Reduce memory usage of rate limiting (#3111)

* Reduce Vec allocations

* Optimize stuff

* Move embedded migrations to separate crate

* Revert "Move embedded migrations to separate crate"

This reverts commit 44b1049970.

* clippy, fmt

* Shrink rate limit allowance to f32

* Initialize rate limit allowance directly

* Add removal of old rate limit buckets

* Improve readability

* Remove usage of is_okay_and for Rust 1.67 compatibility

* Add dhat-heap feature

* Fix api_benchmark.sh and add run_and_benchmark.sh

* Revert "Fix api_benchmark.sh and add run_and_benchmark.sh"

This reverts commit b4528e5b85.

* Revert "Add dhat-heap feature"

This reverts commit 08e835d487.

* Manually revert remaining stuff

* Use Ipv6Addr in RateLimitStorage

* Shrink last_checked in RateLimitBucket to 32 bits

* Fix rate_limit::get_ip

* Stuff (#1)

* Update rate_limiter.rs

* Update mod.rs

* Update scheduled_tasks.rs

* Fix rate_limiter.rs

* Dullbananas patch 1 (#2)

* Update rate_limiter.rs

* Update mod.rs

* Update scheduled_tasks.rs

* Fix rate_limiter.rs

* Rate limit IPv6 addresses in groups

* Fmt lib.rs

* woodpicker trigger

* Refactor and comment `check_rate_limit_full`

* Add `test_split_ipv6`

* Replace -2.0 with UNINITIALIZED_TOKEN_AMOUNT

* Add `test_rate_limiter`

---------

Co-authored-by: Dessalines <dessalines@users.noreply.github.com>

Cargo.lock

@@ -1685,6 +1685,26 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b5320ae4c3782150d900b79807611a59a99fc9a1d61d686faafc24b93fc8d7ca"
 
+[[package]]
+name = "enum-map"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "988f0d17a0fa38291e5f41f71ea8d46a5d5497b9054d5a759fae2cbb819f2356"
+dependencies = [
+ "enum-map-derive",
+]
+
+[[package]]
+name = "enum-map-derive"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a4da76b3b6116d758c7ba93f7ec6a35d2e2cf24feda76c6e38a375f4d5c59f2"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 1.0.103",
+]
+
 [[package]]
 name = "enum_delegate"
 version = "0.2.0"
@@ -2816,6 +2836,7 @@ dependencies = [
  "deser-hjson",
  "diesel",
  "doku",
+ "enum-map",
  "futures",
  "html2text",
  "http",

crates/utils/Cargo.toml

@@ -45,6 +45,7 @@ jsonwebtoken = "8.1.1"
 lettre = "0.10.1"
 markdown-it = "0.5.0"
 totp-rs = { version = "5.0.2", features = ["gen_secret", "otpauth"] }
+enum-map = "2.5"
 
 [dev-dependencies]
 reqwest = { workspace = true }

crates/utils/src/lib.rs

@@ -14,21 +14,12 @@ pub mod request;
 pub mod utils;
 pub mod version;
 
-use std::{fmt, time::Duration};
+use std::time::Duration;
 
 pub type ConnectionId = usize;
 
 pub const REQWEST_TIMEOUT: Duration = Duration::from_secs(10);
 
-#[derive(PartialEq, Eq, Hash, Debug, Clone)]
-pub struct IpAddr(pub String);
-
-impl fmt::Display for IpAddr {
-  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    write!(f, "{}", self.0)
-  }
-}
-
 #[macro_export]
 macro_rules! location_info {
   () => {

crates/utils/src/rate_limit/mod.rs

@@ -1,14 +1,18 @@
-use crate::{error::LemmyError, IpAddr};
+use crate::error::LemmyError;
 use actix_web::dev::{ConnectionInfo, Service, ServiceRequest, ServiceResponse, Transform};
+use enum_map::enum_map;
 use futures::future::{ok, Ready};
-use rate_limiter::{RateLimitStorage, RateLimitType};
+use rate_limiter::{InstantSecs, RateLimitStorage, RateLimitType};
 use serde::{Deserialize, Serialize};
 use std::{
   future::Future,
+  net::{IpAddr, Ipv4Addr, SocketAddr},
   pin::Pin,
   rc::Rc,
+  str::FromStr,
   sync::{Arc, Mutex},
   task::{Context, Poll},
+  time::Duration,
 };
 use tokio::sync::{mpsc, mpsc::Sender, OnceCell};
 use typed_builder::TypedBuilder;
@@ -105,6 +109,35 @@ impl RateLimitCell {
     Ok(())
   }
 
