org.eclipse.jgit.storage.file.PackIndexWriter Maven / Gradle / Ivy
/*
* Copyright (C) 2008, Robin Rosenberg
* Copyright (C) 2008, Shawn O. Pearce
* 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
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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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.storage.file;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.security.DigestOutputStream;
import java.text.MessageFormat;
import java.util.List;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.transport.PackedObjectInfo;
import org.eclipse.jgit.util.NB;
import org.eclipse.jgit.util.io.SafeBufferedOutputStream;
/**
* Creates a table of contents to support random access by {@link PackFile}.
*
* Pack index files (the .idx suffix in a pack file pair)
* provides random access to any object in the pack by associating an ObjectId
* to the byte offset within the pack where the object's data can be read.
*/
public abstract class PackIndexWriter {
/** Magic constant indicating post-version 1 format. */
protected static final byte[] TOC = { -1, 't', 'O', 'c' };
/**
* Create a new writer for the oldest (most widely understood) format.
*
* This method selects an index format that can accurate describe the
* supplied objects and that will be the most compatible format with older
* Git implementations.
*
* Index version 1 is widely recognized by all Git implementations, but
* index version 2 (and later) is not as well recognized as it was
* introduced more than a year later. Index version 1 can only be used if
* the resulting pack file is under 4 gigabytes in size; packs larger than
* that limit must use index version 2.
*
* @param dst
* the stream the index data will be written to. If not already
* buffered it will be automatically wrapped in a buffered
* stream. Callers are always responsible for closing the stream.
* @param objs
* the objects the caller needs to store in the index. Entries
* will be examined until a format can be conclusively selected.
* @return a new writer to output an index file of the requested format to
* the supplied stream.
* @throws IllegalArgumentException
* no recognized pack index version can support the supplied
* objects. This is likely a bug in the implementation.
*/
@SuppressWarnings("fallthrough")
public static PackIndexWriter createOldestPossible(final OutputStream dst,
final List objs) {
int version = 1;
LOOP: for (final PackedObjectInfo oe : objs) {
switch (version) {
case 1:
if (PackIndexWriterV1.canStore(oe))
continue;
version = 2;
case 2:
break LOOP;
}
}
return createVersion(dst, version);
}
/**
* Create a new writer instance for a specific index format version.
*
* @param dst
* the stream the index data will be written to. If not already
* buffered it will be automatically wrapped in a buffered
* stream. Callers are always responsible for closing the stream.
* @param version
* index format version number required by the caller. Exactly
* this formatted version will be written.
* @return a new writer to output an index file of the requested format to
* the supplied stream.
* @throws IllegalArgumentException
* the version requested is not supported by this
* implementation.
*/
public static PackIndexWriter createVersion(final OutputStream dst,
final int version) {
switch (version) {
case 1:
return new PackIndexWriterV1(dst);
case 2:
return new PackIndexWriterV2(dst);
default:
throw new IllegalArgumentException(MessageFormat.format(
JGitText.get().unsupportedPackIndexVersion,
Integer.valueOf(version)));
}
}
/** The index data stream we are responsible for creating. */
protected final DigestOutputStream out;
/** A temporary buffer for use during IO to {link #out}. */
protected final byte[] tmp;
/** The entries this writer must pack. */
protected List entries;
/** SHA-1 checksum for the entire pack data. */
protected byte[] packChecksum;
/**
* Create a new writer instance.
*
* @param dst
* the stream this instance outputs to. If not already buffered
* it will be automatically wrapped in a buffered stream.
*/
protected PackIndexWriter(final OutputStream dst) {
out = new DigestOutputStream(dst instanceof BufferedOutputStream ? dst
: new SafeBufferedOutputStream(dst),
Constants.newMessageDigest());
tmp = new byte[4 + Constants.OBJECT_ID_LENGTH];
}
/**
* Write all object entries to the index stream.
*
* After writing the stream passed to the factory is flushed but remains
* open. Callers are always responsible for closing the output stream.
*
* @param toStore
* sorted list of objects to store in the index. The caller must
* have previously sorted the list using {@link PackedObjectInfo}'s
* native {@link Comparable} implementation.
* @param packDataChecksum
* checksum signature of the entire pack data content. This is
* traditionally the last 20 bytes of the pack file's own stream.
* @throws IOException
* an error occurred while writing to the output stream, or this
* index format cannot store the object data supplied.
*/
public void write(final List toStore,
final byte[] packDataChecksum) throws IOException {
entries = toStore;
packChecksum = packDataChecksum;
writeImpl();
out.flush();
}
/**
* Writes the index file to {@link #out}.
*
* Implementations should go something like:
*
*
* writeFanOutTable();
* for (final PackedObjectInfo po : entries)
* writeOneEntry(po);
* writeChecksumFooter();
*
*
*
* Where the logic for writeOneEntry is specific to the index
* format in use. Additional headers/footers may be used if necessary and
* the {@link #entries} collection may be iterated over more than once if
* necessary. Implementors therefore have complete control over the data.
*
* @throws IOException
* an error occurred while writing to the output stream, or this
* index format cannot store the object data supplied.
*/
protected abstract void writeImpl() throws IOException;
/**
* Output the version 2 (and later) TOC header, with version number.
*
* Post version 1 all index files start with a TOC header that makes the
* file an invalid version 1 file, and then includes the version number.
* This header is necessary to recognize a version 1 from a version 2
* formatted index.
*
* @param version
* version number of this index format being written.
* @throws IOException
* an error occurred while writing to the output stream.
*/
protected void writeTOC(final int version) throws IOException {
out.write(TOC);
NB.encodeInt32(tmp, 0, version);
out.write(tmp, 0, 4);
}
/**
* Output the standard 256 entry first-level fan-out table.
*
* The fan-out table is 4 KB in size, holding 256 32-bit unsigned integer
* counts. Each count represents the number of objects within this index
* whose {@link ObjectId#getFirstByte()} matches the count's position in the
* fan-out table.
*
* @throws IOException
* an error occurred while writing to the output stream.
*/
protected void writeFanOutTable() throws IOException {
final int[] fanout = new int[256];
for (final PackedObjectInfo po : entries)
fanout[po.getFirstByte() & 0xff]++;
for (int i = 1; i < 256; i++)
fanout[i] += fanout[i - 1];
for (final int n : fanout) {
NB.encodeInt32(tmp, 0, n);
out.write(tmp, 0, 4);
}
}
/**
* Output the standard two-checksum index footer.
*
* The standard footer contains two checksums (20 byte SHA-1 values):
*
* - Pack data checksum - taken from the last 20 bytes of the pack file.
* - Index data checksum - checksum of all index bytes written, including
* the pack data checksum above.
*
*
* @throws IOException
* an error occurred while writing to the output stream.
*/
protected void writeChecksumFooter() throws IOException {
out.write(packChecksum);
out.on(false);
out.write(out.getMessageDigest().digest());
}
}