/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Eclipse Foundation, Inc. nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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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 org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.revwalk.ObjectWalk;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.storage.pack.ObjectReuseAsIs;
/**
* Reads an {@link ObjectDatabase} for a single thread.
* <p>
* Readers that can support efficient reuse of pack encoded objects should also
* implement the companion interface {@link ObjectReuseAsIs}.
*/
public abstract class ObjectReader {
/** Type hint indicating the caller doesn't know the type. */
public static final int OBJ_ANY = -1;
/**
* 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 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 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<ObjectId>(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 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 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;
* {@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 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 ObjectLoader} for accessing the object.
* @throws MissingObjectException
* the object does not exist.
* @throws 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;
* {@link #OBJ_ANY} if the object type is not known, or does not
* matter to the caller.
* @return a {@link ObjectLoader} for accessing the object.
* @throws MissingObjectException
* the object does not exist.
* @throws IncorrectObjectTypeException
* typeHint was not OBJ_ANY, and the object's actual type does
* not match typeHint.
* @throws IOException
* the object store cannot be accessed.
*/
public abstract ObjectLoader open(AnyObjectId objectId, int typeHint)
throws MissingObjectException, IncorrectObjectTypeException,
IOException;
/**
* Asynchronous object opening.
*
* @param <T>
* type of identifier being supplied.
* @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;
public boolean next() throws MissingObjectException, IOException {
if (idItr.hasNext()) {
cur = idItr.next();
return true;
} else {
return false;
}
}
public T getCurrent() {
return cur;
}
public ObjectId getObjectId() {
return cur;
}
public ObjectLoader open() throws IOException {
return ObjectReader.this.open(cur, OBJ_ANY);
}
public boolean cancel(boolean mayInterruptIfRunning) {
return true;
}
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;
* {@link #OBJ_ANY} if the object type is not known, or does not
* matter to the caller.
* @return size of object in bytes.
* @throws MissingObjectException
* the object does not exist.
* @throws IncorrectObjectTypeException
* typeHint was not OBJ_ANY, and the object's actual type does
* not match typeHint.
* @throws 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 <T>
* type of identifier being supplied.
* @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;
public boolean next() throws MissingObjectException, IOException {
if (idItr.hasNext()) {
cur = idItr.next();
sz = getObjectSize(cur, OBJ_ANY);
return true;
} else {
return false;
}
}
public T getCurrent() {
return cur;
}
public ObjectId getObjectId() {
return cur;
}
public long getSize() {
return sz;
}
public boolean cancel(boolean mayInterruptIfRunning) {
return true;
}
public void release() {
// Since we are sequential by default, we don't
// have any state to clean up if we terminate early.
}
};
}
/**
* Advice from a {@link RevWalk} that a walk is starting from these roots.
*
* @param walk
* the revision pool that is using this reader.
* @param roots
* starting points of the revision walk. The starting points have
* their headers parsed, but might be missing bodies.
* @throws IOException
* the reader cannot initialize itself to support the walk.
*/
public void walkAdviceBeginCommits(RevWalk walk, Collection<RevCommit> roots)
throws IOException {
// Do nothing by default, most readers don't want or need advice.
}
/**
* Advice from an {@link ObjectWalk} that trees will be traversed.
*
* @param ow
* the object pool that is using this reader.
* @param min
* the first commit whose root tree will be read.
* @param max
* the last commit whose root tree will be read.
* @throws IOException
* the reader cannot initialize itself to support the walk.
*/
public void walkAdviceBeginTrees(ObjectWalk ow, RevCommit min, RevCommit max)
throws IOException {
// Do nothing by default, most readers don't want or need advice.
}
/** Advice from that a walk is over. */
public void walkAdviceEnd() {
// Do nothing by default, most readers don't want or need advice.
}
/**
* 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.
*/
public void release() {
// Do nothing.
}
}