+  /// Remove buckets older than the given duration
+  pub fn remove_older_than(&self, mut duration: Duration) {
+    let mut guard = self
+      .rate_limit
+      .lock()
+      .expect("Failed to lock rate limit mutex for reading");
+    let rate_limit = &guard.rate_limit_config;
+
+    // If any rate limit interval is greater than `duration`, then the largest interval is used instead. This preserves buckets that would not pass the rate limit check.
+    let max_interval_secs = enum_map! {
+      RateLimitType::Message => rate_limit.message_per_second,
+      RateLimitType::Post => rate_limit.post_per_second,
+      RateLimitType::Register => rate_limit.register_per_second,
+      RateLimitType::Image => rate_limit.image_per_second,
+      RateLimitType::Comment => rate_limit.comment_per_second,
+      RateLimitType::Search => rate_limit.search_per_second,
+    }
+    .into_values()
+    .max()
+    .and_then(|max| u64::try_from(max).ok())
+    .unwrap_or(0);
+
+    duration = std::cmp::max(duration, Duration::from_secs(max_interval_secs));
+
+    guard
+      .rate_limiter
+      .remove_older_than(duration, InstantSecs::now())
+  }
+
   pub fn message(&self) -> RateLimitedGuard {
     self.kind(RateLimitType::Message)
   }
@@ -163,7 +196,7 @@ impl RateLimitedGuard {
     };
     let limiter = &mut guard.rate_limiter;
 
-    limiter.check_rate_limit_full(self.type_, &ip_addr, kind, interval)
+    limiter.check_rate_limit_full(self.type_, ip_addr, kind, interval, InstantSecs::now())
   }
 }
 
@@ -222,13 +255,37 @@ where
 }
 
 fn get_ip(conn_info: &ConnectionInfo) -> IpAddr {
-  IpAddr(
+  conn_info
-    conn_info
+    .realip_remote_addr()
-      .realip_remote_addr()
+    .and_then(parse_ip)
-      .unwrap_or("127.0.0.1:12345")
+    .unwrap_or(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)))
-      .split(':')
+}
-      .next()
+
-      .unwrap_or("127.0.0.1")
+fn parse_ip(addr: &str) -> Option<IpAddr> {
-      .to_string(),
+  if let Some(s) = addr.strip_suffix(']') {
-  )
+    IpAddr::from_str(s.get(1..)?).ok()
+  } else if let Ok(ip) = IpAddr::from_str(addr) {
+    Some(ip)
+  } else if let Ok(socket) = SocketAddr::from_str(addr) {
+    Some(socket.ip())
+  } else {
+    None
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  #[test]
+  fn test_parse_ip() {
+    let ip_addrs = [
+      "1.2.3.4",
+      "1.2.3.4:8000",
+      "2001:db8::",
+      "[2001:db8::]",
+      "[2001:db8::]:8000",
+    ];
+    for addr in ip_addrs {
+      assert!(super::parse_ip(addr).is_some(), "failed to parse {addr}");
+    }
+  }
 }

crates/utils/src/rate_limit/rate_limiter.rs

@@ -1,15 +1,50 @@
-use crate::IpAddr;
+use enum_map::{enum_map, EnumMap};
-use std::{collections::HashMap, time::Instant};
+use once_cell::sync::Lazy;
-use strum::IntoEnumIterator;
+use std::{
+  collections::HashMap,
+  net::{IpAddr, Ipv4Addr, Ipv6Addr},
+  time::{Duration, Instant},
+};
 use tracing::debug;
 
