com.google.gerrit.server.edit.tree.TreeCreator Maven / Gradle / Ivy
// Copyright (C) 2017 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.edit.tree;
import static com.google.common.collect.ImmutableList.toImmutableList;
import static java.util.Objects.requireNonNull;
import com.google.common.collect.ImmutableList;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.eclipse.jgit.dircache.DirCache;
import org.eclipse.jgit.dircache.DirCacheBuilder;
import org.eclipse.jgit.dircache.DirCacheEditor;
import org.eclipse.jgit.dircache.DirCacheEntry;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
/**
* A creator for a new Git tree. To create the new tree, the tree of another commit is taken as a
* basis and modified. Alternatively, an empty tree can serve as base.
*/
public class TreeCreator {
private final ObjectId baseTreeId;
private final ImmutableList baseParents;
private final List treeModifications = new ArrayList<>();
public static TreeCreator basedOn(RevCommit baseCommit) {
requireNonNull(baseCommit, "baseCommit is required");
return new TreeCreator(baseCommit.getTree(), ImmutableList.copyOf(baseCommit.getParents()));
}
public static TreeCreator basedOnTree(
ObjectId baseTreeId, ImmutableList baseParents) {
requireNonNull(baseTreeId, "baseTreeId is required");
return new TreeCreator(baseTreeId, baseParents);
}
public static TreeCreator basedOnEmptyTree() {
return new TreeCreator(ObjectId.zeroId(), ImmutableList.of());
}
private TreeCreator(ObjectId baseTreeId, ImmutableList baseParents) {
this.baseTreeId = requireNonNull(baseTreeId, "baseTree is required");
this.baseParents = baseParents;
}
/**
* Apply modifications to the tree which is taken as a basis. If this method is called multiple
* times, the modifications are applied subsequently in exactly the order they were provided
* (though JGit applies some internal optimizations which involve sorting, too).
*
* Beware: All provided {@link TreeModification}s (even from previous calls of
* this method) must touch different file paths!
*
* @param treeModifications modifications which should be applied to the base tree
*/
public void addTreeModifications(List treeModifications) {
requireNonNull(treeModifications, "treeModifications must not be null");
this.treeModifications.addAll(treeModifications);
}
/**
* Creates the new tree. When this method is called, the specified base tree is read from the
* repository, the specified modifications are applied, and the resulting tree is written to the
* object store of the repository.
*
* @param repository the affected Git repository
* @return the {@code ObjectId} of the created tree
* @throws IOException if problems arise when accessing the repository
*/
public ObjectId createNewTreeAndGetId(Repository repository) throws IOException {
ensureTreeModificationsDoNotTouchSameFiles();
DirCache newTree = createNewTree(repository);
return writeAndGetId(repository, newTree);
}
private void ensureTreeModificationsDoNotTouchSameFiles() {
// The current implementation of TreeCreator doesn't properly support modifications which touch
// the same files even if they are provided in a logical order. One reason for this is that
// JGit's DirCache implementation sorts the given path edits which is necessary due to the
// nature of the Git index. The internal sorting doesn't seem to be the only issue, though. Even
// applying the modifications in batches within different, subsequent DirCaches just held in
// memory didn't seem to work. We might need to fully write each batch to disk before creating
// the next.
ImmutableList filePaths =
treeModifications.stream()
.flatMap(treeModification -> treeModification.getFilePaths().stream())
.collect(toImmutableList());
long distinctFilePathNum = filePaths.stream().distinct().count();
if (filePaths.size() != distinctFilePathNum) {
throw new IllegalStateException(
String.format(
"TreeModifications must not refer to the same file paths. This would have"
+ " unexpected/wrong behavior! Found file paths: %s.",
filePaths));
}
}
private DirCache createNewTree(Repository repository) throws IOException {
DirCache newTree = readBaseTree(repository);
List pathEdits = getPathEdits(repository);
applyPathEdits(newTree, pathEdits);
return newTree;
}
private DirCache readBaseTree(Repository repository) throws IOException {
try (ObjectReader objectReader = repository.newObjectReader()) {
DirCache dirCache = DirCache.newInCore();
DirCacheBuilder dirCacheBuilder = dirCache.builder();
if (!ObjectId.zeroId().equals(baseTreeId)) {
dirCacheBuilder.addTree(new byte[0], DirCacheEntry.STAGE_0, objectReader, baseTreeId);
}
dirCacheBuilder.finish();
return dirCache;
}
}
private List getPathEdits(Repository repository) throws IOException {
List pathEdits = new ArrayList<>();
for (TreeModification treeModification : treeModifications) {
pathEdits.addAll(
treeModification.getPathEdits(repository, baseTreeId, ImmutableList.copyOf(baseParents)));
}
return pathEdits;
}
private static void applyPathEdits(DirCache tree, List pathEdits) {
DirCacheEditor dirCacheEditor = tree.editor();
pathEdits.forEach(dirCacheEditor::add);
dirCacheEditor.finish();
}
private static ObjectId writeAndGetId(Repository repository, DirCache tree) throws IOException {
try (ObjectInserter objectInserter = repository.newObjectInserter()) {
ObjectId treeId = tree.writeTree(objectInserter);
objectInserter.flush();
return treeId;
}
}
}