ckdb - handle duplicate messages

src/ckdb.c

@@ -1038,6 +1038,7 @@ static K_STORE *workerstatus_store;
 
 static char logname[512];
 #define LOGFILE(_msg) rotating_log(logname, _msg)
+#define LOGDUP "dup."
 
 void logmsg(int loglevel, const char *fmt, ...)
 {
@@ -6198,14 +6199,18 @@ static void *listener(void *arg)
 {
 	proc_instance_t *pi = (proc_instance_t *)arg;
 	unixsock_t *us = &pi->us;
-	char *end, *ans, *rep, *buf = NULL;
+	char *end, *ans, *rep, *buf = NULL, *dot;
+	char *last_msg = NULL, *last_reply = NULL;
 	char cmd[CMD_SIZ+1], id[ID_SIZ+1], reply[1024+1];
-	enum cmd_values cmdnum;
+	// Minimise the size in case of garbage
+	char duptype[16+1];
+	enum cmd_values cmdnum, last_cmd = 9001;
 	int sockd, which_cmds;
 	pthread_t summzer;
 	K_ITEM *item;
 	size_t siz;
 	tv_t now;
+	bool dup;
 
 	create_pthread(&summzer, summariser, NULL);
 
@@ -6246,13 +6251,47 @@ static void *listener(void *arg)
 			else
 				LOGWARNING("Empty message in listener");
 		} else {
-			// Log everything we get (for now)
+			/* For duplicates:
+			 *  System: shutdown and ping are always processed,
+			 *	    so for any others, send a ping between them
+			 *	    if you need to send the same message twice
+			 *  Web: if the pool didn't do anything since the original
+			 *	 then the reply could be wrong for any reply that
+			 *	 changes over time ... however if the pool is busy
+			 *	 and we get the same request repeatedly, this will
+			 *	 reduce the load - thus always send the same reply
+			 *  Pool: must not process it, must send back the same reply
+			 *  TODO: remember last message/reply per source
+			 */
+			if (last_msg && strcmp(last_msg, buf) == 0) {
+				dup = true;
+				// This means an exact duplicate of the last non-dup
+				snprintf(reply, sizeof(reply), "%s%ld,%ld", LOGDUP, now.tv_sec, now.tv_usec);
+				LOGFILE(reply);
+				cmdnum = last_cmd;
+
+				STRNCPY(duptype, buf);
+				dot = strchr(duptype, '.');
+				if (dot)
+					*dot = '\0';
+				LOGWARNING("Duplicate '%s' message received", duptype);
+			} else {
+				dup = false;
 				LOGFILE(buf);
 				cmdnum = breakdown(buf, &which_cmds, cmd, id);
+				last_cmd = cmdnum;
+			}
 			switch (cmdnum) {
 				case CMD_REPLY:
+					if (dup)
+						send_unix_msg(sockd, last_reply);
+					else {
 						snprintf(reply, sizeof(reply), "%s.%ld.?.", id, now.tv_sec);
+						if (last_reply)
+							free(last_reply);
+						last_reply = strdup(reply);
 						send_unix_msg(sockd, reply);
+					}
 					break;
 				case CMD_SHUTDOWN:
 					LOGWARNING("Listener received shutdown message, terminating ckdb");
@@ -6261,10 +6300,14 @@ static void *listener(void *arg)
 					break;
 				case CMD_PING:
 					LOGDEBUG("Listener received ping request");
+					// Generate a new reply each time even on dup
 					snprintf(reply, sizeof(reply), "%s.%ld.ok.pong", id, now.tv_sec);
 					send_unix_msg(sockd, reply);
 					break;
 				default:
+					if (dup)
+						send_unix_msg(sockd, last_reply);
+					else {
 						// TODO: optionally get by/code/inet from transfer here instead?
 						ans = cmds[which_cmds].func(cmd, id, &now, (char *)"code",
 									    (char *)__func__,
@@ -6274,9 +6317,13 @@ static void *listener(void *arg)
 						snprintf(rep, siz, "%s.%ld.%s", id, now.tv_sec, ans);
 						free(ans);
 						ans = NULL;
+						if (last_reply)
+							free(last_reply);
+						last_reply = strdup(rep);
 						send_unix_msg(sockd, rep);
 						free(rep);
 						rep = NULL;
+					}
 					break;
 			}
 		}
@@ -6298,6 +6345,8 @@ static void *listener(void *arg)
 	}
 
 	dealloc(buf);
+	if (last_reply)
+		free(last_reply);
 	close_unix_socket(us->sockd, us->path);
 	return NULL;
 }