Telegram Database Library

TDLib (Telegram Database Library) — is a cross-platform, fully functional Telegram client. It is designed to simplify creation of a custom Telegram client.

TDLib has many advantages. Notably TDLib is:

• Cross-platform: TDLib can be used on Android, iOS, Windows, macOS, Linux, Windows Phone, WebAssembly, watchOS, tvOS, Tizen, Cygwin. It should also work on other *nix systems with or without minimal effort.
• Multilanguage: TDLib can be easily used with any programming language that is able to execute C functions. Additionally it already has native bindings to Java (using JNI) and C# (using C++/CLI).
• Easy to use: TDLib takes care of all network implementation details, encryption and local data storage.
• High-performance: in the Telegram Bot API, each TDLib instance handles more than 18000 active bots simultaneously.
• Well-documented: all TDLib API methods and public interfaces are fully documented.
• Consistent: TDLib guarantees that all updates will be delivered in the right order.
• Reliable: TDLib remains stable on slow and unstable Internet connections.
• Secure: all local data is encrypted using a user-provided encryption key.
• Fully-asynchronous: requests to TDLib don't block each other or anything else, responses will be sent when they are available.

TDLib source code is available on github.

You might also be interested in the library documentation, list of available options and prebuilt library for Android.