Merge #15463: rpc: Speedup getaddressesbylabel

710a713 rpc: Speedup getaddressesbylabel (João Barbosa)

Pull request description:

  Fixes #15447. Same approach of #14984, this change avoids duplicate key check when building the JSON response in memory.

ACKs for commit 710a71:
  MarcoFalke:
    utACK 710a713
  ryanofsky:
    utACK 710a713. Just new comments and assert since last review.

Tree-SHA512: 77c95df9ff3793e348619aa070e6fd36df9da1b461d708ab146652cb3699f1a472ef6eb38dafdb8374375cbc97daef07635fcb0501961f167a023309513742e2

Author: MarcoFalke

src/wallet/rpcwallet.cpp

@@ -3683,9 +3683,20 @@ static UniValue getaddressesbylabel(const JSONRPCRequest& request)
 
     // Find all addresses that have the given label
     UniValue ret(UniValue::VOBJ);
+    std::set<std::string> addresses;
     for (const std::pair<const CTxDestination, CAddressBookData>& item : pwallet->mapAddressBook) {
         if (item.second.name == label) {
-            ret.pushKV(EncodeDestination(item.first), AddressBookDataToJSON(item.second, false));
+            std::string address = EncodeDestination(item.first);
+            // CWallet::mapAddressBook is not expected to contain duplicate
+            // address strings, but build a separate set as a precaution just in
+            // case it does.
+            bool unique = addresses.emplace(address).second;
+            assert(unique);
+            // UniValue::pushKV checks if the key exists in O(N)
+            // and since duplicate addresses are unexpected (checked with
+            // std::set in O(log(N))), UniValue::__pushKV is used instead,
+            // which currently is O(1).
+            ret.__pushKV(address, AddressBookDataToJSON(item.second, false));
         }
     }