Bugfix: RPC: Attempt to delete cookie tmp before creating it

May be needed if we ended up with a read-only tmp file

Author: luke-jr

src/rpc/request.cpp

@@ -112,6 +112,11 @@ bool GenerateAuthCookie(std::string* cookie_out, std::optional<fs::perms> cookie
     if (filepath_tmp.empty()) {
         return true; // -norpccookiefile
     }
+    try {
+        fs::remove(filepath_tmp);
+    } catch (const fs::filesystem_error& e) {
+        // ignore
+    }
     file.open(filepath_tmp);
     if (!file.is_open()) {
         LogWarning("Unable to open cookie authentication file %s for writing", fs::PathToString(filepath_tmp));

test/functional/rpc_users.py

@@ -200,7 +200,10 @@ def run_test(self):
         cookie_path =     self.nodes[0].chain_path / ".cookie"
         cookie_path_tmp = self.nodes[0].chain_path / ".cookie.tmp"
         cookie_path_tmp.mkdir()
+        cookie_path_tmp_subdir = cookie_path_tmp / "subdir"
+        cookie_path_tmp_subdir.mkdir()
         self.nodes[0].assert_start_raises_init_error(expected_msg=init_error)
+        cookie_path_tmp_subdir.rmdir()
         cookie_path_tmp.rmdir()
         assert not cookie_path.exists()
         self.restart_node(0)