org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/BlockReader.java - sop/jgit - Git at Google

 /*
  * Copyright (C) 2017, 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
  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 package org.eclipse.jgit.internal.storage.reftable;

 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.eclipse.jgit.internal.storage.reftable.BlockWriter.compare;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.FILE_BLOCK_TYPE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.FILE_HEADER_LEN;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.INDEX_BLOCK_TYPE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.LOG_BLOCK_TYPE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.OBJ_BLOCK_TYPE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.REF_BLOCK_TYPE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_1ID;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_2ID;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_NONE;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_TEXT;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_TYPE_MASK;
 import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.reverseUpdateIndex;
 import static org.eclipse.jgit.lib.Constants.OBJECT_ID_LENGTH;
 import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
 import static org.eclipse.jgit.lib.Ref.Storage.NEW;
 import static org.eclipse.jgit.lib.Ref.Storage.PACKED;

 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;

 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.io.BlockSource;
 import org.eclipse.jgit.lib.CheckoutEntry;
 import org.eclipse.jgit.lib.InflaterCache;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectIdRef;
 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.ReflogEntry;
 import org.eclipse.jgit.lib.SymbolicRef;
 import org.eclipse.jgit.util.IntList;
 import org.eclipse.jgit.util.NB;
 import org.eclipse.jgit.util.RawParseUtils;

 /** Reads a single block for {@link ReftableReader}. */
 class BlockReader {
 	private byte blockType;
 	private long endPosition;

 	private byte[] buf;
 	private int bufLen;
 	private int ptr;

 	private int keysStart;
 	private int keysEnd;
 	private int restartIdx;
 	private int restartCount;

 	private byte[] nameBuf = new byte[256];
 	private int nameLen;
 	private int valueType;

 	byte type() {
 		return blockType;
 	}

 	long endPosition() {
 		return endPosition;
 	}

 	boolean next() {
 		return ptr < keysEnd;
 	}

 	void parseKey() {
 		int pfx = readVarint32();
 		valueType = readVarint32();
 		int sfx = valueType >>> 3;
 		if (pfx + sfx > nameBuf.length) {
 			int n = Math.max(pfx + sfx, nameBuf.length * 2);
 			nameBuf = Arrays.copyOf(nameBuf, n);
 		}
 		System.arraycopy(buf, ptr, nameBuf, pfx, sfx);
 		ptr += sfx;
 		nameLen = pfx + sfx;
 	}

 	String name() {
 		int len = nameLen;
 		if (blockType == LOG_BLOCK_TYPE) {
 			len -= 9;
 		}
 		return RawParseUtils.decode(UTF_8, nameBuf, 0, len);
 	}

 	boolean match(byte[] match, boolean matchIsPrefix) {
 		int len = nameLen;
 		if (blockType == LOG_BLOCK_TYPE) {
 			len -= 9;
 		}
 		if (matchIsPrefix) {
 			return len >= match.length
 					&& compare(
 							match, 0, match.length,
 							nameBuf, 0, match.length) == 0;
 		}
 		return compare(match, 0, match.length, nameBuf, 0, len) == 0;
 	}

 	boolean matchAbbrevId(byte[] match) {
 		int n = Math.min(match.length, nameLen);
 		return compare(match, 0, n, nameBuf, 0, n) == 0;
 	}

 	long readIndex() throws IOException {
 		if (blockType != INDEX_BLOCK_TYPE) {
 			throw invalidBlock();
 		}

 		readVarint32(); // skip prefix length
 		int n = readVarint32() >>> 3;
 		ptr += n; // skip name
 		return readVarint64();
 	}

 	Ref readRef() throws IOException {
 		String name = RawParseUtils.decode(UTF_8, nameBuf, 0, nameLen);
 		switch (valueType & VALUE_TYPE_MASK) {
 		case VALUE_NONE: // delete
 			return newRef(name);

 		case VALUE_1ID:
 			return new ObjectIdRef.PeeledNonTag(PACKED, name, readValueId());

 		case VALUE_2ID: { // annotated tag
 			ObjectId id1 = readValueId();
 			ObjectId id2 = readValueId();
 			return new ObjectIdRef.PeeledTag(PACKED, name, id1, id2);
 		}

