Add Context::addLink() and Context::getLinks() to register HTML header content such as <link rel="preconnect">

classes/context/Context.class.php

@@ -41,6 +41,7 @@ class Context
 	public $html_footer = '';
 	public $body_header = '';
 	public $body_class = [];
+	public $link_rels = [];
 
 	/**
 	 * The current page's SEO information.
@@ -2494,7 +2495,7 @@ class Context
 	 */
 	public static function getHtmlHeader(): string
 	{
-		return self::$_instance->html_header;
+		return self::$_instance->html_header === '' ? '' : (self::$_instance->html_header . "\n");
 	}
 
 	/**
@@ -2602,6 +2603,28 @@ class Context
 		return self::$_instance->html_footer;
 	}
 
+	/**
+	 * Add <link> such as <link rel="preconnect" href="https://webfonts.example.com" />
+	 *
+	 * @param string $url
+	 * @param string $rel
+	 * @return void
+	 */
+	public static function addLink(string $url, string $rel): void
+	{
+		self::$_instance->link_rels[$url] = $rel;
+	}
+
+	/**
+	 * Returns added <link> list
+	 *
+	 * @return array
+	 */
+	public static function getLinks(): array
+	{
+		return self::$_instance->link_rels;
+	}
+
 	/**
 	 * Get config file
 	 *

common/tpl/common_layout.html

@@ -50,6 +50,9 @@
 @if (!empty($mobicon_url))
 <link rel="apple-touch-icon" href="{{ $mobicon_url }}" />
 @endif
+@foreach (Context::getLinks() as $link_url => $link_rel)
+<link rel="{{ $link_rel }}" href="{{ $link_url }}" />
+@endforeach
 
 <!-- OTHER HEADERS -->
 @foreach (Context::getOpenGraphData() as $og_metadata)