如何向设置android:isolatedProcess的Android Service传递PDF文件生成缩略图

我需要在设置了isolatedProcess = true的Android Service中，为来自不可信来源的PDF文件生成缩略图。这么做是因为不可信文件存在安全风险，Android PdfRenderer文档也明确建议：

如果文件来自不可信来源，建议在独立的隔离进程中运行渲染器，并赋予最小权限，以此限制安全漏洞的影响范围。

但现在遇到了文件传递的难题：

• 若通过Intent以byteArray形式传递文档，会触发TransactionTooLargeException；
• 若传递文件URI并尝试用ContentResolver打开InputStream，会抛出隔离进程无权访问ContentResolver的异常。

更新：附上关键代码片段

Android Manifest #

<application>
    ...
       <service
                android:name=".util.thumbnail.ThumbnailCreationService"
                android:isolatedProcess="true"
                android:exported="false"
                android:process=":remote" />
    </application>

Activity通过Message Handler向Service发送数据 #

class MainActivity : Activity {  
    ...
     /**
         * Class for interacting with the main interface of the service.
         */
        private val mConnection: ServiceConnection = object : ServiceConnection {
            override fun onServiceConnected(
                className: ComponentName,
                service: IBinder
            ) {
                mService = Messenger(service)
                registerClient(mMessenger)
            }
    
            override fun onServiceDisconnected(className: ComponentName) {
                mService = null
                unregisterClient(mMessenger)
                Timber.d("Service disconnected")
            }
        }
    
    fun sendMessageToService(fileUri: Uri){
       mService?.let {
            val msg = Message.obtain(
                null,
                MSG_CREATE_THUMBNAIL, this.hashCode(), 0
            )
            val bundle = Bundle()
            // 向Service发送文档URI
            bundle.putString(ARG_DOCUMENT_DATA_URI, fileUri.toString())
            // 若传递文档数据会触发TransactionTooLargeException
            // bundle.putByteArray(ARG_DOCUMENT_DATA, document)
            bundle.putString(ARG_DOCUMENT_MIME_TYPE, mimeType)
            msg.data = bundle
            it.send(msg)
        }
    }

Service: ThumbnailCreationService #

class ThumbnailCreationService : Service() {
    
        var mClients = ArrayList<Messenger>()
    
        /**
         * 处理来自客户端的消息
         */
        internal class IncomingHandler(private val thumbnailCreationService: ThumbnailCreationService) : Handler(Looper.getMainLooper()) {
    
            override fun handleMessage(msg: Message) {
                Timber.d("Retrieved client message: ${msg.what}")
                when (msg.what) {
                    MSG_CREATE_THUMBNAIL -> {
                        msg.data?.let {
                            val uri = Uri.parse(it.getString(ARG_DOCUMENT_DATA_URI))
                            thumbnailCreationService.loadDocumentData(uri)
                        }
                    }
                    else -> super.handleMessage(msg)
                }
            }
        }
    
        protected fun loadDocumentData(uri: Uri) =
    // 此处contentResolver会崩溃，因为隔离进程无权访问ContentResolver
            this.contentResolver.openInputStream(uri)?.use {
                IOHandler.readFileUriContent(it)
            } 
    }

堆栈信息 #

java.lang.SecurityException: Isolated process not allowed to call getContentProvider
                                                                                                        at android.os.Parcel.createExceptionOrNull(Parcel.java:3011)
                                                                                                        at android.os.Parcel.createException(Parcel.java:2995)
                                                                                                        at android.os.Parcel.readException(Parcel.java:2978)
                                                                                                        at android.os.Parcel.readException(Parcel.java:2920)
                                                                                                        at android.app.IActivityManager$Stub$Proxy.getContentProvider(IActivityManager.java:5224)
                                                                                                        at android.app.ActivityThread.acquireProvider(ActivityThread.java:7019)
                                                                                                        at android.app.ContextImpl$ApplicationContentResolver.acquireUnstableProvider(ContextImpl.java:3420)
                                                                                                        at android.content.ContentResolver.acquireUnstableProvider(ContentResolver.java:2526)
                                                                                                        at android.content.ContentResolver.openTypedAssetFileDescriptor(ContentResolver.java:2011)
                                                                                                        at android.content.ContentResolver.openAssetFileDescriptor(ContentResolver.java:1842)
                                                                                                        at android.content.ContentResolver.openInputStream(ContentResolver.java:1518)

内容的提问来源于stack exchange，提问作者Snake