Generate new keys for inactive seeds after marking used

When a key from an inactive seed is used, generate replacements
to fill a keypool that would have been there.

src/wallet/scriptpubkeyman.cpp

@@ -12,6 +12,9 @@
 #include <util/translation.h>
 #include <wallet/scriptpubkeyman.h>
 
+//! Value for the first BIP 32 hardened derivation. Can be used as a bit mask and as a value. See BIP 32 for more details.
+const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
+
 bool LegacyScriptPubKeyMan::GetNewDestination(const OutputType type, CTxDestination& dest, std::string& error)
 {
     LOCK(cs_KeyStore);
@@ -290,6 +293,43 @@ bool LegacyScriptPubKeyMan::GetReservedDestination(const OutputType type, bool i
     return true;
 }
 
+bool LegacyScriptPubKeyMan::TopUpInactiveHDChain(const CKeyID seed_id, int64_t index, bool internal)
+{
+    LOCK(cs_KeyStore);
+
+    if (m_storage.IsLocked()) return false;
+
+    auto it = m_inactive_hd_chains.find(seed_id);
+    if (it == m_inactive_hd_chains.end()) {
+        return false;
+    }
+
+    CHDChain& chain = it->second;
+
+    // Top up key pool
+    int64_t target_size = std::max(gArgs.GetArg("-keypool", DEFAULT_KEYPOOL_SIZE), (int64_t) 1);
+
+    // "size" of the keypools. Not really the size, actually the difference between index and the chain counter
+    // Since chain counter is 1 based and index is 0 based, one of them needs to be offset by 1.
+    int64_t kp_size = (internal ? chain.nInternalChainCounter : chain.nExternalChainCounter) - (index + 1);
+
+    // make sure the keypool fits the user-selected target (-keypool)
+    int64_t missing = std::max(target_size - kp_size, (int64_t) 0);
+
+    if (missing > 0) {
+        WalletBatch batch(m_storage.GetDatabase());
+        for (int64_t i = missing; i > 0; --i) {
+            GenerateNewKey(batch, chain, internal);
+        }
+        if (internal) {
+            WalletLogPrintf("inactive seed with id %s added %d internal keys\n", HexStr(seed_id), missing);
+        } else {
+            WalletLogPrintf("inactive seed with id %s added %d keys\n", HexStr(seed_id), missing);
+        }
+    }
+    return true;
+}
+
 void LegacyScriptPubKeyMan::MarkUnusedAddresses(const CScript& script)
 {
     LOCK(cs_KeyStore);
@@ -297,13 +337,28 @@ void LegacyScriptPubKeyMan::MarkUnusedAddresses(const CScript& script)
     for (const auto& keyid : GetAffectedKeys(script, *this)) {
         std::map<CKeyID, int64_t>::const_iterator mi = m_pool_key_to_index.find(keyid);
         if (mi != m_pool_key_to_index.end()) {
-            WalletLogPrintf("%s: Detected a used keypool key, mark all keypool key up to this key as used\n", __func__);
+            WalletLogPrintf("%s: Detected a used keypool key, mark all keypool keys up to this key as used\n", __func__);
             MarkReserveKeysAsUsed(mi->second);
 
             if (!TopUp()) {
                 WalletLogPrintf("%s: Topping up keypool failed (locked wallet)\n", __func__);
             }
         }
+
+        // Find the key's metadata and check if it's seed id (if it has one) is inactive, i.e. it is not the current m_hd_chain seed id.
+        // If so, TopUp the inactive hd chain
+        auto it = mapKeyMetadata.find(keyid);
+        if (it != mapKeyMetadata.end()){
+            CKeyMetadata meta = it->second;
+            if (!meta.hd_seed_id.IsNull() && meta.hd_seed_id != m_hd_chain.seed_id) {
+                bool internal = (meta.key_origin.path[1] & ~BIP32_HARDENED_KEY_LIMIT) != 0;
+                int64_t index = meta.key_origin.path[2] & ~BIP32_HARDENED_KEY_LIMIT;
+
+                if (!TopUpInactiveHDChain(meta.hd_seed_id, index, internal)) {
+                    WalletLogPrintf("%s: Adding inactive seed keys failed\n", __func__);
+                }
+            }
+        }
     }
 }
 
@@ -975,8 +1030,6 @@ CPubKey LegacyScriptPubKeyMan::GenerateNewKey(WalletBatch &batch, CHDChain& hd_c
     return pubkey;
 }
 
-const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
-
 void LegacyScriptPubKeyMan::DeriveNewChildKey(WalletBatch &batch, CKeyMetadata& metadata, CKey& secret, CHDChain& hd_chain, bool internal)
 {
     // for now we use a fixed keypath scheme of m/0'/0'/k

src/wallet/scriptpubkeyman.h

@@ -333,6 +333,18 @@ private:
      */
     bool ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool, bool fRequestedInternal);
 
+    /**
+     * Like TopUp() but adds keys for inactive HD chains.
+     * Ensures that there are at least -keypool number of keys derived after the given index.
+     *
+     * @param seed_id the CKeyID for the HD seed.
+     * @param index the index to start generating keys from
+     * @param internal whether the internal chain should be used. true for internal chain, false for external chain.
+     *
+     * @return true if seed was found and keys were derived. false if unable to derive seeds
+     */
+    bool TopUpInactiveHDChain(const CKeyID seed_id, int64_t index, bool internal);
+
 public:
     using ScriptPubKeyMan::ScriptPubKeyMan;