degesch: resolve the issue with less(1) and SO/SI

Now that I've learnt what exactly these characters are and how they
ended up in attribute strings, we can just eliminate them and disable
`backlog_helper_strip_formatting`.  Saner defaults, again.

I've also added skipping of terminfo delay sequences, so now it's less
of an issue to pipe raw attribute sequences into backlog helpers.

1 files changed, 25 insertions, 10 deletions

diff --git a/degesch.c b/degesch.c
index 5c172f5..4639da7 100644
--- a/degesch.c
+++ b/degesch.c
@@ -2445,11 +2445,6 @@ static struct config_schema g_config_behaviour[] =
 	  .default_  = "off",
 	  .on_change = on_config_debug_mode_change },
 
-	// GNU screen has an ^O in its formatting attributes reset string,
-	// therefore we can't just pipe raw formatting to `less -R`.
-	// You can use the -r switch, however that makes `less` very confused
-	// about line wrapping, and the result is suboptimal.
-
 	{ .name      = "backlog_limit",
 	  .comment   = "Maximum number of lines stored in the backlog",
 	  .type      = CONFIG_ITEM_INTEGER,
@@ -2463,7 +2458,7 @@ static struct config_schema g_config_behaviour[] =
 	{ .name      = "backlog_helper_strip_formatting",
 	  .comment   = "Strip formatting from backlog helper input",
 	  .type      = CONFIG_ITEM_BOOLEAN,
-	  .default_  = "on" },
+	  .default_  = "off" },
 
 	{ .name      = "reconnect_delay_growing",
 	  .comment   = "Growing factor for reconnect delay",
@@ -2785,15 +2780,35 @@ struct attr_printer
 #define ATTR_PRINTER_INIT(ctx, stream) { ctx->attrs, stream, true }
 
 static void
+attr_printer_filtered_puts (FILE *stream, const char *attr)
+{
+	for (; *attr; attr++)
+	{
+		// sgr/set_attributes and sgr0/exit_attribute_mode like to enable or
+		// disable the ACS with SO/SI (e.g. for TERM=screen), however `less -R`
+		// does not skip over these characters and it screws up word wrapping
+		if (*attr == 14 /* SO */ || *attr == 15 /* SI */)
+			continue;
+
+		// Trivially skip delay sequences intended to be processed by tputs()
+		const char *end = NULL;
+		if (attr[0] == '$' && attr[1] == '<' && (end = strchr (attr, '>')))
+			attr = end;
+		else
+			fputc (*attr, stream);
+	}
+}
+
+static void
 attr_printer_tputs (struct attr_printer *self, const char *attr)
 {
 	terminal_printer_fn printer = get_attribute_printer (self->stream);
 	if (printer)
 		tputs (attr, 1, printer);
 	else
-		// We shouldn't really do this but we need it to
-		// output formatting to the backlog
-		fputs (attr, self->stream);
+		// We shouldn't really do this but we need it to output formatting
+		// to the backlog helper--it should be SGR-only
+		attr_printer_filtered_puts (self->stream, attr);
 }
 
 static void
@@ -3604,7 +3619,7 @@ explode_text (struct exploder *self, const char *text)
 	// Throw away any potentially harmful control characters first
 	struct str filtered = str_make ();
 	for (const char *p = text; *p; p++)
-		if (!strchr ("\a\b\x1b", *p))
+		if (!strchr ("\a\b\x0e\x0f\x1b" /* BEL BS SO SI ESC */, *p))
 			str_append_c (&filtered, *p);
 
 	size_t term_len = 0;