add rel meta links for prev and next page

app/helpers/posts_helper.rb

@@ -1,4 +1,22 @@
 module PostsHelper
+  def next_page_url
+    current_page = (params[:page] || 1).to_i
+    dup_params = params.dup
+    dup_params[:page] = current_page + 1
+    url_for(dup_params).html_safe
+  end
+
+  def prev_page_url
+    current_page = (params[:page] || 1).to_i
+    if current_page >= 2
+      dup_params = params.dup
+      dup_params[:page] = current_page - 1
+      url_for(dup_params).html_safe
+    else
+      nil
+    end
+  end
+
   def missed_post_search_count_js
     return nil unless Danbooru.config.enable_post_search_counts
     

app/views/posts/index.html.erb

@@ -63,7 +63,11 @@
 
 <%= content_for(:html_header) do %>
   <link href="<%= posts_path(:format => 'atom', :tags => params[:tags]) %>" rel="alternate" title="ATOM" type="application/atom+xml" />
-  <%= content_tag(:link, nil, rel: "prefetch", href: posts_path(tags: params[:tags], page: (params[:page] || 1).to_i + 1), as: "html", crossorigin: "use-credentials") %>
+  <%= content_tag(:link, nil, rel: "prefetch", href: next_page_url, as: "html", crossorigin: "use-credentials") %>
+  <%= content_tag :link, nil, rel: "next", href: next_page_url %>
+  <% if prev_page_url %>
+    <%= content_tag :link, nil, rel: "prev", href: prev_page_url %>
+  <% end %>
   <% if @post_set.has_wiki? %>
     <meta name="description" content="<%= @post_set.wiki_page.presenter.blurb %>">
   <% else %>