| // Copyright 2020 The Bazel Authors. All rights reserved. |
| // |
| // 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.devtools.build.lib.actions.cache; |
| |
| import com.google.devtools.build.lib.actions.FileArtifactValue; |
| import com.google.devtools.build.lib.util.Fingerprint; |
| import com.google.devtools.build.lib.util.VarInt; |
| import com.google.devtools.build.lib.vfs.DigestUtils; |
| import java.io.IOException; |
| import java.io.OutputStream; |
| import java.nio.ByteBuffer; |
| import java.util.Map; |
| import javax.annotation.Nullable; |
| |
| /** Utility class for digests/metadata relating to the action cache. */ |
| public final class MetadataDigestUtils { |
| private MetadataDigestUtils() {} |
| |
| /** |
| * @param source the byte buffer source. |
| * @return the digest from the given buffer. |
| */ |
| public static byte[] read(ByteBuffer source) { |
| int size = VarInt.getVarInt(source); |
| byte[] bytes = new byte[size]; |
| source.get(bytes); |
| return bytes; |
| } |
| |
| /** Write the digest to the output stream. */ |
| public static void write(byte[] digest, OutputStream sink) throws IOException { |
| VarInt.putVarInt(digest.length, sink); |
| sink.write(digest); |
| } |
| |
| /** |
| * Computes an order-independent digest from the given (path, metadata) pairs. |
| * |
| * <p>Note that as discussed in https://github.com/bazelbuild/bazel/issues/15660, using {@link |
| * DigestUtils#xor} to achieve order-independence is questionable in case it is possible that |
| * multiple string keys map to the same bytes when passed through {@link Fingerprint#addString} |
| * (due to lossy conversion from UTF-16 to UTF-8). We expect however that paths are represented as |
| * latin1 bytes encoded as a string, so the concern does not apply. |
| * |
| * @param mdMap A collection of (execPath, FileArtifactValue) pairs. Values may be null. |
| */ |
| public static byte[] fromMetadata(Map<String, FileArtifactValue> mdMap) { |
| byte[] result = new byte[1]; // reserve the empty string |
| // Profiling showed that MessageDigest engine instantiation was a hotspot, so create one |
| // instance for this computation to amortize its cost. |
| Fingerprint fp = new Fingerprint(); |
| for (Map.Entry<String, FileArtifactValue> entry : mdMap.entrySet()) { |
| result = DigestUtils.xor(result, getDigest(fp, entry.getKey(), entry.getValue())); |
| } |
| return result; |
| } |
| |
| private static byte[] getDigest(Fingerprint fp, String execPath, @Nullable FileArtifactValue md) { |
| fp.addString(execPath); |
| if (md != null) { |
| md.addTo(fp); |
| } |
| return fp.digestAndReset(); |
| } |
| } |