com.google.gerrit.server.git.ChainedReceiveCommands.java Source code

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Here is the source code for com.google.gerrit.server.git.ChainedReceiveCommands.java

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// Copyright (C) 2016 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;

import static com.google.common.base.MoreObjects.firstNonNull;
import static com.google.common.base.Preconditions.checkArgument;

import org.eclipse.jgit.lib.BatchRefUpdate;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.transport.ReceiveCommand;

import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Collection of {@link ReceiveCommand}s that supports multiple updates per ref.
 * <p>
 * The underlying behavior of {@link BatchRefUpdate} is undefined (an
 * implementations vary) when more than one command per ref is added. This class
 * works around that limitation by allowing multiple updates per ref, as long as
 * the previous new SHA-1 matches the next old SHA-1.
 */
public class ChainedReceiveCommands {
    private final Map<String, ReceiveCommand> commands = new LinkedHashMap<>();
    private final Map<String, ObjectId> oldIds = new HashMap<>();

    public boolean isEmpty() {
        return commands.isEmpty();
    }

    /**
     * Add a command.
     *
     * @param cmd command to add. If a command has been previously added for the
     *     same ref, the new SHA-1 of the most recent previous command must match
     *     the old SHA-1 of this command.
     */
    public void add(ReceiveCommand cmd) {
        checkArgument(!cmd.getOldId().equals(cmd.getNewId()), "ref update is a no-op: %s", cmd);
        ReceiveCommand old = commands.get(cmd.getRefName());
        if (old == null) {
            commands.put(cmd.getRefName(), cmd);
            return;
        }
        checkArgument(old.getResult() == ReceiveCommand.Result.NOT_ATTEMPTED,
                "cannot chain ref update %s after update %s with result %s", cmd, old, old.getResult());
        checkArgument(cmd.getOldId().equals(old.getNewId()),
                "cannot chain ref update %s after update %s with different new ID", cmd, old);
        commands.put(cmd.getRefName(), new ReceiveCommand(old.getOldId(), cmd.getNewId(), cmd.getRefName()));
    }

    /**
     * Get the latest value of a ref according to this sequence of commands.
     * <p>
     * Once the value for a ref is read once, it is cached in this instance, so
     * that multiple callers using this instance for lookups see a single
     * consistent snapshot.
     *
     * @param repo repository to read from, if result is not cached.
     * @param refName name of the ref.
     * @return value of the ref, taking into account commands that have already
     *     been added to this instance. Null if the ref is deleted, matching the
     *     behavior of {@link Repository#exactRef(String)}.
     */
    public ObjectId getObjectId(Repository repo, String refName) throws IOException {
        ReceiveCommand cmd = commands.get(refName);
        if (cmd != null) {
            return zeroToNull(cmd.getNewId());
        }
        ObjectId old = oldIds.get(refName);
        if (old != null) {
            return zeroToNull(old);
        }
        Ref ref = repo.exactRef(refName);
        ObjectId id = ref != null ? ref.getObjectId() : null;
        // Cache missing ref as zeroId to match value in commands map.
        oldIds.put(refName, firstNonNull(id, ObjectId.zeroId()));
        return id;
    }

    private static ObjectId zeroToNull(ObjectId id) {
        if (id == null || id.equals(ObjectId.zeroId())) {
            return null;
        }
        return id;
    }

    /**
     * Add commands from this instance to a native JGit batch update.
     * <p>
     * Exactly one command per ref will be added to the update. The old SHA-1 will
     * be the old SHA-1 of the first command added to this instance for that ref;
     * the new SHA-1 will be the new SHA-1 of the last command.
     *
     * @param bru batch update
     */
    public void addTo(BatchRefUpdate bru) {
        for (ReceiveCommand cmd : commands.values()) {
            bru.addCommand(cmd);
        }
    }

    /** @return an unmodifiable view of commands. */
    public Map<String, ReceiveCommand> getCommands() {
        return Collections.unmodifiableMap(commands);
    }
}