Milestone 5, Project 2 all done
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ridethepig
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@ -51,4 +51,19 @@
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一个坑：不要使用前面实现的 `connect_to_upstream`，因为它无法连接到已经被移出可用列表的 upstream（不如说它根本就不让自己选 upstream），但是我们这里需要测试每个 upstream。
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### Milestone 5
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实现请求速率限制。针对每个 IP 限制一段时间内的请求数量，如果次数过多就返回 `HTTP 429`。提到了三个算法，leaky bucket、fixed window 和 sliding window。leaky bucket 不太适合这里的要求，就不管了。
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这里实现了 fixed window 和 sliding window。这两个玩意基本上一样，fixed window 简单一点，单纯记录每个 time unit 里面请求的次数，达到上限就丢掉，开始下一个 unit 的时候就重置计数器。这就导致了一个问题，如果请求集中在计数器重置的时间点附近，就会导致短时间内的请求速率翻倍，实际上超过了限制。 sliding window 在此基础上考虑了上一个 unit，按照一定比例将上一次 unit 的请求计数折算到当前的请求计数中，从而避免了上述的问题。一种简单的实现方式就是，记录当前 unit 的计数和上个 unit 的计数，考虑当前时刻向前推一个 unit 的窗口，用窗口和上个 unit 重叠的比例进行折算。写成算式就是 $\frac{UNIT - (time.now - cur\_unit\_start)}{UNIT} \times prev\_cnt + cur\_ cnt$。
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具体实现上，用一个 `HashMap<String, RateRecord>` 来维护 IP 地址到请求次数的信息。因为一个 IP 地址会发起多个 connection，所以得把数据放到全局的 `ProxyState` 里面再用 `Arc<Mutex<>>` 裹起来。封装了 `RateRecord` 类型来存放前面提到的这些数据，然后写了几个简单的小函数来让 handler 代码更加简洁一些。这些都不是什么难绷的事情，最难绷的是 `HashMap` 居然不支持直接修改内容，下面细说遇到的问题。
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遇到的问题
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1. `HashMap` 不能直接修改 `value` 的内容，说是要实现 `IndexMut` 这个 trait，但是 `HashMap` 没实现，所以不能像实现了这个 trait 的 `Vec` 类型那样直接 `map[key] = newvalue`，而是要用非常别扭的 `(*map.get_mut(&key).unwrap()).field = new_val_for_field` 来写。
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2. 对于 primitive 类型之间的显式类型转换好像可以直接用 `as xx`，这个东西好像是编译器实现的，因此既不需要标准库也不需要什么其他的转换方法。不过剩下的转换就要通过 `From` 和 `Into` 这些 trait 来整了。
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3. 最后就是，直接运行 `cargo test` 的时候有可能会在 `assert_eq!(total_request_count, rate_limit_threshold);` 这个断言上报错，不过单独测这一个点的时候从来不会错。根据打印信息判断，这大概是由于前面实现的 health check 的线程发送的检查请求也被计算在累计请求数中，所以导致这个东西爆炸。至于为啥会出现这个事情，可能是随机数（或者是 cpu 性能问题）导致测试时间过长，然后 health check 的线程开始执行了。
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## 附加任务？
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实验设计者提供了不少的可选项，看上去都挺棒的，但是我懒得自己写测试了，所以就不做了捏，啦啦啦。
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@ -4,8 +4,8 @@ mod response;
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use clap::Parser;
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use rand::{Rng, SeedableRng};
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// use std::net::{TcpListener, TcpStream};
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use std::sync::Arc;
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use tokio::{net::{TcpListener, TcpStream}, io::AsyncWriteExt};
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use std::{collections::HashMap, sync::Arc};
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use tokio::net::{TcpListener, TcpStream};
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/// Contains information parsed from the command-line invocation of balancebeam. The Clap macros
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/// provide a fancy way to automatically construct a command-line argument parser.
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@ -33,24 +33,79 @@ struct CmdOptions {
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max_requests_per_minute: usize,
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}
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struct RateRecord {
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count: usize,
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pre_count: usize,
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max_count: usize,
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last_time: std::time::Instant,
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}
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impl RateRecord {
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const TIME_UNIT: u64 = 60;
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pub fn new(max_count: usize) -> RateRecord {
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RateRecord {
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count: 0,
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pre_count: 0,
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max_count,
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last_time: std::time::Instant::now(),
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}
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}
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pub fn update(&mut self) {
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// log::debug!("[Cur]{:?} [Last]{:?} [Diff]{:?} [Cnt]{}", cur_time, last_time, diff, rate_record[&client_ip].count);
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let cur_time = std::time::Instant::now();
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let diff_unit = cur_time.duration_since(self.last_time).as_secs() / Self::TIME_UNIT;
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if diff_unit > 0 {
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self.pre_count = if diff_unit == 1 {
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self.count
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} else {
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0 // if diff is greater than a unit, then there should be 0 reqs in the last unit
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};
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self.count = 1;
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self.last_time += std::time::Duration::from_secs(diff_unit * Self::TIME_UNIT);
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}
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if self.count <= self.max_count {
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self.count += 1; // to avoid overflow if time unit is long enough
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}
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}
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#[allow(dead_code)]
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pub fn check(&self) -> bool {
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return self.count > self.max_count;
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}
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#[allow(dead_code)]
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pub fn check_sliding_window(&self) -> bool {
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let count_f64 = self.count as f64;
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let pre_count_f64 = self.pre_count as f64;
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let cur_time = std::time::Instant::now();
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let time_unit_f64 = Self::TIME_UNIT as f64;
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let pre_ratio =
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(time_unit_f64 - cur_time.duration_since(self.last_time).as_secs_f64()) / time_unit_f64;
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let final_count = pre_count_f64 * pre_ratio + count_f64;
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// log::debug!("pre_ratio:{pre_ratio}, pre_count:{pre_count_f64}, count:{count_f64} final_count:{final_count}");
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return final_count > self.max_count as f64;
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}
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}
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/// Contains information about the state of balancebeam (e.g. what servers we are currently proxying
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/// to, what servers have failed, rate limiting counts, etc.)
