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ARCHITECTURE.md

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Architecture

General architecture and description of gotd.

Subprojects:

Name Description
getdoc Documentation extraction (method descriptions, error messages, etc.)
tl Schema parser and writer
ige AES-IGE block cipher for crypto

Code generation

See the internal/gen package for code generation implementation. We use text/template.

Generated packages:

Name Description
tg The latest Telegram layer
tg/e2e Secret chats schema
internal/mt MTProto schema

Pipeline

  1. Schema is parsed from _schema/telegram.tl
  2. Embedded docs are loaded from getdoc if available
  3. Bindings (interim representation) are generated
  4. Type definitions are generated
  5. Templates are executed with (4) in context
  6. Source code is formatted and written to tl_*_gen.go files.

Layers of abstraction

Telegram

High-level API with helpers, like downloader or uploader. Ideally, every telegram functionality should have sugared helper that is convenient to use.

Can handle reconnects, DC migration, connection pooling, session management.

It is also possible to call methods directly from tg.Client, because telegram.Client implements the Invoker interface:

// Invoker can invoke raw MTProto RPC calls.
type Invoker interface {
	Invoke(ctx context.Context, input bin.Encoder, output bin.Decoder) error
}

MTProto

Low-level API abstracts out a single MTProto connection and handles it for a life cycle. Implements background pings with keepalive.

Uses internal/mt (MTProto schema), internal/proto (MTProto-related implementation) and internal/rpc (request-response handling, retries, acknowledgements) internally.

And it uses internal/exchange for the key exchange process and internal/crypto for encryption.

Crypto

All cryptographical primitives that are used in key exchange or encryption are implemented in internal/crypto package.

Also, the internal/crypto/srp implements Secure Remote Password (2FA).

Binary protocol

See bin package for implementation of MTProto basic types (de-)serialization.

We do a non-streaming approach, assuming that messages are fully available in memory, so bin.Buffer is just a wrapper for byte slices that can read and write values.

We don't do a reflection-based approach, each serialization and deserialization is generated from the schema, and is constant.