Merge bitcoin/bitcoin#24165: p2p: extend inbound eviction protection by network to CJDNS peers

b7be28cac50046b9f2ddfe63ecafccc80649a36c test: add combined CJDNS/I2P/localhost/onion eviction protection tests (Jon Atack)
0a1bb84770b403ab5cbd9d5474c76f91ce58e8f6 test: add tests for inbound eviction protection of CJDNS peers (Jon Atack)
0c00c0c981fc0b6cec101e68e8c1aeda1ccf33bb test: fix off-by-one logic in an eviction protection test (Jon Atack)
f7b8094d611531c6b41a94715dbc01f56257ccd2 p2p: extend inbound eviction protection by network to CJDNS peers (Jon Atack)

Pull request description:

  Extend inbound eviction protection for peers connected over CJDNS, as is the case for peers connected via onion, localhost, and I2P since #21261 and #20197.  CJDNS peers seem to have better min ping latency than onion and I2P peers but still higher than that of unencrypted IPv4/6 peers and can be disadvantaged under our eviction criteria. They are also very few in number, which is a further reason to protect them, as the goal of this logic is to favorise the diversity of our peer connections.  CJDNS support was added in #23077 for the upcoming v23 release.

ACKs for top commit:
  laanwj:
    Concept and code review ACK b7be28cac50046b9f2ddfe63ecafccc80649a36c
  w0xlt:
    tACK b7be28c

Tree-SHA512: 89ebdd217602e16ae14b9bd0d5a25fc09f9b2384c951f820bc0f5a6d8452bbc9042065db817d5d5296c0ad22988491a83fc5b9a611e660c40ebd4f03448c4061

3 files changed, 156 insertions, 21 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 15616613d2..9bb264a38a 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -928,17 +928,17 @@ void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& evicti
     // Protect the half of the remaining nodes which have been connected the longest.
     // This replicates the non-eviction implicit behavior, and precludes attacks that start later.
     // To favorise the diversity of our peer connections, reserve up to half of these protected
-    // spots for Tor/onion, localhost and I2P peers, even if they're not longest uptime overall.
-    // This helps protect these higher-latency peers that tend to be otherwise
+    // spots for Tor/onion, localhost, I2P, and CJDNS peers, even if they're not longest uptime
+    // overall. This helps protect these higher-latency peers that tend to be otherwise
     // disadvantaged under our eviction criteria.
     const size_t initial_size = eviction_candidates.size();
     const size_t total_protect_size{initial_size / 2};
 
-    // Disadvantaged networks to protect: I2P, localhost, Tor/onion. In case of equal counts, earlier
-    // array members have first opportunity to recover unused slots from the previous iteration.
+    // Disadvantaged networks to protect. In the case of equal counts, earlier array members
+    // have the first opportunity to recover unused slots from the previous iteration.
     struct Net { bool is_local; Network id; size_t count; };
-    std::array<Net, 3> networks{
-        {{false, NET_I2P, 0}, {/* localhost */ true, NET_MAX, 0}, {false, NET_ONION, 0}}};
+    std::array<Net, 4> networks{
+        {{false, NET_CJDNS, 0}, {false, NET_I2P, 0}, {/*localhost=*/true, NET_MAX, 0}, {false, NET_ONION, 0}}};
 
     // Count and store the number of eviction candidates per network.
     for (Net& n : networks) {
diff --git a/src/net.h b/src/net.h
index 3f4c8e38ec..bbc253e7ff 100644
--- a/src/net.h
+++ b/src/net.h
@@ -1316,6 +1316,8 @@ struct NodeEvictionCandidate
  *
  * - I2P peers
  *
+ * - CJDNS peers
+ *
  * This helps protect these privacy network peers, which tend to be otherwise
  * disadvantaged under our eviction criteria for their higher min ping times
  * relative to IPv4/IPv6 peers, and favorise the diversity of peer connections.
diff --git a/src/test/net_peer_eviction_tests.cpp b/src/test/net_peer_eviction_tests.cpp
index 78ad24a408..6ec3fb0c6b 100644
--- a/src/test/net_peer_eviction_tests.cpp
+++ b/src/test/net_peer_eviction_tests.cpp
@@ -90,7 +90,7 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
     // Test protection of onion, localhost, and I2P peers...
 