 		case VALUE_TEXT: {
 			String val = readValueString();
 			if (val.startsWith("ref: ")) { //$NON-NLS-1$
 				return new SymbolicRef(name, newRef(val.substring(5)));
 			} else if (val.length() >= OBJECT_ID_STRING_LENGTH) {
 				String idStr = val.substring(0, OBJECT_ID_STRING_LENGTH);
 				if (ObjectId.isId(idStr)) {
 					ObjectId id = ObjectId.fromString(idStr);
 					return new ObjectIdRef.Unpeeled(PACKED, name, id);
 				}
 			}
 			return newRef(name);
 		}

 		default:
 			throw invalidBlock();
 		}
 	}

 	IntList readBlockList() {
 		int n = valueType & VALUE_TYPE_MASK;
 		if (n == 0) {
 			n = readVarint32();
 		}
 		IntList b = new IntList(n);
 		b.add(readVarint32());
 		for (int j = 1; j < n; j++) {
 			int prior = b.get(j - 1);
 			b.add(prior + readVarint32());
 		}
 		return b;
 	}

 	long readLogUpdateIndex() {
 		return reverseUpdateIndex(NB.decodeUInt64(nameBuf, nameLen - 8));
 	}

 	ReflogEntry readLog() {
 		ObjectId oldId = readValueId();
 		ObjectId newId = readValueId();
 		long ms = readVarint64() * 1000L;
 		short tz = readInt16();
 		String name = readValueString();
 		String email = readValueString();
 		String comment = readValueString();

 		return new ReflogEntry() {
 			@Override
 			public ObjectId getOldId() {
 				return oldId;
 			}

 			@Override
 			public ObjectId getNewId() {
 				return newId;
 			}

 			@Override
 			public PersonIdent getWho() {
 				return new PersonIdent(name, email, ms, tz);
 			}

 			@Override
 			public String getComment() {
 				return comment;
 			}

 			@Override
 			public CheckoutEntry parseCheckout() {
 				return null;
 			}
 		};
 	}

 	private ObjectId readValueId() {
 		ObjectId id = ObjectId.fromRaw(buf, ptr);
 		ptr += OBJECT_ID_LENGTH;
 		return id;
 	}

 	private String readValueString() {
 		int len = readVarint32();
 		int end = ptr + len;
 		String s = RawParseUtils.decode(UTF_8, buf, ptr, end);
 		ptr = end;
 		return s;
 	}

 	void readBlock(BlockSource src, long pos, int estBlockSize)
 			throws IOException {
 		readBlockIntoBuf(src, pos, estBlockSize);
 		parseBlockStart(pos);
 	}

 	private void readBlockIntoBuf(BlockSource src, long pos, int size)
 			throws IOException {
 		ByteBuffer b = src.read(pos, size);
 		bufLen = b.position();
 		if (bufLen <= 0) {
 			throw invalidBlock();
 		}
 		if (b.hasArray() && b.arrayOffset() == 0) {
 			buf = b.array();
 		} else {
 			buf = new byte[bufLen];
 			b.flip();
 			b.get(buf);
 		}
 		endPosition = pos + bufLen;
 	}

 	private void parseBlockStart(long pos) throws IOException {
 		ptr = 0;
 		if (pos == 0) {
 			if (bufLen == FILE_HEADER_LEN) {
 				setupEmptyFileBlock();
 				return;
 			}
 			ptr += FILE_HEADER_LEN; // first block begins with file header
 		}

 		int typeAndSize = NB.decodeInt32(buf, ptr);
 		ptr += 4;

 		blockType = (byte) (typeAndSize >>> 24);
 		int blockLen;
 		if ((blockType & INDEX_BLOCK_TYPE) == INDEX_BLOCK_TYPE) {
 			// Index blocks are allowed to grow up to 31-bit blockSize.
 			blockType = INDEX_BLOCK_TYPE;
 			blockLen = decodeIndexSize(typeAndSize);
 		} else {
 			blockLen = typeAndSize & 0xffffff;
 		}
 		if (blockType == LOG_BLOCK_TYPE) {
 			// Log blocks must be inflated after the header.
 			long deflatedSize = inflateBuf(blockLen);
 			endPosition = pos + 4 + deflatedSize;
 		}
 		if (bufLen < blockLen) {
 			throw invalidBlock();
 		} else if (bufLen > blockLen) {
 			bufLen = blockLen;
 		}

