dnsdist: Save history to home-dir

Closes PowerDNS#4562

pdns/dnsdist-console.cc

@@ -21,6 +21,7 @@
  */
 #include "dnsdist.hh"
 #include "sodcrypto.hh"
+#include "pwd.h"
 
 #if defined (__OpenBSD__)
 #include <readline/readline.h>
@@ -85,14 +86,25 @@ void doClient(ComboAddress server, const std::string& command)
     return; 
   }
 
+  string histfile;
+  struct passwd* pwd = getpwuid(getuid());
+  const char *homedir = getenv("HOME");
+  if (pwd)
+    histfile = string(pwd->pw_dir);
+  if (homedir) // $HOME overrides what the OS tells us
+    histfile = string(homedir);
+  if (histfile.empty()) // Fall back to CWD
+    histfile = "./";
+  histfile.append(".dnsdist_history");
+
   set<string> dupper;
   {
-    ifstream history(".dnsdist_history");
+    ifstream history(histfile);
     string line;
     while(getline(history, line))
       add_history(line.c_str());
   }
-  ofstream history(".dnsdist_history", std::ios_base::app);
+  ofstream history(histfile, std::ios_base::app);
   string lastline;
   for(;;) {
     char* sline = readline("> ");