1 files changed, 94 insertions, 0 deletions
diff --git a/packages/BackupEncryption/src/com/android/server/backup/encryption/chunk/ChunkListingMap.java b/packages/BackupEncryption/src/com/android/server/backup/encryption/chunk/ChunkListingMap.java
new file mode 100644
index 000000000000..51d7d532c920
--- /dev/null
+++ b/packages/BackupEncryption/src/com/android/server/backup/encryption/chunk/ChunkListingMap.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2019 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.android.server.backup.encryption.chunk;
+
+import android.annotation.Nullable;
+
+import com.android.server.backup.encryption.protos.nano.ChunksMetadataProto;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Chunk listing in a format optimized for quick look up of chunks via their hash keys. This is
+ * useful when building an incremental backup. After a chunk has been produced, the algorithm can
+ * quickly look up whether the chunk existed in the previous backup by checking this chunk listing.
+ * It can then tell the server to use that chunk, through telling it the position and length of the
+ * chunk in the previous backup's blob.
+ */
+public class ChunkListingMap {
+
+    private final Map<ChunkHash, Entry> mChunksByHash;
+
+    /** Construct a map from a {@link ChunksMetadataProto.ChunkListing} protobuf */
+    public static ChunkListingMap fromProto(ChunksMetadataProto.ChunkListing chunkListingProto) {
+        Map<ChunkHash, Entry> entries = new HashMap<>();
+
+        long start = 0;
+
+        for (ChunksMetadataProto.Chunk chunk : chunkListingProto.chunks) {
+            entries.put(new ChunkHash(chunk.hash), new Entry(start, chunk.length));
+            start += chunk.length;
+        }
+
+        return new ChunkListingMap(entries);
+    }
+
+    private ChunkListingMap(Map<ChunkHash, Entry> chunksByHash) {
+        // This is only called from the {@link #fromProto} method, so we don't
+        // need to take a copy.
+        this.mChunksByHash = chunksByHash;
+    }
+
+    /** Returns {@code true} if there is a chunk with the given SHA-256 MAC key in the listing. */
+    public boolean hasChunk(ChunkHash hash) {
+        return mChunksByHash.containsKey(hash);
+    }
+
+    /**
+     * Returns the entry for the chunk with the given hash.
+     *
+     * @param hash The SHA-256 MAC of the plaintext of the chunk.
+     * @return The entry, containing position and length of the chunk in the backup blob, or null if
+     *     it does not exist.
+     */
+    @Nullable
+    public Entry getChunkEntry(ChunkHash hash) {
+        return mChunksByHash.get(hash);
+    }
+
+    /** Information about a chunk entry in a backup blob - i.e., its position and length. */
+    public static final class Entry {
+        private final int mLength;
+        private final long mStart;
+
+        private Entry(long start, int length) {
+            mLength = length;
+            mStart = start;
+        }
+
+        /** Returns the length of the chunk in bytes. */
+        public int getLength() {
+            return mLength;
+        }
+
+        /** Returns the start position of the chunk in the backup blob, in bytes. */
+        public long getStart() {
+            return mStart;
+        }
+    }
+}