 		keysStart = ptr;
 		if (blockType != FILE_BLOCK_TYPE) {
 			restartCount = NB.decodeUInt16(buf, bufLen - 2);
 			restartIdx = bufLen - (restartCount * 3 + 2);
 			keysEnd = restartIdx;
 		} else {
 			keysEnd = keysStart;
 		}
 	}

 	static int decodeIndexSize(int typeAndSize) {
 		return typeAndSize & 0x7fffffff;
 	}

 	private long inflateBuf(int blockLen) throws IOException {
 		byte[] dst = new byte[4 + blockLen];
 		System.arraycopy(buf, 0, dst, 0, 4);

 		long deflatedSize = 0;
 		Inflater inf = InflaterCache.get();
 		try {
 			inf.setInput(buf, ptr, bufLen - ptr);
 			for (int o = 4;;) {
 				int n = inf.inflate(dst, o, dst.length - o);
 				o += n;
 				if (inf.finished()) {
 					deflatedSize = inf.getBytesRead();
 					break;
 				} else if (n <= 0) {
 					throw invalidBlock();
 				}
 			}
 		} catch (DataFormatException e) {
 			throw invalidBlock(e);
 		} finally {
 			InflaterCache.release(inf);
 		}

 		buf = dst;
 		bufLen = dst.length;
 		return deflatedSize;
 	}

 	private void setupEmptyFileBlock() {
 		// An empty reftable has only the file header in first block.
 		blockType = FILE_BLOCK_TYPE;
 		ptr = FILE_HEADER_LEN;
 		restartCount = 0;
 		restartIdx = bufLen;
 		keysStart = bufLen;
 		keysEnd = bufLen;
 	}

 	void verifyIndex() throws IOException {
 		if (blockType != INDEX_BLOCK_TYPE) {
 			throw invalidBlock();
 		}
 	}

 	int seekKey(byte[] key) {
 		return seek(key, true);
 	}

 	int seekAbbrevId(byte[] key) {
 		return seek(key, false);
 	}

 	private static int compareKey(boolean useKeyLen, byte[] a,
 			byte[] b, int bi, int bLen) {
 		if (useKeyLen) {
 			return compare(a, 0, a.length, b, bi, bLen);
 		}
 		int n = Math.min(bLen, a.length);
 		return compare(a, 0, n, b, bi, n);
 	}

 	private int seek(byte[] key, boolean useKeyLen) {
 		int low = 0;
 		int end = restartCount;
 		for (;;) {
 			int mid = (low + end) >>> 1;
 			int p = NB.decodeUInt24(buf, restartIdx + mid * 3);
 			ptr = p + 1; // skip 0 prefix length
 			int n = readVarint32() >>> 3;
 			int cmp = compareKey(useKeyLen, key, buf, ptr, n);
 			if (cmp < 0) {
 				end = mid;
 			} else if (cmp == 0) {
 				ptr = p;
 				return 0;
 			} else /* if (cmp > 0) */ {
 				low = mid + 1;
 			}
 			if (low >= end) {
 				return seekToKey(key, useKeyLen, p, low, cmp);
 			}
 		}
 	}

 	private int seekToKey(byte[] key, boolean useKeyLen,
 			int rPtr, int rIdx, int rCmp) {
 		if (rCmp < 0) {
 			if (rIdx == 0) {
 				ptr = keysStart;
 				return -1;
 			}
 			ptr = NB.decodeUInt24(buf, restartIdx + (rIdx - 1) * 3);
 		} else {
 			ptr = rPtr;
 		}

 		int cmp;
 		do {
 			int savePtr = ptr;
 			parseKey();
 			cmp = compareKey(useKeyLen, key, nameBuf, 0, nameLen);
 			if (cmp <= 0) {
 				// cmp < 0, name should be in this block, but is not.
 				// cmp = 0, block is positioned at name.
 				ptr = savePtr;
 				return cmp < 0 && savePtr == keysStart ? -1 : 0;
 			}
 			skipValue();
 		} while (ptr < keysEnd);
 		return cmp;
 	}

