com.google.gerrit.server.patch.gitfilediff.FileHeaderUtil Maven / Gradle / Ivy
// Copyright (C) 2020 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.gerrit.server.patch.gitfilediff;
import static java.nio.charset.StandardCharsets.UTF_8;
import com.google.common.collect.ImmutableList;
import com.google.gerrit.entities.Patch;
import com.google.gerrit.entities.Patch.PatchType;
import java.util.Optional;
import org.eclipse.jgit.patch.CombinedFileHeader;
import org.eclipse.jgit.patch.FileHeader;
import org.eclipse.jgit.util.IntList;
import org.eclipse.jgit.util.RawParseUtils;
/** A utility class for the {@link FileHeader} JGit object */
public class FileHeaderUtil {
private static final Byte NUL = '\0';
/**
* The maximum number of characters to lookup in the binary file {@link FileHeader}. This is used
* to scan the file header for the occurrence of the {@link #NUL} character.
*
* This limit assumes a uniform distribution of all characters, hence the probability of the
* occurrence of each character = (1 / 256). We want to find the limit that makes the prob. of
* finding {@link #NUL} > 0.999. 1 - (255 / 256) ^ N > 0.999 yields N = 1766. We set the limit to
* this value multiplied by 10 for more confidence.
*/
private static final int BIN_FILE_MAX_SCAN_LIMIT = 20000;
/** Converts the {@link FileHeader} parameter to a String representation. */
static String toString(FileHeader header) {
return new String(FileHeaderUtil.toByteArray(header), UTF_8);
}
/** Converts the {@link FileHeader} parameter to a byte array. */
static byte[] toByteArray(FileHeader header) {
int end = getEndOffset(header);
if (header.getStartOffset() == 0 && end == header.getBuffer().length) {
return header.getBuffer();
}
final byte[] buf = new byte[end - header.getStartOffset()];
System.arraycopy(header.getBuffer(), header.getStartOffset(), buf, 0, buf.length);
return buf;
}
/** Splits the {@code FileHeader} string to a list of strings, one string per header line. */
public static ImmutableList getHeaderLines(FileHeader fileHeader) {
String fileHeaderString = toString(fileHeader);
return getHeaderLines(fileHeaderString);
}
public static ImmutableList getHeaderLines(String header) {
return getHeaderLines(header.getBytes(UTF_8));
}
static ImmutableList getHeaderLines(byte[] header) {
final IntList lineStartOffsets = RawParseUtils.lineMap(header, 0, header.length);
final ImmutableList.Builder headerLines =
ImmutableList.builderWithExpectedSize(lineStartOffsets.size() - 1);
for (int i = 1; i < lineStartOffsets.size() - 1; i++) {
final int b = lineStartOffsets.get(i);
int e = lineStartOffsets.get(i + 1);
if (header[e - 1] == '\n') {
e--;
}
headerLines.add(RawParseUtils.decode(UTF_8, header, b, e));
}
return headerLines.build();
}
/**
* Returns the old file path associated with the {@link FileHeader}, or empty if the file is
* {@link com.google.gerrit.entities.Patch.ChangeType#ADDED} or {@link
* com.google.gerrit.entities.Patch.ChangeType#REWRITE}.
*/
public static Optional getOldPath(FileHeader header) {
Patch.ChangeType changeType = getChangeType(header);
return switch (changeType) {
case DELETED, COPIED, RENAMED, MODIFIED -> Optional.of(header.getOldPath());
case ADDED, REWRITE -> Optional.empty();
};
}
/**
* Returns the new file path associated with the {@link FileHeader}, or empty if the file is
* {@link com.google.gerrit.entities.Patch.ChangeType#DELETED}.
*/
public static Optional getNewPath(FileHeader header) {
Patch.ChangeType changeType = getChangeType(header);
return switch (changeType) {
case DELETED -> Optional.empty();
case ADDED, MODIFIED, REWRITE, COPIED, RENAMED -> Optional.of(header.getNewPath());
};
}
/** Returns the change type associated with the file header. */
public static Patch.ChangeType getChangeType(FileHeader header) {
// In Gerrit, we define our own entities of the JGit entities, so that we have full control
// over their behaviors (e.g. making sure that these entities are immutable so that we can add
// them as fields of keys / values of persisted caches).
// TODO(ghareeb): remove the dead code of the value REWRITE and all its handling
return switch (header.getChangeType()) {
case ADD -> Patch.ChangeType.ADDED;
case MODIFY -> Patch.ChangeType.MODIFIED;
case DELETE -> Patch.ChangeType.DELETED;
case RENAME -> Patch.ChangeType.RENAMED;
case COPY -> Patch.ChangeType.COPIED;
default -> throw new IllegalArgumentException("Unsupported type " + header.getChangeType());
};
}
public static PatchType getPatchType(FileHeader header) {
PatchType patchType =
switch (header.getPatchType()) {
case UNIFIED -> Patch.PatchType.UNIFIED;
case GIT_BINARY, BINARY -> Patch.PatchType.BINARY;
default ->
throw new IllegalArgumentException("Unsupported type " + header.getPatchType());
};
if (patchType != PatchType.BINARY) {
byte[] buf = header.getBuffer();
// TODO(ghareeb): should we adjust the max limit threshold?
// JGit sometimes misses the detection of binary files. In this case we look into the file
// header for the occurrence of NUL characters, which is a definite signal that the file is
// binary. We limit the number of characters to lookup to avoid performance bottlenecks.
for (int ptr = header.getStartOffset();
ptr < Math.min(header.getEndOffset(), BIN_FILE_MAX_SCAN_LIMIT);
ptr++) {
if (buf[ptr] == NUL) {
// It's really binary, but Git couldn't see the nul early enough to realize its binary,
// and instead produced the diff.
//
// Force it to be a binary; it really should have been that.
return PatchType.BINARY;
}
}
}
return patchType;
}
/**
* Returns the end offset of the diff header line of the {@code FileHeader parameter} before the
* appearance of any file edits (diff hunks).
*/
private static int getEndOffset(FileHeader fileHeader) {
if (fileHeader instanceof CombinedFileHeader) {
return fileHeader.getEndOffset();
}
if (!fileHeader.getHunks().isEmpty()) {
return fileHeader.getHunks().get(0).getStartOffset();
}
return fileHeader.getEndOffset();
}
}