     // Expect 1/4 onion peers to be protected from eviction,
-    // if no localhost or I2P peers.
+    // if no localhost, I2P, or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_is_local = false;
@@ -101,7 +101,7 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         random_context));
 
     // Expect 1/4 onion peers and 1/4 of the other peers to be protected,
-    // sorted by longest uptime (lowest m_connected), if no localhost or I2P peers.
+    // sorted by longest uptime (lowest m_connected), if no localhost, I2P or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_connected = std::chrono::seconds{c.id};
@@ -113,7 +113,7 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         random_context));
 
     // Expect 1/4 localhost peers to be protected from eviction,
-    // if no onion or I2P peers.
+    // if no onion, I2P, or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_is_local = (c.id == 1 || c.id == 9 || c.id == 11);
@@ -124,7 +124,7 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         random_context));
 
     // Expect 1/4 localhost peers and 1/4 of the other peers to be protected,
-    // sorted by longest uptime (lowest m_connected), if no onion or I2P peers.
+    // sorted by longest uptime (lowest m_connected), if no onion, I2P, or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_connected = std::chrono::seconds{c.id};
@@ -136,7 +136,7 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         random_context));
 
     // Expect 1/4 I2P peers to be protected from eviction,
-    // if no onion or localhost peers.
+    // if no onion, localhost, or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_is_local = false;
@@ -146,8 +146,8 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         /*unprotected_peer_ids=*/{},
         random_context));
 
-    // Expect 1/4 I2P peers and 1/4 of the other peers to be protected,
-    // sorted by longest uptime (lowest m_connected), if no onion or localhost peers.
+    // Expect 1/4 I2P peers and 1/4 of the other peers to be protected, sorted
+    // by longest uptime (lowest m_connected), if no onion, localhost, or CJDNS peers.
     BOOST_CHECK(IsProtected(
         num_peers, [](NodeEvictionCandidate& c) {
             c.m_connected = std::chrono::seconds{c.id};
@@ -158,6 +158,29 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         /*unprotected_peer_ids=*/{3, 5, 6, 7, 8, 11},
         random_context));
 
+    // Expect 1/4 CJDNS peers to be protected from eviction,
+    // if no onion, localhost, or I2P peers.
+    BOOST_CHECK(IsProtected(
+        num_peers, [](NodeEvictionCandidate& c) {
+            c.m_is_local = false;
+            c.m_network = (c.id == 2 || c.id == 7 || c.id == 10) ? NET_CJDNS : NET_IPV4;
+        },
+        /*protected_peer_ids=*/{2, 7, 10},
+        /*unprotected_peer_ids=*/{},
+        random_context));
+
+    // Expect 1/4 CJDNS peers and 1/4 of the other peers to be protected, sorted
+    // by longest uptime (lowest m_connected), if no onion, localhost, or I2P peers.
+    BOOST_CHECK(IsProtected(
+        num_peers, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = false;
+            c.m_network = (c.id == 4 || c.id > 8) ? NET_CJDNS : NET_IPV6;
+        },
+        /*protected_peer_ids=*/{0, 1, 2, 4, 9, 10},
+        /*unprotected_peer_ids=*/{3, 5, 6, 7, 8, 11},
+        random_context));
+
     // Tests with 2 networks...
 
     // Combined test: expect having 1 localhost and 1 onion peer out of 4 to
@@ -289,16 +312,16 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
     BOOST_CHECK(IsProtected(
         4, [](NodeEvictionCandidate& c) {
             c.m_connected = std::chrono::seconds{c.id};
-            c.m_is_local = (c.id == 3);
-            if (c.id == 4) {
+            c.m_is_local = (c.id == 2);
+            if (c.id == 3) {
                 c.m_network = NET_I2P;
-            } else if (c.id == 2) {
+            } else if (c.id == 1) {
                 c.m_network = NET_ONION;
             } else {
                 c.m_network = NET_IPV6;
             }
         },
-        /*protected_peer_ids=*/{0, 4},
+        /*protected_peer_ids=*/{0, 3},
         /*unprotected_peer_ids=*/{1, 2},
         random_context));
 
@@ -416,15 +439,15 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         /*unprotected_peer_ids=*/{6, 7, 8, 9, 10, 11, 16, 19, 20, 21, 22, 23},
         random_context));
 
