Inter-process communication

AIDL (Android Interface Definition Language) и коммуникация между процессами (IPC) [https://habrahabr.ru/post/139432/]

Основы безопасности операционной системы Android. Безопасность на уровне Application Framework. Binder IPC [https://habr.com/post/176093/]

Android IPC Mechanism [pdf]

What the Zygote!? [https://medium.com/@voodoomio/what-the-zygote-76f852d887d9]

Exploring Android Processes [https://medium.com/@kelvinma/exploring-android-processes-bf74ba63552c]

Communication between apps in Android

Problems to solve by communication

apps can start each other and can receive a result
apps can send notification about events
providing data
providing methods (RPC)
providing UI

Android API to communicate

startActivity, startActivityForResult
sendBroadcast
ContentProvider
AIDL, Messenger
system services: Notification listener, Mediasession etc.

How does it work under the hood

Binder [https://developer.android.com/reference/android/os/Binder]

Features of startActivityForResult

transaction has 1 Mb limit
user leave your app
hence OS can kill your app or user might don’t come back to the app
you can pass primitive types, String, Parcelable, Serializable and list of them
the main goal – start other activities and receive their result

Features of sendBroadcast

at the moment there are 2 queues: for foreground and for background priority

&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
/**&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
 * BROADCASTS&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
 *&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
 * We keep two broadcast queues and associated bookkeeping, one for those at&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
 * foreground priority, and one for normal (background-priority) broadcasts.&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
 */&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>

transaction has 1 Mb limit
delivery time is not guaranteed
asynchronously
you don’t know when receiver receive Intent
you can pass primitive types, String, Parcelable, Serializable and list of them
the main goals:
- notify about events if delivery time is not important
- if delivery time is important and receiver is in foreground
- you can receiver system events

AIDL

[https://developer.android.com/guide/components/aidl]

you can pass primitive types, String, Parcelable, Interface and list of them
AIDL can do everything
you can invoke another app methods synchronously and asynchronously
receive data by your own callback or by Messenger

1 Mb limit [https://developer.android.com/reference/android/os/TransactionTooLargeException]

&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
The Binder transaction failed because it was too large.&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
During a remote procedure call, the arguments and the return value of the call are transferred as Parcel objects stored in the Binder transaction buffer. If the arguments or the return value are too large to fit in the transaction buffer, then the call will fail and TransactionTooLargeException will be thrown.&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>
The Binder transaction buffer has a limited fixed size, currently 1Mb, which is shared by all transactions in progress for the process. Consequently this exception can be thrown when there are many transactions in progress even when most of the individual transactions are of moderate size.&amp;amp;amp;lt;br&amp;amp;amp;gt;&amp;amp;lt;br&amp;amp;gt;&amp;lt;br&amp;gt;&lt;br&gt;<br>

the main goal is RPC

ContentProvider

a row in cursor has 2 Mb limit
a number of rows is not limited
synchronously
you can pass primitive types, String, byte[], other data types use toString
the main goal is data transfer

System services

AccountManager – a way to store and share account info
App widgets
NotificationListenerService – a way to get all notification
Mediasession

Android Binder Framework [ https://android.jlelse.eu/android-binder-framework-8a28fb38699a ]

[https://t.me/android_live/585]

Подробнее о JSON RPC
[https://medium.com/nuances-of-programming/%D0%BF%D0%BE%D0%B4%D1%80%D0%BE%D0%B1%D0%BD%D0%B5%D0%B5-%D0%BE-json-rpc-b4ad927edcaf]

REST? Возьмите тупой JSON-RPC
[https://habr.com/ru/post/441854/]

gRPC в качестве протокола межсервисного взаимодействия. Доклад Яндекса
[https://habr.com/ru/company/yandex/blog/484068/]

Announcing gRPC Kotlin 1.0 for Android and Cloud
[https://developers.googleblog.com/2020/12/announcing-grpc-kotlin-10-for-android.html]

The legend about AIDL. Part 1. The roots
[https://unbreakable-titan.medium.com/the-legend-about-aidl-part-1-the-roots-c144be38d9a4]

Уязвимости в реализации межпроцессного взаимодействия в Android-приложениях
[https://habr.com/ru/company/odnoklassniki/blog/525280/]