 		} else {
 			pckOut.writeString(
 					GitProtocolConstants.SECTION_ACKNOWLEDGMENTS + '\n');
 			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, false),
 					accumulator);
 			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 (!wantedRefs.isEmpty()) {
 				if (sectionSent) {
 					pckOut.writeDelim();
 				}
 				pckOut.writeString("wanted-refs\n"); //$NON-NLS-1$
 				for (Map.Entry<String, ObjectId> entry :
 						wantedRefs.entrySet()) {
 					pckOut.writeString(entry.getValue().getName() + ' ' +
 							entry.getKey() + '\n');
 				}
 				sectionSent = true;
 			}
 
 			if (sectionSent)
 				pckOut.writeDelim();
 			if (!pckOut.isUsingSideband()) {
 				// sendPack will write "packfile\n" for us if sideband-all is used.
 				// But sideband-all is not used, so we have to write it ourselves.
 				pckOut.writeString(
 						GitProtocolConstants.SECTION_PACKFILE + '\n');
 			}
 
 			accumulator.timeNegotiating = Duration
 					.between(negotiateStart, Instant.now()).toMillis();
 
 			sendPack(accumulator,
 					req,
 					req.getClientCapabilities().contains(OPTION_INCLUDE_TAG)
 						? db.getRefDatabase().getRefsByPrefix(R_TAGS)
 						: null,
 					unshallowCommits, deepenNots, pckOut);
 			// 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(PacketLineOut pckOut) throws IOException {
 		String command;
 		try {
 			command = pckIn.readString();
 		} catch (EOFException eof) {
 			/* EOF when awaiting command is fine */
 			return true;
 		}
 		if (PacketLineIn.isEnd(command)) {
 			// 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(pckOut);
 			return false;
 		}
 		if (command.equals("command=" + COMMAND_FETCH)) { //$NON-NLS-1$
 			fetchV2(pckOut);
 			return false;
 		}
 		throw new PackProtocolException(MessageFormat
 				.format(JGitText.get().unknownTransportCommand, command));
 	}
 
 	@SuppressWarnings("nls")
 	private List<String> getV2CapabilityAdvertisement() {
 		ArrayList<String> caps = new ArrayList<>();
 		caps.add("version 2");
 		caps.add(COMMAND_LS_REFS);
 		boolean advertiseRefInWant = transferConfig.isAllowRefInWant()
 				&& db.getConfig().getBoolean("uploadpack", null,
 						"advertiserefinwant", true);
 		caps.add(COMMAND_FETCH + '='
 				+ (transferConfig.isAllowFilter() ? OPTION_FILTER + ' ' : "")
 				+ (advertiseRefInWant ? CAPABILITY_REF_IN_WANT + ' ' : "")
 				+ (transferConfig.isAdvertiseSidebandAll()
 						? OPTION_SIDEBAND_ALL + ' '
 						: "")
 				+ (cachedPackUriProvider != null ? "packfile-uris " : "")
 				+ OPTION_SHALLOW);
 		caps.add(CAPABILITY_SERVER_OPTION);
 		return caps;
 	}
 
 	private void serviceV2(PacketLineOut pckOut) 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(pckOut)) {
 				// Repeat until an empty command or EOF.
 			}
 			return;
 		}
 
 		try {
 			serveOneCommandV2(pckOut);
 		} 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(FetchRequest req,
 			IOConsumer<ObjectId> shallowFunc,
 			IOConsumer<ObjectId> unshallowFunc,
 			List<ObjectId> deepenNots)
 			throws IOException {
 		if (req.getClientCapabilities().contains(OPTION_DEEPEN_RELATIVE)) {
 			// TODO(jonathantanmy): Implement deepen-relative
 			throw new UnsupportedOperationException();
 		}
 
 		int walkDepth = req.getDepth() == 0 ? Integer.MAX_VALUE
 				: req.getDepth() - 1;
 		try (DepthWalk.RevWalk depthWalk = new DepthWalk.RevWalk(
 				walk.getObjectReader(), walkDepth)) {
 
 			depthWalk.setDeepenSince(req.getDeepenSince());
 
 			// Find all the commits which will be shallow
 			for (ObjectId o : req.getWantIds()) {
 				try {
 					depthWalk.markRoot(depthWalk.parseCommit(o));
 				} catch (IncorrectObjectTypeException notCommit) {
 					// Ignore non-commits in this loop.
 				}
 			}
 
 			depthWalk.setDeepenNots(deepenNots);
 
