refactor: RPC 'listlabels', encapsulate 'CWallet::ListAddrBookLabels' functionality

Mainly to not access 'm_address_book' externally.

Author: furszy

src/wallet/rpc/addresses.cpp

@@ -733,13 +733,7 @@ RPCHelpMan listlabels()
     }
 
     // Add to a set to sort by label name, then insert into Univalue array
-    std::set<std::string> label_set;
-    for (const std::pair<const CTxDestination, CAddressBookData>& entry : pwallet->m_address_book) {
-        if (entry.second.IsChange()) continue;
-        if (purpose.empty() || entry.second.purpose == purpose) {
-            label_set.insert(entry.second.GetLabel());
-        }
-    }
+    std::set<std::string> label_set = pwallet->ListAddrBookLabels(purpose);
 
     UniValue ret(UniValue::VARR);
     for (const std::string& name : label_set) {

src/wallet/wallet.cpp

@@ -2373,6 +2373,20 @@ std::vector<CTxDestination> CWallet::ListAddrBookAddresses(const std::optional<A
     return result;
 }
 
+std::set<std::string> CWallet::ListAddrBookLabels(const std::string& purpose) const
+{
+    AssertLockHeld(cs_wallet);
+    std::set<std::string> label_set;
+    ForEachAddrBookEntry([&](const CTxDestination& _dest, const std::string& _label,
+                             const std::string& _purpose, bool _is_change) {
+        if (_is_change) return;
+        if (purpose.empty() || _purpose == purpose) {
+            label_set.insert(_label);
+        }
+    });
+    return label_set;
+}
+
 bool ReserveDestination::GetReservedDestination(CTxDestination& dest, bool internal, bilingual_str& error)
 {
     m_spk_man = pwallet->GetScriptPubKeyMan(type, internal);

src/wallet/wallet.h

@@ -648,6 +648,11 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
      */
     std::vector<CTxDestination> ListAddrBookAddresses(const std::optional<AddrBookFilter>& filter) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+    /**
+     * Retrieve all the known labels in the address book
+     */
+    std::set<std::string> ListAddrBookLabels(const std::string& purpose) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
+
     /**
      * Walk-through the address book entries.
      * Stops when the provided 'ListAddrBookFunc' returns false.