-#[derive(Debug, Clone)]
+const UNINITIALIZED_TOKEN_AMOUNT: f32 = -2.0;
-struct RateLimitBucket {
+
-  last_checked: Instant,
+static START_TIME: Lazy<Instant> = Lazy::new(Instant::now);
-  allowance: f64,
+
+/// Smaller than `std::time::Instant` because it uses a smaller integer for seconds and doesn't
+/// store nanoseconds
+#[derive(PartialEq, Debug, Clone, Copy)]
+pub struct InstantSecs {
+  secs: u32,
 }
 
-#[derive(Eq, PartialEq, Hash, Debug, EnumIter, Copy, Clone, AsRefStr)]
+impl InstantSecs {
+  pub fn now() -> Self {
+    InstantSecs {
+      secs: u32::try_from(START_TIME.elapsed().as_secs())
+        .expect("server has been running for over 136 years"),
+    }
+  }
+
+  fn secs_since(self, earlier: Self) -> u32 {
+    self.secs.saturating_sub(earlier.secs)
+  }
+
+  fn to_instant(self) -> Instant {
+    *START_TIME + Duration::from_secs(self.secs.into())
+  }
+}
+
+#[derive(PartialEq, Debug, Clone)]
+struct RateLimitBucket {
+  last_checked: InstantSecs,
+  /// This field stores the amount of tokens that were present at `last_checked`.
+  /// The amount of tokens steadily increases until it reaches the bucket's capacity.
+  /// Performing the rate-limited action consumes 1 token.
+  tokens: f32,
+}
+
+#[derive(Debug, enum_map::Enum, Copy, Clone, AsRefStr)]
 pub(crate) enum RateLimitType {
   Message,
   Register,
@@ -19,79 +54,263 @@ pub(crate) enum RateLimitType {
   Search,
 }
 
-/// Rate limiting based on rate type and IP addr
+type Map<K, C> = HashMap<K, RateLimitedGroup<C>>;
-#[derive(Debug, Clone, Default)]
+
-pub struct RateLimitStorage {
+#[derive(PartialEq, Debug, Clone)]
-  buckets: HashMap<RateLimitType, HashMap<IpAddr, RateLimitBucket>>,
+struct RateLimitedGroup<C> {
+  total: EnumMap<RateLimitType, RateLimitBucket>,
+  children: C,
 }
 
-impl RateLimitStorage {
+impl<C: Default> RateLimitedGroup<C> {
-  fn insert_ip(&mut self, ip: &IpAddr) {
+  fn new(now: InstantSecs) -> Self {
-    for rate_limit_type in RateLimitType::iter() {
+    RateLimitedGroup {
-      if self.buckets.get(&rate_limit_type).is_none() {
+      total: enum_map! {
-        self.buckets.insert(rate_limit_type, HashMap::new());
+        _ => RateLimitBucket {
-      }
+          last_checked: now,
-
+          tokens: UNINITIALIZED_TOKEN_AMOUNT,
-      if let Some(bucket) = self.buckets.get_mut(&rate_limit_type) {
+        },
-        if bucket.get(ip).is_none() {
+      },
-          bucket.insert(
+      children: Default::default(),
-            ip.clone(),
-            RateLimitBucket {
-              last_checked: Instant::now(),
-              allowance: -2f64,
-            },
-          );
-        }
-      }
     }
   }
 
-  /// Rate limiting Algorithm described here: https://stackoverflow.com/a/668327/1655478
+  fn check_total(
-  ///
-  /// Returns true if the request passed the rate limit, false if it failed and should be rejected.
-  #[allow(clippy::float_cmp)]
-  pub(super) fn check_rate_limit_full(
     &mut self,
     type_: RateLimitType,
-    ip: &IpAddr,
+    now: InstantSecs,
-    rate: i32,
+    capacity: i32,
-    per: i32,
+    secs_to_refill: i32,
   ) -> bool {
-    self.insert_ip(ip);
+    let capacity = capacity as f32;
-    if let Some(bucket) = self.buckets.get_mut(&type_) {
+    let secs_to_refill = secs_to_refill as f32;
-      if let Some(rate_limit) = bucket.get_mut(ip) {
-        let current = Instant::now();
-        let time_passed = current.duration_since(rate_limit.last_checked).as_secs() as f64;
 
