Fix Aes128DataSourceTest portability issue

For background on why doing this works, see below. I don't want to change
how we get our Cipher instance in non-test code, since PKCS7 always works
on Android. It's only when the tests are running on a non-Android host
machine that they can fail. An alternative would be to make it an androidTest,
but androidTests are slow.

------

Background:

"While Java considers PKCS5 and PKCS7 padding to be the "same" (and
one should always use the string "AES/CBC/PKCS5Padding" because
"AES/CBC/PKCS7Padding" will cause NoSuchAlgorithmException to be thrown
when initializing an AES block cipher using the Java crypto API), I
consider this a gross misnaming in the Java platform because the pure
technical definitions of these paddings are not the same."

Ref: https://stackoverflow.com/questions/10193567/java-security-nosuchalgorithmexceptioncannot-find-any-provider-supporting-aes-e

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=207234518

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/Aes128DataSource.java

@@ -40,12 +40,12 @@ import javax.crypto.spec.SecretKeySpec;
 /**
  * A {@link DataSource} that decrypts data read from an upstream source, encrypted with AES-128 with
  * a 128-bit key and PKCS7 padding.
- * <p>
- * Note that this {@link DataSource} does not support being opened from arbitrary offsets. It is
+ *
+ * <p>Note that this {@link DataSource} does not support being opened from arbitrary offsets. It is
  * designed specifically for reading whole files as defined in an HLS media playlist. For this
  * reason the implementation is private to the HLS package.
  */
-/* package */ final class Aes128DataSource implements DataSource {
+/* package */ class Aes128DataSource implements DataSource {
 
   private final DataSource upstream;
   private final byte[] encryptionKey;
@@ -65,15 +65,15 @@ import javax.crypto.spec.SecretKeySpec;
   }
 
   @Override
-  public void addTransferListener(TransferListener transferListener) {
+  public final void addTransferListener(TransferListener transferListener) {
     upstream.addTransferListener(transferListener);
   }
 
   @Override
-  public long open(DataSpec dataSpec) throws IOException {
+  public final long open(DataSpec dataSpec) throws IOException {
     Cipher cipher;
     try {
-      cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
+      cipher = getCipherInstance();
     } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
       throw new RuntimeException(e);
     }
@@ -95,7 +95,7 @@ import javax.crypto.spec.SecretKeySpec;
   }
 
   @Override
-  public int read(byte[] buffer, int offset, int readLength) throws IOException {
+  public final int read(byte[] buffer, int offset, int readLength) throws IOException {
     Assertions.checkNotNull(cipherInputStream);
     int bytesRead = cipherInputStream.read(buffer, offset, readLength);
     if (bytesRead < 0) {
@@ -105,12 +105,12 @@ import javax.crypto.spec.SecretKeySpec;
   }
 
   @Override
-  public @Nullable Uri getUri() {
+  public final @Nullable Uri getUri() {
     return upstream.getUri();
   }
 
   @Override
-  public Map<String, List<String>> getResponseHeaders() {
+  public final Map<String, List<String>> getResponseHeaders() {
     return upstream.getResponseHeaders();
   }
 
@@ -121,4 +121,8 @@ import javax.crypto.spec.SecretKeySpec;
       upstream.close();
     }
   }
+
+  protected Cipher getCipherInstance() throws NoSuchPaddingException, NoSuchAlgorithmException {
+    return Cipher.getInstance("AES/CBC/PKCS7Padding");
+  }
 }

library/hls/src/test/java/com/google/android/exoplayer2/source/hls/Aes128DataSourceTest.java

@@ -23,6 +23,9 @@ import com.google.android.exoplayer2.upstream.DataSource;
 import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.TransferListener;
 import java.io.IOException;
+import java.security.NoSuchAlgorithmException;
+import javax.crypto.Cipher;
+import javax.crypto.NoSuchPaddingException;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
@@ -34,7 +37,7 @@ public class Aes128DataSourceTest {
   @Test
   public void test_OpenCallsUpstreamOpen_CloseCallsUpstreamClose() throws IOException {
     UpstreamDataSource upstream = new UpstreamDataSource();
-    Aes128DataSource testInstance = new Aes128DataSource(upstream, new byte[16], new byte[16]);
+    Aes128DataSource testInstance = new TestAes123DataSource(upstream, new byte[16], new byte[16]);
     assertThat(upstream.opened).isFalse();
 
     Uri uri = Uri.parse("http.abc.com/def");
@@ -54,7 +57,7 @@ public class Aes128DataSourceTest {
             throw new IOException();
           }
         };
-    Aes128DataSource testInstance = new Aes128DataSource(upstream, new byte[16], new byte[16]);
+    Aes128DataSource testInstance = new TestAes123DataSource(upstream, new byte[16], new byte[16]);
     assertThat(upstream.opened).isFalse();
 
     Uri uri = Uri.parse("http.abc.com/def");
@@ -72,6 +75,25 @@ public class Aes128DataSourceTest {
     assertThat(upstream.closedCalled).isTrue();
   }
 
+  private static class TestAes123DataSource extends Aes128DataSource {
+
+    public TestAes123DataSource(DataSource upstream, byte[] encryptionKey, byte[] encryptionIv) {
+      super(upstream, encryptionKey, encryptionIv);
+    }
+
+    @Override
+    protected Cipher getCipherInstance() throws NoSuchPaddingException, NoSuchAlgorithmException {
+      try {
+        return super.getCipherInstance();
+      } catch (NoSuchAlgorithmException e) {
+        // Some host machines may not provide an algorithm for "AES/CBC/PKCS7Padding", however on
+        // such machines it's possible to get a functionally identical algorithm by requesting
+        // "AES/CBC/PKCS5Padding".
+        return Cipher.getInstance("AES/CBC/PKCS5Padding");
+      }
+    }
+  }
+
   private static class UpstreamDataSource implements DataSource {
 
     public boolean opened;