ObjectReader.java

/*
 * Copyright (C) 2010, 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.lib;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.eclipse.jgit.annotations.NonNull;
import org.eclipse.jgit.annotations.Nullable;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.internal.revwalk.BitmappedObjectReachabilityChecker;
import org.eclipse.jgit.internal.revwalk.BitmappedReachabilityChecker;
import org.eclipse.jgit.internal.revwalk.PedestrianObjectReachabilityChecker;
import org.eclipse.jgit.internal.revwalk.PedestrianReachabilityChecker;
import org.eclipse.jgit.revwalk.ObjectReachabilityChecker;
import org.eclipse.jgit.revwalk.ObjectWalk;
import org.eclipse.jgit.revwalk.ReachabilityChecker;
import org.eclipse.jgit.revwalk.RevWalk;

/**
 * Reads an {@link org.eclipse.jgit.lib.ObjectDatabase} for a single thread.
 * <p>
 * Readers that can support efficient reuse of pack encoded objects should also
 * implement the companion interface
 * {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs}.
 */
public abstract class ObjectReader implements AutoCloseable {
    /** Type hint indicating the caller doesn't know the type. */
    public static final int OBJ_ANY = -1;

    /**
     * The threshold at which a file will be streamed rather than loaded
     * entirely into memory.
     * @since 4.6
     */
    protected int streamFileThreshold;

    /**
     * Construct a new reader from the same data.
     * <p>
     * Applications can use this method to build a new reader from the same data
     * source, but for an different thread.
     *
     * @return a brand new reader, using the same data source.
     */
    public abstract ObjectReader newReader();

    /**
     * Obtain a unique abbreviation (prefix) of an object SHA-1.
     *
     * This method uses a reasonable default for the minimum length. Callers who
     * don't care about the minimum length should prefer this method.
     *
     * The returned abbreviation would expand back to the argument ObjectId when
     * passed to {@link #resolve(AbbreviatedObjectId)}, assuming no new objects
     * are added to this repository between calls.
     *
     * @param objectId
     *            object identity that needs to be abbreviated.
     * @return SHA-1 abbreviation.
     * @throws java.io.IOException
     *             the object store cannot be read.
     */
    public AbbreviatedObjectId abbreviate(AnyObjectId objectId)
            throws IOException {
        return abbreviate(objectId, 7);
    }

    /**
     * Obtain a unique abbreviation (prefix) of an object SHA-1.
     *
     * The returned abbreviation would expand back to the argument ObjectId when
     * passed to {@link #resolve(AbbreviatedObjectId)}, assuming no new objects
     * are added to this repository between calls.
     *
     * The default implementation of this method abbreviates the id to the
     * minimum length, then resolves it to see if there are multiple results.
     * When multiple results are found, the length is extended by 1 and resolve
     * is tried again.
     *
     * @param objectId
     *            object identity that needs to be abbreviated.
     * @param len
     *            minimum length of the abbreviated string. Must be in the range
     *            [2, {@value Constants#OBJECT_ID_STRING_LENGTH}].
     * @return SHA-1 abbreviation. If no matching objects exist in the
     *         repository, the abbreviation will match the minimum length.
     * @throws java.io.IOException
     *             the object store cannot be read.
     */
    public AbbreviatedObjectId abbreviate(AnyObjectId objectId, int len)
            throws IOException {
        if (len == Constants.OBJECT_ID_STRING_LENGTH)
            return AbbreviatedObjectId.fromObjectId(objectId);

        AbbreviatedObjectId abbrev = objectId.abbreviate(len);
        Collection<ObjectId> matches = resolve(abbrev);
        while (1 < matches.size() && len < Constants.OBJECT_ID_STRING_LENGTH) {
            abbrev = objectId.abbreviate(++len);
            List<ObjectId> n = new ArrayList<>(8);
            for (ObjectId candidate : matches) {
                if (abbrev.prefixCompare(candidate) == 0)
                    n.add(candidate);
            }
            if (1 < n.size())
                matches = n;
            else
                matches = resolve(abbrev);
        }
        return abbrev;
    }