-    // Combined test: expect having 8 localhost, 4 I2P, and 3 onion peers out of
-    // 24 to protect 2 of each (6 total), plus 6 others for 12/24 total, sorted
-    // by longest uptime.
+    // Combined test: expect having 8 localhost, 4 CJDNS, and 3 onion peers out
+    // of 24 to protect 2 of each (6 total), plus 6 others for 12/24 total,
+    // sorted by longest uptime.
     BOOST_CHECK(IsProtected(
         24, [](NodeEvictionCandidate& c) {
             c.m_connected = std::chrono::seconds{c.id};
             c.m_is_local = (c.id > 15);
             if (c.id > 10 && c.id < 15) {
-                c.m_network = NET_I2P;
+                c.m_network = NET_CJDNS;
             } else if (c.id > 6 && c.id < 10) {
                 c.m_network = NET_ONION;
             } else {
@@ -434,6 +457,116 @@ BOOST_AUTO_TEST_CASE(peer_protection_test)
         /*protected_peer_ids=*/{0, 1, 2, 3, 4, 5, 7, 8, 11, 12, 16, 17},
         /*unprotected_peer_ids=*/{6, 9, 10, 13, 14, 15, 18, 19, 20, 21, 22, 23},
         random_context));
+
+    // Tests with 4 networks...
+
+    // Combined test: expect having 1 CJDNS, 1 I2P, 1 localhost and 1 onion peer
+    // out of 5 to protect 1 CJDNS, 0 I2P, 0 localhost, 0 onion and 1 other peer
+    // (2 total), sorted by longest uptime; stable sort breaks tie with array
+    // order of CJDNS first.
+    BOOST_CHECK(IsProtected(
+        5, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = (c.id == 3);
+            if (c.id == 4) {
+                c.m_network = NET_CJDNS;
+            } else if (c.id == 1) {
+                c.m_network = NET_I2P;
+            } else if (c.id == 2) {
+                c.m_network = NET_ONION;
+            } else {
+                c.m_network = NET_IPV6;
+            }
+        },
+        /* protected_peer_ids */ {0, 4},
+        /* unprotected_peer_ids */ {1, 2, 3},
+        random_context));
+
+    // Combined test: expect having 1 CJDNS, 1 I2P, 1 localhost and 1 onion peer
+    // out of 7 to protect 1 CJDNS, 0, I2P, 0 localhost, 0 onion and 2 other
+    // peers (3 total) sorted by longest uptime; stable sort breaks tie with
+    // array order of CJDNS first.
+    BOOST_CHECK(IsProtected(
+        7, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = (c.id == 4);
+            if (c.id == 6) {
+                c.m_network = NET_CJDNS;
+            } else if (c.id == 5) {
+                c.m_network = NET_I2P;
+            } else if (c.id == 3) {
+                c.m_network = NET_ONION;
+            } else {
+                c.m_network = NET_IPV4;
+            }
+        },
+        /*protected_peer_ids=*/{0, 1, 6},
+        /*unprotected_peer_ids=*/{2, 3, 4, 5},
+        random_context));
+
+    // Combined test: expect having 1 CJDNS, 1 I2P, 1 localhost and 1 onion peer
+    // out of 8 to protect 1 CJDNS, 1 I2P, 0 localhost, 0 onion and 2 other
+    // peers (4 total) sorted by longest uptime; stable sort breaks tie with
+    // array order of CJDNS first.
+    BOOST_CHECK(IsProtected(
+        8, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = (c.id == 3);
+            if (c.id == 5) {
+                c.m_network = NET_CJDNS;
+            } else if (c.id == 6) {
+                c.m_network = NET_I2P;
+            } else if (c.id == 3) {
+                c.m_network = NET_ONION;
+            } else {
+                c.m_network = NET_IPV6;
+            }
+        },
+        /*protected_peer_ids=*/{0, 1, 5, 6},
+        /*unprotected_peer_ids=*/{2, 3, 4, 7},
+        random_context));
+
+    // Combined test: expect having 2 CJDNS, 2 I2P, 4 localhost, and 2 onion
+    // peers out of 16 to protect 1 CJDNS, 1 I2P, 1 localhost, 1 onion (4/16
+    // total), plus 4 others for 8 total, sorted by longest uptime.
+    BOOST_CHECK(IsProtected(
+        16, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = (c.id > 5);
+            if (c.id == 11 || c.id == 15) {
+                c.m_network = NET_CJDNS;
+            } else if (c.id == 10 || c.id == 14) {
+                c.m_network = NET_I2P;
+            } else if (c.id == 8 || c.id == 9) {
+                c.m_network = NET_ONION;
+            } else {
+                c.m_network = NET_IPV4;
+            }
+        },
+        /*protected_peer_ids=*/{0, 1, 2, 3, 6, 8, 10, 11},
+        /*unprotected_peer_ids=*/{4, 5, 7, 9, 12, 13, 14, 15},
+        random_context));
+
+    // Combined test: expect having 6 CJDNS, 1 I2P, 1 localhost, and 4 onion
+    // peers out of 24 to protect 2 CJDNS, 1 I2P, 1 localhost, and 2 onions (6
+    // total), plus 6 others for 12/24 total, sorted by longest uptime.
+    BOOST_CHECK(IsProtected(
+        24, [](NodeEvictionCandidate& c) {
+            c.m_connected = std::chrono::seconds{c.id};
+            c.m_is_local = (c.id == 13);
+            if (c.id > 17) {
+                c.m_network = NET_CJDNS;
+            } else if (c.id == 17) {
+                c.m_network = NET_I2P;
+            } else if (c.id == 12 || c.id == 14 || c.id == 15 || c.id == 16) {
+                c.m_network = NET_ONION;
+            } else {
+                c.m_network = NET_IPV6;
+            }
+        },
+        /*protected_peer_ids=*/{0, 1, 2, 3, 4, 5, 12, 13, 14, 17, 18, 19},
+        /*unprotected_peer_ids=*/{6, 7, 8, 9, 10, 11, 15, 16, 20, 21, 22, 23},
+        random_context));
 }
 
 // Returns true if any of the node ids in node_ids are selected for eviction.