Make Cipher.update return null for empty input.

Cipher.update(byte[], int, int inputLen) is supposed to return null
when inputLen is zero. This CL makes it so. Prior to this CL, this
method returned an empty byte array.

Bug: 19100173
Change-Id: I5698f11f76a17dd8fc2509be5d8ec9369a888eaf

2 files changed, 13 insertions, 3 deletions

diff --git a/luni/src/main/java/javax/crypto/Cipher.java b/luni/src/main/java/javax/crypto/Cipher.java
index 2e3b341..889ac9f 100644
--- a/luni/src/main/java/javax/crypto/Cipher.java
+++ b/luni/src/main/java/javax/crypto/Cipher.java
@@ -1005,8 +1005,7 @@ public class Cipher {
      *            the offset in the input to start.
      * @param inputLen
      *            the length of the input to transform.
-     * @return the transformed bytes in a new buffer, or {@code null} if the
-     *         input has zero length.
+     * @return the transformed bytes in a new buffer, or {@code null} if {@code inputLen} is zero.
      * @throws IllegalStateException
      *             if this cipher instance is not initialized for encryption or
      *             decryption.
@@ -1023,7 +1022,7 @@ public class Cipher {
             throw new IllegalArgumentException("input == null");
         }
         checkInputOffsetAndCount(input.length, inputOffset, inputLen);
-        if (input.length == 0) {
+        if (inputLen == 0) {
             return null;
         }
         return getSpi().engineUpdate(input, inputOffset, inputLen);
diff --git a/luni/src/test/java/libcore/javax/crypto/CipherTest.java b/luni/src/test/java/libcore/javax/crypto/CipherTest.java
index c89886c..29112fb 100644
--- a/luni/src/test/java/libcore/javax/crypto/CipherTest.java
+++ b/luni/src/test/java/libcore/javax/crypto/CipherTest.java
@@ -2797,6 +2797,17 @@ public final class CipherTest extends TestCase {
         }
     }
 
+    public void testCipher_Update_WithZeroLengthInput_ReturnsNull() throws Exception {
+        SecretKey key = new SecretKeySpec(AES_128_KEY, "AES");
+        Cipher c = Cipher.getInstance("AES/ECB/NoPadding");
+        c.init(Cipher.ENCRYPT_MODE, key);
+        assertNull(c.update(new byte[0]));
+        assertNull(c.update(new byte[c.getBlockSize() * 2], 0, 0));
+
+        // Try with non-zero offset just in case the implementation mixes up offset and inputLen
+        assertNull(c.update(new byte[c.getBlockSize() * 2], 16, 0));
+    }
+
     private void checkCipher_ShortBlock_Failure(CipherTestParam p, String provider) throws Exception {
         SecretKey key = new SecretKeySpec(p.key, "AES");
         Cipher c = Cipher.getInstance(