From fa92394f80ddcfd1f1ce95da2d5213a0a972e8d4 Mon Sep 17 00:00:00 2001
From: Michael Tremer <michael.tremer@ipfire.org>
Date: Fri, 5 Jun 2026 14:30:01 +0000
Subject: [PATCH] graphs: Render an empty graph if there are no sources

Graphs like temperature graphs don't have any data sources whatsoever
for example in a virtual machine. Because rrdtool would normally fail,
we will instead create an empty graph that even has the correct labels
and shows a note at the bottom.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
---
 src/daemon/graph.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/src/daemon/graph.c b/src/daemon/graph.c
index 19cfff9..1f8720e 100644
--- a/src/daemon/graph.c
+++ b/src/daemon/graph.c
@@ -36,6 +36,9 @@
 #include "string.h"
 #include "time.h"
 
+// Include graph macros
+#include "graphs/graph.h"
+
 // Maximum length of the title/vlabel
 #define TITLE_MAX		128
 #define VLABEL_MAX		64
@@ -283,6 +286,28 @@ static void td_graph_reset_locale(td_ctx* ctx, char* locale) {
 		ERROR(ctx, "Failed to reset the locale to '%s': %m\n", locale);
 }
 
+static int td_graph_empty(td_graph* self, td_args* args) {
+	int r;
+
+	// Draw a line so that something will get rendered
+	r = td_args_push(args, "HRULE:0" COLOR_AXIS);
+	if (r < 0)
+		return r;
+
+	// Add an empty line
+	PRINT_EMPTY_LINE(args);
+
+	// Add a message that explains that no data is available
+	r = td_args_push(args, "COMMENT:%s\\c", _("No Data Available"));
+	if (r < 0)
+		return r;
+
+	// Add another empty line
+	PRINT_EMPTY_LINE(args);
+
+	return 0;
+}
+
 int td_graph_render(td_graph* self, const char* object,
 		const td_graph_render_options* options, char** buffer, size_t* length) {
 	td_args* args = NULL;
@@ -463,6 +488,16 @@ int td_graph_render(td_graph* self, const char* object,
 	if (r < 0)
 		goto ERROR;
 
+	// We cannot render the graph if there are no sources
+	if (!td_args_has_sources(args)) {
+		DEBUG(self->ctx, "Graph has no sources\n");
+
+		// Show nothing
+		r = td_graph_empty(self, args);
+		if (r < 0)
+			goto ERROR;
+	}
+
 	// Dump the command
 	r = td_args_dump(args);
 	if (r < 0)
-- 
2.47.3