banman: save the banlist in a JSON format on disk

Save the banlist in `banlist.json` instead of `banlist.dat`.

This makes it possible to store Tor v3 entries in the banlist on disk
(and any other addresses that cannot be serialized in addrv1 format).

Only read `banlist.dat` if it exists and `banlist.json` does not
exist (first start after an upgrade).

Supersedes https://github.com/bitcoin/bitcoin/pull/20904
Resolves https://github.com/bitcoin/bitcoin/issues/19748

3 files changed, 21 insertions, 6 deletions

diff --git a/src/test/denialofservice_tests.cpp b/src/test/denialofservice_tests.cpp
index 57178d015d..5668ead1fb 100644
--- a/src/test/denialofservice_tests.cpp
+++ b/src/test/denialofservice_tests.cpp
@@ -191,7 +191,7 @@ BOOST_AUTO_TEST_CASE(stale_tip_peer_management)
 BOOST_AUTO_TEST_CASE(peer_discouragement)
 {
     const CChainParams& chainparams = Params();
-    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
+    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist", nullptr, DEFAULT_MISBEHAVING_BANTIME);
     auto connman = std::make_unique<ConnmanTestMsg>(0x1337, 0x1337, *m_node.addrman);
     auto peerLogic = PeerManager::make(chainparams, *connman, *m_node.addrman, banman.get(),
                                        *m_node.scheduler, *m_node.chainman, *m_node.mempool, false);
@@ -285,7 +285,7 @@ BOOST_AUTO_TEST_CASE(peer_discouragement)
 BOOST_AUTO_TEST_CASE(DoS_bantime)
 {
     const CChainParams& chainparams = Params();
-    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
+    auto banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist", nullptr, DEFAULT_MISBEHAVING_BANTIME);
     auto connman = std::make_unique<CConnman>(0x1337, 0x1337, *m_node.addrman);
     auto peerLogic = PeerManager::make(chainparams, *connman, *m_node.addrman, banman.get(),
                                        *m_node.scheduler, *m_node.chainman, *m_node.mempool, false);
diff --git a/src/test/fuzz/banman.cpp b/src/test/fuzz/banman.cpp
index 759a70a857..cca41e79ae 100644
--- a/src/test/fuzz/banman.cpp
+++ b/src/test/fuzz/banman.cpp
@@ -9,8 +9,10 @@
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
 #include <test/util/setup_common.h>
+#include <util/readwritefile.h>
 #include <util/system.h>
 
+#include <cassert>
 #include <cstdint>
 #include <limits>
 #include <string>
@@ -38,8 +40,20 @@ FUZZ_TARGET_INIT(banman, initialize_banman)
     int limit_max_ops{300};
     FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
     SetMockTime(ConsumeTime(fuzzed_data_provider));
-    const fs::path banlist_file = gArgs.GetDataDirNet() / "fuzzed_banlist.dat";
-    fs::remove(banlist_file);
+    fs::path banlist_file = gArgs.GetDataDirNet() / "fuzzed_banlist";
+
+    const bool start_with_corrupted_banlist{fuzzed_data_provider.ConsumeBool()};
+    if (start_with_corrupted_banlist) {
+        const std::string sfx{fuzzed_data_provider.ConsumeBool() ? ".dat" : ".json"};
+        assert(WriteBinaryFile(banlist_file.string() + sfx,
+                               fuzzed_data_provider.ConsumeRandomLengthString()));
+    } else {
+        const bool force_read_and_write_to_err{fuzzed_data_provider.ConsumeBool()};
+        if (force_read_and_write_to_err) {
+            banlist_file = fs::path{"path"} / "to" / "inaccessible" / "fuzzed_banlist";
+        }
+    }
+
     {
         BanMan ban_man{banlist_file, nullptr, ConsumeBanTimeOffset(fuzzed_data_provider)};
         while (--limit_max_ops >= 0 && fuzzed_data_provider.ConsumeBool()) {
@@ -80,5 +94,6 @@ FUZZ_TARGET_INIT(banman, initialize_banman)
                 });
         }
     }
-    fs::remove(banlist_file);
+    fs::remove(banlist_file.string() + ".dat");
+    fs::remove(banlist_file.string() + ".json");
 }
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index e105e85e47..f71d9148b6 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -196,7 +196,7 @@ TestingSetup::TestingSetup(const std::string& chainName, const std::vector<const
     }
 
     m_node.addrman = std::make_unique<CAddrMan>();
-    m_node.banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist.dat", nullptr, DEFAULT_MISBEHAVING_BANTIME);
+    m_node.banman = std::make_unique<BanMan>(m_args.GetDataDirBase() / "banlist", nullptr, DEFAULT_MISBEHAVING_BANTIME);
     m_node.connman = std::make_unique<CConnman>(0x1337, 0x1337, *m_node.addrman); // Deterministic randomness for tests.
     m_node.peerman = PeerManager::make(chainparams, *m_node.connman, *m_node.addrman,
                                        m_node.banman.get(), *m_node.scheduler, *m_node.chainman,