Merge bitcoin#15367: feature: Added ability for users to add a startu…

…p command

090530c feature: Added ability for users to add a startup command (Ben Carman)

Pull request description:

  Thoughts for adding the feature is for users to be able to add things like electrum-personal-server or lnd to run whenever Bitcoin Core is running.  Open to feedback about the feature.

ACKs for top commit:
  MarcoFalke:
    re-ACK 090530c
  dongcarl:
    tACK 090530c

Tree-SHA512: ba514d2fc8b4fb12b781c1a9c89845a25fce0b80ba7c907761cde4abb81edd03fa643682edc895986dc20b273ac3b95769508806db7fbd99ec28623f85c41e67

doc/release-notes-15367.md

@@ -0,0 +1,6 @@
+Configuration option changes
+----------------------------
+
+- The `startupnotify` option is used to specify a command to
+  execute when Dash Core has finished with its startup
+  sequence. (#5728)

src/init.cpp

@@ -539,6 +539,9 @@ void SetupServerArgs(NodeContext& node)
             "(default: 0 = disable pruning blocks, 1 = allow manual pruning via RPC, >%u = automatically prune block files to stay under the specified target size in MiB)", MIN_DISK_SPACE_FOR_BLOCK_FILES / 1024 / 1024), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-settings=<file>", strprintf("Specify path to dynamic settings data file. Can be disabled with -nosettings. File is written at runtime and not meant to be edited by users (use %s instead for custom settings). Relative paths will be prefixed by datadir location. (default: %s)", BITCOIN_CONF_FILENAME, BITCOIN_SETTINGS_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-syncmempool", strprintf("Sync mempool from other nodes on start (default: %u)", DEFAULT_SYNC_MEMPOOL), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+#if HAVE_SYSTEM
+    argsman.AddArg("-startupnotify=<cmd>", "Execute command on startup.", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+#endif
 #ifndef WIN32
     argsman.AddArg("-sysperms", "Create new files with system default permissions, instead of umask 077 (only effective with disabled wallet functionality)", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 #else
@@ -859,6 +862,17 @@ static void CleanupBlockRevFiles()
     }
 }
 
+#if HAVE_SYSTEM
+static void StartupNotify(const ArgsManager& args)
+{
+    std::string cmd = args.GetArg("-startupnotify", "");
+    if (!cmd.empty()) {
+        std::thread t(runCommand, cmd);
+        t.detach(); // thread runs free
+    }
+}
+#endif
+
 static void PeriodicStats(ArgsManager& args, const CTxMemPool& mempool)
 {
     assert(args.GetBoolArg("-statsenabled", DEFAULT_STATSD_ENABLE));
@@ -2537,5 +2551,9 @@ bool AppInitMain(const CoreContext& context, NodeContext& node, interfaces::Bloc
         banman->DumpBanlist();
     }, DUMP_BANS_INTERVAL);
 
+#if HAVE_SYSTEM
+    StartupNotify(args);
+#endif
+
     return true;
 }