From fb20fcc6d1036fe6de86f2b4388fb55951d9c6ac Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Sat, 31 Oct 2026 20:53:22 +0100
Subject: libp2p: add prefer option

---
 src/transport/libp2p/book.rs | 66 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 64 insertions(+), 2 deletions(-)

(limited to 'src/transport/libp2p/book.rs')

diff --git a/src/transport/libp2p/book.rs b/src/transport/libp2p/book.rs
index ceb9d27..b495719 100644
--- a/src/transport/libp2p/book.rs
+++ b/src/transport/libp2p/book.rs
@@ -48,6 +48,8 @@ pub(super) struct Book {
     pub(super) announced: Vec<Multiaddr>,
     /// `Libp2pConfig::ignore`: not published (but announced), not dialled.
     pub(super) ignored: Vec<IpRange>,
+    /// `Libp2pConfig::prefer`: addresses there first (`preference`).
+    pub(super) preferred: Vec<IpRange>,
     /// `Libp2pConfig::relay`: this node relays, and says so.
     pub(super) serving: bool,
     /// Relays named to pick (configured, listed), by peer: picked first.
@@ -265,6 +267,7 @@ impl Book {
             }
         }
         direct.retain(|address| !first.contains(address));
+        direct.sort_by_key(|address| self.preferred_range(address));
         first.extend(direct);
         first.retain(|address| !ignored(&self.ignored, address));
         first
@@ -469,9 +472,11 @@ impl Book {
 
     /// `peer`, connected, identified itself at `listen` (`published`): its direct
     /// addresses are those from now on, while connected (`remember`); those through
-    /// relays and by name stay.
+    /// relays and by name stay. Kept in order of `preference`: of a peer with many,
+    /// the ones that matter stay (`ADDRESSES_PER_PEER`).
     pub(super) fn identified(&mut self, peer: PeerId, listen: Vec<Multiaddr>) {
-        let listen: Vec<Multiaddr> = listen.into_iter().map(without_peer).collect();
+        let mut listen: Vec<Multiaddr> = listen.into_iter().map(without_peer).collect();
+        listen.sort_by_key(|address| self.preference(address));
         if let Some(known) = self.addresses.get_mut(&peer) {
             known.retain(|address| !is_ip(address) || listen.contains(address));
         }
@@ -483,6 +488,63 @@ impl Book {
     }
 }
 
+impl Book {
+    /// Where a peer's `address` comes, first first: in a range `libp2p-prefer` names
+    /// (by the range's place), then public, then through a relay or by name, then a
+    /// private one (another LAN, a container bridge).
+    fn preference(&self, address: &Multiaddr) -> (u8, usize) {
+        let range = self.preferred_range(address);
+        if range != usize::MAX {
+            return (0, range);
+        }
+        match ip_of(address).filter(|_| is_ip(address)) {
+            Some(ip) if is_public(ip) => (1, 0),
+            Some(_) => (3, 0),
+            None => (2, 0),
+        }
+    }
+
+    /// The place of the first range of `libp2p-prefer` that has `address`; for an
+    /// address none has, `usize::MAX`: after them.
+    fn preferred_range(&self, address: &Multiaddr) -> usize {
+        ip_of(address)
+            .filter(|_| is_ip(address))
+            .and_then(|ip| self.preferred.iter().position(|range| range.contains(ip)))
+            .unwrap_or(usize::MAX)
+    }
+}
+
+/// The IP address `address` starts with, if any.
+fn ip_of(address: &Multiaddr) -> Option<std::net::IpAddr> {
+    match address.iter().next() {
+        Some(Protocol::Ip4(ip)) => Some(ip.into()),
+        Some(Protocol::Ip6(ip)) => Some(ip.into()),
+        _ => None,
+    }
+}
+
+/// Whether `ip` can be reached from the internet, as far as its range tells.
+fn is_public(ip: std::net::IpAddr) -> bool {
+    use std::net::IpAddr;
+    match ip {
+        IpAddr::V4(ip) => {
+            // 100.64.0.0/10: carrier-grade NAT.
+            let shared = ip.octets()[0] == 100 && (ip.octets()[1] & 0xc0) == 64;
+            !(ip.is_private()
+                || ip.is_loopback()
+                || ip.is_link_local()
+                || ip.is_unspecified()
+                || shared)
+        }
+        IpAddr::V6(ip) => {
+            !(ip.is_loopback()
+                || ip.is_unspecified()
+                || ip.is_unique_local()
+                || ip.is_unicast_link_local())
+        }
+    }
+}
+
 /// Whether `address` is a direct one at an IP address (not through a relay, nor a name).
 pub(super) fn is_ip(address: &Multiaddr) -> bool {
     matches!(
-- 
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