rpc: take ownership of the file by WriteUTXOSnapshot()

Have `WriteUTXOSnapshot()` take rvalue reference to make it obvious that
it takes ownership of the file.

src/rpc/blockchain.cpp

@@ -82,7 +82,7 @@ UniValue WriteUTXOSnapshot(
     CCoinsViewCursor* pcursor,
     CCoinsStats* maybe_stats,
     const CBlockIndex* tip,
-    AutoFile& afile,
+    AutoFile&& afile,
     const fs::path& path,
     const fs::path& temppath,
     const std::function<void()>& interruption_point = {});
@@ -3114,7 +3114,14 @@ static RPCHelpMan dumptxoutset()
         }
     }
 
-    UniValue result = WriteUTXOSnapshot(*chainstate, cursor.get(), &stats, tip, afile, path, temppath, node.rpc_interruption_point);
+    UniValue result = WriteUTXOSnapshot(*chainstate,
+                                        cursor.get(),
+                                        &stats,
+                                        tip,
+                                        std::move(afile),
+                                        path,
+                                        temppath,
+                                        node.rpc_interruption_point);
     fs::rename(temppath, path);
 
     result.pushKV("path", path.utf8string());
@@ -3166,7 +3173,7 @@ UniValue WriteUTXOSnapshot(
     CCoinsViewCursor* pcursor,
     CCoinsStats* maybe_stats,
     const CBlockIndex* tip,
-    AutoFile& afile,
+    AutoFile&& afile,
     const fs::path& path,
     const fs::path& temppath,
     const std::function<void()>& interruption_point)
@@ -3240,12 +3247,19 @@ UniValue WriteUTXOSnapshot(
 UniValue CreateUTXOSnapshot(
     node::NodeContext& node,
     Chainstate& chainstate,
-    AutoFile& afile,
+    AutoFile&& afile,
     const fs::path& path,
     const fs::path& tmppath)
 {
     auto [cursor, stats, tip]{WITH_LOCK(::cs_main, return PrepareUTXOSnapshot(chainstate, node.rpc_interruption_point))};
-    return WriteUTXOSnapshot(chainstate, cursor.get(), &stats, tip, afile, path, tmppath, node.rpc_interruption_point);
+    return WriteUTXOSnapshot(chainstate,
+                             cursor.get(),
+                             &stats,
+                             tip,
+                             std::move(afile),
+                             path,
+                             tmppath,
+                             node.rpc_interruption_point);
 }
 
 static RPCHelpMan loadtxoutset()

src/rpc/blockchain.h

@@ -51,7 +51,7 @@ void CalculatePercentilesByWeight(CAmount result[NUM_GETBLOCKSTATS_PERCENTILES],
 UniValue CreateUTXOSnapshot(
     node::NodeContext& node,
     Chainstate& chainstate,
-    AutoFile& afile,
+    AutoFile&& afile,
     const fs::path& path,
     const fs::path& tmppath);
 

src/test/util/chainstate.h

@@ -47,8 +47,11 @@ CreateAndActivateUTXOSnapshot(
     FILE* outfile{fsbridge::fopen(snapshot_path, "wb")};
     AutoFile auto_outfile{outfile};
 
-    UniValue result = CreateUTXOSnapshot(
+    UniValue result = CreateUTXOSnapshot(node,
-        node, node.chainman->ActiveChainstate(), auto_outfile, snapshot_path, snapshot_path);
+                                         node.chainman->ActiveChainstate(),
+                                         std::move(auto_outfile), // Will close auto_outfile.
+                                         snapshot_path,
+                                         snapshot_path);
     LogPrintf(
         "Wrote UTXO snapshot to %s: %s\n", fs::PathToString(snapshot_path.make_preferred()), result.write());