fix: escape Prometheus label values (#2702)

fix: escape Prometheus label values (#2699)

Co-authored-by: potatosips <potatosips@users.noreply.github.com>

src/test/unit/prometheus.spec.ts

@@ -0,0 +1,26 @@
+import { describe, expect, test } from 'vitest';
+
+import {
+  escapePrometheusLabelValue,
+  formatPrometheusLabels,
+} from '#server/utils/prometheus';
+
+describe('Prometheus label formatting', () => {
+  test('escapes quotes, backslashes, and newlines in label values', () => {
+    expect(escapePrometheusLabelValue('vpn"client')).toBe('vpn\\"client');
+    expect(escapePrometheusLabelValue('path\\client')).toBe('path\\\\client');
+    expect(escapePrometheusLabelValue('line one\nline two')).toBe(
+      'line one\\nline two'
+    );
+  });
+
+  test('formats escaped values without changing scalar values', () => {
+    expect(
+      formatPrometheusLabels({
+        interface: 'wg"0',
+        enabled: true,
+        name: 'home\\office\npeer',
+      })
+    ).toBe('interface="wg\\"0",enabled="true",name="home\\\\office\\npeer"');
+  });
+});