 			RevCommit o;
 			boolean atLeastOne = false;
 			while ((o = depthWalk.next()) != null) {
 				DepthWalk.Commit c = (DepthWalk.Commit) o;
 				atLeastOne = true;
 
 				boolean isBoundary = (c.getDepth() == walkDepth) || c.isBoundary();
 
 				// Commits at the boundary which aren't already shallow in
 				// the client need to be marked as such
 				if (isBoundary && !req.getClientShallowCommits().contains(c)) {
 					shallowFunc.accept(c.copy());
 				}
 
 				// Commits not on the boundary which are shallow in the client
 				// need to become unshallowed
 				if (!isBoundary && req.getClientShallowCommits().remove(c)) {
 					unshallowFunc.accept(c.copy());
 				}
 			}
 			if (!atLeastOne) {
 				throw new PackProtocolException(
 					JGitText.get().noCommitsSelectedForShallow);
 			}
 		}
 	}
 
 	/*
 	 * 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;
 		}
 
 		Map<String, Ref> advertisedOrDefaultRefs = getAdvertisedOrDefaultRefs();
 
 		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);
 		findSymrefs(adv, advertisedOrDefaultRefs);
 		advertised = adv.send(advertisedOrDefaultRefs.values());
 
 		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;
 	}
 
 	/**
 	 * 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 (currentRequest == null)
 			throw new RequestNotYetReadException();
 		return currentRequest.getDepth();
 	}
 
 	/**
 	 * Deprecated synonym for {@code getFilterSpec().getBlobLimit()}.
 	 *
 	 * @return filter blob limit requested by the client, or -1 if no limit
 	 * @since 5.3
 	 * @deprecated Use {@link #getFilterSpec()} instead
 	 */
 	@Deprecated
 	public final long getFilterBlobLimit() {
 		return getFilterSpec().getBlobLimit();
 	}
 
 	/**
 	 * Returns the filter spec for the current request. Valid only after
 	 * calling recvWants(). This may be a no-op filter spec, but it won't be
 	 * null.
 	 *
 	 * @return filter requested by the client
 	 * @since 5.4
 	 */
 	public final FilterSpec getFilterSpec() {
 		if (currentRequest == null) {
 			throw new RequestNotYetReadException();
 		}
 		return currentRequest.getFilterSpec();
 	}
 
 	/**
 	 * 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() {
 		if (currentRequest != null && currentRequest.getAgent() != null) {
 			return currentRequest.getAgent();
 		}
 
 		return userAgent;
 	}
 
 	private boolean negotiate(FetchRequest req,
 			PackStatistics.Accumulator accumulator,
 			PacketLineOut pckOut)
 			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 && req.getDepth() > 0)
 					return false;
 				throw eof;
 			}
 
 			if (PacketLineIn.isEnd(line)) {
 				last = processHaveLines(peerHas, last, pckOut, accumulator);
 				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, accumulator);
 
 				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 ObjectIdId.html#ObjectId">ObjectId processHaveLines(List<ObjectId> peerHas, ObjectId last,
 			PacketLineOut out, PackStatistics.Accumulator accumulator)
 			throws IOException {
 		preUploadHook.onBeginNegotiateRound(this, wantIds, peerHas.size());
 		if (wantAll.isEmpty() && !wantIds.isEmpty())
 			parseWants(accumulator);
 		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(PackStatistics.Accumulator accumulator) 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) {
 			accumulator.notAdvertisedWants = notAdvertisedWants.size();
 
 			Instant startReachabilityChecking = Instant.now();
 
 			requestValidator.checkWants(this, notAdvertisedWants);
 
 			accumulator.reachabilityCheckDuration = Duration
 					.between(startReachabilityChecking, Instant.now())
 					.toMillis();
 		}
 
 		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, 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,
 					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 checkNotAdvertisedWants(UploadPack up,
 			List<ObjectId> notAdvertisedWants, Collection<Ref> visibleRefs)
 			throws IOException {
 
