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// Copyright (C) 2010 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.gerrit.server.git.receive;
import static java.util.stream.Collectors.toMap;
import com.google.common.collect.Sets;
import com.google.common.flogger.FluentLogger;
import com.google.gerrit.git.ObjectIds;
import java.io.IOException;
import java.util.Collection;
import java.util.Map;
import java.util.Set;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.transport.AdvertiseRefsHook;
import org.eclipse.jgit.transport.ReceivePack;
import org.eclipse.jgit.transport.ServiceMayNotContinueException;
import org.eclipse.jgit.transport.UploadPack;
/**
* Advertises part of history to git push clients.
*
* <p>This is a hack to work around the lack of negotiation in the send-pack/receive-pack wire
* protocol.
*
* <p>When the server is frequently advancing master by creating merge commits, the client may not
* be able to discover a common ancestor during push. Attempting to push will re-upload a very large
* amount of history. This hook hacks in a fake negotiation replacement by walking history and
* sending recent commits as {@code ".have"} lines in the wire protocol, allowing the client to find
* a common ancestor.
*/
public class HackPushNegotiateHook implements AdvertiseRefsHook {
private static final FluentLogger logger = FluentLogger.forEnclosingClass();
/** Size of an additional ".have" line. */
private static final int HAVE_LINE_LEN = 4 + ObjectIds.STR_LEN + 1 + 5 + 1;
/**
* Maximum number of bytes to "waste" in the advertisement with a peek at this repository's
* current reachable history.
*/
private static final int MAX_EXTRA_BYTES = 8192;
/**
* Number of recent commits to advertise immediately, hoping to show a client a nearby merge base.
*/
private static final int BASE_COMMITS = 64;
/** Number of commits to skip once base has already been shown. */
private static final int STEP_COMMITS = 16;
/** Total number of commits to extract from the history. */
private static final int MAX_HISTORY = MAX_EXTRA_BYTES / HAVE_LINE_LEN;
@Override
public void advertiseRefs(UploadPack us) {
throw new UnsupportedOperationException("HackPushNegotiateHook cannot be used for UploadPack");
}
@Override
public void advertiseRefs(ReceivePack rp) throws ServiceMayNotContinueException {
Map<String, Ref> r = rp.getAdvertisedRefs();
if (r == null) {
try {
r =
rp.getRepository().getRefDatabase().getRefs().stream()
.collect(toMap(Ref::getName, x -> x));
rp.setAdvertisedRefs(r, history(r.values(), rp));
} catch (ServiceMayNotContinueException e) {
throw e;
} catch (IOException e) {
throw new ServiceMayNotContinueException(e);
}
}
}
private Set<ObjectId> history(Collection<Ref> refs, ReceivePack rp) {
Set<ObjectId> alreadySending = rp.getAdvertisedObjects();
if (MAX_HISTORY <= alreadySending.size()) {
return alreadySending;
}
// Scan history until the advertisement is full.
RevWalk rw = rp.getRevWalk();
rw.reset();
try {
Set<ObjectId> tips = idsOf(refs);
for (ObjectId tip : tips) {
try {
rw.markStart(rw.parseCommit(tip));
} catch (IOException badCommit) {
continue;
}
}
Set<ObjectId> history = Sets.newHashSetWithExpectedSize(MAX_HISTORY);
history.addAll(alreadySending);
try {
int stepCnt = 0;
for (RevCommit c; history.size() < MAX_HISTORY && (c = rw.next()) != null; ) {
if (c.getParentCount() <= 1
&& !tips.contains(c)
&& (history.size() < BASE_COMMITS || (++stepCnt % STEP_COMMITS) == 0)) {
history.add(c);
}
}
} catch (IOException err) {
logger.atSevere().withCause(err).log("error trying to advertise history");
}
return history;
} finally {
rw.reset();
}
}
private static Set<ObjectId> idsOf(Collection<Ref> refs) {
Set<ObjectId> r = Sets.newHashSetWithExpectedSize(refs.size());
for (Ref ref : refs) {
if (ref.getObjectId() != null) {
r.add(ref.getObjectId());
}
}
return r;
}
}
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