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add problem 07

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timeshifter
2026-07-15 20:57:39 +02:00
parent 924964fcfb
commit e98de342ff
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problem07/Cargo.lock
Generated
+241
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@@ -0,0 +1,241 @@
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problem07/Cargo.toml
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[package]
name = "problem07"
version = "0.1.0"
edition = "2024"
[dependencies]
anyhow = "1"
tokio = { version = "1", features = ["full"] }
itertools = "0"
problem07/src/main.rs
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use std::{
collections::BTreeMap,
net::SocketAddr,
time::{Duration, Instant},
};
use anyhow::{Result, anyhow, bail, ensure};
use itertools::Itertools;
use tokio::net::UdpSocket;
const RETRANSMISSION_DURATION: Duration = Duration::from_secs(3);
const SESSION_EXPIRY_DURATION: Duration = Duration::from_secs(60);
#[tokio::main]
async fn main() -> Result<()> {
let socket = tokio::net::UdpSocket::bind("0.0.0.0:10000").await?;
let mut read_buffer = vec![0; 1000];
let mut states = BTreeMap::new();
let mut timer = tokio::time::interval(RETRANSMISSION_DURATION);
loop {
tokio::select! {
r = socket.recv_from(&mut read_buffer) => {
let (length, addr) = r?;
let message = match String::from_utf8(read_buffer[..length].to_vec()) {
Ok(s) => s,
Err(e) => {
dbg!(e);
continue;
}
};
let message_type = match MessageType::parse(&message) {
Ok(message) => message,
Err(e) => {
dbg!(e);
continue;
}
};
let session = message_type.session();
let state = states.entry((addr, session)).or_insert(State::Closed);
match message_type {
MessageType::Ack(session, length) => match state {
State::Closed => send_close(&socket, addr, session).await?,
#[allow(clippy::nonminimal_bool)]
State::Open(open) => {
if !(length > open.highest_len_acked_so_far) {
continue;
}
if length > open.sent_so_far {
send_close(&socket, addr, session).await?;
*state = State::Closed;
states.remove(&(addr, session));
continue;
}
if length < open.sent_so_far {
retransmit_payload_data(&socket, addr, open, length).await?;
}
if length > open.highest_len_acked_so_far {
open.highest_len_acked_so_far = length;
}
if open.highest_len_acked_so_far >= open.sent_so_far {
open.unacked_since = None;
}
}
},
MessageType::Close(session) => {
send_close(&socket, addr, session).await?;
*state = State::Closed;
states.remove(&(addr, session));
continue;
}
MessageType::Connect(session) => match state {
State::Closed => {
*state = State::Open(Open::new(session));
let ack_message = send_ack(&socket, addr, session, 0).await?;
state.get_open()?.previous_ack = Some(ack_message);
}
State::Open(_) => {
let ack_message = send_ack(&socket, addr, session, 0).await?;
state.get_open()?.previous_ack = Some(ack_message);
}
},
MessageType::Data(session, pos, data) => match state {
State::Closed => send_close(&socket, addr, session).await?,
State::Open(open) => {
let ack_message = if open.received_up_to == pos {
let unescaped = unescape(&data);
let length = unescaped.len() + open.received_up_to as usize;
let ack_message = send_ack(&socket, addr, session, length).await?;
open.buffer.push_str(&unescaped);
while open.buffer.contains('\n') {
let line = open.reverse_next_line();
let escaped = escape(&line);
send_data(&socket, addr, session, open.sent_so_far, escaped.clone())
.await?;
open.payload_data.push_str(&unescape(escaped.as_str()));
