Delay calculation for E-mail sending under a daily limit with nullmailer

nullmailer-2.2-delay.diff

diff -ur nullmailer-2.2/src/send.cc nullmailer-2.2-delay/src/send.cc
--- nullmailer-2.2/src/send.cc	2018-10-12 16:49:30.000000000 -0400
+++ nullmailer-2.2-delay/src/send.cc	2020-03-10 13:58:17.803978134 -0400
@@ -31,6 +31,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <ctime>
 #include "ac/time.h"
 #include "argparse.h"
 #include "autoclose.h"
@@ -45,6 +46,11 @@
 #include "selfpipe.h"
 #include "setenv.h"
 
+const long LIMIT_DAILY = 550;
+
+const static long DELAY_FAILURES = 15 * 60 * 1000 * 1000;
+const static char *DELAY_FAILURES_STR = "Resting for 15 minutes ...";
+
 const char* cli_program = "nullmailer-send";
 
 selfpipe selfpipe;
@@ -375,6 +381,32 @@
   return true;
 }
 
+int get_dayofmonth()
+{
+	time_t t = time(0);
+	tm* now = localtime(&t);
+	return now->tm_mday;
+}
+
+long delay_recalc() 
+{
+	static int lastday = 0;
+	static long messagecount = 1;
+
+	int today = get_dayofmonth();
+	if (lastday != today) {
+		messagecount = 1;
+		lastday = today;
+	}
+
+	/* Can be refactored:
+	 * float messagedelay = (86400.0 / LIMIT_DAILY) / (LIMIT_DAILY / 2);
+	 * float multiplier = (86400.0 * 2.0) / (LIMIT_DAILY * LIMIT_DAILY) */
+	float delay = (86400.0 * 2.0) / (LIMIT_DAILY * LIMIT_DAILY) * messagecount++;
+	fout << "Delaying message #" << messagecount << " for " << (int)delay << " seconds" << endl;
+	return (long)(delay * 1000.0 * 1000.0);
+}
+
 void send_all()
 {
   if(!load_config()) {
@@ -402,12 +434,16 @@
 	  }
 	}
 	msg++;
+        fout << DELAY_FAILURES_STR << endl;
+        usleep(DELAY_FAILURES);
 	break;
       case permfail:
 	if (bounce_msg(*msg, *remote, output))
 	  messages.remove(msg);
 	else
 	  msg++;
+        fout << DELAY_FAILURES_STR << endl;
+        usleep(DELAY_FAILURES);
 	break;
       default:
 	if(unlink((*msg).filename.c_str()) == -1) {
@@ -416,10 +452,11 @@
 	}
 	else
 	  messages.remove(msg);
+        usleep(delay_recalc());
       }
     }
   }