 	void skipValue() {
 		switch (blockType) {
 		case REF_BLOCK_TYPE:
 			switch (valueType & VALUE_TYPE_MASK) {
 			case VALUE_NONE:
 				return;
 			case VALUE_1ID:
 				ptr += OBJECT_ID_LENGTH;
 				return;
 			case VALUE_2ID:
 				ptr += 2 * OBJECT_ID_LENGTH;
 				return;
 			case VALUE_TEXT:
 				skipString();
 				return;
 			}
 			break;

 		case OBJ_BLOCK_TYPE: {
 			int n = valueType & VALUE_TYPE_MASK;
 			if (n == 0) {
 				n = readVarint32();
 			}
 			while (n-- > 0) {
 				readVarint32();
 			}
 			return;
 		}

 		case INDEX_BLOCK_TYPE:
 			readVarint32();
 			return;

 		case LOG_BLOCK_TYPE:
 			ptr += 2 * OBJECT_ID_LENGTH; // 2x id;
 			readVarint64(); // time
 			ptr += 2; // 2-byte tz
 			skipString(); // name
 			skipString(); // email
 			skipString(); // comment
 			return;
 		}

 		throw new IllegalStateException();
 	}

 	private void skipString() {
 		int n = readVarint32(); // string length
 		ptr += n;
 	}

 	private short readInt16() {
 		return (short) NB.decodeUInt16(buf, ptr += 2);
 	}

 	private int readVarint32() {
 		byte c = buf[ptr++];
 		int val = c & 0x7f;
 		while ((c & 0x80) != 0) {
 			c = buf[ptr++];
 			val++;
 			val <<= 7;
 			val |= (c & 0x7f);
 		}
 		return val;
 	}

 	private long readVarint64() {
 		byte c = buf[ptr++];
 		long val = c & 0x7f;
 		while ((c & 0x80) != 0) {
 			c = buf[ptr++];
 			val++;
 			val <<= 7;
 			val |= (c & 0x7f);
 		}
 		return val;
 	}

 	private static Ref newRef(String name) {
 		return new ObjectIdRef.Unpeeled(NEW, name, null);
 	}

 	private static IOException invalidBlock() {
 		return invalidBlock(null);
 	}

 	private static IOException invalidBlock(Throwable cause) {
 		return new IOException(JGitText.get().invalidReftableBlock, cause);
 	}
 }
	/*
	* Copyright (C) 2017, 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
	* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
	* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
	* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
	* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	package org.eclipse.jgit.internal.storage.reftable;

	import static java.nio.charset.StandardCharsets.UTF_8;
	import static org.eclipse.jgit.internal.storage.reftable.BlockWriter.compare;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.FILE_BLOCK_TYPE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.FILE_HEADER_LEN;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.INDEX_BLOCK_TYPE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.LOG_BLOCK_TYPE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.OBJ_BLOCK_TYPE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.REF_BLOCK_TYPE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_1ID;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_2ID;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_NONE;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_TEXT;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.VALUE_TYPE_MASK;
	import static org.eclipse.jgit.internal.storage.reftable.ReftableConstants.reverseUpdateIndex;
	import static org.eclipse.jgit.lib.Constants.OBJECT_ID_LENGTH;
	import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
	import static org.eclipse.jgit.lib.Ref.Storage.NEW;
	import static org.eclipse.jgit.lib.Ref.Storage.PACKED;

	import java.io.IOException;
	import java.nio.ByteBuffer;
	import java.util.Arrays;
	import java.util.zip.DataFormatException;
	import java.util.zip.Inflater;

	import org.eclipse.jgit.internal.JGitText;
	import org.eclipse.jgit.internal.storage.io.BlockSource;
	import org.eclipse.jgit.lib.CheckoutEntry;
	import org.eclipse.jgit.lib.InflaterCache;
	import org.eclipse.jgit.lib.ObjectId;
	import org.eclipse.jgit.lib.ObjectIdRef;
	import org.eclipse.jgit.lib.PersonIdent;
	import org.eclipse.jgit.lib.Ref;
	import org.eclipse.jgit.lib.ReflogEntry;
	import org.eclipse.jgit.lib.SymbolicRef;
	import org.eclipse.jgit.util.IntList;
	import org.eclipse.jgit.util.NB;
	import org.eclipse.jgit.util.RawParseUtils;

