fix(autonat): prohibit potentially large memory consumption

Autonat uses `Vec` for the servers field to hold a list of `PeerId` when calling `Behaviour::add_server`, but there is no check to prevent duplicated entries of the `PeerId`, which would cause unnecessary allocation overtime with repeated calls to the function.

Resolves #3733.

Pull-Request: #3736.

protocols/autonat/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 0.10.2 - unreleased
+
+- Store server `PeerId`s in `HashSet` to avoid duplicates and lower memory consumption.
+  See [PR 3736].
+
+[PR 3736]: https://github.com/libp2p/rust-libp2p/pull/3736
+
 ## 0.10.1
 
 - Migrate from `prost` to `quick-protobuf`. This removes `protoc` dependency. See [PR 3312].

protocols/autonat/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-autonat"
 edition = "2021"
 rust-version = "1.62.0"
 description = "NAT and firewall detection for libp2p"
-version = "0.10.1"
+version = "0.10.2"
 authors = ["David Craven <david@craven.ch>", "Elena Frank <elena.frank@protonmail.com>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

protocols/autonat/src/behaviour.rs

@@ -42,7 +42,7 @@ use libp2p_swarm::{
     PollParameters, THandler, THandlerInEvent, THandlerOutEvent, ToSwarm,
 };
 use std::{
-    collections::{HashMap, VecDeque},
+    collections::{HashMap, HashSet, VecDeque},
     iter,
     task::{Context, Poll},
     time::Duration,
@@ -170,7 +170,7 @@ pub struct Behaviour {
     config: Config,
 
     // Additional peers apart from the currently connected ones, that may be used for probes.
-    servers: Vec<PeerId>,
+    servers: HashSet<PeerId>,
 
     // Assumed NAT status.
     nat_status: NatStatus,
@@ -227,7 +227,7 @@ impl Behaviour {
             inner,
             schedule_probe: Delay::new(config.boot_delay),
             config,
-            servers: Vec::new(),
+            servers: HashSet::new(),
             ongoing_inbound: HashMap::default(),
             ongoing_outbound: HashMap::default(),
             connected: HashMap::default(),
@@ -266,7 +266,7 @@ impl Behaviour {
     /// These peers are used for dial-request even if they are currently not connection, in which case a connection will be
     /// establish before sending the dial-request.
     pub fn add_server(&mut self, peer: PeerId, address: Option<Multiaddr>) {
-        self.servers.push(peer);
+        self.servers.insert(peer);
         if let Some(addr) = address {
             self.inner.add_address(&peer, addr);
         }

protocols/autonat/src/behaviour/as_client.rs

@@ -35,7 +35,7 @@ use libp2p_swarm::{
 };
 use rand::{seq::SliceRandom, thread_rng};
 use std::{
-    collections::{HashMap, VecDeque},
+    collections::{HashMap, HashSet, VecDeque},
     task::{Context, Poll},
     time::Duration,
 };
@@ -90,7 +90,7 @@ pub struct AsClient<'a> {
     pub connected: &'a HashMap<PeerId, HashMap<ConnectionId, Option<Multiaddr>>>,
     pub probe_id: &'a mut ProbeId,
 
-    pub servers: &'a Vec<PeerId>,
+    pub servers: &'a HashSet<PeerId>,
     pub throttled_servers: &'a mut Vec<(PeerId, Instant)>,
 
     pub nat_status: &'a mut NatStatus,