Merge #17428: p2p: Try to preserve outbound block-relay-only connections during restart

a490d074b3491427afbd677f5fa635b910f8bb34 doc: Add anchors.dat to files.md (Hennadii Stepanov)
0a85e5a7bc8dc6587963e2e37ac1b087a1fc97fe p2p: Try to connect to anchors once (Hennadii Stepanov)
5543c7ab285e90256cbbf9858249e028c9611cda p2p: Fix off-by-one error in fetching address loop (Hennadii Stepanov)
4170b46544231e7cf1d64ac3baa314083be37502 p2p: Integrate DumpAnchors() and ReadAnchors() into CConnman (Hennadii Stepanov)
bad16aff490dcf87722fbfe202a869fb24c734e1 p2p: Add CConnman::GetCurrentBlockRelayOnlyConns() (Hennadii Stepanov)
c29272a157d09a8125788c1b860e89b63b4cb36c p2p: Add ReadAnchors() (Hennadii Stepanov)
567008d2a0c95bd972f4031f31647c493d1bc2e8 p2p: Add DumpAnchors() (Hennadii Stepanov)

Pull request description:

  This is an implementation of #17326:
  - all (currently 2) outbound block-relay-only connections (#15759) are dumped to `anchors.dat` file
  - on restart a node tries to connect to the addresses from `anchors.dat`

  This PR prevents a type of eclipse attack when an attacker exploits a victim node restart to force it to connect to new, probably adversarial, peers.

ACKs for top commit:
  jnewbery:
    code review ACK a490d074b3
  laanwj:
    Code review ACK a490d074b3491427afbd677f5fa635b910f8bb34

Tree-SHA512: 0f5098a3882f2814be1aa21de308cd09e6654f4e7054b79f3cfeaf26bc02b814ca271497ed00018d199ee596a8cb9b126acee8b666a29e225b08eb2a49b02ddd

1 files changed, 20 insertions, 0 deletions

diff --git a/src/addrdb.cpp b/src/addrdb.cpp
index f3e8a19de2..27f22826a9 100644
--- a/src/addrdb.cpp
+++ b/src/addrdb.cpp
@@ -10,6 +10,7 @@
 #include <clientversion.h>
 #include <cstdint>
 #include <hash.h>
+#include <logging/timer.h>
 #include <random.h>
 #include <streams.h>
 #include <tinyformat.h>
@@ -156,3 +157,22 @@ bool CAddrDB::Read(CAddrMan& addr, CDataStream& ssPeers)
     }
     return ret;
 }
+
+void DumpAnchors(const fs::path& anchors_db_path, const std::vector<CAddress>& anchors)
+{
+    LOG_TIME_SECONDS(strprintf("Flush %d outbound block-relay-only peer addresses to anchors.dat", anchors.size()));
+    SerializeFileDB("anchors", anchors_db_path, anchors);
+}
+
+std::vector<CAddress> ReadAnchors(const fs::path& anchors_db_path)
+{
+    std::vector<CAddress> anchors;
+    if (DeserializeFileDB(anchors_db_path, anchors)) {
+        LogPrintf("Loaded %i addresses from %s\n", anchors.size(), anchors_db_path.filename());
+    } else {
+        anchors.clear();
+    }
+
+    fs::remove(anchors_db_path);
+    return anchors;
+}