Merge #273: Crate docs for servers::upd module

7014a46 docs: [#271] crate docs for servers::udp mod (Jose Celano)

Pull request description:

  Documentation for the `crate::servers::udp` module. The UDP tracker.

ACKs for top commit:
  josecelano:
    ACK 7014a46

Tree-SHA512: 6c39d30c4163e3fc64a102aefb2e51715ceb7fe967124cea39ee6b678244c0bbe944a94901f59fed8e90bc03b44bdfae38cf3a29b9cbe4dd339ac295844078d4

cSpell.json

@@ -1,6 +1,7 @@
 {
     "words": [
         "appuser",
+        "Arvid",
         "AUTOINCREMENT",
         "automock",
         "Avicora",
@@ -21,6 +22,7 @@
         "chrono",
         "clippy",
         "completei",
+        "connectionless",
         "dockerhub",
         "downloadedi",
         "filesd",
@@ -47,6 +49,7 @@
         "nanos",
         "nextest",
         "nocapture",
+        "Norberg",
         "numwant",
         "oneshot",
         "ostr",
@@ -59,6 +62,7 @@
         "reqwest",
         "rerequests",
         "rngs",
+        "routable",
         "rusqlite",
         "rustfmt",
         "Rustls",
@@ -82,6 +86,7 @@
         "Vagaa",
         "Vuze",
         "whitespaces",
+        "XBTT",
         "Xtorrent",
         "Xunlei",
         "xxxxxxxxxxxxxxxxxxxxd",

src/lib.rs

@@ -428,7 +428,6 @@
 //! - [BEP 15](https://www.bittorrent.org/beps/bep_0015.html): UDP Tracker Protocol for `BitTorrent`
 //! - [BEP 23](https://www.bittorrent.org/beps/bep_0023.html): Tracker Returns Compact Peer Lists
 //! - [BEP 27](https://www.bittorrent.org/beps/bep_0027.html): Private Torrents
-//! - [BEP 41](https://www.bittorrent.org/beps/bep_0041.html): UDP Tracker Protocol Extensions
 //! - [BEP 48](https://www.bittorrent.org/beps/bep_0048.html): Tracker Protocol Extension: Scrape
 //!
 //! # Contributing

src/servers/http/mod.rs

@@ -43,7 +43,7 @@
 //!
 //! Parameter | Type | Description | Required |  Default | Example
 //! ---|---|---|---|---|---
-//! [`info_hash`](crate::servers::http::v1::requests::announce::Announce::info_hash) | percent encoded of 40-byte array | The `Info Hash` of the torrent. | Yes | No | `%81%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00`
+//! [`info_hash`](crate::servers::http::v1::requests::announce::Announce::info_hash) | percent encoded of 20-byte array | The `Info Hash` of the torrent. | Yes | No | `%81%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00`
 //! `peer_addr` | string |The IP address of the peer. | No | No | `2.137.87.41`
 //! [`downloaded`](crate::servers::http::v1::requests::announce::Announce::downloaded) | positive integer |The number of bytes downloaded by the peer. | No | `0` | `0`
 //! [`uploaded`](crate::servers::http::v1::requests::announce::Announce::uploaded) | positive integer | The number of bytes uploaded by the peer. | No | `0` | `0`
@@ -220,7 +220,7 @@
 //!
 //! Parameter | Type | Description | Required |  Default | Example
 //! ---|---|---|---|---|---
-//! [`info_hash`](crate::servers::http::v1::requests::scrape::Scrape::info_hashes) | percent encoded of 40-byte array | The `Info Hash` of the torrent. | Yes | No | `%81%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00`
+//! [`info_hash`](crate::servers::http::v1::requests::scrape::Scrape::info_hashes) | percent encoded of 20-byte array | The `Info Hash` of the torrent. | Yes | No | `%81%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00`
 //!
 //! > **NOTICE**: you can scrape multiple torrents at the same time by passing
 //! multiple `info_hash` parameters.

src/servers/http/percent_encoding.rs

@@ -19,7 +19,7 @@ use crate::shared::bit_torrent::info_hash::{ConversionError, InfoHash};
 use crate::tracker::peer::{self, IdConversionError};
 
