WIP to use content:// Uris for album art.

This addresses #235

At the moment, the first time art is retrieved it doesn't appear.
Subsequent loads will show the images.

This is likely related to Glide not observing the Uri for changes. This
might work on other form factors (for example, Automotive OS) but it
also might be necessary to update the MediaItems themselves.

The change is probably going to wait until January 2021 to be resolved.

common/src/main/AndroidManifest.xml

@@ -39,7 +39,7 @@
 
         <provider
             android:name=".library.AlbumArtContentProvider"
-            android:authorities="com.example.android.uamp.media.library.provider"
+            android:authorities="com.example.android.uamp"
             android:exported="true" />
 
     </application>

common/src/main/java/com/example/android/uamp/media/extensions/FileExt.kt

@@ -35,4 +35,4 @@ fun File.asAlbumArtContentUri(): Uri {
         .build()
 }
 
-private const val AUTHORITY = "com.example.android.uamp.media.library.provider"
+private const val AUTHORITY = "com.example.android.uamp"

common/src/main/java/com/example/android/uamp/media/library/AlbumArtContentProvider.kt

@@ -17,29 +17,64 @@
 package com.example.android.uamp.media.library
 
 import android.content.ContentProvider
+import android.content.ContentResolver
 import android.content.ContentValues
 import android.database.Cursor
 import android.net.Uri
 import android.os.ParcelFileDescriptor
+import android.util.Log
+import com.bumptech.glide.Glide
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.launch
 import java.io.File
 import java.io.FileNotFoundException
 
 class AlbumArtContentProvider : ContentProvider() {
 
+    companion object {
+        private val uriMap = mutableMapOf<Uri, Uri>()
+
+        fun mapUri(uri: Uri): Uri {
+            val path = uri.encodedPath?.substring(1)?.replace('/', ':') ?: return Uri.EMPTY
+            val contentUri = Uri.Builder()
+                .scheme(ContentResolver.SCHEME_CONTENT)
+                .authority("com.example.android.uamp")
+                .path(path)
+                .build()
+            uriMap[contentUri] = uri
+            return contentUri
+        }
+    }
+
     override fun onCreate() = true
 
     override fun openFile(uri: Uri, mode: String): ParcelFileDescriptor? {
         val context = this.context ?: return null
-        val file = File(uri.path)
-        if (!file.exists()) {
-            throw FileNotFoundException(uri.path)
-        }
-        // Only allow access to files under cache path
-        val cachePath = context.cacheDir.path
-        if (!file.path.startsWith(cachePath)) {
-            throw FileNotFoundException()
+        val remoteUri = uriMap[uri] ?: throw FileNotFoundException(uri.path)
+
+        val file = File(context.cacheDir, uri.path)
+        return if (!file.exists()) {
+            GlobalScope.launch(Dispatchers.IO) {
+                // Use Glide to download the album art
+                val cacheFile = Glide.with(context)
+                    .asFile()
+                    .load(remoteUri)
+                    .submit()
+                    .get()
+
+                // Rename the file Glide created to match our own scheme.
+                cacheFile.renameTo(file)
+
+                // Notify the caller that the artwork has been updated.
+                context.contentResolver.notifyChange(uri, null)
+            }
+
+            // Provide placeholder art until the correct art can be downloaded.
+            context.assets.openFd("default_art.png").parcelFileDescriptor
+        } else {
+            ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY)
         }
-        return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY)
     }
 
     override fun insert(uri: Uri, values: ContentValues?): Uri? = null

common/src/main/java/com/example/android/uamp/media/library/JsonSource.kt

@@ -98,12 +98,13 @@ class JsonSource(private val source: Uri) : AbstractMusicSource() {
                         song.image = baseUri + song.image
                     }
                 }
+                val imageUri = AlbumArtContentProvider.mapUri(Uri.parse(song.image))
 
                 MediaMetadataCompat.Builder()
                     .from(song)
                     .apply {
-                        displayIconUri = song.image // Used by ExoPlayer and Notification
-                        albumArtUri = song.image
+                        displayIconUri = imageUri.toString() // Used by ExoPlayer and Notification
+                        albumArtUri = imageUri.toString()
                     }
                     .build()
             }.toList()