org.eclipse.jgit/src/org/eclipse/jgit/internal/ketch/LocalReplica.java

/*
 * Copyright (C) 2016, 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.internal.ketch;

import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod.ALL_REFS;
import static org.eclipse.jgit.internal.ketch.KetchReplica.CommitMethod.TXN_COMMITTED;
import static org.eclipse.jgit.lib.RefDatabase.ALL;
import static org.eclipse.jgit.transport.ReceiveCommand.Result.OK;
import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import org.eclipse.jgit.internal.storage.reftree.RefTreeDatabase;
import org.eclipse.jgit.lib.BatchRefUpdate;
import org.eclipse.jgit.lib.NullProgressMonitor;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.RefDatabase;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.transport.ReceiveCommand;
import org.eclipse.jgit.util.time.MonotonicClock;
import org.eclipse.jgit.util.time.ProposedTimestamp;

/**
 * Ketch replica running on the same system as the
 * {@link org.eclipse.jgit.internal.ketch.KetchLeader}.
 */
public class LocalReplica extends KetchReplica {
	/**
	 * Configure a local replica.
	 *
	 * @param leader
	 *            instance this replica follows.
	 * @param name
	 *            unique-ish name identifying this replica for debugging.
	 * @param cfg
	 *            how Ketch should treat the local system.
	 */
	public LocalReplica(KetchLeader leader, String name, ReplicaConfig cfg) {
		super(leader, name, cfg);
	}

	/** {@inheritDoc} */
	@Override
	protected String describeForLog() {
		return String.format("%s (leader)", getName()); //$NON-NLS-1$
	}

	/**
	 * Initializes local replica by reading accepted and committed references.
	 * <p>
	 * Loads accepted and committed references from the reference database of
	 * the local replica and stores their current ObjectIds in memory.
	 *
	 * @param repo
	 *            repository to initialize state from.
	 * @throws IOException
	 *             cannot read repository state.
	 */
	void initialize(Repository repo) throws IOException {
		RefDatabase refdb = repo.getRefDatabase();
		if (refdb instanceof RefTreeDatabase) {
			RefTreeDatabase treeDb = (RefTreeDatabase) refdb;
			String txnNamespace = getSystem().getTxnNamespace();
			if (!txnNamespace.equals(treeDb.getTxnNamespace())) {
				throw new IOException(MessageFormat.format(
						KetchText.get().mismatchedTxnNamespace,
						txnNamespace, treeDb.getTxnNamespace()));
			}
			refdb = treeDb.getBootstrap();
		}
		initialize(refdb.exactRef(
				getSystem().getTxnAccepted(),
				getSystem().getTxnCommitted()));
	}

	/** {@inheritDoc} */
	@Override
	protected void startPush(ReplicaPushRequest req) {
		getSystem().getExecutor().execute(() -> {
			MonotonicClock clk = getSystem().getClock();
			try (Repository git = getLeader().openRepository();
					ProposedTimestamp ts = clk.propose()) {
				try {
					update(git, req, ts);
					req.done(git);
				} catch (Throwable err) {
					req.setException(git, err);
				}
			} catch (IOException err) {
				req.setException(null, err);
			}
		});
	}

	/** {@inheritDoc} */
	@Override
	protected void blockingFetch(Repository repo, ReplicaFetchRequest req)
			throws IOException {
		throw new IOException(KetchText.get().cannotFetchFromLocalReplica);
	}

	private void update(Repository git, ReplicaPushRequest req,
			ProposedTimestamp ts) throws IOException {
		RefDatabase refdb = git.getRefDatabase();
		CommitMethod method = getCommitMethod();

		// Local replica probably uses RefTreeDatabase, the request should
		// be only for the txnNamespace, so drop to the bootstrap layer.
		if (refdb instanceof RefTreeDatabase) {
			if (!isOnlyTxnNamespace(req.getCommands())) {
				return;
			}

			refdb = ((RefTreeDatabase) refdb).getBootstrap();
			method = TXN_COMMITTED;
		}

		BatchRefUpdate batch = refdb.newBatchUpdate();
		batch.addProposedTimestamp(ts);
		batch.setRefLogIdent(getSystem().newCommitter(ts));
		batch.setRefLogMessage("ketch", false); //$NON-NLS-1$
		batch.setAllowNonFastForwards(true);

		// RefDirectory updates multiple references sequentially.
		// Run everything else first, then accepted (if present),
		// then committed (if present). This ensures an earlier
		// failure will not update these critical references.
		ReceiveCommand accepted = null;
		ReceiveCommand committed = null;
		for (ReceiveCommand cmd : req.getCommands()) {
			String name = cmd.getRefName();
			if (name.equals(getSystem().getTxnAccepted())) {
				accepted = cmd;
			} else if (name.equals(getSystem().getTxnCommitted())) {
				committed = cmd;
			} else {
				batch.addCommand(cmd);
			}
		}
		if (committed != null && method == ALL_REFS) {
			Map<String, Ref> refs = refdb.getRefs(ALL);
			batch.addCommand(prepareCommit(git, refs, committed.getNewId()));
		}
		if (accepted != null) {
			batch.addCommand(accepted);
		}
		if (committed != null) {
			batch.addCommand(committed);
		}

		try (RevWalk rw = new RevWalk(git)) {
			batch.execute(rw, NullProgressMonitor.INSTANCE);
		}

		// KetchReplica only cares about accepted and committed in
		// advertisement. If they failed, store the current values
		// back in the ReplicaPushRequest.
		List<String> failed = new ArrayList<>(2);
		checkFailed(failed, accepted);
		checkFailed(failed, committed);
		if (!failed.isEmpty()) {
			String[] arr = failed.toArray(new String[0]);
			req.setRefs(refdb.exactRef(arr));
		}
	}

	private static void checkFailed(List<String> failed, ReceiveCommand cmd) {
		if (cmd != null && cmd.getResult() != OK) {
			failed.add(cmd.getRefName());
		}
	}

	private boolean isOnlyTxnNamespace(Collection<ReceiveCommand> cmdList) {
		// Be paranoid and reject non txnNamespace names, this
		// is a programming error in Ketch that should not occur.

		String txnNamespace = getSystem().getTxnNamespace();
		for (ReceiveCommand cmd : cmdList) {
			if (!cmd.getRefName().startsWith(txnNamespace)) {
				cmd.setResult(REJECTED_OTHER_REASON,
						MessageFormat.format(
								KetchText.get().outsideTxnNamespace,
								cmd.getRefName(), txnNamespace));
				ReceiveCommand.abort(cmdList);
				return false;
			}
		}
		return true;
	}
}