 		ObjectReader reader = up.getRevWalk().getObjectReader();
 
 		try (RevWalkvWalk.html#RevWalk">RevWalk walk = new RevWalk(reader)) {
 			walk.setRetainBody(false);
 			// Missing "wants" throw exception here
 			List<RevObject> wantsAsObjs = objectIdsToRevObjects(walk,
 					notAdvertisedWants);
 			List<RevCommit> wantsAsCommits = wantsAsObjs.stream()
 					.filter(obj -> obj instanceof RevCommit)
 					.map(obj -> (RevCommit) obj)
 					.collect(Collectors.toList());
 			boolean allWantsAreCommits = wantsAsObjs.size() == wantsAsCommits
 					.size();
 			boolean repoHasBitmaps = reader.getBitmapIndex() != null;
 
 			if (!allWantsAreCommits) {
 				if (!repoHasBitmaps && !up.transferConfig.isAllowFilter()) {
 					// Checking unadvertised non-commits without bitmaps
 					// requires an expensive manual walk. Use allowFilter as an
 					// indication that the server operator is willing to pay
 					// this cost. Reject the request otherwise.
 					RevObject nonCommit = wantsAsObjs
 							.stream()
 							.filter(obj -> !(obj instanceof RevCommit))
 							.limit(1)
 							.collect(Collectors.toList()).get(0);
 					throw new WantNotValidException(nonCommit);
 				}
 
 				try (ObjectWalk objWalk = walk.toObjectWalkWithSameObjects()) {
 					Stream<RevObject> startersAsObjs = importantRefsFirst(visibleRefs)
 							.map(UploadPack::refToObjectId)
 							.map(objId -> objectIdToRevObject(objWalk, objId))
 							.filter(Objects::nonNull); // Ignore missing tips
 
 					ObjectReachabilityChecker reachabilityChecker = reader
 							.createObjectReachabilityChecker(objWalk);
 					Optional<RevObject> unreachable = reachabilityChecker
 							.areAllReachable(wantsAsObjs, startersAsObjs);
 					if (unreachable.isPresent()) {
 						throw new WantNotValidException(unreachable.get());
 					}
 				}
 				return;
 			}
 
 			// All wants are commits, we can use ReachabilityChecker
 			ReachabilityChecker reachabilityChecker = reader
 					.createReachabilityChecker(walk);
 
 			Stream<RevCommit> reachableCommits = importantRefsFirst(visibleRefs)
 					.map(UploadPack::refToObjectId)
 					.map(objId -> objectIdToRevCommit(walk, objId))
 					.filter(Objects::nonNull); // Ignore missing tips
 
 			Optional<RevCommit> unreachable = reachabilityChecker
 					.areAllReachable(wantsAsCommits, reachableCommits);
 			if (unreachable.isPresent()) {
 				throw new WantNotValidException(unreachable.get());
 			}
 
 		} catch (MissingObjectException notFound) {
 			throw new WantNotValidException(notFound.getObjectId(), notFound);
 		}
 	}
 
 	static Stream<Ref> importantRefsFirst(
 			Collection<Ref> visibleRefs) {
 		Predicate<Ref> startsWithRefsHeads = ref -> ref.getName()
 				.startsWith(Constants.R_HEADS);
 		Predicate<Ref> startsWithRefsTags = ref -> ref.getName()
 				.startsWith(Constants.R_TAGS);
 		Predicate<Ref> allOther = ref -> !startsWithRefsHeads.test(ref)
 				&& !startsWithRefsTags.test(ref);
 
 		return Stream.concat(
 				visibleRefs.stream().filter(startsWithRefsHeads),
 				Stream.concat(
 						visibleRefs.stream().filter(startsWithRefsTags),
 						visibleRefs.stream().filter(allOther)));
 	}
 
 	private static ObjectId refToObjectId(Ref ref) {
 		return ref.getObjectId() != null ? ref.getObjectId()
 				: ref.getPeeledObjectId();
 	}
 
 	/**
 	 * Translate an object id to a RevCommit.
 	 *
 	 * @param walk
 	 *            walk on the relevant object storae
 	 * @param objectId
 	 *            Object Id
 	 * @return RevCommit instance or null if the object is missing
 	 */
 	@Nullable
 	private static RevCommit objectIdToRevCommit(RevWalk walk,
 			ObjectId objectId) {
 		if (objectId == null) {
 			return null;
 		}
 
 		try {
 			return walk.parseCommit(objectId);
 		} catch (IOException e) {
 			return null;
 		}
 	}
 
