ferogram-mtproto 0.3.8

MTProto 2.0 session management, message framing, DH key exchange and transport abstractions
Documentation 
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// Copyright (c) Ankit Chaubey <ankitchaubey.dev@gmail.com>
//
// ferogram: async Telegram MTProto client in Rust
// https://github.com/ankit-chaubey/ferogram
//
// Licensed under either the MIT License or the Apache License 2.0.
// See the LICENSE-MIT or LICENSE-APACHE file in this repository:
// https://github.com/ankit-chaubey/ferogram
//
// Feel free to use, modify, and share this code.
// Please keep this notice when redistributing.

use std::time::{SystemTime, UNIX_EPOCH};

/// A 64-bit MTProto message identifier.
///
/// Per the spec: the lower 32 bits are derived from the current Unix time;
/// the upper 32 bits are a monotonically increasing counter within the second.
/// The least significant two bits must be zero for client messages.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct MessageId(pub u64);

impl MessageId {
    /// Generate a new message ID using the system clock and the session-local counter.
    ///
    /// MTProto msg_id layout:
    ///   bits 63–32: Unix timestamp in seconds (upper 32 bits)
    ///   bits 31–2:  intra-second sequencing counter (lower 30 bits, × 4)
    ///   bits 1–0:   must be 0b00 for client messages
    ///
    /// The previous implementation accepted a `_counter` parameter but silently
    /// ignored it, routing all calls through a process-wide `GLOBAL_MSG_COUNTER`.
    /// The session-local `msg_counter` in `Session` was incremented uselessly.
    /// Uses the caller-supplied `counter` directly so each `Session` instance
    /// drives its own monotonic sequence without a global side-channel.
    pub(crate) fn generate(counter: u32) -> Self {
        let unix_secs = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();
        // upper 32 bits = seconds, lower 30 bits = counter × 4 (bits 1-0 = 0b00)
        let id = (unix_secs << 32) | (u64::from(counter) << 2);
        Self(id)
    }
}

/// A framed MTProto message ready to be sent.
#[derive(Debug)]
pub struct Message {
    /// Unique identifier for this message.
    pub id: MessageId,
    /// Session-scoped sequence number (even for content-unrelated, odd for content-related).
    pub seq_no: i32,
    /// The serialized TL body (constructor ID + fields).
    pub body: Vec<u8>,
}

impl Message {
    /// Construct a new plaintext message (used before key exchange).
    pub fn plaintext(id: MessageId, seq_no: i32, body: Vec<u8>) -> Self {
        Self { id, seq_no, body }
    }

    /// Serialize the message into the plaintext wire format:
    ///
    /// ```text
    /// auth_key_id:long  (0 for plaintext)
    /// message_id:long
    /// message_data_length:int
    /// message_data:bytes
    /// ```
    pub fn to_plaintext_bytes(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(8 + 8 + 4 + self.body.len());
        buf.extend(0i64.to_le_bytes()); // auth_key_id = 0
        buf.extend(self.id.0.to_le_bytes()); // message_id
        buf.extend((self.body.len() as u32).to_le_bytes()); // length
        buf.extend(&self.body);
        buf
    }
}