-        // The initial value
+    #[allow(clippy::indexing_slicing)] // `EnumMap` has no `get` funciton
-        if rate_limit.allowance == -2f64 {
+    let bucket = &mut self.total[type_];
-          rate_limit.allowance = f64::from(rate);
-        };
 
-        rate_limit.last_checked = current;
+    if bucket.tokens == UNINITIALIZED_TOKEN_AMOUNT {
-        rate_limit.allowance += time_passed * (f64::from(rate) / f64::from(per));
+      bucket.tokens = capacity;
-        if rate_limit.allowance > f64::from(rate) {
+    }
-          rate_limit.allowance = f64::from(rate);
-        }
 
-        if rate_limit.allowance < 1.0 {
+    let secs_since_last_checked = now.secs_since(bucket.last_checked) as f32;
-          debug!(
+    bucket.last_checked = now;
-            "Rate limited type: {}, IP: {}, time_passed: {}, allowance: {}",
+
-            type_.as_ref(),
+    // For `secs_since_last_checked` seconds, increase `bucket.tokens`
-            ip,
+    // by `capacity` every `secs_to_refill` seconds
-            time_passed,
+    bucket.tokens += {
-            rate_limit.allowance
+      let tokens_per_sec = capacity / secs_to_refill;
-          );
+      secs_since_last_checked * tokens_per_sec
-          false
+    };
-        } else {
+
-          rate_limit.allowance -= 1.0;
+    // Prevent `bucket.tokens` from exceeding `capacity`
-          true
+    if bucket.tokens > capacity {
-        }
+      bucket.tokens = capacity;
-      } else {
+    }
-        true
+
-      }
+    if bucket.tokens < 1.0 {
+      // Not enough tokens yet
+      debug!(
+        "Rate limited type: {}, time_passed: {}, allowance: {}",
+        type_.as_ref(),
+        secs_since_last_checked,
+        bucket.tokens
+      );
+      false
     } else {
+      // Consume 1 token
+      bucket.tokens -= 1.0;
       true
     }
   }
 }
+
+/// Rate limiting based on rate type and IP addr
+#[derive(PartialEq, Debug, Clone, Default)]
+pub struct RateLimitStorage {
+  /// One bucket per individual IPv4 address
+  ipv4_buckets: Map<Ipv4Addr, ()>,
+  /// Seperate buckets for 48, 56, and 64 bit prefixes of IPv6 addresses
+  ipv6_buckets: Map<[u8; 6], Map<u8, Map<u8, ()>>>,
+}
+
+impl RateLimitStorage {
+  /// Rate limiting Algorithm described here: https://stackoverflow.com/a/668327/1655478
+  ///
+  /// Returns true if the request passed the rate limit, false if it failed and should be rejected.
+  pub(super) fn check_rate_limit_full(
+    &mut self,
+    type_: RateLimitType,
+    ip: IpAddr,
+    capacity: i32,
+    secs_to_refill: i32,
+    now: InstantSecs,
+  ) -> bool {
+    let mut result = true;
+
+    match ip {
+      IpAddr::V4(ipv4) => {
+        // Only used by one address.
+        let group = self
+          .ipv4_buckets
+          .entry(ipv4)
+          .or_insert(RateLimitedGroup::new(now));
+
+        result &= group.check_total(type_, now, capacity, secs_to_refill);
+      }
+
+      IpAddr::V6(ipv6) => {
+        let (key_48, key_56, key_64) = split_ipv6(ipv6);
+
+        // Contains all addresses with the same first 48 bits. These addresses might be part of the same network.
+        let group_48 = self
+          .ipv6_buckets
+          .entry(key_48)
+          .or_insert(RateLimitedGroup::new(now));
+        result &= group_48.check_total(type_, now, capacity.saturating_mul(16), secs_to_refill);
+
+        // Contains all addresses with the same first 56 bits. These addresses might be part of the same network.
+        let group_56 = group_48
+          .children
+          .entry(key_56)
+          .or_insert(RateLimitedGroup::new(now));
+        result &= group_56.check_total(type_, now, capacity.saturating_mul(4), secs_to_refill);
+
+        // A group with no children. It is shared by all addresses with the same first 64 bits. These addresses are always part of the same network.
+        let group_64 = group_56
+          .children
+          .entry(key_64)