open.sent_so_far += line.len() as u32;
open.unacked_since = Some(Instant::now());
}
open.received_up_to = length as u32;
Some(ack_message)
} else {
match &open.previous_ack {
Some(ack) => {
send_previous_ack(&socket, addr, ack.clone()).await?;
}
None => {
let ack_message = send_ack(&socket, addr, session, 0).await?;
state.get_open()?.previous_ack = Some(ack_message);
}
}
None
};
if let Some(ack_message) = ack_message {
state.get_open()?.previous_ack = Some(ack_message);
}
}
},
}
}
_ = timer.tick() => {
let now = Instant::now();
let mut expired = vec![];
for ((addr, _), state) in states.iter_mut() {
#[allow(clippy::collapsible_if)]
if let State::Open(open) = state {
if open.highest_len_acked_so_far < open.sent_so_far {
if let Some(since) = open.unacked_since {
if now.duration_since(since) >= SESSION_EXPIRY_DURATION {
send_close(&socket, *addr, open.session).await?;
expired.push(addr);
} else if now.duration_since(open.last_retransmit) >= RETRANSMISSION_DURATION {
let tail = open.payload_data
.chars()
.enumerate()
.filter(|(idx, _)| *idx >= open.highest_len_acked_so_far as usize)
.map(|(_, s)| s)
.collect::<String>();
send_data(&socket, *addr, open.session, open.highest_len_acked_so_far, tail).await?;
open.last_retransmit = now;
}
}
}
}
}
}
}
}
}
async fn retransmit_payload_data(
socket: &UdpSocket,
addr: SocketAddr,
open: &Open,
length: u32,
) -> Result<()> {
let mut pos = None;
let mut data = String::new();
for (idx, ch) in open
.payload_data
.chars()
.enumerate()
.filter(|(idx, _)| *idx >= length as usize)
{
if pos.is_none() {
pos = Some(idx)
}
data.push(ch);
}
send_data(socket, addr, open.session, pos.unwrap() as u32, data).await?;
Ok(())
}
async fn send_previous_ack(
socket: &UdpSocket,
addr: SocketAddr,
previous_ack: String,
) -> Result<()> {
socket.send_to(&previous_ack.into_bytes(), addr).await?;
Ok(())
}
async fn send_close(socket: &UdpSocket, addr: SocketAddr, session: u32) -> Result<()> {
socket
.send_to(&format!("/close/{session}/").into_bytes(), addr)
.await?;
Ok(())
}
async fn send_ack(
socket: &UdpSocket,
addr: SocketAddr,
session: u32,
length: usize,
) -> Result<String> {
let message = format!("/ack/{session}/{length}/");
socket.send_to(&message.clone().into_bytes(), addr).await?;
Ok(message)
}
async fn send_data(
socket: &UdpSocket,
addr: SocketAddr,
session: u32,
mut pos: u32,
data: String,
) -> Result<()> {
let message = format!("/data/{session}/{pos}/{data}/");
if message.len() < 1_000 {
socket.send_to(&message.into_bytes(), addr).await?;
} else {
let divisor = (message.len() as f64 / 1_000.).ceil() as usize;
let length = message.len() as usize / divisor - 100; // safety margin
let mut pointer = 0;
loop {
let chunk: String = data.chars().skip(pointer).take(length).collect();
if chunk.is_empty() {
break;
}
let message = format!("/data/{session}/{pos}/{chunk}/");
socket.send_to(&message.into_bytes(), addr).await?;
let unescaped_length = unescape(&chunk).len();
pointer += length;
pos += unescaped_length as u32;
}
}
Ok(())
}
#[derive(Debug)]
enum State {
Closed,
Open(Open),
}
impl State {
fn get_open(&mut self) -> Result<&mut Open> {
match self {
State::Closed => Err(anyhow!("not open")),
State::Open(open) => Ok(open),
}
}
}
#[derive(Debug)]
struct Open {
previous_ack: Option<String>,
received_up_to: u32,
buffer: String,
sent_so_far: u32,
highest_len_acked_so_far: u32,
payload_data: String,
unacked_since: Option<Instant>,
last_retransmit: Instant,
session: u32,
}
impl Open {
fn new(session: u32) -> Self {
Self {