 	/**
 	 * Translate an object id to a RevObject.
 	 *
 	 * @param walk
 	 *            walk on the relevant object storage
 	 * @param objectId
 	 *            Object Id
 	 * @return RevObject instance or null if the object is missing
 	 */
 	@Nullable
 	private static RevObject objectIdToRevObject(RevWalk walk,
 			ObjectId objectId) {
 		if (objectId == null) {
 			return null;
 		}
 
 		try {
 			return walk.parseAny(objectId);
 		} catch (IOException e) {
 			return null;
 		}
 	}
 
 	// Resolve the ObjectIds into RevObjects. Any missing object raises an
 	// exception
 	private static List<RevObject> objectIdsToRevObjects(RevWalk walk,
 			Iterable<ObjectId> objectIds)
 			throws MissingObjectException, IOException {
 		List<RevObject> result = new ArrayList<>();
 		for (ObjectId objectId : objectIds) {
 			result.add(walk.parseAny(objectId));
 		}
 		return result;
 	}
 
 	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 req
 	 *            request in process
 	 * @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
 	 * @param deepenNots
 	 *            objects that the client specified using --shallow-exclude
 	 * @param pckOut
 	 *            output writer
 	 * @throws IOException
 	 *             if an error occurred while generating or writing the pack.
 	 */
 	private void sendPack(PackStatistics.Accumulator accumulator,
 			FetchRequest req,
 			@Nullable Collection<Ref> allTags,
 			List<ObjectId> unshallowCommits,
 			List<ObjectId> deepenNots,
 			PacketLineOut pckOut) throws IOException {
 		Set<String> caps = req.getClientCapabilities();
 		boolean sideband = caps.contains(OPTION_SIDE_BAND)
 				|| caps.contains(OPTION_SIDE_BAND_64K);
 
 		if (sideband) {
 			errOut = new SideBandErrorWriter();
 
 			int bufsz = SideBandOutputStream.SMALL_BUF;
 			if (req.getClientCapabilities().contains(OPTION_SIDE_BAND_64K)) {
 				bufsz = SideBandOutputStream.MAX_BUF;
 			}
 			OutputStream packOut = new SideBandOutputStream(
 					SideBandOutputStream.CH_DATA, bufsz, rawOut);
 
 			ProgressMonitor pm = NullProgressMonitor.INSTANCE;
 			if (!req.getClientCapabilities().contains(OPTION_NO_PROGRESS)) {
 				msgOut = new SideBandOutputStream(
 						SideBandOutputStream.CH_PROGRESS, bufsz, rawOut);
 				pm = new SideBandProgressMonitor(msgOut);
 			}
 
 			sendPack(pm, pckOut, packOut, req, accumulator, allTags,
 					unshallowCommits, deepenNots);
 			pckOut.end();
 		} else {
 			sendPack(NullProgressMonitor.INSTANCE, pckOut, rawOut, req,
 					accumulator, allTags, unshallowCommits, deepenNots);
 		}
 	}
 
 	/**
 	 * Send the requested objects to the client.
 	 *
 	 * @param pm
 	 *            progress monitor
 	 * @param pckOut
 	 *            PacketLineOut that shares the output with packOut
 	 * @param packOut
 	 *            packfile output
 	 * @param req
 	 *            request being processed
 	 * @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
 	 * @param deepenNots
 	 *            objects that the client specified using --shallow-exclude
 	 * @throws IOException
 	 *             if an error occurred while generating or writing the pack.
 	 */
 	private void sendPack(ProgressMonitor pm, PacketLineOut pckOut,
 			OutputStream packOut, FetchRequest req,
 			PackStatistics.Accumulator accumulator,
 			@Nullable Collection<Ref> allTags, List<ObjectId> unshallowCommits,
 			List<ObjectId> deepenNots) throws IOException {
 		if (wantAll.isEmpty()) {
 			preUploadHook.onSendPack(this, wantIds, commonBase);
 		} else {
 			preUploadHook.onSendPack(this, wantAll, commonBase);
 		}
 		msgOut.flush();
 
 		// Advertised objects and refs are not used from here on and can be
 		// cleared.
 		advertised = null;
 		refs = null;
 