+          .or_insert(RateLimitedGroup::new(now));
+
+        result &= group_64.check_total(type_, now, capacity, secs_to_refill);
+      }
+    };
+
+    if !result {
+      debug!("Rate limited IP: {ip}");
+    }
+
+    result
+  }
+
+  /// Remove buckets older than the given duration
+  pub(super) fn remove_older_than(&mut self, duration: Duration, now: InstantSecs) {
+    // Only retain buckets that were last used after `instant`
+    let Some(instant) = now.to_instant().checked_sub(duration) else { return };
+
+    let is_recently_used = |group: &RateLimitedGroup<_>| {
+      group
+        .total
+        .values()
+        .all(|bucket| bucket.last_checked.to_instant() > instant)
+    };
+
+    self.ipv4_buckets.retain(|_, group| is_recently_used(group));
+
+    self.ipv6_buckets.retain(|_, group_48| {
+      group_48.children.retain(|_, group_56| {
+        group_56
+          .children
+          .retain(|_, group_64| is_recently_used(group_64));
+        !group_56.children.is_empty()
+      });
+      !group_48.children.is_empty()
+    })
+  }
+}
+
+fn split_ipv6(ip: Ipv6Addr) -> ([u8; 6], u8, u8) {
+  let [a0, a1, a2, a3, a4, a5, b, c, ..] = ip.octets();
+  ([a0, a1, a2, a3, a4, a5], b, c)
+}
+
+#[cfg(test)]
+mod tests {
+  #[test]
+  fn test_split_ipv6() {
+    let ip = std::net::Ipv6Addr::new(
+      0x0011, 0x2233, 0x4455, 0x6677, 0x8899, 0xAABB, 0xCCDD, 0xEEFF,
+    );
+    assert_eq!(
+      super::split_ipv6(ip),
+      ([0x00, 0x11, 0x22, 0x33, 0x44, 0x55], 0x66, 0x77)
+    );
+  }
+
+  #[test]
+  fn test_rate_limiter() {
+    let mut rate_limiter = super::RateLimitStorage::default();
+    let mut now = super::InstantSecs::now();
+
+    let ips = [
+      "123.123.123.123",
+      "1:2:3::",
+      "1:2:3:0400::",
+      "1:2:3:0405::",
+      "1:2:3:0405:6::",
+    ];
+    for ip in ips {
+      let ip = ip.parse().unwrap();
+      let message_passed =
+        rate_limiter.check_rate_limit_full(super::RateLimitType::Message, ip, 2, 1, now);
+      let post_passed =
+        rate_limiter.check_rate_limit_full(super::RateLimitType::Post, ip, 3, 1, now);
+      assert!(message_passed);
+      assert!(post_passed);
+    }
+
+    #[allow(clippy::indexing_slicing)]
+    let expected_buckets = |factor: f32, tokens_consumed: f32| {
+      let mut buckets = super::RateLimitedGroup::<()>::new(now).total;
+      buckets[super::RateLimitType::Message] = super::RateLimitBucket {
+        last_checked: now,
+        tokens: (2.0 * factor) - tokens_consumed,
+      };
+      buckets[super::RateLimitType::Post] = super::RateLimitBucket {
+        last_checked: now,
+        tokens: (3.0 * factor) - tokens_consumed,
+      };
+      buckets
+    };
+
+    let bottom_group = |tokens_consumed| super::RateLimitedGroup {
+      total: expected_buckets(1.0, tokens_consumed),
+      children: (),
+    };
+
+    assert_eq!(
+      rate_limiter,
+      super::RateLimitStorage {
+        ipv4_buckets: [([123, 123, 123, 123].into(), bottom_group(1.0)),].into(),
+        ipv6_buckets: [(
+          [0, 1, 0, 2, 0, 3],
+          super::RateLimitedGroup {
+            total: expected_buckets(16.0, 4.0),
+            children: [
+              (
+                0,
+                super::RateLimitedGroup {
+                  total: expected_buckets(4.0, 1.0),
+                  children: [(0, bottom_group(1.0)),].into(),
+                }
+              ),
+              (
+                4,
+                super::RateLimitedGroup {
+                  total: expected_buckets(4.0, 3.0),
+                  children: [(0, bottom_group(1.0)), (5, bottom_group(2.0)),].into(),
+                }
+              ),
+            ]
+            .into(),
+          }
+        ),]
+        .into(),
+      }
+    );
+
+    now.secs += 2;
+    rate_limiter.remove_older_than(std::time::Duration::from_secs(1), now);
+    assert!(rate_limiter.ipv4_buckets.is_empty());
+    assert!(rate_limiter.ipv6_buckets.is_empty());
+  }
+}