previous_ack: None,
received_up_to: 0,
buffer: String::new(),
sent_so_far: 0,
highest_len_acked_so_far: 0,
payload_data: String::new(),
unacked_since: None,
last_retransmit: Instant::now(),
session,
}
}
fn reverse_next_line(&mut self) -> String {
// we checked outside whether this contains a newline
let idx = self.buffer.find('\n').unwrap();
let mut line: String = self
.buffer
.drain(0..=idx)
.take_while(|c| *c != '\n')
.collect();
line = line.chars().rev().collect();
line.push('\n');
line
}
}
enum MessageType {
Ack(u32, u32),
Close(u32),
Connect(u32),
Data(u32, u32, String),
}
impl MessageType {
#[allow(unstable_name_collisions)]
fn parse(s: &str) -> Result<Self> {
dbg!(s);
ensure!(s.starts_with('/'));
ensure!(s.ends_with('/'));
ensure!(s.len() < 1_000);
let mut split = s.split('/');
split.next(); // omit first '/' which is now an empty string
let message_type = split.next().ok_or(anyhow!("malformed message"))?;
let result = match message_type {
"ack" => {
let session =
parse_num(split.next().ok_or(anyhow!("missing session identifier"))?)?;
let length = parse_num(split.next().ok_or(anyhow!("ack missing length"))?)?;
ensure!(split.next() == Some(""), "ack packet missed trailing '/'");
ensure!(
split.next().is_none(),
"extra fields in ack packet? {:?}",
split.next()
);
MessageType::Ack(session, length)
}
"close" => {
let session = parse_num(&parse_session_packet(&mut split)?)?;
MessageType::Close(session)
}
"connect" => {
let session = parse_num(&parse_session_packet(&mut split)?)?;
MessageType::Connect(session)
}
"data" => {
let session = parse_num(
split
.next()
.ok_or_else(|| anyhow!("missing session identifier"))?,
)?;
let position = parse_num(
split
.next()
.ok_or_else(|| anyhow!("missing position identifier"))?,
)?;
ensure!(
split.next_back() == Some(""),
"data packet missed trailing '/'"
);
let data: Vec<_> = split.clone().collect();
for i in 0..data.len() - 1 {
// all but ultimate segment must end with '\', otherwise there's inproper
// escaping
ensure!(
data[i].ends_with('\\'),
"extra fields in data part: {data:?}"
);
}
let data = split.intersperse("/").collect();
// let some = split.nth(1); // nth(1) because of clone() just earlier
// ensure!(some.is_none(), "extra fields in data packet? {some:?}",);
MessageType::Data(session, position, data)
}
_ => bail!("unknown message type"),
};
Ok(result)
}
fn session(&self) -> u32 {
match self {
MessageType::Ack(s, _) => *s,
MessageType::Close(s) => *s,
MessageType::Connect(s) => *s,
MessageType::Data(s, _, _) => *s,
}
}
}
fn parse_num(s: &str) -> Result<u32> {
let n: u64 = s.parse()?;
ensure!(n < 2147483648);
Ok(n as u32)
}
fn parse_session_packet(split: &mut std::str::Split<'_, char>) -> Result<String> {
let session = split
.next()
.ok_or(anyhow!("missing session identifier"))?
.to_string();
ensure!(
split.next() == Some(""),
"session packet missed trailing '/'"
);
let some = split.next();
ensure!(some.is_none(), "extra fields in session packet?: {some:?}",);
Ok(session)
}
fn escape(s: &str) -> String {
s.replace('\\', "\\\\").replace('/', "\\/")
}
fn unescape(s: &str) -> String {
s.replace("\\\\", "\\").replace("\\/", "/")
}
#[cfg(test)]
mod tests {
use crate::MessageType;
#[test]
fn parse_data_packet() {
let s = "/data/1234567/0/hey\\/huhu\\\\bar/";
let parsed = MessageType::parse(s).unwrap();
match parsed {
MessageType::Data(session, pos, data) => {
assert_eq!(session, 1234567);
assert_eq!(pos, 0);
assert_eq!(data, "hey\\/huhu\\\\bar");
}
_ => panic!("wrong type parsed"),
}
}
}