 		PackConfig cfg = packConfig;
 		if (cfg == null)
 			cfg = new PackConfig(db);
 		@SuppressWarnings("resource") // PackWriter is referenced in the finally
 										// block, and is closed there
 		final PackWriterorage/pack/PackWriter.html#PackWriter">PackWriter pw = new PackWriter(cfg, walk.getObjectReader(),
 				accumulator);
 		try {
 			pw.setIndexDisabled(true);
 			if (req.getFilterSpec().isNoOp()) {
 				pw.setUseCachedPacks(true);
 			} else {
 				pw.setFilterSpec(req.getFilterSpec());
 				pw.setUseCachedPacks(false);
 			}
 			pw.setUseBitmaps(
 					req.getDepth() == 0
 							&& req.getClientShallowCommits().isEmpty()
 							&& req.getFilterSpec().getTreeDepthLimit() == -1);
 			pw.setClientShallowCommits(req.getClientShallowCommits());
 			pw.setReuseDeltaCommits(true);
 			pw.setDeltaBaseAsOffset(
 					req.getClientCapabilities().contains(OPTION_OFS_DELTA));
 			pw.setThin(req.getClientCapabilities().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 (req.getDepth() > 0 || req.getDeepenSince() != 0 || !deepenNots.isEmpty()) {
 				int walkDepth = req.getDepth() == 0 ? Integer.MAX_VALUE
 						: req.getDepth() - 1;
 				pw.setShallowPack(req.getDepth(), unshallowCommits);
 
 				@SuppressWarnings("resource") // Ownership is transferred below
 				DepthWalk.RevWalk dw = new DepthWalk.RevWalk(
 						walk.getObjectReader(), walkDepth);
 				dw.setDeepenSince(req.getDeepenSince());
 				dw.setDeepenNots(deepenNots);
 				dw.assumeShallow(req.getClientShallowCommits());
 				rw = dw;
 			}
 
 			if (wantAll.isEmpty()) {
 				pw.preparePack(pm, wantIds, commonBase,
 						req.getClientShallowCommits());
 			} else {
 				walk.reset();
 
 				ObjectWalk ow = rw.toObjectWalkWithSameObjects();
 				pw.preparePack(pm, ow, wantAll, commonBase, PackWriter.NONE);
 				rw = ow;
 			}
 
 			if (req.getClientCapabilities().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;
 
 					objectId = ref.getObjectId();
 					if (pw.willInclude(peeledId) && !pw.willInclude(objectId)) {
 						RevObject o = rw.parseAny(objectId);
 						addTagChain(o, pw);
 						pw.addObject(o);
 					}
 				}
 			}
 
 			if (pckOut.isUsingSideband()) {
 				if (req instanceof FetchV2Request &&
 						cachedPackUriProvider != null &&
 						!((FetchV2Request) req).getPackfileUriProtocols().isEmpty()) {
 					FetchV2Request reqV2 = (FetchV2Request) req;
 					pw.setPackfileUriConfig(new PackWriter.PackfileUriConfig(
 							pckOut,
 							reqV2.getPackfileUriProtocols(),
 							cachedPackUriProvider));
 				} else {
 					// PackWriter will write "packfile-uris\n" and "packfile\n"
 					// for us if provided a PackfileUriConfig. In this case, we
 					// are not providing a PackfileUriConfig, so we have to
 					// write this line ourselves.
 					pckOut.writeString(
 							GitProtocolConstants.SECTION_PACKFILE + '\n');
 				}
 			}
 			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();
 		}
 	}
 
 	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 void addTagChain(
 			RevObject o, PackWriter pw) throws IOException {
 		while (Constants.OBJ_TAG == o.getType()) {
 			RevTag t = (RevTag) o;
 			o = t.getObject();
 			if (o.getType() == Constants.OBJ_TAG && !pw.willInclude(o.getId())) {
 				walk.parseBody(o);
 				pw.addObject(o);
 			}
 		}
 	}
 
 	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;
 			}
 		}
 	}
 
 	private interface ErrorWriter {
 		void writeError(String message) throws IOException;
 	}
 
 	private class SideBandErrorWriter implements ErrorWriter {
 		@Override
 		public void writeError(String message) throws IOException {
 			@SuppressWarnings("resource" /* java 7 */)
 			SideBandOutputStream err = new SideBandOutputStream(
 					SideBandOutputStream.CH_ERROR,
 					SideBandOutputStream.SMALL_BUF, requireNonNull(rawOut));
 			err.write(Constants.encode(message));
 			err.flush();
 		}
 	}
 
 	private class PackProtocolErrorWriter implements ErrorWriter {
 		@Override
 		public void writeError(String message) throws IOException {
 			new PacketLineOut(requireNonNull(rawOut))
 					.writeString("ERR " + message + '\n'); //$NON-NLS-1$
 		}
 	}
 }