    /**
     * Resolve an abbreviated ObjectId to its full form.
     *
     * This method searches for an ObjectId that begins with the abbreviation,
     * and returns at least some matching candidates.
     *
     * If the returned collection is empty, no objects start with this
     * abbreviation. The abbreviation doesn't belong to this repository, or the
     * repository lacks the necessary objects to complete it.
     *
     * If the collection contains exactly one member, the abbreviation is
     * (currently) unique within this database. There is a reasonably high
     * probability that the returned id is what was previously abbreviated.
     *
     * If the collection contains 2 or more members, the abbreviation is not
     * unique. In this case the implementation is only required to return at
     * least 2 candidates to signal the abbreviation has conflicts. User
     * friendly implementations should return as many candidates as reasonably
     * possible, as the caller may be able to disambiguate further based on
     * context. However since databases can be very large (e.g. 10 million
     * objects) returning 625,000 candidates for the abbreviation "0" is simply
     * unreasonable, so implementors should draw the line at around 256 matches.
     *
     * @param id
     *            abbreviated id to resolve to a complete identity. The
     *            abbreviation must have a length of at least 2.
     * @return candidates that begin with the abbreviated identity.
     * @throws java.io.IOException
     *             the object store cannot be read.
     */
    public abstract Collection<ObjectId> resolve(AbbreviatedObjectId id)
            throws IOException;

    /**
     * Does the requested object exist in this database?
     *
     * @param objectId
     *            identity of the object to test for existence of.
     * @return true if the specified object is stored in this database.
     * @throws java.io.IOException
     *             the object store cannot be accessed.
     */
    public boolean has(AnyObjectId objectId) throws IOException {
        return has(objectId, OBJ_ANY);
    }

    /**
     * Does the requested object exist in this database?
     *
     * @param objectId
     *            identity of the object to test for existence of.
     * @param typeHint
     *            hint about the type of object being requested, e.g.
     *            {@link org.eclipse.jgit.lib.Constants#OBJ_BLOB};
     *            {@link #OBJ_ANY} if the object type is not known, or does not
     *            matter to the caller.
     * @return true if the specified object is stored in this database.
     * @throws IncorrectObjectTypeException
     *             typeHint was not OBJ_ANY, and the object's actual type does
     *             not match typeHint.
     * @throws java.io.IOException
     *             the object store cannot be accessed.
     */
    public boolean has(AnyObjectId objectId, int typeHint) throws IOException {
        try {
            open(objectId, typeHint);
            return true;
        } catch (MissingObjectException notFound) {
            return false;
        }
    }

    /**
     * Open an object from this database.
     *
     * @param objectId
     *            identity of the object to open.
     * @return a {@link org.eclipse.jgit.lib.ObjectLoader} for accessing the
     *         object.
     * @throws org.eclipse.jgit.errors.MissingObjectException
     *             the object does not exist.
     * @throws java.io.IOException
     *             the object store cannot be accessed.
     */
    public ObjectLoader open(AnyObjectId objectId)
            throws MissingObjectException, IOException {
        return open(objectId, OBJ_ANY);
    }

    /**
     * Open an object from this database.
     *
     * @param objectId
     *            identity of the object to open.
     * @param typeHint
     *            hint about the type of object being requested, e.g.
     *            {@link org.eclipse.jgit.lib.Constants#OBJ_BLOB};
     *            {@link #OBJ_ANY} if the object type is not known, or does not
     *            matter to the caller.
     * @return a {@link org.eclipse.jgit.lib.ObjectLoader} for accessing the
     *         object.
     * @throws org.eclipse.jgit.errors.MissingObjectException
     *             the object does not exist.
     * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
     *             typeHint was not OBJ_ANY, and the object's actual type does
     *             not match typeHint.
     * @throws java.io.IOException
     *             the object store cannot be accessed.
     */
    public abstract ObjectLoader open(AnyObjectId objectId, int typeHint)
            throws MissingObjectException, IncorrectObjectTypeException,
            IOException;

    /**
     * Returns IDs for those commits which should be considered as shallow.
     *
     * @return IDs of shallow commits
     * @throws java.io.IOException
     */
    public abstract Set<ObjectId> getShallowCommits() throws IOException;

    /**
     * Asynchronous object opening.
     *
     * @param objectIds
     *            objects to open from the object store. The supplied collection
     *            must not be modified until the queue has finished.
     * @param reportMissing
     *            if true missing objects are reported by calling failure with a
     *            MissingObjectException. This may be more expensive for the
     *            implementation to guarantee. If false the implementation may
     *            choose to report MissingObjectException, or silently skip over
     *            the object with no warning.
     * @return queue to read the objects from.
     */
    public <T extends ObjectId> AsyncObjectLoaderQueue<T> open(
            Iterable<T> objectIds, final boolean reportMissing) {
        final Iterator<T> idItr = objectIds.iterator();
        return new AsyncObjectLoaderQueue<T>() {
            private T cur;

            @Override
            public boolean next() throws MissingObjectException, IOException {
                if (idItr.hasNext()) {
                    cur = idItr.next();
                    return true;
                }
                return false;
            }

