feat: add site-wide social preview image settings (#1463)

cotes2020 · web-flow · commit 241bb4df7878 · 2024-01-10T09:04:27.000+08:00
- Add configuration field `social_preview_image` that sets the site-wide default social preview image.  

   For pages that do not have `page.image` set in font matter, the seo tag will use the image specified by `site.social_preview_image` as the Open Graph image.

- Refactored the generation of image URLs to reduce redundant code and enhance fault tolerance for missing or repeated slash `/` when defining image paths.
diff --git a/_config.yml b/_config.yml
@@ -75,6 +75,10 @@ img_cdn: "https://chirpy-img.netlify.app"
 # the avatar on sidebar, support local or CORS resources
 avatar: "/commons/avatar.jpg"
 
+# The URL of the site-wide social preview image used in SEO `og:image` meta tag.
+# It can be overridden by a customized `page.image` in front matter.
+social_preview_image: # string, local or CORS resources
+
 # boolean type, the global switch for TOC in posts.
 toc: true
 
diff --git a/_includes/head.html b/_includes/head.html
@@ -1,5 +1,3 @@
-<!-- The Head -->
-
 <head>
   <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
   <meta name="theme-color" media="(prefers-color-scheme: light)" content="#f7f7f7">
@@ -11,29 +9,38 @@
     content="width=device-width, user-scalable=no initial-scale=1, shrink-to-fit=no, viewport-fit=cover"
   >
 
-  {% capture seo_tags %}
+  {%- capture seo_tags -%}
     {% seo title=false %}
-  {% endcapture %}
+  {%- endcapture -%}
+
+  <!-- Setup Open Graph image -->
 
   {% if page.image %}
-    {% assign img = page.image.path | default: page.image %}
-
-    {% unless img contains '://' %}
-      {% assign img_path = page.img_path | append: '/' | append: img | replace: '//', '/' %}
-      {% capture target %}"{{ img | absolute_url }}"{% endcapture %}
-
-      {% if site.img_cdn contains '//' %}
-        <!-- it's a cross-origin URL -->
-        {% capture replacement %}"{{ site.img_cdn }}{{ img_path }}"{% endcapture %}
-      {% else %}
-        <!-- it's a local file path -->
-        {%- capture replacement -%}
-          "{{ site.img_cdn | append: '/' | append: img_path | replace: '//', '/' | absolute_url }}"
-        {%- endcapture -%}
-      {% endif %}
-
-      {% assign seo_tags = seo_tags | replace: target, replacement %}
+    {% assign src = page.image.path | default: page.image %}
+
+    {% unless src contains '://' %}
+      {%- capture img_url -%}
+        {% include img-url.html src=src img_path=page.img_path %}
+      {%- endcapture -%}
+
+      {%- capture old_url -%}{{ src | absolute_url }}{%- endcapture -%}
+      {%- capture new_url -%}{{ img_url }}{%- endcapture -%}
+
+      {% assign seo_tags = seo_tags | replace: old, new %}
     {% endunless %}
+
+  {% elsif site.social_preview_image %}
+    {%- capture img_url -%}
+      {% include img-url.html src=site.social_preview_image %}
+    {%- endcapture -%}
+
+    {%- capture og_image -%}
+      <meta property="og:image" content="{{ img_url }}" />
+    {%- endcapture -%}
+
+    {% assign old_meta_clip = '<meta name="twitter:card"' %}
+    {% assign new_meta_clip = og_image | append: old_meta_clip %}
+    {% assign seo_tags = seo_tags | replace: old_meta_clip, new_meta_clip %}
   {% endif %}
 
   {{ seo_tags }}
diff --git a/_includes/img-url.html b/_includes/img-url.html
@@ -0,0 +1,24 @@
+{%- comment -%}
+  Generate image final URL based on `site.img_cdn`, `page.img_path`
+
+  Arguments:
+    src - basic image path, required
+    img_path - relative path of image, optional
+
+  Return:
+    image URL
+{%- endcomment -%}
+
+{% assign url = include.src %}
+
+{%- if url -%}
+  {%- comment -%} CND URL {%- endcomment -%}
+  {% assign prefix = site.img_cdn | default: '' | relative_url %}
+
+  {%- comment -%} Add page image path prefix {%- endcomment -%}
+  {% assign url = include.img_path | default: '' | append: '/' | append: url %}
+
+  {% assign url = prefix | append: '/' | append: url | replace: '///', '/' | replace: '//', '/' | replace: ':', ':/' %}
+{%- endif -%}
+
+{{- url -}}
diff --git a/_includes/refactor-content.html b/_includes/refactor-content.html
@@ -48,23 +48,6 @@
   {% assign _img_content = null %}
   {% assign _img_snippets = _content | split: IMG_TAG %}
 
-  <!-- CDN URL -->
-  {% if site.img_cdn %}
-    {% if site.img_cdn contains '//' %}
-      {% assign _path_prefix = site.img_cdn %}
-    {% else %}
-      {% assign _path_prefix = site.img_cdn | relative_url %}
-    {% endif %}
-  {% else %}
-    {% assign _path_prefix = site.baseurl %}
-  {% endif %}
-
-  <!-- Add image path -->
-  {% if page.img_path %}
-    {% assign _path = page.img_path | append: '/' | replace: '//', '/' %}
-    {% assign _path_prefix = _path_prefix | append: _path %}
-  {% endif %}
-
   {% for _img_snippet in _img_snippets %}
     {% if forloop.first %}
       {% assign _img_content = _img_snippet %}
@@ -113,6 +96,12 @@
     {% assign _final_src = null %}
     {% assign _lazyload = true %}
 
+    {%- capture _img_url -%}
+      {% include img-url.html src=_src img_path=page.img_path %}
+    {%- endcapture -%}
+
+    {% assign _path_prefix = _img_url | remove: _src %}
+
     {% unless _src contains '//' %}
       {% assign _final_src = _path_prefix | append: _src %}
       {% assign _src_alt = 'src="' | append: _path_prefix %}
diff --git a/_includes/sidebar.html b/_includes/sidebar.html
@@ -3,18 +3,12 @@
 <aside aria-label="Sidebar" id="sidebar" class="d-flex flex-column align-items-end">
   <header class="profile-wrapper">
     <a href="{{ '/' | relative_url }}" id="avatar" class="rounded-circle">
-      {% if site.avatar != empty and site.avatar %}
-        {% capture avatar_url %}
-            {% if site.avatar contains '://' %}
-              {{ site.avatar }}
-            {% elsif site.img_cdn != empty and site.img_cdn %}
-              {{ site.avatar | prepend: site.img_cdn }}
-            {% else %}
-              {{ site.avatar | relative_url }}
-            {% endif %}
-          {% endcapture %}
-        <img src="{{ avatar_url | strip }}" width="112" height="112" alt="avatar" onerror="this.style.display='none'">
-      {% endif %}
+      {%- if site.avatar != empty and site.avatar -%}
+        {%- capture avatar_url -%}
+          {% include img-url.html src=site.avatar %}
+        {%- endcapture -%}
+        <img src="{{- avatar_url -}}" width="112" height="112" alt="avatar" onerror="this.style.display='none'">
+      {%- endif -%}
     </a>
 
     <h1 class="site-title">
