Merge bitcoin#10939: [init] Check non-emptiness of -blocknotify comma…

…nd prior to executing

cffe85f Skip sys::system(...) call in case of empty command (practicalswift)
6fb8f5f Check that -blocknotify command is non-empty before executing (practicalswift)

Pull request description:

  Check that `-blocknotify` command is non-empty before executing.

  To make the `BlockNotifyCallback(...)` (`-blocknotify`) behaviour consistent with that of:
  * `AlertNotify(...)` (`-alertnotify`)
  * `AddToWallet(...)` (`-walletnotify`)

Tree-SHA512: 18272166793a5a8b9cc2a727bfbcea53d38c329a55bc975c02db601329d608a61c20e026ce4b616193ecd3810dca4d3e2cb3bf773898a51872008a8dba96763e

src/init.cpp

@@ -670,9 +670,10 @@ static void BlockNotifyCallback(bool initialSync, const CBlockIndex *pBlockIndex
         return;
 
     std::string strCmd = gArgs.GetArg("-blocknotify", "");
-
-    boost::replace_all(strCmd, "%s", pBlockIndex->GetBlockHash().GetHex());
-    boost::thread t(runCommand, strCmd); // thread runs free
+    if (!strCmd.empty()) {
+        boost::replace_all(strCmd, "%s", pBlockIndex->GetBlockHash().GetHex());
+        boost::thread t(runCommand, strCmd); // thread runs free
+    }
 }
 
 static bool fHaveGenesis = false;

src/util.cpp

@@ -934,6 +934,7 @@ fs::path GetSpecialFolderPath(int nFolder, bool fCreate)
 
 void runCommand(const std::string& strCommand)
 {
+    if (strCommand.empty()) return;
     int nErr = ::system(strCommand.c_str());
     if (nErr)
         LogPrintf("runCommand error: system(%s) returned %d\n", strCommand, nErr);

src/wallet/wallet.cpp

@@ -1117,7 +1117,7 @@ bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFlushOnClose)
     // notify an external script when a wallet transaction comes in or is updated
     std::string strCmd = gArgs.GetArg("-walletnotify", "");
 
-    if ( !strCmd.empty())
+    if (!strCmd.empty())
     {
         boost::replace_all(strCmd, "%s", wtxIn.GetHash().GetHex());
         boost::thread t(runCommand, strCmd); // thread runs free