1 files changed, 75 insertions, 0 deletions
diff --git a/dx/src/com/android/jack/dx/io/DexHasher.java b/dx/src/com/android/jack/dx/io/DexHasher.java
new file mode 100644
index 00000000..301dd377
--- /dev/null
+++ b/dx/src/com/android/jack/dx/io/DexHasher.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2011 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.jack.dx.io;
+
+import java.io.IOException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.zip.Adler32;
+
+/**
+ * Generates and stores the checksum and signature of a dex file.
+ */
+public final class DexHasher {
+    private static final int CHECKSUM_OFFSET = 8;
+    private static final int CHECKSUM_SIZE = 4;
+    private static final int SIGNATURE_OFFSET = CHECKSUM_OFFSET + CHECKSUM_SIZE;
+    private static final int SIGNATURE_SIZE = 20;
+
+    /**
+     * Returns the signature of all but the first 32 bytes of {@code dex}. The
+     * first 32 bytes of dex files are not specified to be included in the
+     * signature.
+     */
+    public byte[] computeSignature(DexBuffer dex) throws IOException {
+        MessageDigest digest;
+        try {
+            digest = MessageDigest.getInstance("SHA-1");
+        } catch (NoSuchAlgorithmException e) {
+            throw new AssertionError();
+        }
+        int offset = SIGNATURE_OFFSET + SIGNATURE_SIZE;
+
+        byte[] bytes = dex.getBytes();
+        digest.update(bytes, offset, bytes.length - offset);
+        return digest.digest();
+    }
+
+    /**
+     * Returns the checksum of all but the first 12 bytes of {@code dex}.
+     */
+    public int computeChecksum(DexBuffer dex) throws IOException {
+        Adler32 adler32 = new Adler32();
+        int offset = CHECKSUM_OFFSET + CHECKSUM_SIZE;
+
+        byte[] bytes = dex.getBytes();
+        adler32.update(bytes, offset, bytes.length - offset);
+        return (int) adler32.getValue();
+    }
+
+    /**
+     * Generates the signature and checksum of the dex file {@code out} and
+     * writes them to the file.
+     */
+    public void writeHashes(DexBuffer dex) throws IOException {
+        byte[] signature = computeSignature(dex);
+        dex.open(SIGNATURE_OFFSET).write(signature);
+
+        int checksum = computeChecksum(dex);
+        dex.open(CHECKSUM_OFFSET).writeInt(checksum);
+    }
+}