[APT-9577] Add DRM for downloads for offline usage : add DRM support …

…for MPEG-Dash audio playback in both online and offline mode

Create new helper DrmMediaSourceHelper to generate the correct media item with DRM info depending on if the content is downloaded/being downloaded.

If the content is streaming, we only need to include the general DRM info so the DRM license can be fetched from the server to decrypt the encrypted content.
If the content is a download, we need to include all DRM info as well as the DRM key ID so the local DRM license can be used for decryption instead.

Armadillo/src/main/java/com/scribd/armadillo/di/PlaybackModule.kt

@@ -15,6 +15,8 @@ import com.scribd.armadillo.playback.MediaMetadataCompatBuilderImpl
 import com.scribd.armadillo.playback.PlaybackEngineFactoryHolder
 import com.scribd.armadillo.playback.PlaybackStateBuilderImpl
 import com.scribd.armadillo.playback.PlaybackStateCompatBuilder
+import com.scribd.armadillo.playback.mediasource.DrmMediaSourceHelper
+import com.scribd.armadillo.playback.mediasource.DrmMediaSourceHelperImpl
 import com.scribd.armadillo.playback.mediasource.HeadersMediaSourceHelper
 import com.scribd.armadillo.playback.mediasource.HeadersMediaSourceHelperImpl
 import com.scribd.armadillo.playback.mediasource.MediaSourceRetriever
@@ -62,4 +64,8 @@ internal class PlaybackModule {
     @Provides
     @Singleton
     fun mediaSourceHelper(mediaSourceHelperImpl: HeadersMediaSourceHelperImpl): HeadersMediaSourceHelper = mediaSourceHelperImpl
+
+    @Provides
+    @Singleton
+    fun drmMediaSourceHelper(drmMediaSourceHelperImpl: DrmMediaSourceHelperImpl): DrmMediaSourceHelper = drmMediaSourceHelperImpl
 }

Armadillo/src/main/java/com/scribd/armadillo/error/ArmadilloException.kt

@@ -139,3 +139,7 @@ data class DrmDownloadException(val exception: Exception) : ArmadilloException(e
     override val errorCode = 701
 }
 
+data class DrmPlaybackException(val exception: Exception) : ArmadilloException(exception) {
+    override val errorCode = 702
+}
+

Armadillo/src/main/java/com/scribd/armadillo/playback/mediasource/DashMediaSourceGenerator.kt

@@ -1,8 +1,7 @@
 package com.scribd.armadillo.playback.mediasource
 
 import android.content.Context
-import com.google.android.exoplayer2.MediaItem
-import com.google.android.exoplayer2.MediaItem.DrmConfiguration
+import com.google.android.exoplayer2.drm.DefaultDrmSessionManagerProvider
 import com.google.android.exoplayer2.offline.Download
 import com.google.android.exoplayer2.offline.DownloadHelper
 import com.google.android.exoplayer2.source.MediaSource
@@ -14,31 +13,23 @@ import javax.inject.Inject
 
 internal class DashMediaSourceGenerator @Inject constructor(
     private val mediaSourceHelper: HeadersMediaSourceHelper,
-    private val downloadTracker: DownloadTracker) : MediaSourceGenerator {
+    private val downloadTracker: DownloadTracker,
+    private val drmMediaSourceHelper: DrmMediaSourceHelper,
+) : MediaSourceGenerator {
 
     override fun generateMediaSource(context: Context, request: AudioPlayable.MediaRequest): MediaSource {
         val dataSourceFactory = mediaSourceHelper.createDataSourceFactory(context, request)
 
         downloadTracker.getDownload(request.url.toUri())?.let {
             if (it.state != Download.STATE_FAILED) {
-                return DownloadHelper.createMediaSource(it.request, dataSourceFactory)
+                val mediaItem = drmMediaSourceHelper.createMediaItem(context = context, request = request, isDownload = true)
+                return DownloadHelper.createMediaSource(it.request, dataSourceFactory, DefaultDrmSessionManagerProvider().get(mediaItem))
             }
         }
 
-        val mediaItemBuilder = MediaItem.Builder()
-            .setUri(request.url)
-
-        if (request.drmInfo != null) {
-            mediaItemBuilder.setDrmConfiguration(
-                DrmConfiguration.Builder(request.drmInfo.drmType.toExoplayerConstant())
-                    .setLicenseUri(request.drmInfo.licenseServer)
-                    .setLicenseRequestHeaders(request.drmInfo.drmHeaders)
-                    .build()
-            )
-        }
-
+        val mediaItem = drmMediaSourceHelper.createMediaItem(context = context, request = request, isDownload = false)
         return DashMediaSource.Factory(dataSourceFactory)
-            .createMediaSource(mediaItemBuilder.build())
+            .createMediaSource(mediaItem)
     }
 
     override fun updateMediaSourceHeaders(request: AudioPlayable.MediaRequest) = mediaSourceHelper.updateMediaSourceHeaders(request)

Armadillo/src/main/java/com/scribd/armadillo/playback/mediasource/DrmMediaSourceHelper.kt

@@ -0,0 +1,52 @@
+package com.scribd.armadillo.playback.mediasource
+
+import android.content.Context
+import com.google.android.exoplayer2.MediaItem
+import com.scribd.armadillo.encryption.SecureStorage
+import com.scribd.armadillo.error.DrmPlaybackException
+import com.scribd.armadillo.models.AudioPlayable
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * This is a helper responsible for generating the correct media source for an audio request.
+ *
+ * This will apply the correct DRM-related information needed for content decryption (if the content is DRM-protected).
+ * In case of a download media (the content is either downloaded or being downloaded), this includes the DRM key ID used for retrieving
+ * the local DRM license (instead of fetching DRM license from the server).
+ */
+internal interface DrmMediaSourceHelper {
+    fun createMediaItem(
+        context: Context,
+        request: AudioPlayable.MediaRequest,
+        isDownload: Boolean,
+    ): MediaItem
+}
+
+@Singleton
+internal class DrmMediaSourceHelperImpl @Inject constructor(private val secureStorage: SecureStorage) : DrmMediaSourceHelper {
+
+    override fun createMediaItem(context: Context, request: AudioPlayable.MediaRequest, isDownload: Boolean): MediaItem =
+        MediaItem.Builder()
+            .setUri(request.url)
+            .apply {
+                // Apply DRM config if content is DRM-protected
+                val drmConfig = request.drmInfo?.let { drmInfo ->
+                    MediaItem.DrmConfiguration.Builder(drmInfo.drmType.toExoplayerConstant())
+                        .setLicenseUri(drmInfo.licenseServer)
+                        .setLicenseRequestHeaders(drmInfo.drmHeaders)
+                        .apply {
+                            // If the content is a download content, use the saved offline DRM key id.
+                            // This ID is needed to retrieve the local DRM license for content decryption.
+                            if (isDownload) {
+                                secureStorage.getDrmKeyId(context, request.url, drmInfo.drmType.name)?.let { drmKeyId ->
+                                    setKeySetId(drmKeyId)
+                                } ?: throw DrmPlaybackException(IllegalStateException("No DRM key id saved for download content"))
+                            }
+                        }
+                        .build()
+                }
+                setDrmConfiguration(drmConfig)
+            }
+            .build()
+}