 /// Percent decodes a percent encoded infohash. Internally an
-/// [`InfoHash`](crate::shared::bit_torrent::info_hash::InfoHash) is a 40-byte array.
+/// [`InfoHash`](crate::shared::bit_torrent::info_hash::InfoHash) is a 20-byte array.
 ///
 /// For example, given the infohash `3b245504cf5f11bbdbe1201cea6a6bf45aee1bc0`,
 /// it's percent encoded representation is `%3B%24U%04%CF%5F%11%BB%DB%E1%20%1C%EAjk%F4Z%EE%1B%C0`.

src/servers/http/server.rs

@@ -44,15 +44,15 @@ pub enum Error {
     Error(String), // todo: refactor to use thiserror and add more variants for specific errors.
 }
 
-/// A stopped HTTP server.
+/// A HTTP server instance controller with no HTTP instance running.
 #[allow(clippy::module_name_repetitions)]
 pub type StoppedHttpServer<I> = HttpServer<Stopped<I>>;
 
-/// A running HTTP server.
+/// A HTTP server instance controller with a running HTTP instance.
 #[allow(clippy::module_name_repetitions)]
 pub type RunningHttpServer<I> = HttpServer<Running<I>>;
 
-/// A HTTP running server controller.
+/// A HTTP server instance controller.
 ///
 /// It's responsible for:
 ///
@@ -83,12 +83,14 @@ pub struct Stopped<I: HttpServerLauncher> {
 
 /// A running HTTP server state.
 pub struct Running<I: HttpServerLauncher> {
+    /// The address where the server is bound.
     pub bind_addr: SocketAddr,
     task_killer: tokio::sync::oneshot::Sender<u8>,
     task: tokio::task::JoinHandle<I>,
 }
 
 impl<I: HttpServerLauncher + 'static> HttpServer<Stopped<I>> {
+    /// It creates a new `HttpServer` controller in `stopped` state.
     pub fn new(cfg: torrust_tracker_configuration::HttpTracker, launcher: I) -> Self {
         Self {
             cfg,

src/servers/http/v1/requests/announce.rs

@@ -88,7 +88,7 @@ pub struct Announce {
 /// Errors that can occur when parsing the `Announce` request.
 ///
 /// The `info_hash` and `peer_id` query params are special because they contain
-/// binary data. The `info_hash` is a 40-byte SHA1 hash and the `peer_id` is a
+/// binary data. The `info_hash` is a 20-byte SHA1 hash and the `peer_id` is a
 /// 20-byte array.
 #[derive(Error, Debug)]
 pub enum ParseAnnounceQueryError {

src/servers/signals.rs

@@ -1,4 +1,4 @@
-/// This module contains functions to handle signals.
+//! This module contains functions to handle signals.
 use log::info;
 
 /// Resolves on `ctrl_c` or the `terminate` signal.

