feat: calculate dht size estimate without a dequeue

src/common/routing_table.rs

@@ -213,11 +213,8 @@ pub(crate) fn estimate_dht_size(target: Id, nodes: &[Node]) -> usize {
     for node in nodes {
         let xor = target.xor(&node.id);
 
-        let di =
-                    // Round up to the highest u128 and ignore the low part
-                    u128::from_be_bytes(xor.as_bytes()[0..16].try_into().expect("infallible"))
-                    // Round up to 1 to avoid dividing by zero
-                        .max(1);
+        // Round up the lower 4 bytes to get a u128 from u160.
+        let di = u128::from_be_bytes(xor.as_bytes()[0..16].try_into().expect("infallible")) + 1;
 
         // The inverse of the probability of finding (i) nodes at distance (di)
         let estimated_n = i.saturating_mul((u128::MAX / di) as usize);

src/rpc.rs

@@ -3,7 +3,7 @@
 mod query;
 mod socket;
 
-use std::collections::{HashMap, VecDeque};
+use std::collections::HashMap;
 use std::net::{SocketAddr, ToSocketAddrs};
 use std::num::NonZeroUsize;
 use std::time::{Duration, Instant};
@@ -44,7 +44,7 @@ const MAX_CACHED_BUCKETS: usize = 1000;
 
 // If you are making a FIND_NODE requests subsequentially,
 // you can expect the oldest sample to be an hour ago.
-const DHT_SIZE_ESTIMATE_SAMPLE_SIZE: usize = 1024;
+const DHT_SIZE_ESTIMATE_WINDOW: i32 = 1024;
 
 #[derive(Debug)]
 /// Internal Rpc called in the Dht thread loop, useful to create your own actor setup.
@@ -71,7 +71,9 @@ pub struct Rpc {
     /// get query to finish, update the closest_nodes, then `query_all` these.
     put_queries: HashMap<Id, PutQuery>,
 
-    dht_size_estimate_samples: VecDeque<usize>,
+    /// Moving average of the estimated dht size from the lookups within a [DHT_SIZE_ESTIMATE_WINDOW]
+    dht_size_estimate: i32,
+    dht_size_estimate_samples: i32,
 }
 
 impl Rpc {
@@ -112,7 +114,8 @@ impl Rpc {
                 .unwrap_or_else(Instant::now),
             last_table_ping: Instant::now(),
 
-            dht_size_estimate_samples: VecDeque::with_capacity(DHT_SIZE_ESTIMATE_SAMPLE_SIZE),
+            dht_size_estimate: 0,
+            dht_size_estimate_samples: 0,
         })
     }
 
@@ -142,8 +145,7 @@ impl Rpc {
     }
 
     pub fn dht_size_estimate(&self) -> usize {
-        self.dht_size_estimate_samples.iter().sum::<usize>()
-            / self.dht_size_estimate_samples.len().max(1)
+        self.dht_size_estimate as usize
     }
 
     // === Public Methods ===
@@ -175,11 +177,15 @@ impl Rpc {
             if is_done {
                 let closest = query.closest();
 
-                if self.dht_size_estimate_samples.len() >= DHT_SIZE_ESTIMATE_SAMPLE_SIZE {
-                    self.dht_size_estimate_samples.remove(0);
-                }
-                let dht_size_estimate = estimate_dht_size(query.target, &closest);
-                self.dht_size_estimate_samples.push_back(dht_size_estimate);
+                // Calculate moving average
+                let estimate = estimate_dht_size(query.target, &closest) as i32;
+                self.dht_size_estimate_samples =
+                    (self.dht_size_estimate_samples + 1).min(DHT_SIZE_ESTIMATE_WINDOW);
+
+                // TODO: warn if a Horizontal Sybil attack is deteceted.
+
+                self.dht_size_estimate = self.dht_size_estimate
+                    + (estimate - self.dht_size_estimate) / self.dht_size_estimate_samples;
 
                 if let Some(put_query) = self.put_queries.get_mut(id) {
                     put_query.start(&mut self.socket, closest.clone())