src/lib.rs

@@ -121,23 +121,28 @@ pub async fn start_lemmy_server() -> Result<(), LemmyError> {
     .with(TracingMiddleware::default())
     .build();
 
+  let context = LemmyContext::create(
+    pool.clone(),
+    client.clone(),
+    secret.clone(),
+    rate_limit_cell.clone(),
+  );
+
   if scheduled_tasks_enabled {
     // Schedules various cleanup tasks for the DB
-    thread::spawn(move || {
+    thread::spawn({
-      scheduled_tasks::setup(db_url, user_agent).expect("Couldn't set up scheduled_tasks");
+      let context = context.clone();
+      move || {
+        scheduled_tasks::setup(db_url, user_agent, context)
+          .expect("Couldn't set up scheduled_tasks");
+      }
     });
   }
 
   // Create Http server with websocket support
   let settings_bind = settings.clone();
   HttpServer::new(move || {
-    let context = LemmyContext::create(
+    let context = context.clone();
-      pool.clone(),
-      client.clone(),
-      secret.clone(),
-      rate_limit_cell.clone(),
-    );
-
     let federation_config = FederationConfig::builder()
       .domain(settings.hostname.clone())
       .app_data(context.clone())

src/scheduled_tasks.rs

@@ -7,6 +7,7 @@ use diesel::{
 };
 // Import week days and WeekDay
 use diesel::{sql_query, PgConnection, RunQueryDsl};
+use lemmy_api_common::context::LemmyContext;
 use lemmy_db_schema::{
   schema::{
     activity,
@@ -27,7 +28,11 @@ use std::{thread, time::Duration};
 use tracing::{error, info};
 
 /// Schedules various cleanup tasks for lemmy in a background thread
-pub fn setup(db_url: String, user_agent: String) -> Result<(), LemmyError> {
+pub fn setup(
+  db_url: String,
+  user_agent: String,
+  context_1: LemmyContext,
+) -> Result<(), LemmyError> {
   // Setup the connections
   let mut scheduler = Scheduler::new();
 
@@ -55,6 +60,12 @@ pub fn setup(db_url: String, user_agent: String) -> Result<(), LemmyError> {
     clear_old_activities(&mut conn);
   });
 
+  // Remove old rate limit buckets after 1 to 2 hours of inactivity
+  scheduler.every(CTimeUnits::hour(1)).run(move || {
+    let hour = Duration::from_secs(3600);
+    context_1.settings_updated_channel().remove_older_than(hour);
+  });
+
   // Update the Instance Software
   scheduler.every(CTimeUnits::days(1)).run(move || {
     let mut conn = PgConnection::establish(&db_url).expect("could not establish connection");