*** introduce NotifierCmd

*** actually implement most of it

this could take advantage of wip/better-stderr.

to be actually useful, this would need to report both internally
generated and detected events, but typically only for one side.
this is contrary to how a natural implementation would work, which
would report detected events as internal events for the opposite side,
but of course only if a corresponding sync action was actually executed.

=> a directory watcher seems more appropriate in the end

TODO

@@ -25,8 +25,6 @@ add alternative treatments of expired messages. ExpiredMessageMode: Prune
 (delete messages like now), Keep (just don't sync) and Archive (move to
 separate folder - ArchiveSuffix, default .archive).
 
-add support for event notification callbacks.
-
 make it possible to have different mailbox names for far and near side in
 Patterns.
 - use far:near for the pattern

src/config.c

@@ -642,6 +642,8 @@ load_config( const char *where )
 				error( "%s:%d: BufferLimit cannot be zero\n", cfile.file, cfile.line );
 				cfile.err = 1;
 			}
+		} else if (!strcasecmp( "NotifierCmd", cfile.cmd )) {
+			NotifierCmd = nfstrdup( cfile.val );
 		} else if (!getopt_helper( &cfile, &gcops, &global_conf )) {
 			error( "%s:%d: '%s' is not a recognized section-starting or global keyword\n",
 			       cfile.file, cfile.line, cfile.cmd );

src/main_sync.c

@@ -379,6 +379,12 @@ sync_chans( core_vars_t *cvars, char **argv )
 	}
 	mvars->chanptr = chans;
 
+	if (NotifierCmd && !(notifier_pipe = popen( NotifierCmd, "w" ))) {
+		sys_error( "Failed to launch notifier command '%s'", NotifierCmd );
+		cvars->ret = 1;
+		return;
+	}
+
 	if (!cvars->list && (DFlags & PROGRESS)) {
 		init_wakeup( &stats_wakeup, stats_timeout, NULL );
 		stats_timeout( NULL );

src/sync.c

@@ -13,6 +13,9 @@ channel_conf_t *channels;
 group_conf_t *groups;
 
 uint BufferLimit = 10 * 1024 * 1024;
+const char *NotifierCmd;
+
+FILE *notifier_pipe;
 
 int new_total[2], new_done[2];
 int flags_total[2], flags_done[2];
@@ -1544,6 +1547,13 @@ flags_set( int sts, void *aux )
 static void
 flags_set_p2( sync_vars_t *svars, sync_rec_t *srec, int t )
 {
+	if (notifier_pipe) {
+		fprintf( notifier_pipe,
+		         "Event flags\n"
+		         "Store %s\n"
+		         "Box %s\n"
+		         "UID %u\n");
+	}
 	if (srec->status & S_PURGE) {
 		JLOG( "P %u %u", (srec->uid[F], srec->uid[N]), "deleted dummy" );
 		srec->status = (srec->status & ~S_PURGE) | S_PURGED;

src/sync.h

@@ -73,6 +73,9 @@ extern channel_conf_t *channels;
 extern group_conf_t *groups;
 
 extern uint BufferLimit;
+extern const char *NotifierCmd;
+
+extern FILE *notifier_pipe;
 
 extern int new_total[2], new_done[2];
 extern int flags_total[2], flags_done[2];