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

1 files changed, 32 insertions, 3 deletions

diff --git a/src/addrdb.h b/src/addrdb.h
index 8953ebb169..399103c991 100644
--- a/src/addrdb.h
+++ b/src/addrdb.h
@@ -9,6 +9,7 @@
 #include <fs.h>
 #include <net_types.h> // For banmap_t
 #include <serialize.h>
+#include <univalue.h>
 
 #include <string>
 #include <vector>
@@ -36,6 +37,13 @@ public:
         nCreateTime = nCreateTimeIn;
     }
 
+    /**
+     * Create a ban entry from JSON.
+     * @param[in] json A JSON representation of a ban entry, as created by `ToJson()`.
+     * @throw std::runtime_error if the JSON does not have the expected fields.
+     */
+    explicit CBanEntry(const UniValue& json);
+
     SERIALIZE_METHODS(CBanEntry, obj)
     {
         uint8_t ban_reason = 2; //! For backward compatibility
@@ -48,6 +56,12 @@ public:
         nCreateTime = 0;
         nBanUntil = 0;
     }
+
+    /**
+     * Generate a JSON representation of this ban entry.
+     * @return JSON suitable for passing to the `CBanEntry(const UniValue&)` constructor.
+     */
+    UniValue ToJson() const;
 };
 
 /** Access to the (IP) address database (peers.dat) */
@@ -62,15 +76,30 @@ public:
     static bool Read(CAddrMan& addr, CDataStream& ssPeers);
 };
 
-/** Access to the banlist database (banlist.dat) */
+/** Access to the banlist databases (banlist.json and banlist.dat) */
 class CBanDB
 {
 private:
-    const fs::path m_ban_list_path;
+    /**
+     * JSON key under which the data is stored in the json database.
+     */
+    static constexpr const char* JSON_KEY = "banned_nets";
+
+    const fs::path m_banlist_dat;
+    const fs::path m_banlist_json;
 public:
     explicit CBanDB(fs::path ban_list_path);
     bool Write(const banmap_t& banSet);
-    bool Read(banmap_t& banSet);
+
+    /**
+     * Read the banlist from disk.
+     * @param[out] banSet The loaded list. Set if `true` is returned, otherwise it is left
+     * in an undefined state.
+     * @param[out] dirty Indicates whether the loaded list needs flushing to disk. Set if
+     * `true` is returned, otherwise it is left in an undefined state.
+     * @return true on success
+     */
+    bool Read(banmap_t& banSet, bool& dirty);
 };
 
 /**