Externalize Parcelable caching

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/ParcelableCache.java

@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2015 Dominik Schürmann <dominik@dominikschuermann.de>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.sufficientlysecure.keychain.util;
+
+import android.os.Parcel;
+
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * If Parcelables are above 1 MB, Android OS fails to send them via the Binder IPC:
+ * JavaBinder  E  !!! FAILED BINDER TRANSACTION !!!
+ * To overcome this issue this class allows to cache Parcelables, mapped by unique UUIDs,
+ * which are written to the parcel instead of the whole Parcelable.
+ */
+public class ParcelableCache<E extends Object> {
+
+    private static final UUID NULL_UUID = new UUID(0, 0);
+
+    /**
+     * A HashMap of UUID:Object
+     * This is used such that when we become parceled, we are
+     * well below the 1 MB boundary that is specified.
+     */
+    private ConcurrentHashMap<UUID, E> dehydratedLogs = new ConcurrentHashMap<>();
+
+    /**
+     * Dehydrate a Parcelable (such that it is available after deparcelization)
+     * Returns the NULL uuid (0) if you hand it null.
+     *
+     * @param parcelable A Parcelable to dehydrate
+     * @return a UUID, the ticket for your dehydrated Parcelable
+     */
+    private UUID dehydrateParcelable(E parcelable) {
+        if (parcelable == null) {
+            return NULL_UUID;
+        } else {
+            UUID ticket = UUID.randomUUID();
+            dehydratedLogs.put(ticket, parcelable);
+            return ticket;
+        }
+    }
+
+    /**
+     * Rehydrate a Parcelable after going through parcelization,
+     * invalidating its place in the dehydration pool.
+     * This is used such that when parcelized, the Parcelable is no larger than 1 MB.
+     *
+     * @param ticket A UUID ticket that identifies the log in question.
+     * @return An OperationLog.
+     */
+    private E rehydrateParcelable(UUID ticket) {
+        // UUID.equals isn't well documented; we use compareTo instead.
+        if (NULL_UUID.compareTo(ticket) == 0) {
+            return null;
+        } else {
+            E parcelable = dehydratedLogs.get(ticket);
+            dehydratedLogs.remove(ticket);
+            return parcelable;
+        }
+    }
+
+    public E readFromParcelAndGetFromCache(Parcel source) {
+        long mostSig = source.readLong();
+        long leastSig = source.readLong();
+        UUID mTicket = new UUID(mostSig, leastSig);
+        // fetch the dehydrated log out of storage (this removes it from the dehydration pool)
+        return rehydrateParcelable(mTicket);
+    }
+
+
+    public void cacheAndWriteToParcel(E parcelable, Parcel dest) {
+        // Get a ticket for our log.
+        UUID mTicket = dehydrateParcelable(parcelable);
+        // And write out the UUID most and least significant bits.
+        dest.writeLong(mTicket.getMostSignificantBits());
+        dest.writeLong(mTicket.getLeastSignificantBits());
+    }
+
+}