rpc: keep .cookie if it was not generated

Otherwise, starting bitcoind twice may cause the `.cookie`
file generated by the first instance to be deleted by the
second instance shutdown (after failing to obtain a lock).

src/rpc/request.cpp

@@ -80,6 +80,8 @@ static fs::path GetAuthCookieFile(bool temp=false)
     return AbsPathForConfigVal(gArgs, arg);
 }
 
+static bool g_generated_cookie = false;
+
 bool GenerateAuthCookie(std::string *cookie_out)
 {
     const size_t COOKIE_SIZE = 32;
@@ -105,6 +107,7 @@ bool GenerateAuthCookie(std::string *cookie_out)
         LogPrintf("Unable to rename cookie authentication file %s to %s\n", fs::PathToString(filepath_tmp), fs::PathToString(filepath));
         return false;
     }
+    g_generated_cookie = true;
     LogPrintf("Generated RPC authentication cookie %s\n", fs::PathToString(filepath));
 
     if (cookie_out)
@@ -131,7 +134,10 @@ bool GetAuthCookie(std::string *cookie_out)
 void DeleteAuthCookie()
 {
     try {
-        fs::remove(GetAuthCookieFile());
+        if (g_generated_cookie) {
+            // Delete the cookie file if it was generated by this process
+            fs::remove(GetAuthCookieFile());
+        }
     } catch (const fs::filesystem_error& e) {
         LogPrintf("%s: Unable to remove random auth cookie file: %s\n", __func__, fsbridge::get_filesystem_error_message(e));
     }

test/functional/feature_filelock.py

@@ -30,6 +30,9 @@ class FilelockTest(BitcoinTestFramework):
         expected_msg = f"Error: Cannot obtain a lock on data directory {datadir}. {self.config['environment']['PACKAGE_NAME']} is probably already running."
         self.nodes[1].assert_start_raises_init_error(extra_args=[f'-datadir={self.nodes[0].datadir_path}', '-noserver'], expected_msg=expected_msg)
 
+        cookie_file = datadir / ".cookie"
+        assert cookie_file.exists()  # should not be deleted during the second bitcoind instance shutdown
+
         if self.is_wallet_compiled():
             def check_wallet_filelock(descriptors):
                 wallet_name = ''.join([random.choice(string.ascii_lowercase) for _ in range(6)])