	/** Reads a single block for {@link ReftableReader}. */
	class BlockReader {
	private byte blockType;
	private long endPosition;

	private byte[] buf;
	private int bufLen;
	private int ptr;

	private int keysStart;
	private int keysEnd;
	private int restartIdx;
	private int restartCount;

	private byte[] nameBuf = new byte[256];
	private int nameLen;
	private int valueType;

	byte type() {
	return blockType;
	}

	long endPosition() {
	return endPosition;
	}

	boolean next() {
	return ptr < keysEnd;
	}

	void parseKey() {
	int pfx = readVarint32();
	valueType = readVarint32();
	int sfx = valueType >>> 3;
	if (pfx + sfx > nameBuf.length) {
	int n = Math.max(pfx + sfx, nameBuf.length * 2);
	nameBuf = Arrays.copyOf(nameBuf, n);
	}
	System.arraycopy(buf, ptr, nameBuf, pfx, sfx);
	ptr += sfx;
	nameLen = pfx + sfx;
	}

	String name() {
	int len = nameLen;
	if (blockType == LOG_BLOCK_TYPE) {
	len -= 9;
	}
	return RawParseUtils.decode(UTF_8, nameBuf, 0, len);
	}

	boolean match(byte[] match, boolean matchIsPrefix) {
	int len = nameLen;
	if (blockType == LOG_BLOCK_TYPE) {
	len -= 9;
	}
	if (matchIsPrefix) {
	return len >= match.length
	&& compare(
	match, 0, match.length,
	nameBuf, 0, match.length) == 0;
	}
	return compare(match, 0, match.length, nameBuf, 0, len) == 0;
	}

	boolean matchAbbrevId(byte[] match) {
	int n = Math.min(match.length, nameLen);
	return compare(match, 0, n, nameBuf, 0, n) == 0;
	}

	long readIndex() throws IOException {
	if (blockType != INDEX_BLOCK_TYPE) {
	throw invalidBlock();
	}

	readVarint32(); // skip prefix length
	int n = readVarint32() >>> 3;
	ptr += n; // skip name
	return readVarint64();
	}

	Ref readRef() throws IOException {
	String name = RawParseUtils.decode(UTF_8, nameBuf, 0, nameLen);
	switch (valueType & VALUE_TYPE_MASK) {
	case VALUE_NONE: // delete
	return newRef(name);

	case VALUE_1ID:
	return new ObjectIdRef.PeeledNonTag(PACKED, name, readValueId());

	case VALUE_2ID: { // annotated tag
	ObjectId id1 = readValueId();
	ObjectId id2 = readValueId();
	return new ObjectIdRef.PeeledTag(PACKED, name, id1, id2);
	}

	case VALUE_TEXT: {
	String val = readValueString();
	if (val.startsWith("ref: ")) { //$NON-NLS-1$
	return new SymbolicRef(name, newRef(val.substring(5)));
	} else if (val.length() >= OBJECT_ID_STRING_LENGTH) {
	String idStr = val.substring(0, OBJECT_ID_STRING_LENGTH);
	if (ObjectId.isId(idStr)) {
	ObjectId id = ObjectId.fromString(idStr);
	return new ObjectIdRef.Unpeeled(PACKED, name, id);
	}
	}
	return newRef(name);
	}

	default:
	throw invalidBlock();
	}
	}

	IntList readBlockList() {
	int n = valueType & VALUE_TYPE_MASK;
	if (n == 0) {
	n = readVarint32();
	}
	IntList b = new IntList(n);
	b.add(readVarint32());
	for (int j = 1; j < n; j++) {
	int prior = b.get(j - 1);
	b.add(prior + readVarint32());
	}
	return b;
	}

	long readLogUpdateIndex() {
	return reverseUpdateIndex(NB.decodeUInt64(nameBuf, nameLen - 8));
	}

	ReflogEntry readLog() {
	ObjectId oldId = readValueId();
	ObjectId newId = readValueId();
	long ms = readVarint64() * 1000L;
	short tz = readInt16();
	String name = readValueString();
	String email = readValueString();
	String comment = readValueString();

	return new ReflogEntry() {
	@Override
	public ObjectId getOldId() {
	return oldId;
	}

