merge bitcoin#23398: add return message to savemempool RPC

src/rpc/blockchain.cpp

@@ -2643,7 +2643,11 @@ static RPCHelpMan savemempool()
     return RPCHelpMan{"savemempool",
         "\nDumps the mempool to disk. It will fail until the previous dump is fully loaded.\n",
         {},
-        RPCResult{RPCResult::Type::NONE, "", ""},
+        RPCResult{
+            RPCResult::Type::OBJ, "", "",
+            {
+                {RPCResult::Type::STR, "filename", "the directory and file where the mempool was saved"},
+            }},
         RPCExamples{
             HelpExampleCli("savemempool", "")
     + HelpExampleRpc("savemempool", "")
@@ -2652,6 +2656,8 @@ static RPCHelpMan savemempool()
 {
     const CTxMemPool& mempool = EnsureAnyMemPool(request.context);
 
+    const NodeContext& node = EnsureAnyNodeContext(request.context);
+
     if (!mempool.IsLoaded()) {
         throw JSONRPCError(RPC_MISC_ERROR, "The mempool was not loaded yet");
     }
@@ -2660,7 +2666,10 @@ static RPCHelpMan savemempool()
         throw JSONRPCError(RPC_MISC_ERROR, "Unable to dump mempool to disk");
     }
 
-    return NullUniValue;
+    UniValue ret(UniValue::VOBJ);
+    ret.pushKV("filename", fs::path((node.args->GetDataDirNet() / "mempool.dat")).u8string());
+
+    return ret;
 },
     };
 }

test/functional/mempool_persist.py

@@ -133,8 +133,9 @@ class MempoolPersistTest(BitcoinTestFramework):
         mempooldat1 = os.path.join(self.nodes[1].datadir, self.chain, 'mempool.dat')
         self.log.debug("Remove the mempool.dat file. Verify that savemempool to disk via RPC re-creates it")
         os.remove(mempooldat0)
-        self.nodes[0].savemempool()
+        result0 = self.nodes[0].savemempool()
         assert os.path.isfile(mempooldat0)
+        assert_equal(result0['filename'], mempooldat0)
 
         self.log.debug("Stop nodes, make node1 use mempool.dat from node0. Verify it has 6 transactions")
         os.rename(mempooldat0, mempooldat1)