From e640d1eec3d4f67f476a5b8382e4cad8e3c0948d Mon Sep 17 00:00:00 2001
From: Andreas Schildbach <andreas@schildbach.de>
Date: Sat, 5 Apr 2014 23:07:01 +0200
Subject: [PATCH] Cheap test to see if an input stream is a wallet.

---
 .../store/WalletProtobufSerializer.java       | 25 +++++++++++++++++++
 .../store/WalletProtobufSerializerTest.java   | 19 ++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/core/src/main/java/com/google/bitcoin/store/WalletProtobufSerializer.java b/core/src/main/java/com/google/bitcoin/store/WalletProtobufSerializer.java
index b35198ad..50b0bc42 100644
--- a/core/src/main/java/com/google/bitcoin/store/WalletProtobufSerializer.java
+++ b/core/src/main/java/com/google/bitcoin/store/WalletProtobufSerializer.java
@@ -1,5 +1,6 @@
 /**
  * Copyright 2012 Google Inc.
+ * Copyright 2014 Andreas Schildbach
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +26,10 @@ import com.google.bitcoin.script.Script;
 import com.google.bitcoin.wallet.WalletTransaction;
 import com.google.common.collect.Lists;
 import com.google.protobuf.ByteString;
+import com.google.protobuf.CodedInputStream;
 import com.google.protobuf.TextFormat;
+import com.google.protobuf.WireFormat;
+
 import org.bitcoinj.wallet.Protos;
 import org.bitcoinj.wallet.Protos.Wallet.EncryptionType;
 import org.slf4j.Logger;
@@ -693,4 +697,25 @@ public class WalletProtobufSerializer {
             default: confidence.setSource(TransactionConfidence.Source.UNKNOWN); break;
         }
     }
+
+    /**
+     * Cheap test to see if input stream is a wallet. This checks for a magic value at the beginning of the stream.
+     * 
+     * @param is
+     *            input stream to test
+     * @return true if input stream is a wallet
+     */
+    public static boolean isWallet(InputStream is) {
+        try {
+            final CodedInputStream cis = CodedInputStream.newInstance(is);
+            final int tag = cis.readTag();
+            final int field = WireFormat.getTagFieldNumber(tag);
+            if (field != 1) // network_identifier
+                return false;
+            final String network = cis.readString();
+            return NetworkParameters.fromID(network) != null;
+        } catch (IOException x) {
+            return false;
+        }
+    }
 }
diff --git a/core/src/test/java/com/google/bitcoin/store/WalletProtobufSerializerTest.java b/core/src/test/java/com/google/bitcoin/store/WalletProtobufSerializerTest.java
index 9d441df0..9899b9bc 100644
--- a/core/src/test/java/com/google/bitcoin/store/WalletProtobufSerializerTest.java
+++ b/core/src/test/java/com/google/bitcoin/store/WalletProtobufSerializerTest.java
@@ -1,3 +1,20 @@
+/**
+ * Copyright 2012 Google Inc.
+ * Copyright 2014 Andreas Schildbach
+ *
+ * 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.bitcoin.store;
 
 
@@ -246,6 +263,8 @@ public class WalletProtobufSerializerTest {
         ByteArrayOutputStream output = new ByteArrayOutputStream();
         //System.out.println(WalletProtobufSerializer.walletToText(wallet));
         new WalletProtobufSerializer().writeWallet(wallet, output);
+        ByteArrayInputStream test = new ByteArrayInputStream(output.toByteArray());
+        assertTrue(WalletProtobufSerializer.isWallet(test));
         ByteArrayInputStream input = new ByteArrayInputStream(output.toByteArray());
         return new WalletProtobufSerializer().readWallet(input);
     }