/*
* Copyright 2011 Google Inc.
*
* 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.ipc.invalidation.ticl;
import com.google.ipc.invalidation.common.CommonProtos2;
import com.google.ipc.invalidation.common.DigestFunction;
import com.google.ipc.invalidation.external.client.SystemResources.Logger;
import com.google.ipc.invalidation.util.TypedUtil;
import com.google.protobuf.ByteString;
import com.google.protobuf.InvalidProtocolBufferException;
import com.google.protos.ipc.invalidation.Client.PersistentStateBlob;
import com.google.protos.ipc.invalidation.Client.PersistentTiclState;
/**
* Utility methods for handling the Ticl persistent state.
*
*/
public class PersistenceUtils {
/** Serializes a Ticl state blob. */
public static byte[] serializeState(PersistentTiclState state, DigestFunction digestFn) {
ByteString mac = generateMac(state, digestFn);
return CommonProtos2.newPersistentStateBlob(state, mac).toByteArray();
}
/**
* Deserializes a Ticl state blob. Returns either the parsed state or {@code null}
* if it could not be parsed.
*/
public static PersistentTiclState deserializeState(Logger logger, byte[] stateBlobBytes,
DigestFunction digestFn) {
PersistentStateBlob stateBlob;
try {
// Try parsing the envelope protocol buffer.
stateBlob = PersistentStateBlob.parseFrom(stateBlobBytes);
} catch (InvalidProtocolBufferException exception) {
logger.severe("Failed deserializing Ticl state: %s", exception.getMessage());
return null;
}
// Check the mac in the envelope against the recomputed mac from the state.
PersistentTiclState ticlState = stateBlob.getTiclState();
ByteString mac = generateMac(ticlState, digestFn);
if (!TypedUtil.<ByteString>equals(mac, stateBlob.getAuthenticationCode())) {
logger.warning("Ticl state failed MAC check: computed %s vs %s", mac,
stateBlob.getAuthenticationCode());
return null;
}
return ticlState;
}
/** Returns a message authentication code over {@code state}. */
private static ByteString generateMac(PersistentTiclState state, DigestFunction digestFn) {
digestFn.reset();
digestFn.update(state.toByteArray());
return ByteString.copyFrom(digestFn.getDigest());
}
private PersistenceUtils() {
// Prevent instantiation.
}
}