	@Override
	public ObjectId getNewId() {
	return newId;
	}

	@Override
	public PersonIdent getWho() {
	return new PersonIdent(name, email, ms, tz);
	}

	@Override
	public String getComment() {
	return comment;
	}

	@Override
	public CheckoutEntry parseCheckout() {
	return null;
	}
	};
	}

	private ObjectId readValueId() {
	ObjectId id = ObjectId.fromRaw(buf, ptr);
	ptr += OBJECT_ID_LENGTH;
	return id;
	}

	private String readValueString() {
	int len = readVarint32();
	int end = ptr + len;
	String s = RawParseUtils.decode(UTF_8, buf, ptr, end);
	ptr = end;
	return s;
	}

	void readBlock(BlockSource src, long pos, int estBlockSize)
	throws IOException {
	readBlockIntoBuf(src, pos, estBlockSize);
	parseBlockStart(pos);
	}

	private void readBlockIntoBuf(BlockSource src, long pos, int size)
	throws IOException {
	ByteBuffer b = src.read(pos, size);
	bufLen = b.position();
	if (bufLen <= 0) {
	throw invalidBlock();
	}
	if (b.hasArray() && b.arrayOffset() == 0) {
	buf = b.array();
	} else {
	buf = new byte[bufLen];
	b.flip();
	b.get(buf);
	}
	endPosition = pos + bufLen;
	}

	private void parseBlockStart(long pos) throws IOException {
	ptr = 0;
	if (pos == 0) {
	if (bufLen == FILE_HEADER_LEN) {
	setupEmptyFileBlock();
	return;
	}
	ptr += FILE_HEADER_LEN; // first block begins with file header
	}

	int typeAndSize = NB.decodeInt32(buf, ptr);
	ptr += 4;

	blockType = (byte) (typeAndSize >>> 24);
	int blockLen;
	if ((blockType & INDEX_BLOCK_TYPE) == INDEX_BLOCK_TYPE) {
	// Index blocks are allowed to grow up to 31-bit blockSize.
	blockType = INDEX_BLOCK_TYPE;
	blockLen = decodeIndexSize(typeAndSize);
	} else {
	blockLen = typeAndSize & 0xffffff;
	}
	if (blockType == LOG_BLOCK_TYPE) {
	// Log blocks must be inflated after the header.
	long deflatedSize = inflateBuf(blockLen);
	endPosition = pos + 4 + deflatedSize;
	}
	if (bufLen < blockLen) {
	throw invalidBlock();
	} else if (bufLen > blockLen) {
	bufLen = blockLen;
	}

	keysStart = ptr;
	if (blockType != FILE_BLOCK_TYPE) {
	restartCount = NB.decodeUInt16(buf, bufLen - 2);
	restartIdx = bufLen - (restartCount * 3 + 2);
	keysEnd = restartIdx;
	} else {
	keysEnd = keysStart;
	}
	}

	static int decodeIndexSize(int typeAndSize) {
	return typeAndSize & 0x7fffffff;
	}

	private long inflateBuf(int blockLen) throws IOException {
	byte[] dst = new byte[4 + blockLen];
	System.arraycopy(buf, 0, dst, 0, 4);

	long deflatedSize = 0;
	Inflater inf = InflaterCache.get();
	try {
	inf.setInput(buf, ptr, bufLen - ptr);
	for (int o = 4;;) {
	int n = inf.inflate(dst, o, dst.length - o);
	o += n;
	if (inf.finished()) {
	deflatedSize = inf.getBytesRead();
	break;
	} else if (n <= 0) {
	throw invalidBlock();
	}
	}
	} catch (DataFormatException e) {
	throw invalidBlock(e);
	} finally {
	InflaterCache.release(inf);
	}

	buf = dst;
	bufLen = dst.length;
	return deflatedSize;
	}

	private void setupEmptyFileBlock() {
	// An empty reftable has only the file header in first block.
	blockType = FILE_BLOCK_TYPE;
	ptr = FILE_HEADER_LEN;
	restartCount = 0;
	restartIdx = bufLen;
	keysStart = bufLen;
	keysEnd = bufLen;
	}

	void verifyIndex() throws IOException {
	if (blockType != INDEX_BLOCK_TYPE) {
	throw invalidBlock();
	}
	}

