Throw from (pre)acquireSession if the DrmSessionManager isn't prepared

Currently acquireSession() fails with an NPE from
checkNotNull(exoMediaDrm). A follow-up change will result in exoMediaDrm
sometimes being non-null while prepareCount==0 (and in this case we
still want acquireSession() to fail).

preacquireSession() doesn't currently fail in a way the caller can
observe - the same NPE is thrown, but asynchronously and it doesn't
propagate out of the background thread. Throwing directly seems
preferable since it's a clear bug to be trying to preacquire sessions
from an unprepared/released manager.

PiperOrigin-RevId: 375906450

library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java

@@ -487,6 +487,7 @@ public class DefaultDrmSessionManager implements DrmSessionManager {
       Looper playbackLooper,
       @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher,
       Format format) {
+    checkState(prepareCallsCount > 0);
     initPlaybackLooper(playbackLooper);
     PreacquiredSessionReference preacquiredSessionReference =
         new PreacquiredSessionReference(eventDispatcher);
@@ -500,6 +501,7 @@ public class DefaultDrmSessionManager implements DrmSessionManager {
       Looper playbackLooper,
       @Nullable DrmSessionEventListener.EventDispatcher eventDispatcher,
       Format format) {
+    checkState(prepareCallsCount > 0);
     initPlaybackLooper(playbackLooper);
     return acquireSession(
         playbackLooper,

library/core/src/test/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManagerTest.java

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.drm;
 import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
 import static com.google.common.truth.Truth.assertThat;
 import static java.util.concurrent.TimeUnit.SECONDS;
+import static org.junit.Assert.assertThrows;
 
 import android.os.Looper;
 import androidx.annotation.Nullable;
@@ -407,6 +408,31 @@ public class DefaultDrmSessionManagerTest {
     drmSessionManager.release();
   }
 
+  @Test
+  public void managerNotPrepared_acquireSessionAndPreacquireSessionFail() throws Exception {
+    FakeExoMediaDrm.LicenseServer licenseServer =
+        FakeExoMediaDrm.LicenseServer.allowingSchemeDatas(DRM_SCHEME_DATAS);
+    DefaultDrmSessionManager drmSessionManager =
+        new DefaultDrmSessionManager.Builder()
+            .setUuidAndExoMediaDrmProvider(DRM_SCHEME_UUID, uuid -> new FakeExoMediaDrm())
+            .build(/* mediaDrmCallback= */ licenseServer);
+
+    assertThrows(
+        Exception.class,
+        () ->
+            drmSessionManager.acquireSession(
+                /* playbackLooper= */ checkNotNull(Looper.myLooper()),
+                /* eventDispatcher= */ null,
+                FORMAT_WITH_DRM_INIT_DATA));
+    assertThrows(
+        Exception.class,
+        () ->
+            drmSessionManager.preacquireSession(
+                /* playbackLooper= */ checkNotNull(Looper.myLooper()),
+                /* eventDispatcher= */ null,
+                FORMAT_WITH_DRM_INIT_DATA));
+  }
+
   private static void waitForOpenedWithKeys(DrmSession drmSession) {
     // Check the error first, so we get a meaningful failure if there's been an error.
     assertThat(drmSession.getError()).isNull();