            @Override
            public T getCurrent() {
                return cur;
            }

            @Override
            public ObjectId getObjectId() {
                return cur;
            }

            @Override
            public ObjectLoader open() throws IOException {
                return ObjectReader.this.open(cur, OBJ_ANY);
            }

            @Override
            public boolean cancel(boolean mayInterruptIfRunning) {
                return true;
            }

            @Override
            public void release() {
                // Since we are sequential by default, we don't
                // have any state to clean up if we terminate early.
            }
        };
    }

    /**
     * Get only the size of an object.
     * <p>
     * The default implementation of this method opens an ObjectLoader.
     * Databases are encouraged to override this if a faster access method is
     * available to them.
     *
     * @param objectId
     *            identity of the object to open.
     * @param typeHint
     *            hint about the type of object being requested, e.g.
     *            {@link org.eclipse.jgit.lib.Constants#OBJ_BLOB};
     *            {@link #OBJ_ANY} if the object type is not known, or does not
     *            matter to the caller.
     * @return size of object in bytes.
     * @throws org.eclipse.jgit.errors.MissingObjectException
     *             the object does not exist.
     * @throws org.eclipse.jgit.errors.IncorrectObjectTypeException
     *             typeHint was not OBJ_ANY, and the object's actual type does
     *             not match typeHint.
     * @throws java.io.IOException
     *             the object store cannot be accessed.
     */
    public long getObjectSize(AnyObjectId objectId, int typeHint)
            throws MissingObjectException, IncorrectObjectTypeException,
            IOException {
        return open(objectId, typeHint).getSize();
    }

    /**
     * Asynchronous object size lookup.
     *
     * @param objectIds
     *            objects to get the size of from the object store. The supplied
     *            collection must not be modified until the queue has finished.
     * @param reportMissing
     *            if true missing objects are reported by calling failure with a
     *            MissingObjectException. This may be more expensive for the
     *            implementation to guarantee. If false the implementation may
     *            choose to report MissingObjectException, or silently skip over
     *            the object with no warning.
     * @return queue to read object sizes from.
     */
    public <T extends ObjectId> AsyncObjectSizeQueue<T> getObjectSize(
            Iterable<T> objectIds, final boolean reportMissing) {
        final Iterator<T> idItr = objectIds.iterator();
        return new AsyncObjectSizeQueue<T>() {
            private T cur;

            private long sz;

            @Override
            public boolean next() throws MissingObjectException, IOException {
                if (idItr.hasNext()) {
                    cur = idItr.next();
                    sz = getObjectSize(cur, OBJ_ANY);
                    return true;
                }
                return false;
            }

            @Override
            public T getCurrent() {
                return cur;
            }

            @Override
            public ObjectId getObjectId() {
                return cur;
            }

            @Override
            public long getSize() {
                return sz;
            }

            @Override
            public boolean cancel(boolean mayInterruptIfRunning) {
                return true;
            }

            @Override
            public void release() {
                // Since we are sequential by default, we don't
                // have any state to clean up if we terminate early.
            }
        };
    }

    /**
     * Advise the reader to avoid unreachable objects.
     * <p>
     * While enabled the reader will skip over anything previously proven to be
     * unreachable. This may be dangerous in the face of concurrent writes.
     *
     * @param avoid
     *            true to avoid unreachable objects.
     * @since 3.0
     */
    public void setAvoidUnreachableObjects(boolean avoid) {
        // Do nothing by default.
    }

    /**
     * An index that can be used to speed up ObjectWalks.
     *
     * @return the index or null if one does not exist.
     * @throws java.io.IOException
     *             when the index fails to load
     * @since 3.0
     */
    public BitmapIndex getBitmapIndex() throws IOException {
        return null;
    }

    /**
     * Create a reachability checker that will use bitmaps if possible.
     *
     * @param rw
     *            revwalk for use by the reachability checker
     * @return the most efficient reachability checker for this repository.
     * @throws IOException
     *             if it cannot open any of the underlying indices.
     *
     * @since 5.11
     */
    @NonNull
    public ReachabilityChecker createReachabilityChecker(RevWalk rw)
            throws IOException {
        if (getBitmapIndex() != null) {
            return new BitmappedReachabilityChecker(rw);
        }