	int seekKey(byte[] key) {
	return seek(key, true);
	}

	int seekAbbrevId(byte[] key) {
	return seek(key, false);
	}

	private static int compareKey(boolean useKeyLen, byte[] a,
	byte[] b, int bi, int bLen) {
	if (useKeyLen) {
	return compare(a, 0, a.length, b, bi, bLen);
	}
	int n = Math.min(bLen, a.length);
	return compare(a, 0, n, b, bi, n);
	}

	private int seek(byte[] key, boolean useKeyLen) {
	int low = 0;
	int end = restartCount;
	for (;;) {
	int mid = (low + end) >>> 1;
	int p = NB.decodeUInt24(buf, restartIdx + mid * 3);
	ptr = p + 1; // skip 0 prefix length
	int n = readVarint32() >>> 3;
	int cmp = compareKey(useKeyLen, key, buf, ptr, n);
	if (cmp < 0) {
	end = mid;
	} else if (cmp == 0) {
	ptr = p;
	return 0;
	} else /* if (cmp > 0) */ {
	low = mid + 1;
	}
	if (low >= end) {
	return seekToKey(key, useKeyLen, p, low, cmp);
	}
	}
	}

	private int seekToKey(byte[] key, boolean useKeyLen,
	int rPtr, int rIdx, int rCmp) {
	if (rCmp < 0) {
	if (rIdx == 0) {
	ptr = keysStart;
	return -1;
	}
	ptr = NB.decodeUInt24(buf, restartIdx + (rIdx - 1) * 3);
	} else {
	ptr = rPtr;
	}

	int cmp;
	do {
	int savePtr = ptr;
	parseKey();
	cmp = compareKey(useKeyLen, key, nameBuf, 0, nameLen);
	if (cmp <= 0) {
	// cmp < 0, name should be in this block, but is not.
	// cmp = 0, block is positioned at name.
	ptr = savePtr;
	return cmp < 0 && savePtr == keysStart ? -1 : 0;
	}
	skipValue();
	} while (ptr < keysEnd);
	return cmp;
	}

	void skipValue() {
	switch (blockType) {
	case REF_BLOCK_TYPE:
	switch (valueType & VALUE_TYPE_MASK) {
	case VALUE_NONE:
	return;
	case VALUE_1ID:
	ptr += OBJECT_ID_LENGTH;
	return;
	case VALUE_2ID:
	ptr += 2 * OBJECT_ID_LENGTH;
	return;
	case VALUE_TEXT:
	skipString();
	return;
	}
	break;

	case OBJ_BLOCK_TYPE: {
	int n = valueType & VALUE_TYPE_MASK;
	if (n == 0) {
	n = readVarint32();
	}
	while (n-- > 0) {
	readVarint32();
	}
	return;
	}

	case INDEX_BLOCK_TYPE:
	readVarint32();
	return;

	case LOG_BLOCK_TYPE:
	ptr += 2 * OBJECT_ID_LENGTH; // 2x id;
	readVarint64(); // time
	ptr += 2; // 2-byte tz
	skipString(); // name
	skipString(); // email
	skipString(); // comment
	return;
	}

	throw new IllegalStateException();
	}

	private void skipString() {
	int n = readVarint32(); // string length
	ptr += n;
	}

	private short readInt16() {
	return (short) NB.decodeUInt16(buf, ptr += 2);
	}

	private int readVarint32() {
	byte c = buf[ptr++];
	int val = c & 0x7f;
	while ((c & 0x80) != 0) {
	c = buf[ptr++];
	val++;
	val <<= 7;
	val \|= (c & 0x7f);
	}
	return val;
	}

	private long readVarint64() {
	byte c = buf[ptr++];
	long val = c & 0x7f;
	while ((c & 0x80) != 0) {
	c = buf[ptr++];
	val++;
	val <<= 7;
	val \|= (c & 0x7f);
	}
	return val;
	}

	private static Ref newRef(String name) {
	return new ObjectIdRef.Unpeeled(NEW, name, null);
	}

	private static IOException invalidBlock() {
	return invalidBlock(null);
	}

	private static IOException invalidBlock(Throwable cause) {
	return new IOException(JGitText.get().invalidReftableBlock, cause);
	}
	}