src/servers/udp/connection_cookie.rs

@@ -1,3 +1,71 @@
+//! Logic for generating and verifying connection IDs.
+//!
+//! The UDP tracker requires the client to connect to the server before it can
+//! send any data. The server responds with a random 64-bit integer that the
+//! client must use to identify itself.
+//!
+//! This connection ID is used to avoid spoofing attacks. The client must send
+//! the connection ID in all requests to the server. The server will ignore any
+//! requests that do not contain the correct connection ID.
+//!
+//! The simplest way to implement this would be to generate a random number when
+//! the client connects and store it in a hash table. However, this would
+//! require the server to store a large number of connection IDs, which would be
+//! a waste of memory. Instead, the server generates a connection ID based on
+//! the client's IP address and the current time. This allows the server to
+//! verify the connection ID without storing it.
+//!
+//! This module implements this method of generating connection IDs. It's the
+//! most common way to generate connection IDs. The connection ID is generated
+//! using a time based algorithm and it is valid for a certain amount of time
+//! (usually two minutes). The connection ID is generated using the following:
+//!
+//! ```text
+//! connection ID = hash(client IP + current time slot + secret seed)
+//! ```
+//!
+//! Time slots are two minute intervals since the Unix epoch. The secret seed is
+//! a random number that is generated when the server starts. And the client IP
+//! is used in order generate a unique connection ID for each client.
+//!
+//! The BEP-15 recommends a two-minute time slot.
+//!
+//! ```text
+//! Timestamp (seconds from Unix epoch):
+//! |------------|------------|------------|------------|
+//! 0            120          240          360          480
+//! Time slots (two-minutes time extents from Unix epoch):
+//! |------------|------------|------------|------------|
+//! 0            1            2            3            4
+//! Peer connections:
+//! Peer A       |-------------------------|
+//! Peer B                    |-------------------------|
+//! Peer C              |------------------|
+//! Peer A connects at timestamp 120 slot 1 -> connection ID will be valid from timestamp 120 to 360
+//! Peer B connects at timestamp 240 slot 2 -> connection ID will be valid from timestamp 240 to 480
+//! Peer C connects at timestamp 180 slot 1 -> connection ID will be valid from timestamp 180 to 360
+//! ```
+//! > **NOTICE**: connection ID is always the same for a given peer
+//! (socket address) and time slot.
+//!
+//! > **NOTICE**: connection ID will be valid for two time extents, **not two
+//! minutes**. It'll be valid for the the current time extent and the next one.
+//!
+//! Refer to [`Connect`](crate::servers::udp#connect) for more information about
+//! the connection process.
+//!
+//! ## Advantages
+//!
+//! - It consumes less memory than storing a hash table of connection IDs.
+//! - It's easy to implement.
+//! - It's fast.
+//!
+//! ## Disadvantages
+//!
+//! - It's not very flexible. The connection ID is only valid for a certain
+//! amount of time.
+//! - It's not very accurate. The connection ID is valid for more than two
+//! minutes.
 use std::net::SocketAddr;
 use std::panic::Location;
 
@@ -12,16 +80,19 @@ pub type SinceUnixEpochTimeExtent = TimeExtent;
 
 pub const COOKIE_LIFETIME: TimeExtent = TimeExtent::from_sec(2, &60);
 
+/// Converts a connection ID into a connection cookie.
 #[must_use]
 pub fn from_connection_id(connection_id: &ConnectionId) -> Cookie {
     connection_id.0.to_le_bytes()
 }
 
+/// Converts a connection cookie into a connection ID.
 #[must_use]
 pub fn into_connection_id(connection_cookie: &Cookie) -> ConnectionId {
     ConnectionId(i64::from_le_bytes(*connection_cookie))
 }
 
+/// Generates a new connection cookie.
 #[must_use]
 pub fn make(remote_address: &SocketAddr) -> Cookie {
     let time_extent = cookie_builder::get_last_time_extent();
@@ -30,6 +101,8 @@ pub fn make(remote_address: &SocketAddr) -> Cookie {
     cookie_builder::build(remote_address, &time_extent)
 }
 
+/// Checks if the supplied `connection_cookie` is valid.
+///
 /// # Panics
 ///
 /// It would panic if the `COOKIE_LIFETIME` constant would be an unreasonably large number.

src/servers/udp/error.rs

@@ -1,24 +1,30 @@
+//! Error types for the UDP server.
 use std::panic::Location;
 
 use thiserror::Error;
 use torrust_tracker_located_error::LocatedError;
 
+/// Error returned by the UDP server.
 #[derive(Error, Debug)]
 pub enum Error {
+    /// Error returned when the domain tracker returns an error.
     #[error("tracker server error: {source}")]
     TrackerError {
         source: LocatedError<'static, dyn std::error::Error + Send + Sync>,
     },
 
+    /// Error returned from a third-party library (aquatic_udp_protocol).
     #[error("internal server error: {message}, {location}")]
     InternalServer {
         location: &'static Location<'static>,
         message: String,
     },
 
+    /// Error returned when the connection id could not be verified.
     #[error("connection id could not be verified")]
     InvalidConnectionId { location: &'static Location<'static> },
 
+    /// Error returned when the request is invalid.
     #[error("bad request: {source}")]
     BadRequest {
         source: LocatedError<'static, dyn std::error::Error + Send + Sync>,