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///
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/// You should add fields to this struct in later milestones.
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struct ProxyState {
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/// How frequently we check whether upstream servers are alive (Milestone 4)
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#[allow(dead_code)]
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active_health_check_interval: usize,
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/// Where we should send requests when doing active health checks (Milestone 4)
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#[allow(dead_code)]
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active_health_check_path: String,
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/// Maximum number of requests an individual IP can make in a minute (Milestone 5)
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#[allow(dead_code)]
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max_requests_per_minute: usize,
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/// Addresses of servers that we are proxying to
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upstream_addresses: Vec<String>,
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/// Dead upstream marks
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upstream_status: Arc<tokio::sync::Mutex<Vec<usize>>>,
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/// Rate limiting counter
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rate_limit_counter: Arc<tokio::sync::Mutex<HashMap<String, RateRecord>>>,
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}
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async fn disable_upstream(state: &ProxyState, index: usize) {
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@ -103,10 +158,18 @@ fn active_health_check(state: Arc<ProxyState>) {
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}
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};
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if response.status() != 200 {
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log::info!("[HealthCheck] Get bad HTTP response {} from {}", response.status(), upstream);
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log::info!(
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"[HealthCheck] Get bad HTTP response {} from {}",
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response.status(),
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upstream
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);
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disable_upstream(&state, count - 1).await;
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} else {
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log::debug!("[HealthCheck] Get good HTTP response {} from {}", response.status(), upstream);
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log::debug!(
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"[HealthCheck] Get good HTTP response {} from {}",
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response.status(),
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upstream
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);
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let mut upstream_status = state.upstream_status.lock().await;
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if let None = upstream_status.iter().position(|&r| r == count - 1) {
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upstream_status.push(count - 1);
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@ -115,8 +178,7 @@ fn active_health_check(state: Arc<ProxyState>) {
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}
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}
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}
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}
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);
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});
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}
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#[tokio::main]
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@ -158,6 +220,7 @@ async fn main() -> std::io::Result<()> {
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active_health_check_path: options.active_health_check_path,
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max_requests_per_minute: options.max_requests_per_minute,
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upstream_status: Arc::new(tokio::sync::Mutex::new(upstream_status)),
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rate_limit_counter: Arc::new(tokio::sync::Mutex::new(HashMap::new())),
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};
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let astate = Arc::new(state);
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// let _ = tokio::spawn(async move {
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@ -252,7 +315,6 @@ async fn handle_connection(mut client_conn: TcpStream, state: &ProxyState) {
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}
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};
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let upstream_ip = client_conn.peer_addr().unwrap().ip().to_string();
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// The client may now send us one or more requests. Keep trying to read requests until the
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// client hangs up or we get an error.
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loop {
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@ -289,6 +351,28 @@ async fn handle_connection(mut client_conn: TcpStream, state: &ProxyState) {
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upstream_ip,
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request::format_request_line(&request)
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);
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// rate limit stuff
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// Note: rate limit test may fail in the last assertion when running all tests
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// The reason is that health check requests may be counted as requests that escaped rate-limiting,
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// this never fails in unit test
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if state.max_requests_per_minute != 0 {
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let mut rate_record = state.rate_limit_counter.lock().await;
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if !rate_record.contains_key(&client_ip) {
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rate_record.insert(
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client_ip.clone(),
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RateRecord::new(state.max_requests_per_minute),
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);
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}
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(*rate_record.get_mut(&client_ip).unwrap()).update();
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if rate_record[&client_ip].check() {
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let response = response::make_http_error(http::StatusCode::TOO_MANY_REQUESTS);
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log::info!("Drop request due to rate limiting");
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drop(rate_record);
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send_response(&mut client_conn, &response).await;
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continue;
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}
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drop(rate_record);
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}
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// Add X-Forwarded-For header so that the upstream server knows the client's IP address.
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// (We're the ones connecting directly to the upstream server, so without this header, the
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