        return new PedestrianReachabilityChecker(true, rw);
    }

    /**
     * Create an object reachability checker that will use bitmaps if possible.
     *
     * This reachability checker accepts any object as target. For checks
     * exclusively between commits, use
     * {@link #createReachabilityChecker(RevWalk)}.
     *
     * @param ow
     *            objectwalk for use by the reachability checker
     * @return the most efficient object reachability checker for this
     *         repository.
     *
     * @throws IOException
     *             if it cannot open any of the underlying indices.
     *
     * @since 5.11
     */
    @NonNull
    public ObjectReachabilityChecker createObjectReachabilityChecker(
            ObjectWalk ow) throws IOException {
        if (getBitmapIndex() != null) {
            return new BitmappedObjectReachabilityChecker(ow);
        }

        return new PedestrianObjectReachabilityChecker(ow);
    }

    /**
     * Get the {@link org.eclipse.jgit.lib.ObjectInserter} from which this
     * reader was created using {@code inserter.newReader()}
     *
     * @return the {@link org.eclipse.jgit.lib.ObjectInserter} from which this
     *         reader was created using {@code inserter.newReader()}, or null if
     *         this reader was not created from an inserter.
     * @since 4.4
     */
    @Nullable
    public ObjectInserter getCreatedFromInserter() {
        return null;
    }

    /**
     * {@inheritDoc}
     * <p>
     * Release any resources used by this reader.
     * <p>
     * A reader that has been released can be used again, but may need to be
     * released after the subsequent usage.
     *
     * @since 4.0
     */
    @Override
    public abstract void close();

    /**
     * Sets the threshold at which a file will be streamed rather than loaded
     * entirely into memory
     *
     * @param threshold
     *            the new threshold
     * @since 4.6
     */
    public void setStreamFileThreshold(int threshold) {
        streamFileThreshold = threshold;
    }

    /**
     * Returns the threshold at which a file will be streamed rather than loaded
     * entirely into memory
     *
     * @return the threshold in bytes
     * @since 4.6
     */
    public int getStreamFileThreshold() {
        return streamFileThreshold;
    }

    /**
     * Wraps a delegate ObjectReader.
     *
     * @since 4.4
     */
    public abstract static class Filter extends ObjectReader {
        /**
         * @return delegate ObjectReader to handle all processing.
         * @since 4.4
         */
        protected abstract ObjectReader delegate();

        @Override
        public ObjectReader newReader() {
            return delegate().newReader();
        }

        @Override
        public AbbreviatedObjectId abbreviate(AnyObjectId objectId)
                throws IOException {
            return delegate().abbreviate(objectId);
        }

        @Override
        public AbbreviatedObjectId abbreviate(AnyObjectId objectId, int len)
                throws IOException {
            return delegate().abbreviate(objectId, len);
        }

        @Override
        public Collection<ObjectId> resolve(AbbreviatedObjectId id)
                throws IOException {
            return delegate().resolve(id);
        }

        @Override
        public boolean has(AnyObjectId objectId) throws IOException {
            return delegate().has(objectId);
        }

        @Override
        public boolean has(AnyObjectId objectId, int typeHint) throws IOException {
            return delegate().has(objectId, typeHint);
        }

        @Override
        public ObjectLoader open(AnyObjectId objectId)
                throws MissingObjectException, IOException {
            return delegate().open(objectId);
        }

        @Override
        public ObjectLoader open(AnyObjectId objectId, int typeHint)
                throws MissingObjectException, IncorrectObjectTypeException,
                IOException {
            return delegate().open(objectId, typeHint);
        }

        @Override
        public Set<ObjectId> getShallowCommits() throws IOException {
            return delegate().getShallowCommits();
        }

        @Override
        public <T extends ObjectId> AsyncObjectLoaderQueue<T> open(
                Iterable<T> objectIds, boolean reportMissing) {
            return delegate().open(objectIds, reportMissing);
        }

        @Override
        public long getObjectSize(AnyObjectId objectId, int typeHint)
                throws MissingObjectException, IncorrectObjectTypeException,
                IOException {
            return delegate().getObjectSize(objectId, typeHint);
        }

        @Override
        public <T extends ObjectId> AsyncObjectSizeQueue<T> getObjectSize(
                Iterable<T> objectIds, boolean reportMissing) {
            return delegate().getObjectSize(objectIds, reportMissing);
        }

        @Override
        public void setAvoidUnreachableObjects(boolean avoid) {
            delegate().setAvoidUnreachableObjects(avoid);
        }

        @Override
        public BitmapIndex getBitmapIndex() throws IOException {
            return delegate().getBitmapIndex();
        }

        @Override
        @Nullable
        public ObjectInserter getCreatedFromInserter() {
            return delegate().getCreatedFromInserter();
        }

        @Override
        public void close() {
            delegate().close();
        }
    }
}