2 files changed, 70 insertions, 0 deletions
diff --git a/lib/banzai/filter/truncate_visible_filter.rb b/lib/banzai/filter/truncate_visible_filter.rb
new file mode 100644
index 00000000000..edd6efd4706
--- /dev/null
+++ b/lib/banzai/filter/truncate_visible_filter.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+module Banzai
+  module Filter
+    class TruncateVisibleFilter < HTML::Pipeline::Filter
+      # Truncates the document to `truncate_visible_max_chars` characters,
+      # excluding any HTML tags.
+
+      MATCH_CODE = 'pre > code > .line'
+
+      def call
+        return doc unless context[:truncate_visible_max_chars].present?
+
+        max_chars = context[:truncate_visible_max_chars]
+        content_length = 0
+        @truncated = false
+
+        doc.traverse do |node|
+          if node.text? || node.content.empty?
+            if truncated
+              node.remove
+              next
+            end
+
+            handle_line_breaks(node)
+            truncate_content(content_length, max_chars, node)
+
+            content_length += node.content.length
+          end
+
+          truncate_if_block(node)
+        end
+
+        doc
+      end
+
+      private
+
+      attr_reader :truncated
+
+      def truncate_content(content_length, max_chars, node)
+        num_remaining = max_chars - content_length
+        return unless node.content.length > num_remaining
+
+        node.content = node.content.truncate(num_remaining)
+        @truncated = true
+      end
+
+      # Handle line breaks within a node
+      def handle_line_breaks(node)
+        return unless node.content.strip.lines.length > 1
+
+        node.content = "#{node.content.lines.first.chomp}..."
+        @truncated = true
+      end
+
+      # If `node` is the first block element, and the
+      # text hasn't already been truncated, then append "..." to the node contents
+      # and return true.  Otherwise return false.
+      def truncate_if_block(node)
+        return if truncated
+        return unless node.element? && (node.description&.block? || node.matches?(MATCH_CODE))
+
+        node.inner_html = "#{node.inner_html}..." if node.next_sibling
+        @truncated = true
+      end
+    end
+  end
+end
diff --git a/lib/banzai/pipeline/post_process_pipeline.rb b/lib/banzai/pipeline/post_process_pipeline.rb
index da2262cdf83..f8035698b9b 100644
--- a/lib/banzai/pipeline/post_process_pipeline.rb
+++ b/lib/banzai/pipeline/post_process_pipeline.rb
@@ -5,6 +5,7 @@ module Banzai
     class PostProcessPipeline < BasePipeline
       def self.filters
         @filters ||= FilterArray[
+          Filter::TruncateVisibleFilter,
           *internal_link_filters,
           Filter::AbsoluteLinkFilter,
           Filter::BroadcastMessagePlaceholdersFilter